Synthesis and Crystallization Behavior of Equisequential ADMET

Aug 5, 2016 - Jérémie LacombeSamuel PearsonFranz PiroltSébastien NorsicFranck D'AgostoChristophe BoissonCorinne Soulié-Ziakovic. Macromolecules ...
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Synthesis and Crystallization Behavior of Equisequential ADMET Polyethylene Containing Arylene Ether Defects: Remarkable Effects of Substitution Position and Arylene Size Shao-Fei Song, Yin-Tian Guo, Rui-Yang Wang, Zhi-Sheng Fu, Jun-Ting Xu,* and Zhi-Qiang Fan* MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China S Supporting Information *

ABSTRACT: A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which can be ascribed to the matchable configuration of the defects in the main chain with the conformation of PE in the crystals. When the defects become naphthylene ether units, the crystallization and melting behaviors of the polymers are similar to or different from those of the precision PEs with phenylene ether defects, depending on the substitution position. This shows that both the substitution position in the arylene ether defects and the defect size exert effects on crystallization, melting behaviors, and chain stacking of precision PEs.

1. INTRODUCTION It is well-known that macroscopic properties of polymers are mainly determined by their chain structure.1−3 Defects in a polymer chain, in spite of low quantity, can have vital effects on crystallization, thermal, and mechanical properties of polymer. The defects in polymer chains include chain ends, comonomer units, coupling units, and stereo- and regio-defects. When the polymer chain is crystalline, these defects can be either included into or excluded from the polymer crystal, depending on the type and size of the defects.4−10 In some rigid linear polymers, the configuration of arylene units, namely ortho-, meta-, or para-arylene units, has been proved to be a key structure factor influencing the polymer properties.11−15 For instance, their disubstitution position may influence the aggregation behavior of polymer backbones and thus the gas permeability of the material.16 Moreover, the πconjugation length of rigid polymers may vary with kink © XXXX American Chemical Society

linkages (ortho-, meta-, and para-), leading to different optical and photoluminescence performances.17 As a result, if disubstituted arylene units are introduced as defects in crystalline polymer main chains, it is expected that the chain stacking and crystallization behavior may be regulated by the size and disubstitution position of the defects. Cheng et al. investigated the crystallization behavior of poly(ethylene oxide) (PEO) coupled by different benzene dicarbonyl dichloride isomers.18−20 The results showed that introduction of the phenylene ester units reduced the self-diffusion coefficient (Ds) of PEO chains. The 1,4-substitution led to the largest Ds, whereas the 1,2-substitution resulted in the smallest Ds. Accordingly, at higher crystallization temperatures, two Received: June 20, 2016 Revised: August 1, 2016

A

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Co., Ltd. All reactions were conducted under N2 or vacuum using standard Schlenk techniques unless otherwise noted. General Procedures of Monomer Synthesis. 1,2-Benzenediol (2 g, 18.2 mmol) and NaOH (3 g, 75 mmol) were dissolved in 100 mL of DMF in a 250 mL round-bottomed Schlenk flask. After the mixture was stirred for 40 min, 11-bromo-1-undecene (12 g, 51.5 mmol) in DMF (20 mL) was added dropwise. The resulting reaction system was heated at 40 °C and left stirring for 6 h. Subsequently, the reaction system was cooled to ambient temperature and quenched by pouring its content into diethyl ether/water (100 mL + 100 mL). The organic phase was extracted with diethyl ether (200 mL) twice, and the combined organic phase was washed with brine, dried over MgSO4, and then concentrated using a rotary evaporator. The residue was recrystallized from ethanol to obtain 7 g of 1,2-bis(undec-10enyloxy)benzene (ortho-M). Yield: 93%. 1H NMR (400 MHz, CDCl3, ppm): δ = 6.91 (d, J = 9.6 Hz, 4H), 5.83 (ddt, J = 16.9, 10.2, 6.7 Hz, 2H), 5.11−4.86 (m, 4H), 4.00 (t, J = 6.6 Hz, 4H), 2.06 (q, J = 7.0 Hz, 4H), 1.92−1.73 (m, 4H), 1.54−1.43 (m, 4H), 1.43− 1.09 (m, 20H). 13C NMR (101 MHz, CDCl3, ppm): δ = 149.22 (s), 139.23 (s), 121.01 (s), 114.10 (d, J = 11.6 Hz), 69.24 (s), 33.86 (s), 32.01−22.78 (m). Synthesis of meta-M from 1,3-benzenediol and para-M from 1,4-benzenediol followed the same procedures. General Procedures of Polymer Synthesis. Monomer ortho-M (2 g, 4.83 mmol) was placed in a 25 mL flame-dried Schlenk flask under N2. Then the Schlenk flask was placed in the glovebox, and Grubbs’ first-generation catalyst (19.9 mg, 0.5 mol %) was added. The flask was removed from the box and connected to high vacuum. The mixture was stirred at 50 °C, and the temperature was set to 80 °C or higher to enable stirring of the viscous polymer melt. After 72 h of polymerization at 90 °C, the Schlenk flask was opened to air with 5 mL of vinyl ethyl ether being injected, and then the polymer was dissolved in 50 mL of toluene. The solution was poured into acidic methanol to precipitate the polymer. The polymer was filtered, redissolved, and reprecipitated twice to remove the catalyst residuals. The ADMET polymer ortho-P (1.8 g) was recovered as a white solid. Yield: 89%. 1H NMR (400 MHz, CDCl3, ppm): δ = 6.89 (s, 2H), 5.50−5.27 (m, 2H), 3.99 (t, J = 6.7 Hz, 2H), 2.00 (dd, J = 20.0, 4.9 Hz, 2H), 1.90−1.71 (m, 2H), 1.45 (dt, J = 17.2, 8.6 Hz, 2H), 1.30 (s, 10H). 13C NMR (101 MHz, CDCl3, ppm): δ = 148.91 (d, J = 52.3 Hz), 131.47−128.68 (m), 120.38 (d, J = 117.2 Hz), 113.76 (d, J = 51.2 Hz), 68.75 (d, J = 93.2 Hz), 33.73−24.19 (m). GPC (polystyrene calibration): Mn: 25 kDa, Mw: 100 kDa, PDI: 4.0. TGA: 408 °C (5% weight loss). DSC: Tm: 40.4, 54.2 °C. Hydrogenation of Polymers. Polymer ortho-P (1 g), ptoluenesulfonohydrazide (TSH) (2.3 mg, 12 mmol), and tripropylamine (TPA) (1.7 mg, 12 mmol) were weighed and transferred into a 100 mL three-neck flask. 40−50 mL of p-xylene was added by vacuum transfer. The solution was then heated to 130 °C with vigorous stirring under N2 for 12 h. After that another batch of TSH and TPA with equal amount was added, and the reaction last for another 12 h at 130 °C. Subsequently, the mixture was cooled to RT and poured into cold methanol to form a white precipitate. After filtration and washing by toluene and cold methanol for three times and drying in vacuo, 0.86 g of ortho-HP was obtained. Yield: 85%. 1H NMR (400 MHz, CDCl3, ppm): δ = 6.97−6.82 (m, 1H), 4.00 (t, J = 6.7 Hz, 1H), 1.92−1.72 (m, 1H), 1.53−1.41 (m, 1H), 1.41−1.11 (m, 7H). 13C NMR (101 MHz, CDCl3, ppm): δ = 149.21 (s), 120.98 (s), 114.04 (s), 69.25 (s), 29.57 (dd, J = 32.1, 11.3 Hz), 26.07 (s). GPC (polystyrene calibration): Mn: 23.9 kDa, Mw: 57.4 kDa, PDI: 2.4. TGA: 397 °C (5% weight loss). DSC: Tm: 81.7 °C. The synthesis procedures of the other ADMET polymers and the corresponding saturated polymers and their NMR data are provided in the Supporting Information. Characterizations. Nuclear Magnetic Resonance (NMR). 1H NMR (400 MHz) and 13C NMR (101 MHz) spectra were recorded with a Bruker Avance III 400 spectrophotometer, and high temperature 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a Varian Mercury Plus 300 spectrometer using deuterated solvent as the lock and the residual solvent or TMS as internal reference. Chemical shifts for 1H and 13C NMR were

