Synthesis of Poly(methylene-b-Îµ-caprolactone) and Poly(Îµ

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Synthesis of poly(methylene-b-#-caprolactone) and poly(#caprolactone) with linear alkyl end groups. Synthesis, characterization, phase behavior and compatibilization efficacy. Jose Eduardo Baez, Ruobing Zhao, and Kenneth J. Shea Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02596 • Publication Date (Web): 15 Aug 2017 Downloaded from http://pubs.acs.org on August 20, 2017

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Industrial & Engineering Chemistry Research

Synthesis of poly(methylene-b-ε-caprolactone) and poly(ε-caprolactone) with linear alkyl end groups. Synthesis, characterization, phase behavior and compatibilization efficacy José E. Báez, Ruobing Zhao, Kenneth J. Shea*

Department of Chemistry, University of California, Irvine (UCI), Irvine, California 926972025, United States

Keywords. Diblock copolymer, homopolymer, end group, polymethylene, poly(εcaprolactone)

Abstract. Diblock copolymers of poly(methylene-b-ε-caprolactone) (PM-b-PCL) were synthesized in two steps: a) polyhomologation, to obtain following oxidative cleavage of the carbon-boron, (PM, block1), an α-hydroxyl-ω-methyl polymethylene (PMOH, CH3−[CH2]m−OH). Following transfer reaction to the ring-opening polymerization catalyst and b) ring-opening polymerization (ROP) of ε-caprolactone (CL) (PCL, block2). In addition, a series of homopolymers derived from poly(ε-caprolactone) (PCL) oligoesters containing an end group of docosyl (CH3−[CH2]21− or C22) (C22-PCL) were obtained as a model to compare their physical properties by DSC with those of PM-b-PCL. The oligomers derived from PM-b-PCL and C22-PCL were characterized by 1H and 13C NMR, AFM, DSC, GPC and MALDI-TOF. PM-b-PCL and C22-PCL were evaluated as 1

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compatibilizers for PE/PCL polymer blends. Identification and analysis of optimized blocks of PM-b-PCL by POM and SEM showed improved mixing of PE/PCL blends. 1. INTRODUCTION Polyethylene (PE), is one of the most important commodity polymers with applications that include shopping bags, packaging, tubing, and containers. PE is a semicrystalline hydrophobic polymer that is quite stable and resistant to chemical degradation1,2 a property that invites its recycling. However, efforts at efficient recycling lag far beyond the world-wide annual production. Furthermore, the time scale for the biodegradation of PE (extremely long)3-5 which has resulted in a serious environmental consequences6 and bans in some locations of its use for certain non-essential applications.7 In contrast, several semicrystalline aliphatic polyesters such as poly(ε-caprolactone) (PCL)8,9 have far more desirable biodegradation profiles than PE and have made incursions in engineering, biomaterials and a green materials substitutes.8 The cost of PCL, however, prevents its complete replacement of PE as a commodity plastic. One way to decrease the environmental impact of PE without a prohibitive increase in cost is the use of blends of PE with biodegradable aliphatic polyesters.10-12 Practical implementation of this requires a fundamental understanding of the factors that contribute to compatibility between the homopolymers of PCL and PE. Block copolymers are a class of macromolecules produced by joining two or more chemically distinct polymer blocks that are typically thermodynamically incompatible.13 As a result, Diblock copolymers can be used as compatibilizing agents to blend two immiscible polymers. Diblock copolymers of PE-bpolyester offer the best option as compatibilizers to improve blends between PE and aliphatic polyesters.14-16 In addition to functioning as compatibilizing agents, diblock 2


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copolymers on their own undergo segregation of the blocks to produce nanometer-length scale features (5-100 nm) and producing complex nanostructures.17 Block copolymer properties such as their crystalline domain and morphology,18 the self-assembly of semicrystalline block copolymers,19-21 and formation of nanoparticles17 have drawn increasing interest to these systems. Prior studies of diblock copolymers such as poly(ethylene-b-ε-caprolactone) (PE-b-PCL)14,22-26 are interesting due to their physical properties and uses, with special attention to the segregation of phases between the two semicrystalline segments. For example, each block in the PE-b-PCL22-26 diblock copolymer has distinct physical properties that can be detected by conventional thermal analysis (different melting temperature). Each phase contributes to the bulk properties of the material. Analysis of structure-property relationships of diblock copolymers benefits from the controlled synthesis of each segments, ideally by means of a controlled or living polymerizations. The polyhomologation reaction is a living sp3-sp3 carbon-carbon bond forming polymerization for the controlled synthesis of linear polymethylene, a surrogate for PE.27,28 The reaction differs from conventional olefin polymerizations in that the carbon backbone is built one carbon atom at a time from C1 monomers such as ylides giving rise to polymethylene (PM) as a product. Polyhomologation permits the controlled synthesis of linear polymethylene,29,30 telechelic polymethylene,29,31 star polymethylene,32 and block and random copolymers.33-35 In previous work, polyhomologation has been used to synthesize diblock copolymers36,37, including A-B diblock (A = PEG36 or PS37) and B-A-B triblock (A = PDMS36) copolymers, in which B is a PM segment.

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It is well known that ring-opening polymerization (ROP) of lactones is a useful reaction to synthesize aliphatic polyesters such as PCL. Tin octoate [Sn(Oct)2]38-39 and aluminum triisopropoxide Al(OiPr)340-42 are two important catalysts for the ROP of εcaprolactone (CL).38-42 Both Al(OiPr)3 and Sn(Oct)2 catalysts have been shown to operate by a transfer reaction. For example, with Al(OiPr)3 in the presence of a primary or secondary aliphatic alcohol (ROH), transfer reaction occurs to generate a new aluminum alkoxide [Al-OR]. The newly generated aliphatic alcohol acts as an initiator/chain transfer agent in the ROP of lactones. This reaction has been reported for aliphatic alcohols but also been used in the presence of oligomers or polymers with a terminal hydroxyl group [HOoligomer] resulting in the synthesis of block copolymers.40,43 The key to the synthesis of diblock copolymers from the ROP of lactones is a hydroxyl-terminated macroinitiator. For the synthesis of PE-b-PCL, two precursors have been reported. In the first case, an α-hydroxylated 1,4-polybutadiene (PBOH)22-25 was prepared by the anionic polymerization of 1,3-butadiene. The PB segment was then hydrogenated in a second step or after the ROP of the lactone to obtain PE-b-PCL.22-25 In the second case, an α-hydroxylated polyethylene (PEOH) was synthesized by the polymerization of ethylene using metallocenes.14,43 Subsequently, PEOH was used to initiate the ROP of lactones to achieve PE-b-PCL.14 The polyhomologation reaction offers an ideal route for the controlled synthesis of a macroinitiator such as α-hydroxyl polymethylene (PMOH) to obtain copolymers analogous to PE-b-PCL. In a previous work, Ma and coworkers used polyhomologation and ROP to synthesize poly(methylene-b-ε-caprolactone) (PM-b-PCL).44 The study of the effect of aliphatic terminal groups on the physical properties of oligoesters of the PCL45 has also 4


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recently been reported, where the effect of a systematic increase from butyl (C4H9−) to docosyl (C22H45−) end groups was explored and found to have an appreciable effect on the long period (L) between lamellae for PCL, as detected by small-angle x-ray scattering (SAXS).45 In the present study we introduce a longer linear aliphatic end group, a docosyl (C22H45−) in a homopolymer and compare these materials with longer chain linear PM aliphatic blocks in a diblock copolymer such as PM-b-PCL, in terms of physical properties and importantly, their ability to compatibilize PE/PCL blends. In this work, we present an alternative approach for the synthesis of the diblock copolymers PM-b-PCL employing the polyhomologation followed by ROP (Scheme 1). We also describe a systematic analysis of the segregation of the phases of these diblock copolymers containing two semicrystalline segments (detected by DSC) by systematically increasing the PM block size. The aim of this report is to contribute to the understanding of the properties of diblock copolymers with an aliphatic segment such as PM (PM-b-PCL) and their analogous homopolymers derived from oligoesters with a linear alkyl end group such as docosyl (C22-PCL). As part of this effort, a variety of characterization tools has been employed with the aim of identifying differences and similarities between the two types of materials and their effectiveness as compatibilizing agents in polymer blends.

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Scheme 1. Synthesis of a homopolymer (left) and diblock copolymer (right) derived from poly(ε-caprolactone) (PCL) from the ring-opening polymerization (ROP) of ε-caprolactone (CL). 2. EXPERIMENTAL SECTION 2.1. Materials. Trimethylsulfoxonium iodide, benzyltributylammonium chloride, sodium hydride (NaH), and 1-docosanol where supplied by Acros Organics and were used without previous purification. Tri-n-hexylborane [B(hexyl)3] was synthesized according to the procedure previously published.29 All polyhomologations, oxidations, hydrolysis and polymerization reactions were performed under an atmosphere of N2 using a Schlenk line. Anhydrous solvents were used in all reactions here described. ε-Caprolactone (CL) was supplied by Alfa Aesar . CL was dried over calcium hydride (CaH2) for 24 h and distilled ®

under reduced pressure before use. Aluminum triisopropoxide [Al(OiPr)3] and trimethylamine N-oxide were provided by Aldrich and used without purification. ®

Deuterated

solvents

as

chloroform-d

(CDCl3),

tetrachloroethane-d2

(TCE-d2),

dimethylsulfoxide-d6 (DMSO-d6), dioxane-d8 (DXO-d8) and tetrahydrofurane-d8 (THF-d8) were provided by Cambridge Isotope Laboratories, Inc. and dried by molecular sieve before to be used or using glass ampoules sealed. Thin-layer chromatography (TLC) was performed on percolated silica gel plates and using a seebach staining reagent. Column chromatography was conducted using 230-400 mesh silica gel. Polyethylene (PE) linear low density, melt index 1.0 g/10 min (Mn(GPC) = 70,700, Mw/Mn = 3.70) was provided by Aldrich (pellets) and poly(ε-caprolactone) (PCL) (Mn(GPC) = 74,400, 1.60) was prepared by ROP according to a previous reference,46 both polymers were used in the polymer blends.

6


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2.2.

Synthesis

of

α-hydroxyl-ω-methyl

polymethylene

(PM25OH)

[CH3−(CH2)m−OH, DP(NMR) = 25] (Homopolymer). A solution of an ylide (dimethylsulfoxonium methylide) in THF (38 ml, 0.66 M, 25.08 mmol) was placed in a 250 mL Schlenk round-bottom flask adapted to a dry and nitrogen-filled condenser. To reduce the concentration of the ylide to 0.3 M, THF (45.6 ml) was added. The solution was heated in a pre-heated oil bath at 62 °C and then a solution of trihexylborane [B(hex)3] (138.9 mg, 0.522 mmol in 2mL of THF) was quickly added; the solution was stirred. A vigorous exothermic reaction was observed within 10-12 s. After ten minutes, titration of an aliquot of the solution showed that all the ylide was consumed. To start the oxidation of the alkyl borane, trimethylamine N-oxide (TAO, 348 mg, 3.13 mmol) previously dissolved in DMSO (10 ml) and degassed was injected into the reaction medium and the reaction mixture was stirred at reflux (80°C) for 24 h. A solution of NaOH (aq) (10 mL, 10 mmol, 1.0 M) previously degassed was injected into the reaction mixture to start the hydrolysis of the boronic esters at reflux (80 °C) for 24 h. After cooling, the THF was evaporated from the mixture on a rotavap and the polymer was precipitated in an excess of water, filtered, washed twice with water and then with methanol and dried in a vacuum oven at 50 °C overnight to yield a white powder (510 mg, yield = 99 %), Mn(NMR) = 380, Mn(GPC) = 340, Mw/Mn = 1.03. The same pattern of signals in

13

C NMR for both PM25OH

[CH3−(CH2)m−OH, DP(NMR) = 25, PMmOH, where the m value is DP(NMR)] and 1docosanol [CH3−(CH2)21−OH, C22OH] was observed (see supporting information section). Assignment of all peaks of 1-docosanol in the INADEQUATE 2D NMR (Figure S1) and

