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Enzymatic One-Pot Route to Telechelic Polypentadecalactone Epoxide: Synthesis, UV Curing, and Characterization Magnus Eriksson,† Linda Fogelstro¨m,‡ Karl Hult,† Eva Malmstro¨m,‡ Mats Johansson,‡ Stacy Trey,*,‡ and Mats Martinelle*,† Department of Biochemistry, School of Biotechnology, KTH, Royal Institute of Technology, SE-106 91 Stockholm, Sweden, and Department of Fiber and Polymer Technology, School of Chemical Science and Engineering, KTH, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Received July 13, 2009; Revised Manuscript Received August 25, 2009
In an enzymatic one-pot procedure immobilized lipase B from Candida antarctica was used to synthesize semicrystalline diepoxy functional macromonomers based on glycidol, pentadecalactone, and adipic acid. By changing the stoichiometry of the building blocks, macromonomers of controlled molecular weight from 1400 to 2700 g mol-1 could be afforded. The enzyme-catalyzed reaction went to completion (conversion g95%) within 24 h at 60 °C. After removal of the enzyme, the produced macromonomers were used for photopolymerization without any purification. The macromonomers readily copolymerized cationically with a cycloaliphatic diepoxide (Cyracure UVR-6110; CA-dE) to high conversion. The cross-linked copolymers formed a durable film with a degree of crystallinity depending on the macromonomer size and amount of CA-dE used, without CA-dE the macromonomers homopolymerized only to a low degree. Combined with CA-dE conversions of 85-90% were determined by FT-Raman spectroscopy. The films became more durable once reinforced with CA-dE, increasing the cross-link density and reducing the crystallinity of the PDL segments in the films.
Introduction In the past 20 years, the use of lipase catalysis has been employed to synthesize polyesters by condensation or ringopening polymerization.1-4 Lipases are proficient catalysts in acyl-transfer reactions at the methods of esterification, transesterification, polyesterification, and polytransesterification. A variety of polymers have been synthesized by enzymatic methods and interest continues to grow in this field of research.5-11 Enzyme-mediated synthesis of epoxy functionalized ε-caprolactone, has been recently reported.12 Epoxide resins were first developed in Europe in the 1930s. They generally have high adhesive strength, flexibility, resistance to corrosion, insulating properties, have little shrinkage on cure, and are commonly used for metal and underwater adhesion applications. They also are used in formulations for a broad variety of applications including in encapsulation of electrical equipment, laminates, baking enamels, and where alkydes are used.13-16 Most epoxy resins in use today, including diglycidyl ether of bisphenol A, are derived from (chloromethyl) oxirane, otherwise known as epichlorohydrin.17 This chemistry has been used since the advent of epoxide systems, but improved and more economical formulations are always of interest. We have recently expanded the use of lipase-catalyzed polymerization by taking advantage of their selectivity and established one-pot routes to end-functionalized macromonomers containing terminal thiols and acrylates that can be used in a second step for polymerization in tailored networks.18-20 The main focus has been on ring-opening polymerization of ω-pentadecalactone because this molecule cannot be easily ring opened * To whom correspondence should be addressed. Phone: +46 (0)8553 78384 (M.M.); +46 (0)76 201 3569 (S.T.). E-mail:
[email protected] (M.M.);
[email protected] (S.T.). † Department of Biochemistry. ‡ Department of Fiber and Polymer Technology.
by any other method and yields polymer properties similar to low density polyethylene.21,22 Due to the attractive properties of poly(ω-pentadecalactone), including high melting temperatures of close to 100 °C and promising physical properties for application as biomedical implants, this polymer has recently been investigated.23-25 Using lipase catalysis, we intend to produce a toolbox containing polymers of diverse functionalities with tunable properties and molecular weights. Epoxy groups are versatile functional groups with a number of important applications including surface grafting.26,27 In this paper we attempted a one-pot route to create a series of novel polypentadecalactone diepoxide functional polyester of varying degrees of polymerization (DP) 4, 6, and 10, synthesized by the lipase catalyst Pseodozyma antarctica (PalB)28 (commonly referred to as Candida antarctica lipase B). The epoxide species glycidol was combined with a divinyl ester of adipic acid and pentadecalactone (PDL) to achieve a combined ring-opening and condensation polymerization, to form diepoxide polymers of specific DP (Figure 1). The divinyl ester of adipic acid was chosen in this case due to the high reactivity, ensuring reaction completion within 24 h. It is investigated to what extent the molecular weight and functionality can be controlled. Diepoxy macromonomers of DP 4, 6, and 10 were UV homopolymerized and also UV polymerized with 20 wt % of cycloaliphatic diepoxide functional molecule, 3,4epoxycyclohexylmethyl-3′,4′-epoxycyclohexylcarboxylate (Cyracure UVR-6110; CA-dE). CA-dE is a commonly used reactive diluent in cationic coatings that reduces the viscosity of the reactant mixture, while adding increased functionality and crosslink density to the films.17 Film properties such as conversion and degree of crystallinity were investigated as a function of the degree of polymerization.