populations of crystal with extended and once-folded PEO chains were formed in the PEOs containing 1,4- and 1,3substituted phenylene ester units, but only one crystal population with mixed integrally folded PEO chains was observed in the PEO with 1,2-substituted phenylene ester defects. Moreover, although all the three isomers of phenylene ester units were excluded from the PEO crystalline phase, more EO units were excluded along with the para-isomer defects, leading to thinner lamellae and lower melting temperature (Tm). Nevertheless, the differences in crystallization and melting behaviors are not so large among the PEOs containing different disubstituted phenylene ester defects. In addition, we believe that the polymer chain conformation and substitution position of the arylene defects may interact mutually in controlling the chain stacking mode in polymer crystals. The effects of substitution position in arylene defects on crystallization behavior of polymers with zigzag planar conformation in the crystal phase may be different from those with helical conformation in the crystal phase, such as PEO. To our best knowledge, such a point has not been addressed in the literature so far. Recently, acyclic diene metathesis (ADMET) polymerization has attracted extensive research interests.21−27 Based on ADMET, periodical distribution of functional units, which can be viewed as chain defects, along polyethylene backbone can be achieved. Up to now, polyethylenes (PEs) containing various pendant or enchained defects with precise and variable placement have been synthesized.28−33 Because of the precisely defined chain structure, the polymers synthesized by ADMET exhibit some unique properties, which are evidently different from those PEs with randomly distributed defects.34,35 The effect of various chain defects on crystallization behavior of precision PEs prepared by ADMET have been studied.36,37 For example, precision PEs can form more uniform crystal lamellae as compared with random ethylene copolymers.38 The pendant or enchained defects can either be included into the PE crystal or excluded from the crystal, depending on the defect type and size. When the defects are included into the PE crystal, dilation of the unit cell may occur and the chain stacking mode may be altered.39,40 In this work, a new series of PE containing disubstituted arylene ether defects periodically distributed along the main chain were synthesized via ADMET polymerization. In the precision PEs studied in this work, there exist more than one arylene ether defects per chain, so that the effect of chain defects on crystallization can be revealed more clearly. Moreover, PE usually exhibits zigzag planar conformation in the orthorhombic crystal, which is different for the helical conformation of PEO. It is thus interesting to study the relationship between chain conformation and substitution position in the arylene defects. Arylene ether defects of different sizes were also introduced into PE main chain, and the effect of the defect size was investigated.

2. EXPERIMENTAL SECTION Materials. Anhydrous N,N-dimethylformamide (DMF) was refluxed over CaH2 and distilled in the presence of molecular sieves under reduced pressure. Bisphenols including 1,2-benzenediol, 1,3benzenediol, and 1,4-benzenediol were purchased from Energy Chemical and recrystallized from ethanol before use. Grubbs’ firstgeneration catalyst benzylidene−bis(tricyclohexylphosphine)dichlororuthenium was purchased from Sigma-Aldrich. Other chemicals were of analytical grade and used as received from Tokyo Chemical Industry B

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Macromolecules referenced to residual signals from CDCl3 (1H: δ = 7.26 ppm and 13C: δ = 77.23 ppm) and toluene-d8 (1H: δ = 7.09, 7.00, 6.98, and 2.09 ppm and 13C: δ = 137.86, 129.24, 128.33, 125.49, and 20.4 ppm). Thin layer chromatography (TLC) was performed on EMD silica gel coated (250 μm thickness) glass plates for monitoring the monomer synthesis. The TLC plates were developed to produce a visible signature by iodine. Fourier Transform Infrared (FT-IR). FT-IR spectra were recorded on a Bruker Vector 33 FT-IR spectrometer. UV−vis spectra were recorded on a Shimadzu UV-2401PC and a Cary 100 instrument (Varian Australia Pty Ltd.). Gel Permeation Chromatography (GPC). Molecular weight and polydispersity index of the polymers were determined by GPC at 150 °C using two columns (10 μm o.d, 7.8 mm i.d., 300 mm length) with HPLC grade 1,2,4-trichlorobenzene as the mobile phase at a flow rate of 1.0 mL/min. Injections were made at 0.3% w/v sample concentration using a 150 μL injection volume. In the case of universal calibration, retention times were calibrated with polystyrene standards of narrow molecular weight distribution to give numberaverage molecular weight (Mn) and weight-average molecular weight (Mw) values. Thermogravimetric Analysis (TGA). Test of thermal stability was performed on a TA Q50 instrument. The samples were heated from RT to 800 °C at a rate of 10 °C/min with a N2 purging rate set as 20 mL/min. Differential Scanning Calorimetry (DSC). Thermal analysis was carried out on a TA Q200 DSC equipped with a controlled cooling accessory at a heating or cooling rate of 10 °C/min unless otherwise noted. The temperature was calibrated with indium. Samples weighing 3−5 mg were sealed in aluminum pans. The sample was first heated to temperature 30 °C above sample’s melting point and held for 5 min to eliminate thermal history. Subsequently, the sample was cooled to −40 °C, and the nonisothermal crystallization DSC curve was recorded. Finally, the sample was again heated to 140 °C at a rate of 10 °C/min to obtain the second run melting curve, which was used for determining the melting enthalpy (ΔHm) and Tm. The crystallinity XcDSC can be calculated based on ΔHm as follows:

Xc =

ΔHm × 100 ΔHm0

Small-Angle X-ray Scattering (SAXS). Temperature-variable smallangle SAXS experiments were performed at BL16B1 beamline in Shanghai Synchrotron Radiation Facility (SSRF), China. The wavelength of X-ray was 1.24 Å, and the sample-to-detector distance was set as 1800 mm. The average exposure time was 300 s for each scan. Bull tendon was used as standard material for calibrating the scattering vector. Two-dimensional SAXS patterns at room temperature were recorded and converted into one-dimensional SAXS profiles via Fit2D software. The long period LSAXS from SAXS can be determined as follows:

LSAXS = 2π /q

where q is the scattering vector corresponding to the SAXS peak. The lamellar crystal thickness (lc) can be calculated from the long period LSAXS and bulk volume fraction crystallinity Xvol based on the equation

lc = LSAXS × X vol

3. RESULTS AND DISCUSSION Synthesis and Characterization of Monomers and Polymers. Three kinds of diene monomer were synthesized by coupling three isomers (ortho-, meta-, and para-) of dihydroxybenzene with 11-bromoundec-1-ene via Williamson ether reaction. In the subsequent ADMET polymerization of the diene monomers, Grubbs’ first-generation catalyst was preferentially chosen for its commercially availability and, quite importantly, its low isomerization rate compared with other Ru catalysts.43 Hydrogenation of all the ADMET polymers was conducted using 4-methylbenzenesulfonhydrazide (TSH) and tripropylamine (TPA) to produce the saturated ethylene-based polymers, as shown in Schemes S1 and S2 of the Supporting Information. All of the obtained monomers and polymers were characterized by 1H and 13C NMR, respectively. The NMR spectra unequivocally indicate successful synthesis of the monomers, polymerization with high conversion to polymers, and exhaustive hydrogenation, as depicted in Figures S1−S9 of the Supporting Information. Notably, there are distinct differences in the NMR spectra of the hydrogenated polymers: ortho-HP, meta-HP, and para-HP. Particularly worth mentioning is their distinct aromatic signals (Figure 1), as the aromatic signal of ortho-HP appears at 6.89 ppm, that of meta-HP is at 7.15 and 6.50 ppm, and that of para-HP shows at 6.82 ppm. Additionally, because para-HP exhibits semicrystallinity and a higher melting temperature (Table 1), it shows poor solubility in CDCl3; therefore, the signals in NMR are weaker than those of ortho-HP and meta-HP. This fact, to a certain degree, confirms that the disubstituted arylene isomers influence the solubility of the resultant polymers via dominating their microstructures. Molecular Weight and Thermal Stability. GPC data of the resultant polymers are calculated and collected in Table 1, and the GPC curves are shown in Figure 2 and in Figures S12 and S13. Notably, the molecular weight of para-HP is lower than that of polymers ortho-HP and meta-HP. Given that the bulk polymerization of all monomers were conducted under the same conditions like temperature and monomer-to-catalyst ratio, such a difference can be attributed to the higher crystallization temperature (Tc) of para-P than the other

(1)

(293 J cm ) is the fusion enthalpy of the PE with 100% where crystallinity. Wide-Angle X-ray Diffraction (WAXD). WAXD patterns of the precision PEs were obtained on a Rigaku Ultima IV diffractometer, using the Cu Kα radiation (λ = 0.1546 nm) as X-ray source. The value of 2θ ranges from 5° to 60°, and the scanning increment is 0.0167°. The crystallinity (XcWAXD) of PEs with orthorhombic crystal phase was determined from the WAXD patterns in terms of the equation41 Xc WAXD =

A110

A110 + 1.46A 200 + 1.46A 200 + 0.75A a

(2-1)

where A110 and A200 are the area of the (110) and (200) crystalline peaks, respectively, and Aa is the area of the amorphous halo. For PEs with other crystal phases (such as triclinic), a simplified equation was employed to determine the crystallinity (XcWAXD):

XcWAXD =

Ac Ac + A a

(2-2)

where Ac refers to the sum area of the crystalline peaks and Aa is the area of the amorphous halo. The corresponding bulk volume fraction crystallinity Xvol can be calculated from XcWAXD:

X vol =

ρa ρc /XcWAXD − ρc + ρa

(5)

Polarized Light Microscopy (PLM). Observations of macroscopic crystal morphology at various thermal conditions were carried out on an Olympus microscope (BX51) equipped with a hot stage. Thin film specimens of around 0.05 mm thickness were applied for observation.

−3

ΔH0m

(4)

(3)

where ρc and ρa are the densities of the crystalline and amorphous phases (for polyethylene, ρc = 1.000 g cm−3 and ρa = 0.855 g cm−3).42 C

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Figure 2. GPC curves of ortho-HP, meta-HP, and para-HP.

Figure 1. 1H NMR spectra of ortho-HP, meta-HP, and para-HP. Peak intensity of para-HP is rescaled for clarity.

polymers (Figure S14). Because para-P tends to crystallize from the solution during polymerization, early termination of its ADMET chain propagation will happen as a result of chain aggregation from the homogeneous phase of monomers, oligomers, and polymers.44,45 To increase the molecular weight of para-P and para-HP, we have tried to conduct the polymerization in solution like in 1,2-dichlorobenzene. However, the polymer still precipitated slowly, and the product has a low molecular weight as the bulk polymerization system. Easy precipitation of this polymer can be attributed to its microscopic structure and its higher crystallizability.46,47 TGA measurement was conducted to investigate thermal stability of these polymers, as presented in Figure S14. It is found that the decomposition temperature (Td) corresponding to 5% weight loss is 397 °C for ortho-HP, 415 °C for meta-HP, and 390 °C for para-HP (Table 1), which are obviously higher than the Td of commercial PEs (∼300−330 °C) and precision PE without defects (348 °C).48,49 This indicates that introduction of phenylene ether units into PE backbone can enhance the thermal stability of PE. The effect of substitution position on the thermal stability of hydrogenated polymers probably may be partially due to the different bond energy and interaction among the phenylene rings, as revealed by the UV− vis spectra (Figure S11). However, no convincing conclusions can be drawn from this result, since the thermal stability of polymers relies on a variety of factors, including MW, PDI, and the presence of possible species that can affect the thermal decomposition of polymers. Melting and Crystallization Behaviors. The DSC nonisothermal crystallization curves at a cooling rate of 10 °C/min and the subsequent melting curves are shown in Figure 3. The data of Tm, Tc, ΔHm, and XcDSC are summarized in Table 1. The DSC curves of the corresponding unsaturated

Figure 3. DSC nonisothermal crystallization curves and subsequent melting curves of ortho-HP, meta-HP, and para-HP. Data are rescaled and shifted vertically for clarity.

precursors, ortho-P, meta-P, and para-P, are presented in Figures S15−S17. The DSC crystallization traces at other cooling rates and the corresponding melting traces are illustrated in Figures S18−S20. Comparing the crystallization and melting DSC curves of the unsaturated and hydrogenated polymers, one can see that the Tm and Tc of the saturated precision PEs are evidently higher than those of the corresponding unsaturated precursors. This shows that hydrogenation can extend the length of methylene sequence and enhance the crystallizability of the polymer chains. Interestingly, we find that the three precision PEs exhibit distinct melting and crystallization behaviors. First, their Tms are quite different. Tm of the main melting peak is 133.8 °C for para-HP,

Table 1. Data of Molecular Structure, Thermal Stability, and Crystallization for Different Precision PEs polymer

Mna (kDa)

Mwa (kDa)

PDI

Tmb (°C)

ΔHmb (J/g)

Tdc (°C)

XcDSC (%)

XcWAXD (%)

Xvol (%)

LSAXS (nm)

lc (nm)

ortho-HP meta-HP para-HP

23.9 19.8 5.6

57.4 47.0 12.9

2.4 2.3 2.3

81.7 96.5 133.8

85.0 60.5 82.5

397 415 390

29.0 20.6 28.2

29.5 45.4 63.0

26.3 41.6 59.3

9.66 11.22 16.11

2.54 4.66 9.55

Determined via GPC (1 mL/min in 1,2,4-trichlorobenzene) with curves shown in Figure 2, 3 ‰ concentration, using polystyrene calibration. Determined via DSC, 10 °C/min scan rate, values determined from the second scan data, Tm is defined as the peak value(s), and ΔHm from the second melting peak. cGiven as the 5% weight loss temperature, 10 °C/min.