13

13

C NMR sprectrum was made by an

C NMR of 1-dodecanol (Figure S2). NMR

data for α-hydroxyl-ω-methyl polymethylene (PMOH) at 45 °C: 1H NMR (500 MHz, 7



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CDCl3, ppm) (Figure 1a and S3a):δ 3.63 (t, 2H, [−CH2−OH]), 1.57 (quintet, 2H, [−CH2−CH2−OH]), 1.27 (s, 2H, [−CH2−]), 0.89 (t, 3H, [−CH3]), 0.85 (d, 3H, [CH3−CH−]). 13

C

NMR

(125

MHz,

CDCl3,

ppm)

(Figure

S4a

and

S5a)

CH3a−CH2b−CH2c−CH2d−CH2d´−[CH2]me−CH2f´−CH2f−CH2g−CH2h−CH2i−OH: δ 63.10 (i), 32.90 (h), 31.94 (c), 29.70 (e), 29.62 (f´), 29.61 (d´), 29.46 (f), 29.35 (d), 25.79 (g), 22.67 (b), 14.03 (a). IR (cm-1) (Figure S6b): 3273 (ν, O−H), 2954 (νas, CH3), 2916 (νas, CH2), 2848 (νs, CH2), 1462 (δs, CH2), 1060 (ν, C−O), 719 (ρ, CH2). DSC data: Tm = 46 and 71 °C, ΔHm = 182 J/g, xi = 65 %. 2.3. 1-Docosanol [CH3−(CH2)21−OH, C22OH]. NMR data at room temperature: 1H NMR (500 MHz, CDCl3, ppm) (Figure 1b): δ 3.63 (t, 2H, [−CH2−OH]), 1.56 (quintet, 2H, [−CH2−CH2−OH]), 1.25 (s, 2H,[−CH2−]), 0.87 (t, 3H, [−CH3]). CDCl3,

ppm)

(Figure

S1

13

C NMR (125 MHz, and

S4b):

CH3a−CH2b−CH2c−CH2d−CH2d´−[CH2]12e−CH2f´−CH2f−CH2g−CH2h−CH2i−OH: δ 63.08 (i), 32.81 (h), 31.92 (c), 29.69 (e), 29.61(f´), 29.60(d´), 29.43 (f), 29.36 (d), 25.74 (g), 22.68 (b), 14.10 (a). IR (cm-1) (Figure S6a): 3321 (ν, O−H), 2954 (νas, CH3), 2916 (νas, CH2), 2846 (νs, CH2), 1471 (δs, CH2), 1062 (ν, C−O), 729 (ρ, CH2). DSC data: Tm = 73 °C, ΔHm = 246 J/g, xi = 88 %. 2.4. Synthesis of α-hydroxyl-ω-docosyl poly(ε-caprolactone) (C22-PCL10.7) [CH3(CH2)21O−[CO(CH2)5O]n−H, DPPCL(NMR) = 10.7] (homopolymer, a model of diblock copolymer). Inside a glovebox, 27.4 mg (0.1342 mmol) of aluminum isopropoxide Al(OiPr)3 (catalyst) was placed in a 50 ml Schlenk flask and adapted to a distillation system under an argon atmosphere. Next, the entire system was connected to 8


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nitrogen using a Schlenk line (N2/vacuum). Previously, 1-docosanol (initiator, 100 mg, 0.3061 mmol) was dissolved in 10 ml of THF and degassed, and then it was injected into the Schlenk flask containing Al(OiPr)3; the solution was stirred and distilled. After the first distillation, a fresh volume of toluene (6 ml) was added and distilled as part of an azeotropic distillation between isopropanol and toluene. This step was repeated three times, and then the flask was cooled to room temperature. Next, 3 ml of THF (solvent) was added under stirring, and to facilitate the dissolution, the flask was lightly heated with a heat gun. When the solution was transparent, 0.305 ml (2.755 mmol) of ε-caprolactone (CL, monomer) was injected into the solution. After 17 h at room temperature, the reaction was quenched and precipitated with an excess volume of cold methanol, stirred overnight (to dissolve traces of unreacted 1-docosanol) and filtrated, and the powder was dried under vacuum overnight. A white powder was obtained (yield = 77 %). Mn(NMR) = 1540, Mn(GPC) = 1620, Mw/Mn = 1.43. NMR data for α-hydroxyl-ω-docosyl poly(εcaprolactone) (C22-PCL10.7) at room temperature. 1H NMR (500 MHz, CDCl3, ppm) (Figure 4b): δ 4.05 (t, 2H, [−CH2−O−], PCL and t, 2H, [−CH2−O−], docosyl), 3.64 (t, 2H, [−CH2−OH], PCL), 2.30 (t, 2H, [−CH2−(C=O)−], PCL), 1.64 (m, 4H, [−(CH2)2−], PCL), 1.58 (m, 4H, [−(CH2)2−], PCL and quintet, 2H, [−CH2−], docosyl), 1.37 (quintet, 2H, [−CH2−], PCL), 1.24 (s, 2H, [−CH2−], docosyl), 0.87 (t, 3H, [−CH3], docosyl). (125 a

MHz,

CDCl3,

ppm)

(Figure

S7b

and

13

C NMR S8b)

CH3−bCH2−cCH2−dCH2−dĆH2−[eCH2]12−fĆH2−fCH2−gCH2−hCH2−iCH2−O−[jCO−kCH2−l

CH2−mCH2−nCH2−oCH2]n−O−pCO−qCH2−lCH2−mCH2−nCH2−rCH2−O−sCO−tCH2−uCH2−v CH2−wCH2−xCH2−OH: δ 173.60 (s), 173.48 (p), 173.41 (j), 64.42 (i), 64.04 (o), 64.00 (r), 62.48 (x), 34.15 (t), 34.08 (q), 34.03 (k), 32.26 (w), 31.83 (c), 29.60 (e), 29.49 (f´), 29.43 9



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(d´), 29.26 (f), 29.17 (d), 28.56 (h), 28.27 (n), 25.84 (g), 25.45 (m), 25.24 (v), 24.61 (u), 24.49 (l), 22.60 (b), 14.03 (a). IR (cm-1): 2942 (νas, CH3), 2922 (νas, CH2), 2864 (νs, CH3), 2852 (νs, CH2), 1722 (ν, C=O), 1174 (νas, C−(C=O)−O), 1045 (νas, O−C−C), 731 (ρ, CH2). DSC data (Figure 7a): Tm = 48 °C, ΔHm = 114 J/g, ΔHmC22 = 24 J/g, xC22 = 8 %. ΔHmPCL = 90 J/g, xPCL = 66 %. 2.5.

Synthesis

of

α-hydroxyl-ω-ethyl

poly(ε-caprolactone)

(C2-PCL9.9)

[CH3CH2O−[CO(CH2)5O]n−H, DPPCL(NMR) = 9.9] (homopolymer, model of pure PCL). The homopolymer C2-PCL9.9 (Figure S9 and S10) was prepared in the analogous manner as described in the subsection 2.3 but with ethanol (CH3CH2OH) as initiator. Mn(NMR) = 1170. DSC data: Tm = 39,45 °C, ΔHm = 86 J/g, ΔHmPCL = 83 J/g, xPCL = 61 %. 2.6. Synthesis of α-hydroxyl-ω-methyl poly(methylene-b-ε-caprolactone) (PM95-b-PCL7.5)

(Diblock

copolymer)

[CH3(CH2)mO−[CO(CH2)5O]n−H,

DPPM(NMR) = 95, DPPCL(NMR) = 7.5]. Inside a glovebox, 15.3 mg (0.0749 mmol) of aluminum isopropoxide Al(OiPr)3 was placed in a 50 mL Schlenk flask and equipped with a distillation system under an argon atmosphere. Next, the entire system was connected to nitrogen

using

a

Schlenk

line

(N2/vacuum).

Previously,


polymethylene (PM95OH) (200 mg, 0.1587 mmol) was dissolved in 10 mL hot toluene, degassed and then quickly injected into the Schlenk flask with Al(OiPr)3 and stirred, and the solution was distilled. After the first distillation, a fresh volume of toluene (6 ml) was added and distilled (135 °C) as part of an azeotropic distillation between isopropanol and toluene. This step was repeated three times, and then the flask was cooled to 100 °C. Toluene (1.62 ml) was added with stirring, when the solution was transparent 0.17 ml 10


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(1.5384 mmol) of ε-caprolactone (CL) was injected into the solution. After 48 h at 100 °C the reaction was quenched and precipitated with an excess volume of cold methanol, which was then stirred for several hours and filtrated, and the powder was dried under vacuum overnight. A white powder was obtained (yield = 98 %). Mn(NMR) = 2210, Mn(GPC) = 1900, Mw/Mn = 1.20. NMR data for α-hydroxyl-ω-methyl poly(methylene-b-εcaprolactone) (PM95-b-PCL7.5) at 100 °C. 1H NMR (500 MHz, TCE-d2, ppm) (Figure S11) : δ 4.10 (t, 2H, [−CH2−O−], PCL and t, 2H, [−CH2−O−], PM), 3.65 (t, 2H, [−CH2−OH], PCL), 2.33 (t, 2H, [−CH2−(C=O)−], PCL), 1.69 (m, 4H, [−(CH2)2−], PCL), 1.61 (m, 4H, [−(CH2)2−], PCL and quintet, 2H, [−CH2−], PM), 1.43 (quintet, 2H, [−CH2−], PCL), 1.32 (s, 2H, [−CH2−], PM), 0.93 (t, 3H, [−CH3], PM), 0.90 (d, 3H, [CH3−CH−], PM). 13C NMR (125 a

MHz,

TCE-d2,

ppm)

(Figure

S12)

CH3−bCH2−cCH2−dCH2−dĆH2−[eCH2]m−fĆH2−fCH2−gCH2−hCH2−iCH2−O−[jCO−kCH2−l

CH2−mCH2−nCH2−oCH2]n−O−pCO−qCH2−lCH2−mCH2−nCH2−rCH2−O−sCO−tCH2−uCH2−v CH2−wCH2−xCH2−OH: δ 173.01 (s), 172.85 (j,p), 64.20 (i), 63.84 (o), 63.80 (r), 62.36 (x), 34.05 (t), 33.99 (q), 33.95 (k), 32.21 (w), 31.62 (c), 29.38 (e), 29.28 (f´), 29.23 (d´), 28.99 (f), 28.98 (d), 28.58 (h), 28.23 (n), 25.74 (g), 25.38 (m), 25.21 (v), 24.53 (u), 24.38 (l), 22.32 (b), 13.65 (a). IR (cm-1): 2916 (νas, CH2), 2848 (νs, CH2), 1728 (ν, C=O), 1462 (δs, CH2), 1168 (νas, C−(C=O)−O), 1047 (νas, O−C−C), 731 (ρ, CH2). DSC data (Figure 7d): for PM block Tm = 116 °C, ΔHmPM = 106 J/g, xPM

=

38 % and for PCL block Tm = 24 °C,

ΔHmPCL = 13 J/g, xPCL = 9 %. 2.7. Polymer blends. The binary blends of polyethylene (PE) (Mn = 70,700) (70 wt. %) and poly(ε-caprolactone) (PCL) (Mn = 74,400) (30 wt. %) (PE/PCL) and ternary blends of

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PE/PCL/PM-b-PCL or PE/PCL/C22-PCL = 70/30/10 (weight ratio) were obtained by solution mixing in o-xylene at 140 °C. The polymeric species were dissolved in o-xylene at 140 °C until homogeneous dissolution occurs. The blend of polymers was precipitated in an excess of cold hexane, and then filtered, washed and dried under a vacuum oven overnight at 50 °C. In the case of POM, the samples were melted at 140-150 °C and then cooling at room temperature. In the case of SEM, the samples were also melted, and then quenched in liquid nitrogen and cryofractured. The fractured surfaces previously coating with gold (Au) were observed by SEM. 2.8. Characterization techniques. Nuclear Magnetic Resonance (NMR). Solution 1H and 13C NMR spectra were recorded in a room or high temperature on a Bruker DRX500 and Bruker DRX500 with cryoprobe (500 MHz 1H and 125 MHz