10.1021/bm9007925 CCC: $40.75 2009 American Chemical Society Published on Web 10/07/2009
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Figure 1. Enzyme-catalyzed one-pot synthesis of diepoxide-functional PPDL of DP 4, 6, and 10 (m + n). Table 1. Naming Scheme of Diepoxy-PPDL Polymers and Films Based On these Polymers degree of polymerizationa
diepoxy-PPDL
PPDL filmb
4
diepoxy-PPDL-4
PPDL-4 network
6 10
c
CyracurePPDL filmc
CA-PPDL-4 network diepoxy-PPDL-6 PPDL-6 network CA-PPDL-6 network diepoxy-PPDL-10 PPDL-10 network CA-PPDL-10 network
a Degree of polymerization equals m + n in Figure 1. b Homopolymerized. Copolymerized with Cyracure.
Experimental Section Materials. All chemicals were purchased from Sigma-Aldrich, unless otherwise noted. Novozyme 435 (Immobilized lipase B from Candida antarctica) and ω-pentadecalactone (PDL) were dried under vacuum, 5 mbar at 21 °C for 48 h. Glycidol (2,3-epoxide-1-propanol) was dried over activated molecular sieves. Divinyl adipate (stabilized with MEHQ (hydroquinone monomethyl ether(p-methoxyphenol)) was purchased from TCI Europe (Antwerp, Belgium) and used as received. Octyloxydiphenyliodonium hexafluoroantimonate (ODI) was kindly supplied by SSAB Tunnplåt AB (Borla¨nge, Sweden). Cyracure UVR-6110, (CAdE), a cycloaliphatic diepoxide, was supplied by Dow Chemical (Midland, MI). McLUBE 205PS (mold release agent) was supplied by Lotre´c AB (Lidingo¨, Sweden). The naming scheme used in this text is detailed in Table 1. Methods. Enzymatic One-Pot Synthesis Route to Diepoxy Functional PPDL (Diepoxy-PPDL-4,6,10). Glycidol (DP 4 (diepoxy-PPDL4): 331 µL, 5.0 mmol; DP 6 (diepoxy-PPDL-6): 221 µL, 3.3 mmol; DP 10 (diepoxy-PPDL-10): 133 µL, 2.0 mmol), divinyl adipate (DP 4: 495 mg, 2.5 mmol; DP 6: 330 mg, 1.7 mmol; DP 10: 198 mg, 1.0 mmol), and PDL (2.4 g, 10 mmol) were mixed in a 25 mL roundbottom reaction flask. Toluene (4.8 g) was added to the reaction mixture. Addition of 100 mg of Novozyme 435 initiated the reaction, which was allowed to run for 24 h. Reactions were run at 60 °C, magnetically stirred throughout, and were halted by filtering off the immobilized enzyme with a Whatman glass microfiber filter GF/A. Filtered product solutions were dried under reduced pressure to remove the solvent,
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leaving a white polymeric product. Product yield was calculated by dividing the mass of the dry product by the initial mass of the reactants. The dry diepoxy-PPDL polymers were analyzed by 1H and 13C NMR and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS). The average degree of polymerizations (DP) and the molecular weights (Mn) were determined by NMR. Kinetic Study of One-Pot Synthesis Route to Diepoxy Functional PPDL. To determine the comparative reactivity of the three monomers and to observe the polymer DP evolution over time, a kinetic study was performed using NMR. The reaction was performed by combining 55.3 µL (0.83 mmol) glycidol, 82 mg (0.41 mmol) divinyl adipate, and 600 mg (2.5 mmol) PDL with 3 mL (4.5 g) chloroform-d in a 10 mL round-bottom reaction flask. Addition of 25 mg of Novozyme 435 initiated the reaction, which was allowed to run for 24 h at 40 °C. Monomer disappearance and polymer DP was obtained from NMR measurements that were performed in deuterated chloroform. Samples were drawn