a b

D

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Macromolecules which is much higher than that of ortho-HP and meta-HP. metaHP displays a slightly higher Tm than ortho-HP. Based on the Thomson−Gibson equation, the Tm of polymer crystals is mainly determined by the crystal lamella thickness (lc) as well as the free energy of folding surface (σe). This implies that there is a large difference in lc for these three polymers, which will be further discussed in terms of SAXS result. Second, the large difference between Tm and Tc (ΔT = Tm − Tc) for meta-HP shows that a high degree of supercooling is needed for crystallization of this polymer. This indicates that meta-HP is more difficult to crystallize than the other two polymers, which is further verified by its smaller ΔHm. In the melting curve of meta-HP, a cold crystallization peak appears before the melting peak. Cold crystallization implies that crystallization is not completed in the cooling process and thus it further proceeds in the heating process, which usually occurs in polymers with slow crystallization rate. This phenomenon agrees well with the large ΔT for crystallization of this polymer. Cold crystallization was reported for precision PE with dimethyl branch at every 21st backbone atom as well.50 When we increase the cooling rate during crystallization, the cold crystallization peak becomes more obvious (Figure S19). This shows that crystallization of meta-HP is further suppressed when a higher cooling rate is applied. We also investigated the effect of cold crystallization on the macroscopic morphology of meta-HP. Figure 4 shows the

heating rate, the second melting peak at higher temperature, which corresponds to the melting of reorganized crystals, becomes weaker and weaker. This means that at a high heating rate there is no enough time for the metastable crystals to reorganize into more perfect crystals. Quick formation of less ordered mesophase followed by transformation into more ordered structure was also observed for PE with ethyl branches precisely spaced on every 21st carbon during isothermal crystallization.52 The DSC results reveal that the disubstitution position in the phenylene ether units has a great influence on the Tm, Tc, crystallinity, cold crystallization, and melting− recrystallization behaviors. WAXD Result. WAXD patterns of the three precision PEs after being cooled from 160 °C are shown in Figure 5, and the

Figure 5. WAXD patterns of ortho-HP, meta-HP, and para-HP after being cooled from 160 °C to room temperature. Data are rescaled and shifted vertically for clarity.

Figure 4. PLM micrographs of meta-HP at 45 °C (a) and 82 °C (b) after being cooled from 160 °C to room temperature at a rate of 10 °C/min.

WAXD patterns after further annealing at various temperatures are presented in Figure S21. It is found that para-HP exhibits two diffraction peaks at 2θ of 21.20° and 24.17°, which correspond to the (110) and (200) crystal planes of orthorhombic PE crystal,53 respectively. This shows that paraHP has the same crystal structure as common PE and introduction of para-phenylene ether defects into the PE main chain does not alter the crystal structure. A diffraction peak also appears at 2θ of 21.74° for ortho-HP, but this peak is evidently broader than the one at 2θ of 21.20° in para-HP. Moreover, the diffraction peak corresponding to (200) crystal plane cannot be observed for ortho-HP. This shows that the crystal growth along (200) direction in ortho-HP is severely suppressed, and the crystal size in the (110) direction is also smaller than that of para-HP. By contrast, meta-HP exhibits a completely different diffraction pattern from ortho-HP and para-HP. The diffraction peaks of meta-HP are broad and overlapped, but three diffraction peaks can still be discerned at 2θ = 16.01°, 20.20°, and 21.40°. The diffraction peaks at 2θ = 16.01° and 20.20° may be assigned to triclinic crystal structure of PE,8,54 whereas the one at 2θ = 21.40° corresponds to the orthorhombic crystal structure of PE. As a result, mixed orthorhombic and triclinic crystal structures are formed in meta-HP, which is similar to the precision PE with dimethyl branch at every 21st carbon atom.50 After meta-HP is heated to 82 °C and held for 6 h, which is

PLM micrographs of meta-HP at 45 °C (before cold crystallization) and 82 °C (after cold crystallization). It is observed that the macroscopic morphologies of meta-HP before and after cold crystallization are basically the same, showing little effect of cold crystallization. This indicates that cold crystallization mainly takes place inside the crystals preformed in the cooling process. On the other hand, the values of ΔT relatively quite small for ortho-HP and para-HP, indicating easier crystallization in these two polymers. However, multiple crystallization peaks are observed for ortho-HP, for which there is no reasonable explanation currently. By contrast, double melting peaks are observed in the melting DSC curve of para-HP, and there exists a crystallization peaks between them, though single crystallization peak appears in the cooling curve. The location of crystallization peak between two melting peaks usually indicates the occurrence of melting−recrystallization.51 This shows that during crystallization of para-HP metastable crystals with a low Tm are formed quickly. Upon the heating, these metastable crystals are first melted and then reorganize into more perfect crystals with a higher Tm. Further DSC analysis was carried out to verify this speculation by heating para-HP at different rates (5−50 °C/min) after it was cooled from melt at the same rate (10 °C/min), as shown in Figure S20. With increasing the E

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Macromolecules higher than its cold crystallization temperature, there is slight shift of the diffraction peaks in the WAXD pattern (Figure S21), which corresponds to a larger d-space. For orthorhombic PE crystal, the dimensions of the unit cell can be obtained based on the following equations:55 a = 2d(200)

b=

a 2d(110)2/(a 2 − d(110)2)

(6) (7)

where d(200) and d(110) are the distance of (200) and (110) crystalline planes, respectively, which can be calculated from Bragg’s equation as follows: 2d sin θ = nλ

(8)

where θ is the diffraction angle and λ is the wavelength of the X-rays. The calculated values of a and b for para-HP are 7.38 and 5.11 Å, respectively. By comparison with the lattice parameters a (7.40 Å) and b (4.93 Å) of ADMET PE without any branches,54 we can see that the a-axis of para-HP is almost the same as that of linear PE, but the b-axis is evidently larger than that of linear PE. The large value of b implies dilation of the unit cell, which is the result of inclusion of the defects into the unit cell and the defects are selectively enriched along the b-axis direction. It should be pointed out that in ethylene−propylene random copolymers the methyl branches in the propylene units can also be included into the PE crystal lattice. However, it is usually observed that inclusion of the methyl branches leads to dilation of the a-axis, whereas the b-axis basically remains unchanged for ethylene−propylene random copolymers.55,56 Nevertheless, for the precision PE with methyl branch being placed on each 21st carbon, both the diffraction angles corresponding to the (110) and (200) crystal planes shift to lower 2θ, as compared with the linear PE. The calculation shows that both a-axis and b-axis of the PE unit cell become larger after inclusion of the methyl branches.8 Therefore, it is interesting that the type and distribution of the included defects may affect the dilation direction of the PE unit cell and selective location of the defects inside the unit cell. SAXS Result. Figure 6 shows the SAXS profiles of three precision PEs at various temperatures. The scattering peak of ortho-HP is very weak due to low crystallinity; thus, the SAXS curve is Lorentz-corrected. The long period (LSAXS) and lamellar thickness (lc) can be calculated based on eqs 4 and 5, respectively, which are listed in Table 1. It is found that orthoHP exhibits a broad SAXS peak (Figure 6a). The calculated long period and lamella thickness are 9.66 and 2.54 nm, respectively. We compared the lamellar thickness with the length of 20 CH2 groups, which compose the PE segment between two adjacent phenylene ether units. As shown in Figure S22, the length of the extended PE segment with zigzag planar conformation between two adjacent phenylene ether units is about 2.39 nm, which is close to the lc of ortho-HP. Together with the lowest Tm of ortho-HP, we believe that all the phenylene ether units are excluded from the PE crystal lamella as defects. The exclusion of the phenylene ether units from the crystal phase prevents formation of thick lamellae. A single SAXS peak with a long period of 11.22 nm is observed for meta-HP at 25 °C (Figure 6b), and the calculated value of lc based on volume crystallinity is 4.66 nm. Such a value is larger than the extended length of 20 CH2 groups. Considering the existence of both orthorhombic and other crystals in meta-HP, we speculate that the meta-substituted