13

C), chloroform-d

(CDCl3), 1,1,2,2-tetrachloroethane-d2 (TCE-d2), dimethylsulfoxide-d6 (DMSO-d6), 1,4dioxane-d8 (DXO-d8) and tetrahydrofurane-d8 (THF-d8) were used as solvents. Spectra were referenced to the residual solvent protons at δ 7.26, 6.00, 2.50, 3.53 and 3.58 ppm for CDCl3, TCE-d2, DMSO-d6, DXO-d8 and THF-d8 respectively, in the 1H NMR spectrum and the residual solvent carbons at δ 77.0, 73.78, 39.51, 66.66, and 67.57 ppm for CDCl3, TCEd2, DMSO-d6, DXO-d8 and THF-d8, respectively, in the

13

C NMR spectrum. Incredible

natural abundance double quantum transfer experiment (INADEQUATE) were recorded on a Bruker DRX500 with cryoprobe. Fourier Transform Infrared Spectroscopy (FT-IR). FTIR spectra were obtained with the attenuated total reflectance spectroscopy (ATR) technique on powder deposited over a diamond on zinc selenide (ZnSe) crystal in an IRAffinity-1 Shimadzu spectrometer. Differential Scanning Calorimetric (DSC). DSC was 12


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performed in a TA instruments Q2000. Three scans (25-150 °C, 150 °C-−80°C and −80 °C150 °C) were performed by using a heating rate of 10 °C/min and cooling the instrument between runs under nitrogen purge. The melting point (Tm) are given as the maximum of the endothermic transition, and the data presented are taken from the second heating scan. The degree of crystallinity (xi) for homopolymers or diblock copolymers (with double endothermic peaks) of PE and PCL was calculate from the endothermic peak area (ΔHi) by xi = ΔHi/ΔHi0, where ΔHi0 is the heat of fusion for perfect PE (277 J/g),47 and PCL (135.3 J/g)48 crystals. For a sample with a single endothermic peak, the enthalpy of fusion (J/g) corresponding to docosyl (C22) or polymethylene (PM) segment was obtained by the weight fraction (xC22 or xPM) of the segment according to this equation: ΔHC22 = (ΔHi).(xC22) or ΔHPM = (ΔHi).(xPM); in the same manner was obtained the enthalphy of fusion corresponding to PCL according to this equation: ΔHPCL = (ΔHi).(xPCL) (Note: In most of the cases of C22-PCL or PM25-b-PCL12.8, two segments are overlapping in a single peak). Gel Permeation Chromatography (GPC). GPC measurements were determined using two instruments depending of the temperature and solvent to dissolve the samples, the first instrument (to low temperature): gel permeation chromatograph (name) equipped with a refractive index detector, a single column (Polymer Laboratories) at 30 °C were used to elute samples at flow rate of 1.0 ml/min of HPLC-grade THF. polystyrene standars were used for calibration, the second instrument (high temperature): Agilent technologies PLGPC 220 high temperature chromatograph equipped with a refractive index and viscosity detectors. A set of three mesopore columns (Agilent) at 110 °C were used to elute samples at flow rate of 1.0 ml/min of HPLC-grade 1,2,4-trichlorobenzene (TCB). Polystyrene and polyethylene standars (Polymer Laboratories) were used for calibration. Matrix-assisted 13



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Page 14 of 63

laser desorption ionization time-of-flight (MALDI-TOF). MALDI-TOF spectra were recorded in the reflectron mode by using an AB SCIEX TOF/TOF

TM

5800 SYSTEM

equipped with a nitrogen laser emitting at λ = 349 nm, input bandwidth = 1000 MHz with a 3 ns pulse width and working in positive mode and delayed extraction. Different types of matrixes

[2,5-dihydroxybenzoic

acid

(DHB),

2-(4-hydroxyphenylazo)benzoic

acid

(HABA), pyridine-2-carboxylic acid (α-picolinic acid), 3,5-dimethoxy-4-hydroxycinnamic acid (sinapic acid), 2,4,6-trimethylacetophenone, and 1,8,9-anthracenetriol (dithranol)] were tested using homopolymers (Figure S21) and diblock copolymers as a samples. For each type of matrix solution a concentration of 10 mg/ml in THF as solvent was used. Polymers and copolymer samples (3 mg/ml) were dissolved in THF or toluene (at room temperature or hot) and then 10 µl of sample solution was mixed with 10 µl of matrix solution (50/50, vol/vol) in a centrifuge tube (Eppendorf tube), mixed in vortex, and placed different aliquots on a stainless steel plate and evaporating the solvent to make the film before to start the acquisition. Polarized optical microscopy (POM). POM micrographs were obtained using a Variscope 865470-D with digital microscope camera model 844900. Polymers, binary and ternary blends were mounted on glass slides by a thin film melted at 130 °C using a hot plate and making a manual pressure between two slides containing the sample and a cover glass. The samples were cooled at room temperature previously to be analyzed, all samples were collected with magnification of 20x. Scanning electron microscopy (SEM). SEM micrographs were acquired using a FEI Magellan 400 XHR SEM company operated at 5 keV. The general procedure to prepare samples is: in the case of a ternary blend PE/PCL/PM-b-PCL [70/30/10 wt % (210/90/34 mg)] was blended by dissolution in o-xylene (10 ml) at 130 °C and precipitated in excess of cold hexane,

14


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filtrated, dried under vacuum, melted and stirred at 170 °C, quenched under liquid nitrogen and immediately fractured; a few pieces of the cryofractured sample were collected and then mounted on SEM specimens stubs and coated with a thin film of Iridium previously to be analyzed. Atomic force microscopy (AFM). AFM tapping mode micrographs were made using an Asylum Research MFP-3D Stand Alone (Oxford Instruments) using an Igor Pro 6.34A software package and operating under standard alternating current (AC) mode with air topography. Samples were tested using a cantilever of Silicon AFM tapping mode probes with Aluminum reflex coating with a force constant of 40 N/m provided by Ted Pella Inc. (TAP300AL-G). The oligoester and diblock copolymer samples were prepared using solutions of 0.5 wt. % with THF and toluene as solvent, respectively. A thin film was deposit by drop coating on a Silicon wafer previously mounted on a glass slides, the dried films was annealing overnight at 30 °C and 80 °C for samples with low and high Mn of PM, respectively.

3. RESULTS AND DISCUSSION 3.1 Synthesis and characterization of α-hydroxyl-ω-methyl polymethylene (PMOH) [CH3−(CH2)m−OH]. Polyhomologation was used to synthesize α-hydroxyl-ωmethyl polymethylene [CH3−(CH2)m−OH] (PMOH).27-37 Scheme 2 illustrates the synthetic route to obtain PMOH, where the ylide [ CH2−+SOMe2] and trihexylborane [B(C6H13)3] −

were used as the monomer and initiator, respectively. Following polymerization, oxidation, then base hydrolysis the polymer is formed in high yield (Table 1 and 2), with narrow molecular weight distributions (Mw/Mn). The experimental values of the number-average

15



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Page 16 of 63

molecular weight (Mn) Mn(GPC) were generally similar to the theoretical values Mn(calcd) and are consistent with a previous report.29

Scheme 2. Synthesis polyhomologation.

of


polymethylene

(PMOH)

by

Confirmation of the terminal OH groups was achieved by 1H NMR (Figure 1). In the case of PM25OH (Figure 1a and S3a), the characteristic peaks for methylene [d, −CH2OH, δ 3.63] and methyl end groups [a, −CH3, δ 0.89] and the repetitive units [b, −CH2−, δ 1.27] were clearly visible. However, a small doublet peak [f, CH3−CH−, δ 0.85] was observed at low frequency, which was attributable to a methyl branch from a sec-hexyl terminal group (7 % detected by 1H NMR). A 2-hexyl group (reaching up to 14 % in yield)49 is a common regioisomeric byproduct of the hydroboration reaction between 1hexene and borane (Scheme S1), which is usual to produce the initiator trihexylborane 16


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[B(C6H13)3]. Thus, both the hexyl and 2-hexyl isomers of the organoborane are reactive in the initiation step of the polymerization of the ylide. An analogous pure organic molecule such as 1-docosanol [CH3−(CH2)21−OH, MW = 326 g/mol, C22OH, monodisperse molecule] (Figure 1b, S1, and S4b) was used as a model to compare with PM25OH [Mn(GPC) = 340 Da]. This was chosen in part is to access the difference (if any) of polydispersity on their contribution to the properties of both species (C22OH and PM25OH).

17



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Figure 1. 1H NMR (500 MHz) spectra of (a) PM25OH [CH3−(CH2)m−OH, DP(NMR) = 25, Mn(GPC) = 340] and (b) 1-docosanol [CH3−(CH2)21−OH (C22OH), MW = 326], both samples in CDCl3 at 40 °C. 18


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The thermal properties of C22OH and PM25OH were analyzed by DSC (Table 1). In the case of a monodisperse molecule such as C22OH (MW = 326 Da), a single sharp endothermic peak (Tm = 73 °C) and high crystallinity (xi = 88 %) was observed. However, for a polymer such as PM25OH (polydisperse macromolecule, Mn(NMR) = 380 Da), a double peak (Tm = 49 and 71 °C) with moderate crystallinity (xi = 65 %) is seen. These differences are attributable to the molecular weight distribution of PM25OH. The peaks in PM25OH can be explained by different size crystallites or crystallites of similar size but embedded in amorphous domains (Tm = 49 °C) while others are in zones of high crystallinity (Tm = 71 °C). For the cases of relatively high Mn in polymers such as PM62OH and PM95OH, a proportional raise in their melting temperatures and crystallinity was observed. PM95OH (Mn = 1220) exhibits a Tm = 115 °C, compared with a sample PM119OH (Mn =1700, Tm = 109 °C) reported by Ma and coworkers,44 the low value in the Tm for PM119OH can be probably attributed to impurities. 3.2. Synthesis and characterization of diblock copolymers: Poly(methyleneb-ε-caprolactone) (PM-b-PCL). 3.2.1. Synthesis and Characterization. To compare the properties of block copolymers terminated with either PMOHs (macroinitiators) or C22OH groups, the PMOHs were used as precursors to synthesize diblock copolymers by ring-opening polymerization (ROP) of ε-caprolactone (CL) in the presence of aluminum isopropoxide (AlOiPr3) catalyst (Scheme 1). Depending on the Mn of the PMOH the temperature (room temperature or 90 °C) and solvent (THF or toluene) were chosen to insure a homogeneous system. For example, in the case of the ROP of CL by Al(OiPr)3 and PM95OH (Mn(NMR) = 1370, Mn(GPC) = 1260, Mw/Mn = 1.01, Table 2) in the presence of toluene as a solvent at 90 °C, 19



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Page 20 of 63

the reaction proceeds with high yield (90 %). After 48 h, the product poly(methylene-b-εcaprolactone) (PM95-b-PCL7.5) diblock copolymer shows moderate polydispersity (Mn(NMR) = 2210, Mn(GPC) = 1900, Mw/Mn = 1.20,). Using this approach, a series of diblock copolymers with a systematic increase in the content of the polymethylene (PM) segment were synthesized (21-74 wt. %, last column Table 2). 1H (Figure S11) and

13

C

(Figure S12) NMR were used to validate the proposed structure of the diblock copolymers. Figure 2 shows the 13C NMR spectrum for PM25-b-PCL12.8, in which the sequences of both blocks in the diblock copolymer and their terminals groups can clearly be observe d. Additional characterization by INADEQUATE 2D NMR spectroscopy to validate this assignation is presented in supporting information (Figure S1 and S9). The assignment is also consistent with references on terminal groups previously analyzed by

13

C NMR for

polyethylene (PE)50,52, PCL53 and poly(ethylene-b-ε-caprolactone) (PE-b-PCL)26.

20


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Figure 2. 13C NMR (125 MHz) spectrum of PM25-b-PCL12.8 in CDCl3 at 40 °C.