at 10, 20, and 40 min and 1, 2, 3, 4, 5, 6, and 24 h. The calculated DP was expressed as m + n in the product, as shown in Figure 1. The average degree of polymerization (DP) of the products was calculated from NMR analysis by comparing the integration of the peaks at 4.40 (c1), corresponding to the protons on acylated glycidol, and 4.05 ppm (h), corresponding to the protons in the methylene group adjacent to the ester bond of ring opened PDL. Glycidol conversion was calculated by the disappearance of the peak at 2.75 ppm and the appearance of the peak at 4.40 ppm. PDL was studied by the disappearance of the monomer peak at 4.15 ppm and the appearance of the polymer peak at 4.05 ppm. Vinyl adipate was studied by the disappearance of the vinyl peaks at 4.9 and 4.6 ppm. Photopolymerization of Diepoxy Functional PPDL. Three vials were charged with each DP of diepoxy functional PPDL (400 mg), CA-dE (100 mg, 20% w/w or 75, 68, and 61 mol % to PDL of DP 4, 6, and 10, respectively), and the initiator ODI (2% w/w, 10 mg). Three more vials were charged with each DP of diglycidol end-capped poly-PDL (400 mg) and ODI (2% w/w, 8 mg). The mixtures were left to melt at 110 °C for 10 min, mixed until homogeneous, applied to a preheated Teflon mold (0.3 mm thick), and covered with a surface-treated (McLube) quartz microscope slide. The film was cured in the molten state under a UV Fusion Conveyor MC6R equipped with Fusion electrode less bulbs in a BF9 lamp. The sample was passed under the light 10 times with a line speed of 10 m min-1 to give an overall dose of 1 J cm-2 and then left at room temperature to cool and recrystallize. The intensity was determined with a UVICURE Plus from ET, Sterling, VA. Smooth, slightly opaque films resulted. 1 H and 13C NMR Analyses. NMR analyses were performed on a Bruker AM 400 utilizing deuterated chloroform containing 1 vol % TMS as an internal standard. 1H NMR (500 MHz, CDCl3, in ppm): 4.42 (H, q, end group )CHCHAHBO-), 4.05 (2H, t, CH2CH2OCO-), 3.91 (H, q, end group )CHCHAHBO-), 3.21 (H, m, oxirane -OCHAHB CH)), 2.85 (H, q, oxirane -OCHAHBCH)), 2.65 (H, q, oxirane -OCHAHBCH)), 2.40-2.28 (2H, t, -OC(O)CH2CH2-), 1.69-1.61 (4H, m, -CH2CH2(CH2)10CH2CH2-), 1.39-1.18 (20H, m, -CH2CH2(CH2)10CH2CH2-). 13C NMR (500 MHz, CDCl3, in ppm): 173.9, 173.5, 64.7 (end group), 64.4, 49.4 (oxirane of end group), 44.6 (oxirane of end group), 34.4, 34.0, 33.9, 29.7-29.4, 29.2, 29.1, 28.6, 25.9, 25.0, 24.8, 24.4. Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS). To confirm the repeating unit and acquire an understanding of the distribution of the polymer lengths, MALDI-TOF-MS measurements were performed. Specifically, a Bruker UltraFlex MALDI-TOF-MS was used with a SCOUT-MTP Ion Source (Bruker Daltonics) equipped with a N2 laser (337 nm), a gridless ion source, and reflector design. All spectra were acquired using a reflectorpositive method with an acceleration voltage of 25 and a reflector voltage of 26.3 kV. Calibration was performed in order to secure good mass accuracy. As for the sample, a solution of 20 mg of the polymer was dissolved in 1 mL of CHCl3. The matrix utilized was 9-nitroanthrazene. Nitro-anthrazene was prepared as a 0.1 M solution in THF containing 0.1 mM of sodium trifluoro acetate. The samples were prepared by mixing 5 µL of sample with 20 µL of matrix solution.