Figure 6. SAXS profiles of ortho-HP, meta-HP, and para-HP at different temperatures. Data are shifted vertically for clarity. The SAXS data of ortho-HP are Lorentz-corrected.

phenylene ether groups can be either included into or excluded from the PE crystals. When they are included into the PE crystals, other metastable crystals are formed, as reported for other precision PE with branches that can be included into the PE crystal, such as methyl, chlorine, and bromine.57−59 Since F

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Figure 7. Schematic molecular chain stacking models for ortho-HP, meta-HP, and para-HP.

affect the interaction among polymer chains in the crystals and thus the melting enthalpy. Therefore, the crystallinity determined by DSC (XcDSC) is not accurate. This is the reason why we observe a large difference between the values of XcDSC and XcWAXD for meta-HP and para-HP (Table 1). The volume fraction crystallinity Xvol calculated from eq 3 is not enough accurate either, since we do not know the density of the triclinic crystal of meta-HP, and the data of orthorhombic crystal have been used for replacement. Moreover, DSC results show that para-HP may undergo melting−recrystallization upon heating. For this reason, para-HP was also characterized by SAXS at 130 °C after melting−recrystallization. As shown in Figure 6c, the SAXS peak shifts to lower q without appearance of the second peak. This supports the conclusion that more perfect crystals with a larger lc are formed after melting−recrystallization. Chain Stacking. The TGA, DSC, WAXD, and SAXS characterizations revealed that the disubstitution position of the phenylene ether group in the PE main chain has a great influence on the thermal stability, melting and crystallization behaviors, crystal structure, and lamellar thickness. ortho-HP has a very low Tm, and its lc is comparable to the length of the extended PE segment between two adjacent defects. As a result, the ortho-substituted phenylene ether groups are excluded from the PE crystal lattice. The ortho-substitution on a rigid benzene ring forces the PE segments to turn around, which facilitates chain folding of the polymer chains during crystallization. Since

cold crystallization is observed for this polymer, SAXS characterization was carried out at 82 °C after cold crystallization. It is found that the main SAXS peak shifts to low q, implying a larger long period due to annealing (Figure 6b). However, a small shoulder peak also appears at lower q, which is probably produced upon cold crystallization. Because the cold crystallization temperature is higher than the Tc in the cooling process, the crystals formed in the cold crystallization process have a larger long period. The double SAXS peaks in meta-HP also agree with its mixed crystal structures detected by WAXD. The long periods corresponding to the double SAXS peaks at 82 °C are 14.28 and 19.04 nm, respectively. The calculated lcs are evidently larger that the extended length of 20 CH2. Therefore, annealing and cold crystallization can lead to inclusion of the meta-substituted phenylene ether groups in the PE crystal, which are originally excluded from the crystal. The SAXS peak of para-HP at 25 °C is located at q = 0.39 nm−1, and the corresponding long period is 16.11 nm. The derived lc is 9.55 nm, which is much larger than the length of 20 CH2 groups. As a result, the para-phenylene ether units can be definitely included into the PE crystal. Because of the inclusion of the para-phenylene ether units into the PE crystal, the formation of crystal lamella would not be interrupted by the chain defects; thus, thicker lamella can be formed, which is also in accordance with the highest Tm of para-HP, as revealed by DSC. The inclusion of the chain defects into the PE crystal may G

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Macromolecules the ortho-substituted phenylene ether groups are located in the midway of chain folding, it is natural that they are excluded from the crystals. The chain stacking in ortho-HP can be schematically depicted in Figure 7. Moreover, the orthosubstitution in the phenylene ether groups may also enhance the intramolecular interaction among different segments, which favors nucleation in the initial period of crystallization. As a result, a low degree of supercooling (ΔT) is needed for nonisothermal crystallization. WAXD and SAXS results show that there exist both orthorhombic and triclinic PE crystals in meta-HP at room temperature, with the meta-substituted phenylene ether groups being excluded from and included into the PE crystals, respectively. For meta-HP, there are two possibilities for the chain conformation. If the polymer chains adopt all-trans conformation, the meta-substituted phenylene ether groups can be included into the crystals (Figure 7). However, because the meta-substituted phenylene ether group is bulkier than CH2 group and is asymmetric about the PE chain, its inclusion will alter the interchain interaction in the crystals. Therefore, in order to accommodate the meta-substituted phenylene ether groups in the crystals without much increase in free energy, the chain stacking mode in the meta-HP crystals is different from that in linear PE, leading to formation of triclinic crystal. It should be noted that if the meta-substituted phenylene ether groups are aligned to form a thin layer inside the crystals, like other included defects,58−60 the interaction between the phenylene rings may partly compensate for the increase in free energy due to dilation of unit cell. The inclusion of the meta-substituted phenylene ether groups is also kinetically slow, leading to occurrence of cold crystallization. On the other hand, when the CH2 group linked with the O atom adopts gauche conformation, the chain direction is also altered at the phenylene ether group, as in ortho-HP. This will result in chain folding and exclusion of the phenylene ether group from the crystal. In such a situation, orthorhombic crystals are formed. Since the lc of para-HP is much larger than the extended length of 20 CH2, the para-substituted phenylene ether groups are easily be included into the PE crystals upon crystallization. The para-substitution makes it difficult for adjacent PE segments to get close, which is disadvantageous to chain folding. In addition, the para-substituted phenylene group is symmetric about the polymer chain, which is also favorable to its inclusion. The small dilation of the unit cell is not enough to change the chain stacking mode of PE chains; thus, para-HP can crystallize like linear PE. Nevertheless, inclusion of the para-substituted phenylene groups will still add some difficulty in crystallization, which results in imperfect crystals. Therefore, melting−recrystallization occurs upon heating para-HP. We have also noticed that the substitution position in the phenylene ether groups has a great influence on the crystallization behavior of the precision PEs, which is different from that of the PEOs coupled with different benzene dicarbonyl dichloride isomers.18−20 In these PEOs, all the benzene diester isomers are excluded from the PEO crystals. There are only slight differences in Tm and long period among the PEOs with benzene diester defects. There are two reasons for the difference between precision PEs and coupled PEOs. First, there is only single benzene diester defect in each PEO chain, whereas there are many phenylene ether defects per PE chain. As a result, the phenylene ether defects exert a greater effect on chain stacking in precision PEs. Second, the zigzag

planar conformation of PE in the crystals is matchable with the configuration of the rigid phenylene groups; thus, the defects can be included into the crystals more readily as long as the substitution position is suitable, such as meta-HP and para-HP. By contrast, PEO exhibits helical conformation in the crystals, which does not match the configuration of phenylene group. Herein we propose that the match between the configuration of the enchained defects and the conformation of the crystalline segments is a vital factor for the inclusion of the defects into the crystals. Effect of Defect Size. In order to further ascertain the location of the defects, we also synthesized four precision PEs with each naphthylene ether group (1,4-, 2,3-, 2,6-, or 2,7isomers) in the main chain being separated by 20 CH2 units (Scheme S2). Among these samples, the precision PE with 2,3naphthylene ether defects (23NP-HP) has a similar structure with ortho-HP, and in both 23NP-HP and ortho-HP the arylene groups are symmetric with respect to the polymer main chain. The substitution position in the sample with 1,4-substituted naphthylene ether defects (14NP-HP) is also similar to that in para-HP, but the naphthylene ether groups in 14NP-HP are not symmetric with respect to the polymer main chain. By contrast, the 2,6-substitution in the naphthylene group makes the defects symmetric about the polymer main chain, and the obtained precision PE (26NP-HP) is also similar to para-HP with two more C atoms in each defect. The precision PE with 2,7-substituted naphthylene ether defects (27NP-HP) has a similar structure with meta-HP except for two more C atoms along the polymer chain in the defects. Figure 8 shows the nonisothermal crystallization and melting DSC thermograms of the precision PEs containing naphthylene