3.2.2. Thermal properties. Table 3 summarizes the thermal properties of PM-b-PCL species. For the first member of the family, PM25-b-PCL12.8, with a low Mn [Mn(GPC) = 1300 Da], a single sharp endothermic peak at 55 °C (Tm) was observed; based on the composition of PCL (79 wt. %) and the value of Tm, the main contribution to the melting point is attributed to the PCL block. This result suggests that the PM25 block exists mainly as an amorphous phase, in agreement with its low crystallinity (xPM = 7 %). This

21



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Page 22 of 63

composition had not been reported in previous studies of PE-b-PCL14 or PM-b-PCL44, where a double Tm was detected for all diblock copolymers with high Mn. For two samples (PM62-b-PCL8.1 and PM95-b-PCL7.5) with a relatively high content of PM, a double melting point was observed, indicating segregated phases with a double crystalline domain for each block. Hence, in cases with a relatively longer segment of PM, the fusion of PCL decreased its influence on the crystalline domains of PM (xPM = 28 and 38 %). The three species of PM-b-PCL in Table 3 are oligomers (Mn(GPC) = 1300-1900), but the segregation of phases was still observed in two cases (PM62-b-PCL8.1 and PM95-b-PCL7.5) as well as for examples of higher Mns previously reported.14,44 Evidently, the content (wt. %) and Mn of the PM segment (or PCL) in the PM-b-PCL oligomers have an important role in inducing the double segregated phases detected by DSC. In other words, the segregated phases as detected by DSC are not restricted to high Mn diblock copolymers (Mn = 9200 124000);14,44 oligomers such as PM-b-PCL [Mn(GPC) = 1600-1900 Da.] can produce the same effect. 3.3.

Synthesis

and

Characterization

of

α-hydroxyl-ω-docosyl

poly(ε-

caprolactone) (C22-PCL) oligoester: a homopolymer model of diblock copolymer. A long linear aliphatic chain of methylenes in an alcohol such as 1-docosanol [CH3−(CH2)21−OH, C22OH] (monodisperse) is chemically similar to PMOH (polydisperse) materials. We use C22OH as the aliphatic segment of a α-hydroxyl-ω-docosyl poly(εcaprolactone) (C22PCL) homopolymer as a model diblock copolymer to compare with PMb-PCL. C22OH, was used as the initiator to synthesize a series of oligoesters derived from CL (C22-PCL, Scheme 1). C22-PCL oligomers with a gradual increase (from DP(calcd) = 1 to 15) in PCL content were synthesized by ROP of CL using Al(OiPr)3 and C22OH as the 22


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catalyst and initiator, respectively (Table 4). The 1H and

13

C NMR spectra for all

oligomeric species were analyzed and their signals were assigned. In general, all samples showed the same pattern for a α-hydroxyl-ω-docosyl poly(ε-caprolactone) (C22-PCL). (Figure 3b and S8b).

23



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24


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Figure 3. Comparison of 1H NMR (500 MHz) spectra of a) PM25-b-PCL12.8 and b) C22PCL10.7 in CDCl3 at 40 °C.

The oligomeric species from monomer to tetramer (C22-PCL1-4) were isolated by column chromatography (Figure S13) and analyzed by MALDI-TOF (Figure 4) and 1H (Figure S14) and

13

C (Figure S15-S19) NMR spectroscopy, the monomer [C22-PCL0.93

(C22PCLn, where n = DPNMR)] and dimer (C22-PCL1.84) were obtained as pure organic substances (monodisperse species, Figure 4). The trimer (C22-PCL3.6) and tetramer (C22PCL4.6) were isolated as parts of molecular weight distributions. For the rest of the samples (DPcalcd = 5-15, DPNMR = 5.7-18.0, C22-PCL5.7-18.0) a purification was not necessary.

25



Intensity (A.U.)

463.38 479.35 100

80

60

40

Na

+

K

+

Theoretical (Na ) = 463.72

a)

+

+

Theoretical (K ) = 479.83

Monomer

O H3C

O

Monomer MW = 440.74

0 450

500

550

600

Mass (m/z)

593.40 + K

Intensity (A.U.)

120

100

80

b)

+

Theoretical (Na ) = 577.86 +

Theoretical (K ) = 593.97

577.44 Na

Dimer

O

+

O H3C

60

O O

20

0

Dimer

MW = 554.88

450

500

140 120 100 80

20 0

c)

Species

Hexamer 1033.66

Trimer

691.48

Heptamer 1147.74 Octamer 1261.81

450

600

Tetramer 805.55 Pentamer 919.62

60 40

550

Mass (m/z)

160

H

O

40

20

H O

20

20

Intensity (A.U.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 63

600

750

900

1050

1200

1350

Trimer Tetramer Pentamer Hexamer Heptamer Octamer

MW (g/mol) 669.02 783.16 897.30 1011.44 1125.58 1239.72

Theoretical (Na+) 692.00 806.14 920.28 1034.42 1148.56 1262.70

Experimental (Na+) 691.48 805.55 919.62 1033.66 1147.74 1261.81

1500

Mass (m/z)

26


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Figure 4. MALDI-TOF spectrum for different isolated fractions of C22-PCL (DPcalcd = 3) by column chromatography (Figure S13). a) MW(NMR) = 432 (monomer, C22-PCL0.93), b) MW(NMR) = 536 (dimer, C22-PCL1.84), c) Mn(NMR) = 730 (trimer and oligomers, C22PCL3.6) (Table 4) (C22-PCLn, where n = DPNMR).

Table 4, summarizes the thermal properties of the C22-PCL0.93-18.0 species. A single endothermic peak (Tm) was observed by DSC for all C22-PCL samples. Apparently, the docosyl (C22-) terminal group cannot induce a double segregation of phases (double Tm) with a PCL oligoester. However, there is some uncertainty in this conclusion because both peaks (docosyl and PCL) can overlap. For example, Hawker and coworkers54 isolated a 16mer PCL with Tm peaks clearly visualized. Also, C22OH showed a crystalline domain (Table 1). So, in the case from C22PCL16.9 (a single peak by DSC) is expected that its enthalpy of fusion (ΔHm) values is a contribution of C22 and PCL16.9 segments, therefore, a single peak detected by DSC is not regarding the absolute affirmation of a unique type of crystalline microdomain in a homopolymer. On the other hand, in the monomer species C22PCL0.93 the ΔHm had a value of 154 J/g, this contribution is attributed to the C22 segment [a PCL 100 % crystalline has an enthalpy of fusion of 135.3 J/g48], it has been reported that an isolated dimer of PCL is amorphous.54 So, it is assumed that the segment of PCL in the monomer (C22PCL0.93) and dimer (C22PCL1.84) are amorphous. The effect of the C22 end group content on the C22-PCL oligoesters (from monomer to 15 mer) is illustrated in Figure 5 and Table 4. There is a monotonic decrease in the value of Mn that is proportional to Tm up to 38 wt. % (C22-PCL4.6), while an increase in Tm is observed for oligomers with a high content of C22 end group from tetramer to monomer. 27



However, this effect is due not to C22, but rather to the hydroxyl end groups in the PCL and the strong effect of hydrogen bonding in oligomers with low Mn. In this context, the Tm value of pure C22-OH is 73 °C, approximately 9 °C higher than that of the monomeric species (C22-PCL0.93) with five additional aliphatic methylenes; it is well known that polar compounds have a high Tm relative to nonpolar compounds.55

66 64

2500

62 60

Tm Mn

58

2000

Tm(°C)

56 54

1500

52 50

Mn(NMR)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 63

1000

48 46 500

44 42 10

20

30

40

50

60

70

80

wt. % Docosyl end group [-(CH2)21-CH3]

Figure 5. Effect of docosyl (C22) end group (wt. %) on melting point (Tm) of C22-PCL homopolymer (oligoesters).

3.4. Comparison of a diblock copolymer PM-b-PCL vs an homopolymer C22PCL. A comparison of PM-b-PCL species to oligoesters derived from C22-PCL was made 28


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to access structure-property relationships. In the case of the homopolymer C22-PCL10.7 (Mn(NMR) = 1540, Table 4) and the diblock copolymer PM25-b-PCL12.8 (Mn(NMR) = 1840, Table 2), their 1H (Figure 3) and 13C (Figure S8) NMR spectra showed similar profiles in terms of peaks and intensities.

For the straight-chain aliphatic precursor (C22OH and PM25OH) the acquisition of MALDI-TOF spectrum could not be used, this was attributed to the low polarity of the aliphatic chains. However, MALDI-TOF was useful for the analysis of C22-PCL9 and PM25-b-PCL12.8. Figure 6a shows the MALDI-TOF spectrum for the homopolymer C22PCL10.7. The characteristic patterns of a unimodal distribution of a PCL oligoester with a specific degree of polymerization (DP) were seen, including their terminal docosyl groups [CH3−(CH2)21−, C22] [sodium (Na+)]. The DP for a few species is illustrated by the numbers (methylenes in docosyl:PCL = 21:8-11) on the top of the MALDI-TOF curve. In contrast, in Figure 6b, the MALDI-TOF spectrum for the diblock copolymer PM25-bPCL12.8 reflects two superimposed distributions separated by 114 and 14 mass units, corresponding to the molecular weights of the CL and −CH2− comonomers, respectively. The previous peaks assigned for C22-PCL10.7 (Figure 6a) can also be visualized in PM25-bPCL12.8 (Figure 6b), but now part of a family of different molecular weight distributions.

29



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30


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Figure 6. MALDI-TOF spectra (reflectron mode) of a) homopolymer C22-PCL10.7 (CH3(CH2)21O−[CO(CH2)5O]n−H), and b) diblock copolymer PM25-b-PCL12.8 (CH3(CH2)mO−[CO(CH2)5O]n−H). Numbers (m:n) indicate the degree of polymerization (DP) of each segment of (−CH2−)m and (CL)n, respectively. The asterisks indicate a αhydroxyl-ω-(carboxyl acid) PCL species (HA-PCL).

31



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Page 32 of 63

In an expanded view of the MALDI-TOF mass spectrum of C22-PCL10.7 (Figure 7a), fragments between 1200 and 1640 amu are visualized, the zone corresponds to fragments with 8-11 CL repeat units (Na+ and K+ ions). Using the same scale to observe PM25-bPCL12.8 species (Figure 7b), two different patterns were observed: 1) where each DP of PCL the block (DPPCL = 7-11) had its own distribution, with variations in the length of PM (for example PM:PCL = 21-28:8), and 2) a distribution in which each DP of the PM block had a different length of CL (for example PM:PCL = 21:8-11). The latter case is analogous to that of the C22-PCL10.7 homopolymer. Bimodal distribution curves for species with DPPCL = 9-11 can also be observed, which is attributable to the intermolecular transesterification reactions (Scheme S2, supporting information) favored by aluminum alkoxides at high temperatures (80 °C)56 and corroborated by the relatively moderate polydispersity (Mw/Mn = 1.73) determined by HT GPC. Peaks with low intensity attributable to macrocyclic species of ε-caprolactone (CL)n were also detected. It is known that (CL)n is a product of an intramolecular transesterification (Scheme S3) induced by aluminum alkoxides.56 The mass units of the majority of the peaks correspond to α-hydroxyl-ω-methyl terminal groups (Figure S20), evidencing the terminal groups of the PM25-b-PCL12.8 diblock copolymer, which is corroborated by the 1H (Figure 3a) and 13C (Figure S8a) NMR spectra.