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Subsequently, 1 µL of the solution was spotted on the MALDI target and was left to crystallize at room temperature. Normally, 50 pulses were acquired for each sample. Dynamic Mechanical Thermal Analysis (DMTA). To examine the physical properties of the PPDL and CA-PPDL networks, DMTA was performed on a Q800 DMTA (TA-instruments), equipped with a film fixture for tensile testing. Film tension DMTA measurements were performed on rectangular dried film samples (5 × 0.3 mm, width × thickness) were performed between -30 and 140 °C, with a heating rate of 3 °C/min. The tests were performed in controlled strain mode with a frequency of 1 Hz, oscillating amplitude of 0.12 µm, and force track of 125%. FT-Raman Spectroscopy. FT-Raman spectra were acquired for all samples using a Spectra 2000 NIR-Raman with Spectrum software (Perkin-Elmer) to determine the degree of unsaturation remaining in the cross-linked films. Each spectrum was based on 32 scans using 1500 mW laser power. Percent conversion (%C) was calculated by normalizing all spectra to the ester peak at 1730 cm-1 and taking the ratio of the area of the -CH- group on the epoxide ring vibration peak at 1420 cm-1 in the unreacted (U) spectrum and reacted (R) spectrum (eq 1).
R × 100 ) %C U
b
resin
ratio I/M/La
Mnb (g mol-1)
DPb
isolated yield (%)
diepoxy-PPDL-4 diepoxy-PPDL-6 diepoxy-PPDL-10
2:4:1 2:6:1 2:10:1
1400 (1200) 1900 (1700) 2700 (2700)
4.6 (4) 6.8 (6) 10.2 (10)
91 88 90
a I ) initiator (glycidol), M ) monomer (PDL), and L ) divinyl adipate. Determined with NMR (theoretical value within brackets).
(1)
Differential Scanning Calorimetry (DSC). The thermal properties of the polymer and networks were analyzed by DSC. The experiments were performed on a DSC 820 equipped with a sample robot and a cryocooler (Mettler Toledo). The DSC runs were carried out in closed sample pans sealed in air, using the following temperature program; heating from 25 to 140 °C (20 °C min-1), cooling from 100 °C to -50 °C (50 °C min-1), then a second heating and cooling cycle before heating up to 120 °C. Isothermal segments of 5 min were performed at the conclusion of each dynamic segment. The melt enthalpy was determined from the integration of the Tm peak of the second heat. Contact Angle Measurements. Static contact angle measurements were performed on the film to air substrate using a contact angle meter, CAM 200 (KSV). The values reported were taken after the contact angle had reached a stable value, 5 s after deposition of the droplet. Sol Content. Sol content of the films was detected by soaking approximately 40 mg of the films in 10 mL of chloroform for 24 h with slight agitation (Edmund Bu¨hler, 7400 Tu¨bingen). The films were then taken out of the chloroform and dried in a vacuum oven for 48 h at 50 °C. The films were then weighed and this dry weight (M2) was divided by the initial dry weight of the polymer (M1), multiplied by 100 to get a percentage, and then subtracted from 100 to get the percent sol (%S; eq 2).
100 - ((M2/M1) × 100) ) %S
Table 2. Molecular Weights of the Diepoxy PPDL Polymers
(2)
Results and Discussion Enzymatic One-Pot Route to Diepoxide Functional PPDL. A one-step, enzymatic route to difunctionalized polypentalactone (PPDL) macromonomer containing terminal epoxides was developed. Predried components of glycidol, adipic acid divinylester, and PDL in different ratios were mixed with the lipase B from Candida antarctica in the immobilized form of Novozyme 435 (Figure 1). The reactions were performed in warm (60 °C) toluene for 24 h so that the reaction could run to completion, as was determined by the kinetic study. Once removed from the oil bath after reaction completion, the product was viscous and began to crystallize once cooled below 60 °C. Therefore, more solvent (100 wt % of the initial solvent in the reaction) was added to separate the enzyme from the polymer. The product did not need precipitation, only glass
Figure 2. 1H NMR spectrum of diepoxy-PPDL-6 polymer after drying: d′ indicates the shift of the methylene protons in the monomer bound to the terminal glycidol moiety.