Figure 8. Nonisothermal and melting DSC thermograms of 14NP-HP, 23NP-HP, 26NP-HP, and 27NP-HP.

ether groups with different substitution positions. One can see that the Tc and Tm of 23NP-HP are nearly the same as those of ortho-HP. This confirms that both 2,3-substituted naphthylene ether and 1,2-substituted phenylene ether defects are excluded from the PE crystals due to their similar substitution positions. Since the Tm of PE is mainly determined by lc, i.e., the length of PE segments between two adjacent excluded defects, defect size has little effect on Tm. By contrast, it is found that the Tc and Tm of 27NP-HP are 107.9 and 114.3 °C, respectively, which are obviously higher than those of meta-HP. This shows that both 2,7-substituted naphthylene ether and 1,3-substituted phenylene ether defects can be included into the PE crystals. However, due to the stronger interaction among naphthylene ether groups than among phenylene ones, 27NP-HP exhibits a H

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higher Tm. Likewise, 26NP-HP has a higher Tm than para-HP. However, the Tc and Tm of 14NP-HP are 55.5 and 73.9 °C, respectively, which are even lower than those of ortho-HP. This is because the 1,4-substituted naphthylene ether groups are asymmetric with respect to the polymer main chain, which will hinder the close arrangement of polymer chains inside the crystals, and thus are excluded from the PE crystals. Since 1,4substitution is in indeed unfavorable to chain folding, more CH2 units are involved into the exclusion of the defects. Therefore, the lc of the formed crystals is even smaller than that in ortho-HP, in which the defects are excluded from the PE crystals as well. The crystallization and melting behaviors of precision PEs with naphthylene ether defects in the main chain verify that the inclusion or exclusion of the defects strongly depends on the substitution position and defect size.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b01324. Experimental details; Schemes S1 and S2; Figures S1− S22 (PDF)

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REFERENCES

(1) Chen, Z. R.; Kornfield, J. A.; Smith, S. D.; Grothaus, J. T.; Satkowski, M. M. Pathways to Macroscale Order in Nanostructured Block Copolymers. Science 1997, 277, 1248−1253. (2) Bent, J.; Hutchings, L. R.; Richards, R. W.; Gough, T.; Spares, R.; Coates, P. D.; Grillo, I.; Harlen, O. G.; Read, D. J.; Graham, R. S.; Likhtman, A. E.; Groves, D. J.; Nicholson, T. M.; McLeish, T. C. B. Neutron-Mapping Polymer Flow: Scattering, Flow Visualization, and Molecular Theory. Science 2003, 301, 1691−1695. (3) Matyjaszewski, K. Architecturally Complex Polymers with Controlled Heterogeneity. Science 2011, 333, 1104−1105. (4) Calleja, F. J. B.; Ortega, J. C. G.; de Salazar, J. M. Distribution of Chain Defects and Microstructure of Melt Crystallized Polyethylene. Polymer 1978, 19, 1094−1099. (5) Martuscelli, E.; Pracella, M. Effects of Chain Defects on Thermal Behavior of Polyethylene. Polymer 1974, 15, 306−314. (6) Balta-calleja, F. J.; Hosemann, R. Distribution of Chain Defects and Microstructures of Melt Crystallized Polyethylene. 2. Influence of Defect Size and of Plastic-Deformation. J. Polym. Sci., Polym. Phys. Ed. 1980, 18, 1159−1165. (7) Cho, T. Y.; Heck, B.; Strobl, G. Equations Describing Lamellar Structure Parameters and Melting Points of Polyethylene-co-(butene/ octene)s. Colloid Polym. Sci. 2004, 282, 825−832. (8) Rojas, G.; Inci, B.; Wei, Y.; Wagener, K. B. Precision Polyethylene: Changes in Morphology as a Function of Alkyl Branch Size. J. Am. Chem. Soc. 2009, 131, 17376−17386. (9) Tong, Z. Z.; Zhou, B.; Huang, J.; Xu, J. T.; Fan, Z. Q. Regulation of Crystallization Kinetics, Morphology, and Mechanical Properties of Olefinic Blocky Copolymers. Macromolecules 2014, 47, 333−346. (10) Tong, Z. Z.; Huang, Y.; Xu, J. T.; Fu, Z. S.; Fan, Z. Q. Chain Structure, Aggregation State Structure, and Tensile Behavior of Segmented Ethylene-Propylene Copolymers Produced by an Oscillating Unbridged Metallocene Catalyst. J. Phys. Chem. B 2015, 119, 6050−6061. (11) Klapper, M.; Wehrmeister, T.; Müllen, K. Grafting on Poly(ether ether ketone ketone)s (PEEKK) by Anionic Deactivation. Macromolecules 1996, 29, 5805−5809. (12) Ben-Haida, A.; Colquhoun, H. M.; Hodge, P.; Williams, D. J. Synthesis of a Catechol-Based Poly(ether ether ketone) (“o-PEEK”) by Classical Step-Growth Polymerization and by Entropically Driven Ring-Opening Polymerization of Macrocyclic Oligomers. Macromolecules 2006, 39, 6467−6472. (13) Anastasiou, T. J.; Uhrich, K. E. Novel Polyanhydrides with Enhanced Thermal and Stability Properties. Macromolecules 2000, 33, 6217−6221. (14) Fortney, A.; Fossum, E. Soluble, Semi-crystalline PEEK Analogs Based on 3,5-Difluorobenzophenone: Synthesis and Characterization. Polymer 2012, 53, 2327−2333. (15) Taranekar, P.; Abdulbaki, M.; Krishnamoorti, R.; Phanichphant, S.; Waenkaew, P.; Patton, D.; Fulghum, T.; Advincula, R. Structure and Band-Gap Design of a New Series of Light-Emitting Poly(cyanofluorene-alt-o/m/p-phenylenevinylene)-Based Copolymers for Light-Emitting Diodes. Macromolecules 2006, 39, 3848−3854. (16) Brennan, D. J.; White, J. E.; Haag, A. P.; Kram, S. L.; Mang, M. N.; Pikulin, S.; Brown, C. N. Poly(hydroxy amide ethers): New HighBarrier Thermoplastics. Macromolecules 1996, 29, 3707−3716. (17) Ahn, T.; Jang, M. S.; Shim, H. K.; Hwang, D. H.; Zyung, T. Blue Electroluminescent Polymers: Control of Conjugation Lengthen by Kink Linkages and Substituents in the Poly(p-phenylenevinylene)Related Copolymers. Macromolecules 1999, 32, 3279−3285. (18) Lee, S. W.; Chen, E. Q.; Zhang, A. Q.; Yoon, Y.; Moon, B. S.; Lee, S.; Harris, F. W.; Cheng, S. Z. D.; von Meerwall, E. D.; Hsiao, B. S.; Verma, R.; Lando, J. B. Isothermal Thickening and Thinning Processes in Low Molecular Weight Poly(ethylene oxide) Fractions Crystallized from the Melt. 5. Effect of Chain Defects. Macromolecules 1996, 29, 8816−8823. (19) Chen, E. Q.; Lee, S. W.; Zhang, A. Q.; Moon, B. S.; Mann, I.; Harris, F. W.; Cheng, S. Z. D.; Hsiao, B. S.; Yeh, F. J.; von Meerwall, E. D. Isothermal thickening and thinning processes in low molecular