32


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Figure 7. MALDI-TOF spectra (reflectron mode) expanded view for the 1200-1640 m/z fragments of a) homopolymer C22-PCL10.7 (CH3(CH2)21O−[CO(CH2)5O]m−H), where the numbers (21:m) correspond to the contributions of species with the same number of methylenes in the docosyl endgroup (CH2)21 and m to the degree of polymerization (DP) of ε-caprolactone (CL) [CO(CH2)5O]m units in the homopolymer (note: 114 and 16 are the values of the molecular weight of CL and the difference between Na+ and K+ (doping the same species of polymer), respectively) and b) diblock copolymer PM25-b-PCL12.8 (CH3(CH2)nO−[CO(CH2)5O]m−H) with all fragments doped with Na+, where the numbers (n:m) correspond to the DPs of different species of methylene (−CH2−)n and εcaprolactone (CL) [−CO(CH2)5O−]m units in the diblock copolymer, respectively (note: 114 and 14 are the values of the molecular weights of CL and −CH2−, respectively). DPPCLsegment = 7 (star), 8 (triangle), 9 (circle), 10(square), 11(trapezoid), and 12 (rhombus). 33



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To delineate the differences in thermal properties between C22-PCL and PM-b-PCL a DSC analysis was undertaken. For two species such as C22-PCL10.7 [Mn(NMR) = 1540] and PM25-b-PCL12.8 [Mn(NMR) = 1840] with similar aliphatic contents (21%) and Mn but with different chemical natures, the DSC analysis shows for both cases a single endothermic sharp peak (Figure 8 a-b). The melting enthalpy (ΔHm) for C22-PCL10.7 (Table 4) and PM25-b-PCL12.8 (Table 3) does not correspond to the regular values of PCL (Table S1, C2-PCL). This is evidence that the ΔHm involves contributions of both the C22 terminal groups and the PM25 segments. This will be corroborated from an analysis of the crystallization of C22-PCL10.7 and PM25-b-PCL12.8 (vide supra). Double-crystalline diblock copolymers including PE-b-PCL can exhibit segregated phases, with two distinct melting points. 14,26,44,57 Using this criterion, it is possible to conclude that the PM25-b-PCL12.8 and C22-PCL10.7 species do not exhibit evidence of segregated phases (DSC), with the caveat that the aliphatic segments (PM25 or C22) and ester segments (PCL) could be overlapping in a single endothermic peak. Previous reports of double segregated phases for PE-b-PCL were found in materials with relatively high values of Mn for the two segments. This it is expected that longer chains of both blocks eventually can induce more individual crystalline domains. 14,22,26,44 In the present case, the MW of the C22 (in C22-PCL10.7) end group or Mn of the PM25 block (in PM25-b-PCL12.8) and PCL are not large enough to observe a double melting point. We conclude that the differences in the chemical nature between C22-PCL10.7 and PM25-b-PCL12.8 are insufficient to induce phase segregation. In contrast the detected segregation of phases in crystalline diblock copolymers (double endothermic transition) for samples PM62-b-PCL8.1 and PM95-b-PCL7.5, where the Mn(GPC)

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is slightly high than that of the PM25-b-PCL12.8, is due their increase in Mn of the two blocks (Figure 8c-d)

Figure 8. DSC thermograms (second heating) of a) C22-PCL10.7 (C22 = 21 %), b) PM25-bPCL12.8 (PM = 21 %), c) PM62-b-PCL8.1 (PM = 49 %), and d) PM95-b-PCL7.5 (PM = 61 %).

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Greater insight to the effect of the type of substituents such as C22 (in C22-PCL10.7) and PM (in PM25-b-PCL12.8) on the PCL, a new polymeric species derived from PCL containing a shorter alkyl end group such as α-hydroxyl-ω-ethyl PCL (C2-PCL9.9) (Figure S9-S10) was prepared. The purpose of using C2-PCL9.9 is to minimize the effect of size in the alkyl group and eventually observe the contribution of PCL (experimental control). The variation of the end groups such as ethyl (C2), docosyl (C22) and a block of PM (PM25) adjacent to the PCL can show the effect of the end group on the thermal properties of the PCL. These three different polymers were sequentially analyzed by DSC. Figure 9 shows the thermograms of a first cooling and a second heating for the three species with similar DP for PCL: C2-PCL9.9, (DPPCL = 9.9), C22-PCL10.7 (DPPCL = 10.7) and PM25-b-PCL12.8 (DPPCL = 12.8). The reference specimen was C2-PCL9.9 with a short terminal group, expecting the little contribution of the ethyl group to the thermal properties of the PCL homopolymer (Table S1). For the crystallization process (cooling), in the case of C2PCL9.9, a single sharp exothermic peak of crystallization at Tc = 20 °C was observed. Crystallization of C22-PCL10.7 proceeded differently, involving two different phenomena: first, a broad band (Tc1 = 37 °C) before the main peak of crystallization (Tc2 = 32 °C) and second, a higher value of Tc (32 °C) than C2-PCL9.9 (20 °C). These two events of C22PCL10.7 can be explained in terms of the docosyl (C22) end group, where the Tc of 1docosanol (C22OH) is higher than that of C2-PCL9.9 (Tc = 20 °C), so now the C22 terminal group of PCL (in C22-PCL10.7) is responsible for the crystalline domain (xi = 8 %) at 37 °C of C22-PCL10.7 and its crystallization acts as a nucleation agent for the crystallization (Tc = 32 °C) of PCL. To corroborate this idea, the same effect is observed for PM25-b-PCL12.8, 36


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but with higher intensity and an increase in Tc. Now, the broad band (Tc = 57° C) is attributed to the PM25 and this effect was the consequence of the molecular weight distribution from PM25, corroborating the crystalline domains for each species [PM25 (or C22) and PCL]. This also can influence the nucleation of PCL which was also increased (Tc = 42 °C). Therefore, the effects of a PM25 block or C22 end group had effects on the nucleation of PCL, following the pattern PM25 (TcPCL = 42 °C) > C22 (TcPCL = 32 °C) > C2 (TcPCL = 20 °C).

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Figure 9. DSC thermograms [cooling (left) and second heating (right)] of PM25-b-PCL12.8 (Mn(NMR) = 1840, PM = 21 %, a, b), C22-PCL10.7 (Mn(NMR) = 1540, C22 = 21 %, c, d) and C2-PCL9.9 (Mn(NMR) = 1170, Et = 4 %, e, f). 38


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In the fusion process (second heating, Figure 9) in the thermogram of C2-PCL, two endothermic peaks (Tm =39 and 45 °C) were observed. The two signals may be explained in terms of two different sizes of crystallites that arise from two different environments, for example, crystallites immersed in a more amorphous phase (39 °C) and in zones that are less amorphous in the PCL (45 °C). The melting temperature (Tm) for the three oligomers showed an increase according to the tendency C2-PCL9.9 (Tm = 39 and 45 °C) < C22-PCL10.7 (Tm = 48 °C) < PM25-b-PCL12.8 (Tm = 56 °C), which can be attributed to the higher Mn or MW of PM25 and C22 compared to C2. An interesting observation for the C22 end group or a PM25 block attached to PCL is the single sharp peak in comparison with the C2 end group. A previous report describes that the C22 end group induces an increase in the long period (L) between the lamellae of PCL, as detected by SAXS.45 Considering the similarity between C22 and PM25, a probable explanation of the single sharp peak by DSC is that these linear aliphatic chains prevent the formation of different sizes of crystallites in PCL by separation between PCL lamellae, reducing the interaction between lamellae and eventually inducing more order (see AFM analysis). Visualization of the phase-segregation behavior and morphology of PM25-b-PCL12.8 are shown in AFM micrographs (Figure 10a-b). The lamellas are attributed to PCL blocks (white zones) according to their higher PCL content (79 wt. %) and crystallinity (xPCL = 58 %), have an average lamellar thickness of approximately 8 nm, are clearly visualized. The dark zones between lamellas are attributed to the amorphous domains of PCL and PM, which is congruent with the low crystallinity of PM (xPM = 7 %) detected by DSC. The AFM images of C22-PCL10.7 (Figure 10c-d) presented a similar profile of lamellar thickness 39



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(∼ 8nm) in comparison with PM25-b-PCL12.8, which is expected according to the values of crystallinity for the PCL (xPCL = 66 %) and docosyl end groups (xC22 = 8 %), as also quantified by DSC. The lamellar thicknesses for both species are similar (∼ 8 nm); this value is consistent with a previous study of PCL oligomers (Mn= 1400-2300) by SAXS, where the lamellar thickness exhibited values from 6.9 to 8.7 nm.58

Figure 10. Atomic force microscopy (AFM) tapping-mode amplitude images acquired at room temperature for (a, b) PM25-b-PCL12.8 [PM = 21 %] and (c, d) C22-PCL10.7 [C22 = 21 %]. Films made using toluene as solvent at a concentration of 0.5 wt % (drop coating) and annealing at 35 °C overnight.

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3.5 Morphology of PE/PCL blends using PM-b-PCL and C22-PCL as compatibilizers. An application of diblock copolymers such as PE-b-PCL14 and PM-bPCL44 is their use as compatibilizers in blends of polyethylene/poly(ε-caprolactone) (PE/PCL). In this context, it is interesting to test if an oligomeric diblock copolymer such as PM25-b-PCL12.8 has the same property as previously reported for species with high Mn such as PE-b-PCL (Mn = 10000-124000)14 or PM-b-PCL (Mn = 9200-17400)44. The similarity between PM25-b-PCL12.8 and C22-PCL10.7 allows us to address several questions: Are oligomers (PM25-b-PCL12.8 or C22-PCL10.7) effective as compatibilizers of PE/PCL blends, and can a homopolymer such as C22-PCL10.7 act as a compatibilizer of PE/PCL blends? To find the answers to these questions, a series of binary (PE/PCL, 70/30 wt. %) and ternary blends (PE/PCL/PM-b-PCL and PE/PCL/C22-PCL, 70/30/10 wt. %) were prepared by melting (see experimental section) and cooling the blends to room temperature followed by analysis using polarized optical microscopy (POM). The reason for the use of 10 wt. % of PM-b-PCL or C22-PCL to the blend (70/30 wt. %) was to allow comparison with previous work.14,44 In the case of homopolymers such as PE (Figure 11a) and PCL (Figure 11b), multiple spherulites are observed, although each has distinct characteristic colors. In the case of a binary blend of PE/PCL (70/30 wt. %), a separation of phases was clearly observed (Figure 11c), in which PCL is embedded in a PE matrix. However, when a series of oligomeric diblock copolymers were added as compatibilizers to create a ternary blend PE/PM/PM-b-PCL (70/30/10 wt. %), an improvement in the mixing of the two homopolymers was observed (Figure 11d-f). We conclude that oligomers of PM-b-PCL can also be used to achieve better mixing between PE and PCL. However, when oligomeric homopolymers such as C22-PCL with different contents of C22 (13-30 wt. %) were added as

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compatibilizers, a different effect was observed (Figure 11g-i). For oligoesters such as C22PCL10.7 and C22-PCL18.0, with low contents of C22 (wt. %) of 21 % (Figure 11h) and 13 % (Figure 11i), respectively, a separation of phases is clearly observed in both samples. By contrast, using C22-PCL6.6 (C22 = 30 wt. %), an improvement in the polymer mixing was noted (Figure 11g). It is evident that the C22 content is an important factor in the C22-PCL oligomers functioning as compatibilizers. Comparing two different species with the same aliphatic content, PM25-b-PCL12.8 (PM25 = 21 wt. %) and C22-PCL10.7 (C22 = 21 wt. %), these species showed different effects, with PM25-b-PCL12.8 demonstrating a better dispersion of components in the blend than C22-PCL10.7, which perhaps can be attributed to the polydispersity of the PM25 block.

Figure 11. Polarized optical microcopy (POM) (20 microns white bar) of: homopolymers a) PE and b) PCL; blend of homopolymers (70/30 wt. %): c) PE/PCL (reference); blends of homopolymers with PM-b-PCL as compatibilizer (70/30/10 wt. %): d) PE/PCL/PM25-bPCL12.8 [PM = 21 %], e) PE/PCL/PM62-b-PCL8.1 [PM2 = 49 %], and f) PE/PCL/PM95-bPCL7.5 [PM3 = 61 %]; blends of homopolymers with C22-PCL as compatibilizer (70/30/10 wt. %): g) PE/PCL/C22-PCL6.6 [C22 = 30 %], h) PE/PCL/C22-PCL10.7 [C22 = 21 %], and i) PE/PCL/C22-PCL18.0 [C22 = 13 %].

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The surface topography of all PE/PCL blends was studied by SEM. Figure 12 shows micrographs of the same binary and ternary blends that have been described in the POM analysis (Figure 11). For the binary blend PE/PCL (70/30 wt. % Figure 12a-b) used as a reference, two different phases are clearly visualized, a series of spheres attributable to PCL are embedded in a matrix of PE, evidencing a phase separation and corroborating the poor adhesion between the domains of each homopolymer previously visualized by POM. On the other hand, in three series of ternary blends PE/PCL/PM-b-PCL (70/30/10 wt. %), illustrated in Figure 12c-e, a gradual increase in the PM segment content (21-74 wt. %) in PM-b-PCL was evaluated. An improvement in the mixing after the addition of PM-b-PCL is observed, although the separation of phases still prevails, albeit to a significantly lower degree. In the case of PM25-b-PCL12.8 (21 wt. % of PM25) (Figure 12c) the contrast in the separation of phases was more evident than in PM62-b-PCL8.1 (49 wt. % of PM62) or PM95b-PCL7.5 (61 wt. % of PM95), which can be explained in terms of the low content of the PM block in PM25-b-PCL12.8. The use of C22-PCL oligoesters as compatibilizers in PE/PCL blends was also compared (Figure 12f-h). For oligoesters with a lower content of C22 such as C22-PCL10.7 (21 %) and C22-PCL18.0 (13 %), a separation of phases is clearly observed (Figure 12g,h), which is consistent with the observation by POM micrographs (Figure 11hi). Nevertheless, using an oligomer such as C22-PCL6.6 (C22 = 30 %, Figure 10d), a dramatic change was evidenced, with better adhesion and a reduction of PCL domains with a decrease in the diameter of the particles of PCL and their dispersion in the matrix. However, an additional analysis to explore other molecules such as C22-PCL0.93 (C22 = 75 %) and C22-PCL1.84 (C22 = 60 %) as compatibilizers showed poor results, with a clear separation of phases in the PE/PCL/C22-PCL blends (70/30/10 wt. %). So, the window of

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application of C22-PCL oligoesters as compatibilizers is not directly dependent on the C22 content, but an important factor is the Mn of PCL for each C22-PCL species.