filtration, to remove the immobilized enzyme, and once dried in vacuum for 24 h, there was a white powder received. The isolated yield is presented in Table 2. The conversions of the reactants to difunctional epoxy product were greater than 95% in the isolated product, which was determined by 1H NMR after drying. The conversion of the substrates was thoroughly analyzed in the kinetic study, which showed that glycidol, PDL, and vinyl adipate were consumed to >98, >97, and >99% conversion, respectively. The presence of intact epoxide rings as end-groups of the diepoxy-PPDL was confirmed by 1H and 13C NMR (Figure 2). Signals at 3.21, 2.85, and 2.65 ppm are characteristic of acylated glycidol coupled to a polyester backbone. The lack of signal at 3.65 ppm, which corresponds to the methylene group adjacent to the terminal hydroxyl group in the monoepoxide functional PPDL, confirmed that the acylation reaction with the adipic acid divinylester was efficient and the product was difunctional with terminal epoxide groups. The low molecular weight of these diepoxy PPDL polymers made it reliable to determine the Mn and functionality by NMR. The molecular weights, yields, and the DP are shown in Table 2. MALDI-TOF-MS spectra showed a distribution of one major repeating peak that corresponds to the theoretical calculated molecular weight for all three diepoxy-PPDL-polymer DPs, representing complete difunctionalization of all polymer chains (Figure 3). The mass difference between peaks of 240 Da corresponds to the molecular weight of a single PDL unit. Kinetic Study of Enzymatic One-Pot Route to Diepoxide Functional PPDL. A study was performed in chloroform-d as a solvent to follow the kinetics of the substrates (Figure 4). The average degree of polymerization (DP) of the products was calculated from NMR analysis by comparing the integration of the peaks at 4.40 (c1), corresponding to the protons on acylated glycidol, and 4.05 ppm (h), corresponding to the protons in the
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Figure 5. Raman spectra of the polymer diepoxy-PPDL-4 and the UV cured film CA-PPDL-4 network. Figure 3. MALDI-TOF-MS spectrum of diepoxy-PPDL-6 polymer. The bar represents one monomeric unit of 240 Da.
Table 3. Conversion of Epoxy Groups as Measured by Raman and Contact Angle of Water of the PPDL Films and CA-PPDL Films epoxy group conversion (%)
Figure 4. Kinetic data of monomer disappearance and polymer DP with time, as measured by NMR.
methylene group adjacent to the ester bond of ring opened PDL. Glycidol conversion was calculated by the disappearance of the peak at 2.75 ppm and the appearance of the peak at 4.40 ppm. PDL was studied by the disappearance of the monomer peak at 4.15 ppm and the appearance of the polymer peak at 4.05 ppm. Vinyl adipate was studied by the disappearance of the vinyl peaks at 4.9 and 4.6 ppm. The results showed that >98% of the glycidol and >99% of the adipic acid divinyl ester reacted within the first hour generating diglycidyl adipate. This result was expected, since vinyl esters are highly reactive. The ring-opening of the ω-pentadecalactone with glycidol was much slower than the acylation of glycidol with divinyl adipate and was the rate determining step in formation of the polymer. After 24 h, the conversion of glycidol, PDL, and divinyl adipate were >98, >97, and >99%, respectively. Rational for Reaction Conditions and Reactants. The products received from reactions performed in bulk had higher DPs than expected: experimental DPs of 5.8 and 8.9 for targeted DP values of 4 and 6, respectively. This indicated that the solubility of the glycidol may be the problem and was solved by performing the reactions in toluene. Glycidol has a low boiling point of 167 °C, making it difficult to drive the reaction to high conversion because placing the reaction mixture under reduced pressure would result in the loss of glycidol. Instead, divinyl adipate was used, as the formed acetaldehyde gas drives the reaction to the high conversion without the need for reduced
contact angle (° ( 2)
sol content (% ( 0.5)
resin
PPDL
CA-PPDL
PPDL
CA-PPDL
CA-PPDL
diepoxyPPDL-4 diepoxyPPDL-6 diepoxyPPDL-10
20
90
71
73
15
45
85
79
89
16
60
85
81
98
18