4. CONCLUSIONS The above results show that the size and substitution position of the enchained arylene ether defects greatly affect the thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking of precision PEs. The defects are excluded from the PE crystal in ortho-HP, while the defects can be included into the PE crystal in para-HP, and parts of the metasubstituted phenylene ether groups are included into the PE crystal. Accordingly, para-HP has the highest Tm, but the Tm of ortho-HP is the lowest. Moreover, inclusion of the defects leads to dilation of unit cell in para-HP and meta-HP and even change of the crystal structure in meta-HP. Cold crystallization and melting−recrystallization are also observed in meta-HP and para-HP, respectively. The inclusion of the phenylene ether defects into the PE crystal is different from the case in PEOs coupled with benzene dicarbonyl dichloride isomers, which can be interpreted in terms of the matchable configuration of the enchained defects with the conformation of PE in the crystal. As for precision PEs containing naphthylene ether defects, 2,3and 1,4-substitutions also lead to exclusion of the defects from the PE crystal, but 2,6- and 2,7-substitutions result in inclusion of the defects into the PE crystal. These results will be helpful for understanding how chain defects affect polymer crystallization and can guide us to tune polymer properties through design of suitable chain defects.

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AUTHOR INFORMATION

Corresponding Authors

*(J.-T.X.) E-mail: [email protected]. *(Z.-Q.F.) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the National Natural Science Foundation of China (Grant No. 21544004) is gratefully acknowledged. The authors thank beamline BL16B1 at Shanghai Synchrotron Radiation Facility (SSRF) for providing the beam time. I

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Macromolecules weight poly(ethylene oxide) fractions crystallized from the melt: Effects of molecular configurational defects on crystallization, melting, and annealing. In Scattering from polymers: Characterization by X-ray, Neutrons, and Light; Cebe, P., Hsiao, B. S., Lohse, D. J., Eds.; American Chemical Society: 1999; pp 118. (20) Chhajer, M.; Chen, E. Q.; Cheng, S. Z. D. Self-diffusion Coefficients of Flexible Linear Polymers with Local Inhomogeneities at the Center of Each Chain. J. Macromol. Sci., Part B: Phys. 2001, 40, 615−624. (21) Sworen, J. C.; Smith, J. A.; Wagener, K. B.; Baugh, L. S.; Rucker, S. P. Modeling Random Methyl Branching in Ethylene/Propylene Copolymers Using Metathesis Chemistry: Synthesis and Thermal Behavior. J. Am. Chem. Soc. 2003, 125, 2228−2240. (22) Buitrago, C. F.; Jenkins, J. E.; Opper, K. L.; Aitken, B. S.; Wagener, K. B.; Alam, T. M.; Winey, K. I. Room Temperature Morphologies of Precise Acid- and Ion-Containing Polyethylenes. Macromolecules 2013, 46, 9003−9012. (23) Song, W.; Wu, J.; Yang, G.; Han, H.; Xie, M.; Liao, X. Precisely Designed Perylene Bisimide-Substituted Polyethylene with a High Glass Transition Temperature and an Ordered Architecture. RSC Adv. 2015, 5, 68765−68772. (24) Li, Z.-L.; Li, L.; Deng, X.-X.; Lv, A.; Wang, C.-H.; Du, F.-S.; Li, Z.-C. Ethylene-Ethyl Acrylate Copolymers via ADMET Polymerization: Effect of Sequence Distribution on Thermal Properties. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2900−2909. (25) Song, S. F.; He, F.; Fu, Z. S.; Xu, J. T.; Fan, Z. Q. Precision ADMET Polyolefins Containing Dithiane: Synthesis, Thermal Properties, and Macromolecular Transformation. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2468−2475. (26) Ortmann, P.; Lemke, T. A.; Mecking, S. Long-Spaced Polyamides: Elucidating the Gap between Polyethylene Crystallinity and Hydrogen Bonding. Macromolecules 2015, 48, 1463−1472. (27) Ortmann, P.; Wimmer, F. P.; Mecking, S. Long-Spaced Polyketones from ADMET Copolymerizations as Ideal Models for Ethylene/CO Copolymers. ACS Macro Lett. 2015, 4, 704−707. (28) Li, H.; Rojas, G.; Wagener, K. B. Precision Long-Chain Branched Polyethylene via Acyclic Diene Metathesis Polymerization. ACS Macro Lett. 2015, 4, 1225−1228. (29) Leonard, J. K.; Hopkins, T. E.; Chaffin, K.; Wagener, K. B. Semicrystalline Lysine Functionalized Precision Polyolefins. Macromol. Chem. Phys. 2008, 209, 1485−1494. (30) Hall, L. M.; Seitz, M. E.; Winey, K. I.; Opper, K. L.; Wagener, K. B.; Stevens, M. J.; Frischknecht, A. L. Ionic Aggregate Structure in Ionomer Melts: Effect of Molecular Architecture on Aggregates and the Ionomer Peak. J. Am. Chem. Soc. 2012, 134, 574−587. (31) Reimann, S.; Baumeister, U.; Binder, W. H. Synthesis and Crystallization of Precision Polymers with Repetitive Folding Elements. Macromol. Chem. Phys. 2014, 215, 1963−1972. (32) Steinbach, T.; Alexandrino, E. M.; Wahlen, C.; Landfester, K.; Wurm, F. R. Poly(phosphonate)s via Olefin Metathesis: Adjusting Hydrophobicity and Morphology. Macromolecules 2014, 47, 4884− 4893. (33) Simocko, C.; Young, T. C.; Wagener, K. B. ADMET Polymers Containing Precisely Spaced Pendant Boronic Acids and Esters. Macromolecules 2015, 48, 5470−5473. (34) Boz, E.; Wagener, K. B.; Ghosal, A.; Fu, R.; Alamo, R. G. Synthesis and Crystallization of Precision ADMET Polyolefins Containing Halogens. Macromolecules 2006, 39, 4437−4447. (35) Rojas, G.; Wagener, K. B. Precisely and Irregularly Sequenced Ethylene/1-Hexene Copolymers: A Synthesis and Thermal Study. Macromolecules 2009, 42, 1934−1947. (36) Alamo, R. G.; Jeon, K.; Smith, R. L.; Boz, E.; Wagener, K. B.; Bockstaller, M. R. Crystallization of Polyethylenes Containing Chlorines: Precise vs Random Placement. Macromolecules 2008, 41, 7141−7151. (37) Few, C. S.; Wagener, K. B.; Thompson, D. L. Systematic Studies of Morphological Changes of Precision Polyethylene. Macromol. Rapid Commun. 2014, 35, 123−132.