Figure 12. Scanning electron microscopy (SEM) micrographs of cryofractured surfaces under liquid nitrogen for: blends of homopolymers PE/PCL (70/30 wt. %) blank a) 10 µm bar and b) 5 µm bar; blends of homopolymers (5 µm bar) with PM-b-PCL as compatibilizer (70/30/10 wt. %): c) PE/PCL/PM25-b-PCL12.8 [PM = 21 %], d) PE/PCL/PM62-b-PCL8.1 [PM = 49 %], e) PE/PCL/PM95-b-PCL7.5 [PM3 = 61 %]; blends of homopolymers (5 µm bar) with C22-PCL as compatibilizer (70/30/10 wt. %): f) PE/PCL/C22-PCL6.6 [C22 = 30 %], g) PE/PCL/C22-PCL10.7 [C22 = 21 %], and h) PE/PCL/C22-PCL18.0 [C22 = 13 %].

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Comparing our systems respect to previous reports with diblock copolymers with high Mn14,44,59,60 as compatibilizers is evident that diblock copolymers with high Mn showed better polymer mixture detected by SEM. The results in this work establish that the behavior as a compatibilizer of PE/PCL blends is not restricted to diblock copolymers with high Mn such as PE-b-PCL14,59,60 or PM-b-PCL,44 but can also be observed in oligomers derived from PM-b-PCL and some oligoesters such as C22-PCL6.6 [Mn (NMR)= 1080] with a longer aliphatic end group. Based on this evidence, we can conclude that the main parameters for the use of oligomers such as PM-b-PCL or C22-PCL as compatibilizers in PE/PCL blends is the content (wt. %) of aliphatic chains (PM block or C22 end group), which should preferably have values ≥ 30 % and Mn ∼ 1000-2000 Da. and whether the aliphatic chain is part of a PM block or a C22 terminal group. The proportion of PE in the PE/PCL blend (70/30 wt. %) is higher than PCL and it is expected that the best oligomers (PM-b-PCL and C22-PCL) used as compatibilizers may present relative high values of alkyl segment (30-74 wt. %) to improve the dispersion of the PE/PCL blend. Conclusions A series of α-hydroxyl-ω-methyl polymethylenes (CH3−[CH2]m−OH, PMOH) were synthesized by the living polymerization of a ylide. A series of diblock copolymers of poly(methylene-b-ε-caprolactone) (PM-b-PCL) were synthesized by the ring-opening polymerization (ROP) of ε-caprolactone (CL) using PMOH and aluminum isopropoxide [Al(OiPr)3] as a macroinitiator and catalyst, respectively. PM-b-PCL diblock copolymers with an increasing number-average molecular weight (Mn) and different ratios of the PM blocks were compared with a series of analogous homopolymers derived from α-hydroxyl-

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ω-docosyl poly(ε-caprolactone) (PCL) (C22-PCL). The structures were validated by 1H and 13

C NMR, MALDI-TOF MS and FT-IR analysis. AFM images showed a similar lamellar

morphology between PM-b-PCL and C22-PCL (79 wt. % of PCL), where the lamellar thickness was mainly attributed to the crystalline domains of PCL. The weight fraction of PM had a strong effect on the thermal properties of PM-bPCL where a double crystalline domain for materials containing a high wt. % of PM. This is indicative of phase segregation which was linked to the PM content and its Mn. In contrast, all samples of C22-PCL exhibited a single endothermic peak. However, the alkyl segments such as the docosyl (C22) terminal group [CH3−(CH2)21−] and PM block [CH3−(CH2)m−] crystallized before the PCL, and which induced nucleation of PCL. Thus, the crystallization attributed to the alkyl segments (C22 end group or PM block) attached to PCL corroborated the crystalline domains for each species. Oligomers derived from PM-b-PCL and C22-PCL were explored as compatibilizers of polyethylene/poly(ε-caprolactone) (PE/PCL) blends. Trends for improving the mixing of PE/PCL blends was obtained, by POM and SEM. Aliphatic content up to 30 wt. % of PM block (PM-b-PCL) or the docosyl component (C22-PCL) and values of Mn ∼ 1000-2000 Da provided the best results. Therefore, both PM-b-PCL or a terminal group [docosyl, CH3−(CH2)21−] in a homopolymer (C22-PCL) can potentially be used as compatibilizers to improve the PE/PCL blends.

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ASSOCIATED CONTENT Supporting Information Available: Experimental details of synthesis and characterization data (Figures and Tables such as INADEQUATE 2D NMR,1H and

13

C

NMR, MALDI-TOF, FT-IR spectra, DSC thermograms and TLC). This material is available free of charge via the Internet at http://pubs-acs-org.

AUTHOR INFORMATION Corresponding Author *[email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT J.E.B. is much indebted to the University of California Institute for México and the United States (UC MEXUS) and Consejo Nacional de Ciencia y Tecnología (CONACYT) from México for a postdoctoral fellowship (2012-2014). This work was supported by the National Science Foundation, Award No. CHE-1153118. J.E.B. thanks Dr. Beniam Berhane, Dr. John Greaves and Dr. Phillip R. Dennison for their advice with the acquisition of the MALDI-TOF and NMR spectra, respectively. Finally, J.E.B. thanks Dr. Igor

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Barsukov, Dr. Jessica Witt, and Dr. William Gaieck for assistance with the POM, SEM, and AFM, respectively.

REFERENCES (1) Hamad, K.; Kaseem, M.; Deri, F. Recycling of waste from polymer materials: An overview of the recent works. Polym. Degrad. Stab. 2013, 98, 2801-2812. (2) Feuilloley, P.; César, G.; Benguigui, L.; Grohens, Y.; Pillin, I.; Bewa, H.; Lefaux, S.; Jamal, M. Degradation of polyethylene designed for agriculture purpose. J. Polym. Environ. 2005, 13, 349-355. (3) Hakkarainen, M.; Albertsson, A.-C. Environmental degradation of polyethylene (In: Long term properties of polyolefins, volume editor: Ann-Christine Albertsson). Adv. Polym. Sci. 2004, 169: 177-200. (4) Sangale, M.K.; Shahnawaz, M.; Ade, A.B. A review on biodegradation of polythene: The microbial approach. J. Bioremed. Biodeg. 2012, 3, 164. (5) Hayes, D.G.; Dharmalingam, S.; Wadsworth, L.C.; Leonas, K.K.; Miles, C.; Inglis, D.A. In Degradable Polymers and Materials: Principles and Practice, 2nd ed.; ACS Symposium Series: 2012, Vol. 1114, p 201-223. (6) Hirai, H.; Takada, H.; Ogata, Y.; Yamashita, R.; Mizukawa, K.; Saha, M.; Kwan, C.; Moore, C.; Gray, H.; Laursen, D.; Zettler, E.R.; Farrington, J.W.; Reddy, C.M.; Peacock, E.E.; Ward, M.W. Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches. Mar. Pollut. Bull. 2011, 62, 1683-1692. 48


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(7) Hati, S.S.; Dimari, G.A. Polyethylene plastics (PEP): Considerations for its classification as a new type of persistent organic pollutants (POPs) from a developing country’s perspective. Pac. J. Sci. Tech. 2010, 11, 592-597. (8) Luckachan, G.E.; Pillai, C.K.S. Biodegradable polymers- A review on recent trends and emerging perspectives. J. Polym. Environ. 2011, 19, 637-676. (9) Khatiwala, V.K.; Shekhar, N.; Aggarwal, S.; Mandal, U.K. Biodegradation of poly(εcaprolactone) (PCL) film by Alcaligenes faecalis. J. Polym. Environ. 2008, 16, 61-67. (10) de Lourdes-Rezende, M.; dos Santos-Rosa D.; D.D.S.; Fassina-Guedes, C.D.G.; Macedo-Fechine, G.J.; Araújo-Nóbrega, J. Investigation of the effect of addition of calcium stearate on the properties of low-density polyethylene/poly(ε-caprolactone) blends. J. Mater. Sci. 2014, 49, 1544-1555. (11) Madhu, G.; Bhunia, H.; Bajpai, P. Blends of high density polyethylene and poly(Llactic acid): mechanical and thermal properties. Polym. Eng. Sci. 2014, 54, 2155-2160. (12) Gallego, R.; López-Quintana, S.; Basurto, F.; Núñez, K.; Villarreal, N.; Merino, J.C. Synthesis of new compatibilizers to poly(lactic acid) blends. Polym. Eng. Sci. 2014, 54, 522-530. (13) Cowie, J.M.G. and Arrighi, V. In Polymers: Chemistry and physics of modern materials, third ed.; CRC Press Taylor & Francis Group: Florida, 2008; p 121. (14) Lu, Y.; Hu, Y.; Chung, T.C.M. Syntheses of diblock copolymers polyolefin-b-poly(εcaprolactone) and their applications as the polymeric compatilizer. Polymer 2005, 46, 10585-10591. 49



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(15) Anderson, K.S.; Lim, S.H.; Hillmyer, M.A. Toughening of polylactide by melt blending with linear low-density polyethylene. J. Appl. Polym. Sci. 2003, 89, 3757-3768. (16) Wang, Y.; Hillmyer, M.A. Polyethylene-poly(L-lactide) diblock copolymers: synthesis and comparison of poly(L-lactide)/polyethylene blends. J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 2755-2766. (17) Kim, J.K.; Yang, S.Y.; Lee, Y.; Kim, Y. Functional nanomaterials based on block copolymers self-assembly. Prog. Polym. Sci. 2010, 35, 1325-1349. (18) Castillo, R.V.; Müller, A.J. Crystallization and morphology of biodegradable or biostable single and double crystalline block copolymers. Prog. Polym. Sci. 2009, 34, 516560. (19) Darling, S.B. Directly the self-assembly of block copolymers. Prog. Polym. Sci. 2007, 32, 1152-1204. (20) Lynd, N.A.; Meuler, A.J.; Hillmyer, M.A. Polydispersity and block copolymer selfassembly. Prog. Polym. Sci. 2008, 33, 875-893. (21) He, W.-N.; Xu, J.-T. Crystallization assisted self-assembly of semicrystalline block copolymers. Prog. Polym. Sci. 2012, 37, 1350-1400. (22) Nojima, S.; Akutsu, Y.; Washino, A.; Tanimoto, S. Morphology of melt-quenched poly(ε-caprolactone)-block-polyethylene copolymers. Polymer 2004, 45, 7317-7324.

50


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Nojima, S.; Akutsu, Y.; Akaba, M.; Tanimoto, S. Crystallization behavior of poly(εcaprolactone) blocks starting from polyethylene lamellar morphology in poly(εcaprolactone)-block-polyethylene copolymers. Polymer 2005, 46, 4060-4067. (24) Nojima, S.; Kiji, T.; Ohguma, Y. Characteristic melting behavior of double crystalline poly(ε-caprolactone)-block-polyethylene copolymers. Macromolecules 2007, 40, 75667572. (25) Sakurai, T.; Nagakura, H.; Gondo, S.; Nojima, S. Crystallization of poly(εcaprolactone) blocks confined in crystallized lamellar morphology of poly(ε-caprolactone)block-polyethylene copolymers: effects of polyethylene crystallinity and confinement size. Polym. J. 2013, 45, 436-443. (26) Báez, J.E.; Ramírez-Hernández, A.; Marcos-Fernández, A. Synthesis, characterization, and degradation of poly(ethylene-b-ε-caprolactone) diblock copolymer. Polym. Adv. Tech. 2010, 21, 55-64. (27) Luo, J.; Shea, K.J. Polyhomologation. A living C1 polymerization. Acc. Chem. Res. 2010, 43, 1420-1433. (28) Zhang, H.; Alkayal, N.; Gnanou, Y.; Hadjichristidis, N. Polymethylene-based copolymers by polyhomologation or by its combination with controlled/living and living polymerizations. Macromol. Rapid Commun. 2014, 35, 378-390. (29) Busch, B.B.; Paz, M.M.; Shea, K.J.; Staiger, C.L.; Stoddard, J.M.; Walker, J.M.; Zhou, X.-Z.; Zhu, H. The boron-catalyzed polymerization of dimethylsulfoxonium methylide. A living polymethylene synthesis. J. Am. Chem. Soc. 2002, 124, 3636-3646. 51



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(30) Wagner, C.E.; Rodriguez, A.A.; Shea, K.J. Synthesis of linear α-olefins via polyhomologation. Macromolecules 2005, 38, 7286-7291. (31) Busch, B.B.; Staiger, C.L.; Stoddard, J.M.; Shea, K.J. Living polymerization of sulfur ylides.