pressure. The amount of catalyst used was about 5 wt % and was used to complete the reaction within 24 h. As found from the kinetic study, the reaction went to completion within 18-20 h but was left for 24 h to allow for complete conversion. The solvent chosen for this reaction was toluene because of the high boiling point of 111 °C, however, it is easily removed at reduced pressure. The reaction mixture temperature could be lowered from 90 °C in bulk to 60 °C with the addition of solvent. Photopolymerization of Diepoxy Functional PPDL. FTRaman spectroscopy was performed to determine the degree of curing of the films. The ester carbonyl peak (1730 cm-1) did not change during the reaction and was used as internal standard. The -CH on the epoxide ring (1415 cm-1) was clearly visible before cure and was used to calculate the conversion. Spectra in the diepoxy ring vibration region of diepoxy-PPDL-4 polymer and network before and after UV cure are shown in Figure 5. The percent conversion of the epoxide functional groups within the networks, calculated using eq 1, is presented in Table 3. It was expected that the diepoxy-polymer films would have lower conversion due to increases in viscosity and crystallinity with increasing molecular weights. The propensity for the reactants to crystallize, after being taken out of the oven and placed under UV light, inhibits the chains from reacting due to lack of mobility and leads to low conversions. With the addition of CA-PPDL, the number of functional groups per volume greatly increased and the viscosity was decreased, enhancing mobility of the chains. CA-dE also acted as an impurity, which greatly inhibited crystallinity of the PPDL chains. The difference in conversion was large for the homopolymerized diepoxy-PPDL networks, with diepoxy-PPDL-4 network having an epoxy conversion of 20% to diepoxy-PPDL-10 network having a conversion of 60%. The conversion was much higher and consistent with the addition of CA-dE which lowered the viscosity of the system before cure, acting as a reactive diluent, allowing for more chain mobility. There was no significant effect
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Table 4. Thermal Properties of the Diepoxy-PPDL Polymers and Diepoxy-PPDL Networks ∆Hm (J g-1)
Tma (°C) resin diepoxyPPDL-4 diepoxyPPDL-6 diepoxyPPDL-10 b
diepoxyPPDL
PPDL
CAPPDL
diepoxyPPDL
PPDL
CAPPDL
80
59-69b
39
86
54
24
83
79
72
106
74
31
87
85
78
136
99
45
a Tm of high molecular weight poly(ω-pentadecalactone) ) 97 °C.23 Plateau.
of diepoxide polymer molecular weight on the conversion within this range of polymer chain lengths. The value of unreacted epoxide groups was approximately 10-15% for all films and the weight loss observed by soaking the films in chloroform for 24 h to allow migration of unreacted chains confirmed this value. Hydrophilic Character of the Polymers. The contact angle of water increased as the diepoxy-PPDL chains increase in DP from 4 to 10. There is a large range with more hydrophilic films of PPDL-4 networks and hydrophobic films of CA-PPDL-10. It is interesting to note that the DP can be used to tune the hydrophilicity of the network surface. Decreased wettability of further water-based coatings and increased water resistance of the films was observed with higher DP diepoxy-PPDL based networks. Thermal Properties of the Polymers and Networks. The glass transition temperatures (Tg) and melt transition temperatures (Tm) of the diepoxy-PPDLs and cured films were determined by DSC from the second heating. A summary of the thermal properties of the diepoxy-PPDL samples and films is presented in Table 4. It is interesting to note that, as the diepoxy-PPDL DP decreased, there was a larger difference in the Tm before and after cross-linking. This is a result of the increased constraint of the chains once the ends are reacted, decreasing the degree of crystallinity observed by the enthalpy of the Tm (∆Hm). No Tg of the films was observed by DSC as it is suspected to be too broad. The Tm values in Table 4 are reported as the peak maximum. Viscoelastic Properties of the Films. To correlate the properties of the films to increasing degree of polymerization, DMTA measurements were performed. Only the CA-PPDL films could be analyzed by DMTA as the PPDL films were too weak and waxy due to lower conversions and cross-link density (Figure 6) It is observed that the tan δ Tm transition or peak that occurs around 70 °C was broad for all samples, reflecting the large distribution of chain lengths. This broad distribution of chain molecular weights can be beneficial and can allow the samples to hold up to many stresses as a result of this characteristic. In both CA-PPDL-6 and CA-PPDL-10 films there was a β-transition at 26 °C or a second transition observed, in which the origin is unknown at this time. From the tan δ it can also be observed that the intensity was highest for CA-PPDL-4, having the most amorphous content and thus more free volume compared to highly crystalline CAPPDL-10. The storage modulus plots of the CA-PPDL films were very similar. The glassy modulus around 0 °C was actually quite low around 300-400 MPa and was due to the brittle nature of these films. After the thermal transitions, the rubbery modulus dropped to about 10 MPa after 100 °C.