(38) Hosoda, S.; Nozue, Y.; Kawashima, Y.; Suita, K.; Seno, S.; Nagamatsu, T.; Wagener, K. B.; Inci, B.; Zuluaga, F.; Rojas, G.; Leonard, J. K. Effect of the Sequence Length Distribution on the Lamellar Crystal Thickness and Thickness Distribution of Polyethylene: Perfectly Equisequential ADMET Polyethylene vs Ethylene/ α-Olefin Copolymer. Macromolecules 2011, 44, 313−319. (39) Buitrago, C. F.; Opper, K. L.; Wagener, K. B.; Winey, K. I. Precise Acid Copolymer Exhibits a Face-Centered Cubic Structure. ACS Macro Lett. 2012, 1, 71−74. (40) Matsui, K.; Seno, S.; Nozue, Y.; Shinohara, Y.; Amemiya, Y.; Berda, E. B.; Rojas, G.; Wagener, K. B. Influence of Branch Incorporation into the Lamella Crystal on the Crystallization Behavior of Polyethylene with Precisely Spaced Branches. Macromolecules 2013, 46, 4438−4446. (41) Aggarwal, S. L.; Tilley, G. P. Determination of Crystallinity in Polyethylene by X-Ray Diffractometer. J. Polym. Sci. 1955, 18, 17−26. (42) Khariwala, D. U.; Taha, A.; Chum, S. P.; Hiltner, A.; Baer, E. Crystallization Kinetics of Some New Olefinic Block Copolymers. Polymer 2008, 49, 1365−1375. (43) Hong, S. H.; Day, M. W.; Grubbs, R. H. Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions. J. Am. Chem. Soc. 2004, 126, 7414−7415. (44) Mutlu, H.; de Espinosa, L. M.; Meier, M. A. R. Acyclic Diene Metathesis: a Versatile Tool for the Construction of Defined Polymer Architectures. Chem. Soc. Rev. 2011, 40, 1404−1445. (45) Steinmann, M.; Markwart, J.; Wurm, F. R. Poly(alkylidene chlorophosphate)s via Acyclic Diene Metathesis Polymerization: A General Platform for the Postpolymerization Modification of Poly(phosphoester)s. Macromolecules 2014, 47, 8506−8513. (46) Terada, K.; Berda, E. B.; Wagener, K. B.; Sanda, F.; Masuda, T. ADMET Polycondensation of Diketopiperazine-Based Dienes. Polymerization Behavior and Effect of Diketopiperazine on the Properties of the Formed Polymers. Macromolecules 2008, 41, 6041−6046. (47) Li, Z.-L.; Li, L.; Deng, X.-X.; Zhang, L.-J.; Dong, B.-T.; Du, F.-S.; Li, Z.-C. Periodic Vinyl Copolymers Containing γ-Butyrolactone via ADMET Polymerization of Designed Diene Monomers with Built-in Sequence. Macromolecules 2012, 45, 4590−4598. (48) Baughman, T. W.; Sworen, J. C.; Wagener, K. B. Sequenced Ethylene-Propylene Copolymers: Effects of Short Ethylene Run Lengths. Macromolecules 2006, 39, 5028−5036. (49) Boz, E.; Nemeth, A. J.; Wagener, K. B.; Jeon, K.; Smith, R.; Nazirov, F.; Bockstaller, M. R.; Alamo, R. G. Well-Defined Precision Ethylene/Vinyl Fluoride Polymers: Synthesis and Crystalline Properties. Macromolecules 2008, 41, 1647−1653. (50) Qiu, W.; Sworen, J.; Pyda, M.; Nowak-Pyda, E.; Habenschuss, A.; Wagener, K. B.; Wunderlich, B. Effect of the Precise Branching of Polyethylene at Each 21st CH2 Group on Its Phase Transitions, Crystal Structure, and Morphology. Macromolecules 2006, 39, 204− 217. (51) Song, S.; Miao, W.; Wang, Z.; Gong, D.; Chen, Z.-R. Synthesis and Characterization of Precisely-Defined Ethylene-co-Aryl Ether Polymers via ADMET Polymerization. Polymer 2015, 64, 76−83. (52) Nozue, Y.; Kawashima, Y.; Seno, S.; Nagamatsu, T.; Hosoda, S.; Berda, E. B.; Rojas, G.; Baughman, T. W.; Wagener, K. B. Unusual Crystallization Behavior of Polyethylene Having Precisely Spaced Branches. Macromolecules 2011, 44, 4030−4034. (53) Inci, B.; Wagener, K. B. Decreasing the Alkyl Branch Frequency in Precision Polyethylene: Pushing the Limits toward Longer Run Lengths. J. Am. Chem. Soc. 2011, 133, 11872−11875. (54) Inci, B.; Lieberwirth, I.; Steffen, W.; Mezger, M.; Graf, R.; Landfester, K.; Wagener, K. B. Decreasing the Alkyl Branch Frequency in Precision Polyethylene: Effect of Alkyl Branch Size on Nanoscale Morphology. Macromolecules 2012, 45, 3367−3376. (55) Du, Z. X.; Xu, J. T.; Dong, Q.; Fan, Z. Q. Thermal Fractionation and Effect of Comonomer Distribution on the Crystal Structure of Ethylene-Propylene Copolymers. Polymer 2009, 50, 2510−2515. (56) Bassi, I. W.; Corradini, P.; Fagherazzi, G.; Valvassori, A. Crystallization of High Ethylene EPDM Terpolymers in the Stretched State. Eur. Polym. J. 1970, 6, 709−718. J

DOI: 10.1021/acs.macromol.6b01324 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules (57) Lieser, G.; Wegner, G.; Smith, J. A.; Wagener, K. B. Morphology and Packing Behavior of Model Ethylene/Propylene Copolymers with Precise Methyl Branch Placement. Colloid Polym. Sci. 2004, 282, 773− 781. (58) Kaner, P.; Ruiz-Orta, C.; Boz, E.; Wagener, K. B.; Tasaki, M.; Tashiro, K.; Alamo, R. G. Kinetic Control of Chlorine Packing in Crystals of a Precisely Substituted Polyethylene. Toward Advanced Polyolefin Materials. Macromolecules 2014, 47, 236−245. (59) Tasaki, M.; Yamamoto, H.; Hanesaka, M.; Tashiro, K.; Boz, E.; Wagener, K. B.; Ruiz-Orta, C.; Alamo, R. G. Polymorphism and Phase Transitions of Precisely Halogen-Substituted Polyethylene. (1) Crystal Structures of Various Crystalline Modifications of Bromine-Substituted Polyethylene on Every 21st Backbone Carbon. Macromolecules 2014, 47, 4738−4749. (60) Zheng, Y. R.; Tee, H. T.; Wei, Y.; Wu, X. L.; Mezger, M.; Yan, S. K.; Landfester, K.; Wagener, K. B.; Wurm, F. R.; Lieberwirth, I. Morphology and Thermal Properties of Precision Polymers: The Crystallization of Butyl Branched Polyethylene and Polyphosphoesters. Macromolecules 2016, 49, 1321−1330.

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DOI: 10.1021/acs.macromol.6b01324 Macromolecules XXXX, XXX, XXX−XXX