Synthesis

of

terminally

functionalized

and

telechelic

polymethylene.

Macromolecules 2002, 35, 8330-8337. (32) Wagner, C.E.; Kim, J.-S.; Shea, K.J. The polyhomologation of 1-boraadamantane: mapping the migration pathways of a propagating macrotricyclic trialkylborane. J. Am. Chem. Soc. 2003, 125, 12179-12195. (33) Zhou, X.-Z.; Shea, K.J. Ersatz ethylene-propylene copolymers: the synthesis of linear carbon backbone copolymers one carbon atom at a time. J. Am. Chem. Soc. 2000, 122, 11515-11516. (34) Sulc, R.; Zhou, X.-Z.; Shea, K.J. Repetitive sp3-sp3 carbon-carbon bond-forming copolymerizations of primary and tertiary ylides. Synthesis of substituted carbon backbone polymers: poly(cyclopropylidine-co-methylidine). Macromolecules 2006, 39, 4948-4952. (35) Bai, J. Shea, K.J. Copolymers from a single monomer: synthesis of poly(methylideneco-trimethylsilylmethylidene). Macromolecules 2006, 39, 7196-7198. (36) Shea, K.J.; Staiger, C.L.; Lee, S.Y. Synthesis of polymethylene block copolymers by the polyhomologation of organoboranes. Macromolecules 1999, 32, 3157-3158. (37) Zhou, X.-Z.; Shea, K.J. Synthesis of poly(methylene-b-styrene) by sequential living polymerization. Macromolecules 2001, 34, 3111-3114.

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(38) Kowalski, A.; Duda, A.; Penczek, S. Mechanism of cyclic ester polymerization initiated with tin(II) octoate. 2. Macromolecules fitted with tin(II) alkoxide species observed directly in MALDI-TOF spectra. Macromolecules 2000, 33, 689-695. (39) Storey, R.F.; Sherman, J.W. Kinetics and mechanism of the stannous octoate-catalyzed bulk polymerization of ε-caprolactone. Macromolecules 2002, 35, 1504-1512. (40) Duda, A. Preparation of telechelic polyester oligodiols by chain-transfer polymerization. Macromolecules 1994, 27, 576-582. (41) Miola-Delaite, C.; Hamaide, T.; Spitz, R. Anionic coordinated polymerization of εcaprolactone with aluminum, zirconium and some rare earths alkoxides as initiators in the presence of alcohols. Macromol. Chem. Phys. 1999, 200, 1771-1778. (42) Ropson, N.; Dubois, Ph.; Jérôme, R.; Teyssié, Ph. Macromolecular engineering of polylactones and polylactides. 17. Cryometric and viscosimetric analysis of the species active in the ring-opening polymerization of lactones, lactides, and cyclic anhydrides as initiated by aluminum triisopropoxide. Macromolecules 1994, 27, 5950-5956. (43) Ring, J.O.; Thomann, R.; Mülhaupt, R.; Raquez, J.-M.; Degée, P.; Dubois, P. Controlled synthesis and characterization of poly[ethylene-block-(L,L-lactide)]s by combining catalytic ethylene oligomerization with “coordination-insertion” ring-opening polymerization. Macromol. Chem. Phys. 2007, 208, 896-902. (44) Li, Q.-Z.; Zhang, G.Y.; Chen, J.-Z.; Zhao, Q.-L.; Lu, H.-C.; Huang, J.; Wei, L.-H.; D’Agosto, F.; Boisson, C.; Ma, Z. Well-defined polyolefin/poly(ε-caprolactone) diblock

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copolymers: new synthetic strategy and application. J. Polym. Sci. Part A: Polym. Chem. 2011, 49, 511-517. (45) Báez, J.E.; Marcos-Fernández, A.; Galindo-Iranzo, P. On the effect of alkyl end group in poly(ε-caprolactone) oligomers: preparation and characterization. Polym. Plast. Technol. Eng. 2011, 50: 839-850. (46) Báez, J.E.; Martínez-Rosales, M.; Martínez-Richa, A. Ring-opening polymerization of lactones catalyzed by decamolybdate anion. Polymer 2003, 44: 6767-6772. (47) Brandrup, J.; Immergut, E.H. Polymer Handbook, 3rd ed. Wiley-Interscience: New York, 1989; p V/19. (48) Crescenzi, V.; Manzini, G.; Calzolari, G.; Borri, C. Thermodynamics of fusion of poly-β-propiolactone and poly-ε-caprolactone. Comparative analysis of the melting of aliphatic polylactone and polyester chains. Eur. Polym. J. 1972, 8, 449-463. (49) Soderquist, J.A.; Najafi, M.R. Selective oxidation of organoboranes with anhydrous trimethylamine N-oxide. J. Org. Chem. 1986, 51, 1330-1336. (50) Han, C.J.; Lee, M.S.; Byun, D.-J.; Kim, S.-Y. Synthesis of hydroxy-terminated polyethylene via controlled chain transfer reaction and poly(ethylene-b-caprolactone) block copolymer. Macromolecules 2002, 35, 8923-8925. (51) Makio, H.; Fujita, T. Synthesis of chain-end functionalized polyolefins with a bis(phenoxy imine) titanium catalyst. Macromol. Rapid Commun. 2007, 28, 698-703.

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(52) Zhang, Y.; Li, H.; Zhang, Y.; Li, Q.; Ma, Z.; Dong, J.-Y.; Hu, Y. Synthesis and properties of polyethylene-bound antioxidants. Macromol. Chem. Phys. 2014, 215, 763775. (53) Báez, J.E.; Martínez-Richa, A.; Marcos-Fernández, A. One-step route to α-hydroxylω-(carboxylic acid) polylactones using catalysis by decamolybdate anion. Macromolecules 2005, 38, 1599-1608. (54) Takizawa, K.; Tang, C.; Hawker, C.J. Molecularly defined caprolactone oligomers and polymers: synthesis and characterization. J. Am. Chem. Soc. 2008, 130, 1718-1726. (55) Kotz, J.C.; Treichel, P. In Chemistry & Chemical Reactivity, 4th ed.; Saunders College Publishing: Fort Worth, Texas, 1999; pp. 626-628. (56) Kricheldorf, H.R.; Mang, T.; Jonté, J.M. Polylactones. 1. Copolymerization of glycolide and ε-caprolactone. Macromolecules 1984, 17, 2173-2181. (57) Müller, A.J.; Balsamo, V.; Arnal, M.L. Nucleation and crystallization in diblock and triblock copolymers (In: Block copolymers II, volume editor: Volker Abetz). Adv. Polym. Sci. 2005, 190, 1-63. (58) Báez, J.E.; Marcos-Fernández, A. A comparison of three different biodegradable aliphatic oligoesters (PGA, PLLA, and PCL) with similar linear alkyl end groups by DSC and SAXS. Int. J. Polym. Anal. Charact. 2015, 20, 637-644. (59) Mu, J.-S.; Yang, F.; Liu, Z.-S.; Li, Y.-S. Polyethylene-block-poly(ε-caprolactone) diblock copolymers: synthesis and compatibility. Polym. Int. 2014, 63, 2017-2022.

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(60) Descour, C.; Macko, T.; Schreur-Piet, I.; Pepels, M.P.F.; Duchateau, R. In situ compatibilization of alkenyl-terminated polymer blends using cross metathesis. RSC Advances 2015, 5, 9658-9666.

Figure Captions Figure 1. 1H NMR (500 MHz) spectra of (a) PM25OH [CH3−(CH2)m−OH, DP(NMR) = 25, Mn(GPC) = 340] and (b) 1-docosanol [CH3−(CH2)21−OH (C22OH), MW = 326], both samples in CDCl3 at 40 °C. Figure 2. 13C NMR (125 MHz) spectrum of PM25-b-PCL12.8 in CDCl3 at 40 °C. Figure 3. Comparison of 1H NMR (500 MHz) spectra of a) PM25-b-PCL12.8 and b) C22PCL10.7 in CDCl3 at 40 °C. Figure 4. MALDI-TOF spectrum for different isolated fractions of C22-PCL (DPcalcd = 3) by column chromatography (Figure S13). a) MW(NMR) = 432 (monomer, C22-PCL0.93), b) MW(NMR) = 536 (dimer, C22-PCL1.84), c) Mn(NMR) = 730 (trimer and oligomers, C22PCL3.6) (Table 4) (C22-PCLn, where n = DPNMR). Figure 5. Effect of docosyl end group (wt. %) on melting point (Tm) of C22-PCL homopolymer (oligoesters). Figure 6. MALDI-TOF spectra (reflectron mode) of a) homopolymer C22-PCL10.7 (CH3(CH2)21O−[CO(CH2)5O]n−H), and b) diblock copolymer PM25-b-PCL12.8 (CH3(CH2)mO−[CO(CH2)5O]n−H). Numbers (m:n) indicate the degree of polymerization (DP) of each segment of (−CH2−)m and (CL)n, respectively. The asterisks indicate a αhydroxyl-ω-(carboxyl acid) PCL species (HA-PCL). Figure 7. MALDI-TOF spectra (reflectron mode) expanded view for the 1200-1640 m/z fragments of a) homopolymer C22-PCL10.7 (CH3(CH2)21O−[CO(CH2)5O]m−H), where the numbers (21:m) correspond to the contributions of species with the same number of methylenes in the docosyl end group (CH2)21 and m to the degree of polymerization (DP) of ε-caprolactone (CL) [CO(CH2)5O]m units in the homopolymer (note: 114 and 16 are the values of the molecular weight of CL and the difference between Na+ and K+ (doping the same species of polymer), respectively) and b) diblock copolymer PM25-b-PCL12.8 (CH3(CH2)nO−[CO(CH2)5O]m−H) with all fragments doped with Na+, where the numbers (n:m) correspond to the DPs of different species of methylene (−CH2−)n and ε-caprolactone 56