Figure 6. Tan δ plots of CA-PPDL networks.
Conclusions This is one of the first demonstrations of enzyme-catalyzed ring-opening polymerizations resulting in a series of diepoxy functional PPDL polymers. The process is a one-pot synthesis in which the diepoxy polymer product can be directly used due to very high conversion of the substrates. The reaction is run under relatively low temperatures compared to traditional techniques and goes to completion in 24 h. These polymers are viable materials for industry and green chemistry in that PPDL functional polymer can be made with reduced energy consumption. The resulting polymers have low conversions without the addition of other reactants such as CA-PPDL. They are hydrophobic films and became more so with the addition of CA-PPDL, even though the crystallinity of PDL is disrupted, which makes this an ideal polymer to use as a coating in cases where water sensitivity is undesirable. Due to enhanced conversion and cross-link density, the strength of the films increases significantly with the addition of CA-PPDL. These films, as a result of their thermal and physical properties, may be ideal for industrial melt press adhesive applications due to their water insensitivity, their possession of good wetting and adhesive functional groups, and their physical properties. These mixtures were melted at a relatively low temperature of 110 °C and UV cured to form highly crystalline, yet flexible films. These have properties similar to low density polyethylene or polypropylene, while also having the advantage of being epoxide functional, which lends to adhesive properties. Acknowledgment. The KAMI Research Foundation and BiMaC (Biofibre Materials Centre) is appreciatively acknowledged for their financial support.
References and Notes (1) Okumura, S.; Iwai, M.; Tominaga, Y. Agric. Biol. Chem. 1984, 48, 2805. (2) Ajima, A.; Yoshimoto, T.; Takahashi, K.; Tamaura, Y.; Saito, Y.; Inada, Y. Biotechnol. Lett. 1985, 7, 303. (3) Uyama, H.; Kobayashi, S. Chem. Lett. 1993, 1149–1150. (4) Knani, D.; Gutman, A. L.; Kohn, D. H. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 1221–1232. (5) Kobayashi, S. Macromol. Rapid Commun. 2009, 30, 237–266. (6) Matsumura, S.; Takahashi, J. Makromol. Chem. Rapid Commun. 1986, 7, 369. (7) Binns, F.; Roberts, S. M.; Taylor, A.; Williams, C. F. J. Chem. Soc., Perkin Trans. 1993, 1, 899. (8) Linko, Y.-Y.; Wang, Z.-L.; Seppa¨la¨, J. Biocatalysis 1994, 8, 269.
Telechelic Polypentadecalactone Epoxide (9) Kobayashi, S. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 3041– 3056. (10) Gross, R. A.; Kumar, A.; Kalra, B. Chem. ReV. 2001, 101, 2097– 2124. (11) Albertsson, A.-C.; Srivastava, R. K. AdV. Drug DeliVery ReV. 2008, 60, 1077–1093. (12) Zhou, J.; Wang, W.; Villarroya, S.; Thurecht, K.; Howdle, S. M. Chem. Commun. 2008, 5806–5808. (13) Herman, B. S. AdhesiVes, Recent DeVelopments; Noyes Data Corporation: Park Ridge, NJ, 1976; pp 215, 255-256. (14) DiStasio, J. I. Epoxide Resin Technology, DeVelopments since 1979; Noyes Data Corporation: Park Ridge, NJ, 1982; p 1. (15) Hoppe, C. E.; Galante, M. J.; Oyanguren, P. A.; Williams, R. J. Macromol. Mater. Eng. 2005, 290, 456–462. (16) Li, H.; Xingrong, Z.; Wu, W. Polym.-Plast. Technol. Engi. 2008, 47, 978–983. (17) Wicks, Z. W.; Jones, F. N.; Pappas, S. P.; Wicks, D. A. Organic Coatings, 3rd ed.; John Wiley and Sons: Hoboken, NJ, 2007; p 271. ¨ stmark, E.; Malmstro¨m, E.; Hult, A.; Martinelle, M. (18) Hedfors, C.; O Macromolecules 2004, 38, 647–649.
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