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(CL) [−CO(CH2)5O−]m units in the diblock copolymer, respectively (note: 114 and 14 are the values of the molecular weights of CL and −CH2−, respectively). Figure 8. DSC thermograms (second scan) of a) C22-PCL10.7 (C22 = 21 %), b) PM25-bPCL12.8 (PM = 21 %), c) PM62-b-PCL8.1 (PM = 49 %), and d) PM95-b-PCL7.5 (PM = 61 %). Figure 9. DSC thermograms [cooling (left) and second heating (right)] of PM25-b-PCL12.8 (Mn(NMR) = 1840, PM = 21 %, a, b), C22-PCL10.7 (Mn(NMR) = 1540, C22 = 21 %, c, d) and C2-PCL9.9 (Mn(NMR) = 1170, Et = 4 %, e, f). Figure 10. Atomic force microscopy (AFM) tapping-mode amplitude images acquired at room temperature for (a, b) PM25-b-PCL12.8 [PM = 21 %] and (c, d) C22-PCL10.7 [C22 = 21 %]. Films made using toluene as solvent at a concentration of 0.5 wt % (drop coating) and annealing at 35 °C overnight. Figure 11. Polarized optical microcopy (POM) of: homopolymers a) PE and b) PCL; blend of homopolymers (70/30 wt. %): c) PE/PCL blank; blends of homopolymers with PM-bPCL as compatibilizer (70/30/10 wt. %): d) PE/PCL/PM25-b-PCL12.8 [PM = 21 %], e) PE/PCL/PM62-b-PCL8.1 [PM2 = 49 %], and f) PE/PCL/PM95-b-PCL7.5 [PM3 = 61 %]; blends of homopolymers with C22-PCL as compatibilizer (70/30/10 wt. %): g) PE/PCL/C22PCL6.6 [C22 = 30 %], h) PE/PCL/C22-PCL10.7 [C22 = 21 %], and i) PE/PCL/C22-PCL18.0 [C22 = 13 %]. Figure 12. Scanning electron microscopy (SEM) micrographs of cryofractured surfaces under liquid nitrogen for: blends of homopolymers PE/PCL (70/30 wt. %) blank a) 10 µm bar and b) 5 µm bar; blends of homopolymers (5 µm bar) with PM-b-PCL as compatibilizer (70/30/10 wt. %): c) PE/PCL/PM25-b-PCL12.8 [PM = 21 %], d) PE/PCL/PM62-b-PCL8.1 [PM = 49 %], e) PE/PCL/PM95-b-PCL7.5 [PM3 = 61 %]; blends of homopolymers (5 µm bar) with C22-PCL as compatibilizer (70/30/10 wt. %): f) PE/PCL/C22-PCL6.6 [C22 = 30 %], g) PE/PCL/C22-PCL10.7 [C22 = 21 %], and h) PE/PCL/C22-PCL18.0 [C22 = 13 %]. Scheme 1. Synthesis of a homopolymer (left) and diblock copolymer (right) derived from poly(ε-caprolactone) (PCL) from the ring-opening polymerization (ROP) of ε-caprolactone (CL). Scheme 2. Synthesis polyhomologation.

of


polymethylene

(PMOH)

by

57



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Table 1. α-Hydroxyl-ω-methyl polymethylenes [CH3−(CH2)m−OH, PMOH] synthesized by polyhomologation. Thermal properties of PMOH and 1-docosanol [CH3−(CH2)21−OH, C22OH].

DP(calcd)a 21 48 85

Sample C22OHf PM25OHj,h PM62OHj,i PM95OHj,i

DP(NMR)b 25 62 95

DP(GPC)c 22 54 87

Mn(GPC)c 326g 340 790 1260

Mw/Mnc 1.03 1.04 1.01

Tm (°C)d 73 49,71 104 115

ΔHm (J/g)d 246 182 218 230

xi (%)e 88 65 78 83

a

Obtained from the equation DP(calcd) = [(Ylide/B(hexyl)3)/A] + B, where A is the number of main chains per atom of boron and B is the number of methylenes in the hexyl group, with values of 3 and 5, respectively; Mn(calcd) = DP(calcd) × MWCH2 + MWter, MWCH2 and MWter represent the molecular weights of methylene repetitive unit in the polymer and the terminal group with values of 14 g/mol (−CH2−) and 32 (CH3−, HO−), respectively. b DP(NMR) = (Ipol/#Hpol)/(Iter/#Hter) + 2, where Ipol and Iter represent the values of the integrals obtained by 1H NMR from the polymethylene (1.27 (CDCl3) or 1.35 ppm (TCE-d2), [−CH2−]) and the methyl terminal group (0.87 (CDCl3) or 0.96 ppm (TCE-d2) peaks, [−CH3]), respectively; #Hpol and #Hter represent the numbers of protons attributed to each integral of the polymer and methyl terminal group, with values of 2 and 3, respectively; the value of 2 that is added in the last part of the equation indicates that both methylenes close to the hydroxyl end group (−CH2b−CH2a−OH, δa = 3.66 and δb =1.62 ppm) are not included in Ipol because they have different chemical shifts. Mn(NMR) = DP(NMR) × MWCH2 + MWter. c Determined by hightemperature gel permeation chromatography (HT-GPC) using polyethylene standards and calculated from DP(GPC) = (Mn(GPC) − MWter)/MWCH2, where Mn(GPC) is obtained by HT-GPC. d Quantified by DSC. e Calculated from the equation xi = ΔHm/ΔH0m × 100, where ΔH0m is the heat of fusion for perfect PE crystals (277 J/g).47 f Commercial sample from Aldrich . g Molecular weight (g/mol) of a pure linear aliphatic alcohol (monodisperse). j PMnOH, where n value is from DP(NMR), polymerizations were carried out using THFh (62 °C) or THF:toluenei (50:50, vol:vol) (90 °C) as solvents for 10 min. i ®

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Table 2. Diblock copolymers synthesized by the ring-opening polymerization (ROP) of lactones, using α-hydroxyl-ω-methyl polymethylene (PMOH) as precursors. Sample PM25OH PM25-b-PCL10.9g PM25-b-PCL12.8g PM62OH PM62-b-PCL8.1h PM95OH PM95-b-PCL7.5h

T (°C) r.t. 80 90 90

DPPCL (calcd)a 9.2 8.2 10.5 9.6

DPPCL (NMR)b 10.9 12.8 8.1 7.5

Mn(calcd)

Mn(NMR)c

Mn(GPC)d

Mw/Mnd

320i 1430j 1310j 700i 2090j 1220i 2450j

380 1620 1840 900 1820 1360 2220

340 1900 1300 790 1670 1260 1900

1.03 1.23 1.73 1.04 1.46 1.01 1.20

Yield (%)e 99 87 99 99 99 85 90

PM (wt%)f 100 23 21 100 49 100 61

a

Calculated from the molar ratio lactone/PMOH. b Obtained from the equation DPPCL(NMR) = [Ipol/#Hpol]/[Iter/#Hter], where Ipol and Iter represent the integrals obtained by 1H NMR from the polyester [−CH2−(C=O)−O−] and methyl [−CH3] terminal group peaks, and #Hpol and #Hter represent the numbers of protons assigned for each integral. c Deduced from 1H NMR by analysis of terminal groups. d Determined by high−temperature gel permeation chromatography (HT GPC) using polyethylene standards. e Calculated by gravimetric analysis. f Determined by the equation PM = Mn(PMOH)/Mn(PM-b-PCL) × 100, from the values by Mn(NMR). g,h Reaction time of 17g or 48h h. i Calculated from the equation Mn(calcd) = DP(calcd) × (MW(CH2) + MW(CH3OH), where MW is the molecular weight of methylene (14 g/mol) or methanol as an end group (32 g/mol); obtained from the equation DP(calcd) = [(ylide/B(hexyl)3)/A] + B, where A is the number of main chains per atom of boron and B is the number of methylenes in the hexyl group, with values of 3 and 5, respectively. j Determined from the equation Mn(calcd) = Mn(NMR)PMOH + MnPolyester, where Mnpolyester = DPPester(calcd) × MWCL, where DPPester(calcd) = lactone/PMOH molar ratio and MWCL is the molecular weight of CL = 114 g/mol.

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Table 3. Thermal properties of PM-b-PCL diblock copolymers.

Sample

Mn(GPC)a

PM25-b-PCL12.8 PM62-b-PCL8.1 PM95-b-PCL7.5

1300 1670 1900

PM (wt. %)b 21 49 61

TmPM (°C)c 55 104 116

TmPCL (°C)c 55 43 24

ΔHm (J/g)c, 100 78,26 106,13

ΔHmPM (J/g)c,d 21 78 106

ΔHmPCL (J/g)c,e 79 26 13

xPM (%)c,f 7 28 38

xPCL (%)b,g 58 19 9

a

Determined by high-temperature gel permeation chromatography (HT GPC) using polyethylene standards. b Determined by the equation PM = Mn(PMOH)/Mn(PM-b-Polyester) × 100, from the values by Mn(NMR). c Obtained by DSC. d Determined from the equation ΔHmPM = ΔHm.fPM, where fPM is the weight fraction of the PM. e Determined from the equation ΔHmPCL = ΔHm − (ΔHm.fPM). f Calculated from ΔHmPM using the equation xi = ΔHmPM/ΔH0mPE × 100, where ΔH0mPE is the enthalpy of fusion for a perfect PE crystal (277.0 J/g).47 g Calculated from ΔHmPCL using the equation xi = ΔHmPCL/ΔH0mPCL × 100, where ΔH0mPCL is the enthalpy of fusion for a perfect PCL crystal (135.3 J/g).48

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Table 4. Thermal properties of α-hydroxyl-ω-docosyl poly(ε-caprolactone)s (C22-PCLs).a

DPcalcdb DPNMRc,d Mn(NMR)c,e

Sample C22-PCL0.93lm C22-PCL1.84lm C22-PCL3.6l C22-PCL4.6l C22-PCL5.7 C22-PCL6.6 C22-PCL7.6 C22-PCL8.9 C22-PCL10.7 C22-PCL12.3 C22-PCL13.6 C22-PCL14.7 C22-PCL15.9 C22-PCL16.9 C22-PCL18.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0.93 1.84 3.6 4.6 5.7 6.6 7.6 8.9 10.7 12.3 13.6 14.7 15.9 16.9 18.0

432 536 730 860 970 1080 1190 1340 1540 1730 1870 2000 2140 2250 2380

wt.% C22c,f 75 60 44 38 33 30 27 24 21 18 17 16 15 14 13

Tm g (°C) 64 57 47 47 44 45 46 47 48 50 51 52 52 52 53

ΔHmg (J/g) 154 135 122 117 126 127 121 118 114 107 106 104 99 99 98

ΔHC22g,h (J/g) 154 135 53 44 41 38 32 28 24 19 18 16 14 13 12

ΔHPCLg,i (J/g) -n -n 69 73 85 89 89 90 90 88 88 88 85 86 86

x

55 48 19 15 14 13 11 10 8 6 6 5 5 4 5

a

Oligomers synthesized by ring-opening polymerization of ε-caprolactone (CL) using Al(OiPr)3 and 1-docosanol as catalyst and initiator, respectively, and polymerization with THF as solvent at room temperature by 17 h under nitrogen atmosphere, C22-PCLn, where n = DPNMR. b Calculated from the feed molar ratio CL/1-docosanol (monomer/initiator). c Calculated by 1H NMR. d Obtained from end group analysis from the equation DPPester(NMR) = [Ipol/#Hpol]/[Iter/#Hter], where Ipol and Iter represent the integrals obtained by 1H NMR from the polyester [−CH2−(C=O)−O−, δ 2.30] and methyl [−CH3, δ 0.87] terminal group peaks and #Hpol and #Hter represent the numbers of protons assigned for each integral, with values of 2 and 3, respectively. e Determined from the equation Mn(NMR) = (DPPCL × MWCL) + MW1-docosanol, where MW is the molecular weight of CL or 1-docosanol. f Obtained from the equation wt. % C22 = [MW1-docosanol/Mn(NMR)] × 100, where MW1-docosanol is the molecular weight of 1-docosanol. g Obtained by DSC analysis. h Determined from the equation ΔHC22 = ΔHm.xC22 where xC22 is the weight fraction of docosyl end group [−(CH2)21−CH3] in the PCL oligoester. i

61


g,j

C22

x

g,k

PCL

-n -n 51 53 62 65 65 66 66 65 65 65 62 63 63


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Determined from the equation ΔHPCL = ΔHm − (ΔHm.xC22), where xC22 is the weight fraction of the docosyl end groups in the PCL oligoester. j Calculated from ΔHC22 using the equation xi = ΔHC22/ΔH0PE × 100, where ΔH0PE is the enthalpy of fusion for a perfect PE crystal (277.0 J/g).47 k Calculated from ΔHPCL using the equation xi = ΔHPCL/ΔH0mPCL × 100, where ΔH0PCL is the enthalpy of fusion of a perfect PCL crystal (135.3 J/g).48 l Species isolated by column chromatography. m Species isolated (by column chromatography) as a molecule without a molecular weight distribution (monodisperse). n amorphous PCL is assuming for monomer and dimer due to previous reference.54

Synthesis of poly(methylene-b-ε-caprolactone) and poly(εcaprolactone) with linear alkyl end groups. Synthesis, characterization, phase behavior and compatibilization efficacy. José E. Báez, Ruobing Zhao, Kenneth J. Shea*

Department of Chemistry, University of California, Irvine (UCI), Irvine, California 926972025, United States

Table of Contents

Diblock copolymer

Homopolymer

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Synthesis of Poly(methylene-b-Îµ-caprolactone) and Poly(Îµ

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