Functional Polyethylenes with Precisely Placed Thioethers and

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Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

Functional Polyethylenes with Precisely Placed Thioethers and Sulfoniums through Thiol−Ene Polymerization Michael T. Kwasny, Carolyn M. Watkins, Nicholas D. Posey, Megan E. Matta, and Gregory N. Tew* Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States S Supporting Information *

ABSTRACT: The precise functionalization of polyethylenes, often accomplished through acyclic diene metathesis polymerization (ADMET), is a significant area of research that has improved polyethylene properties and performance. Here, the synthesis of precisely functionalized polyethylenes was accomplished using the thiol−ene step-growth (TES) polymerization. The simplicity and versatility of this technique allowed for the synthesis of a variety of polymers and enabled the study of carbon spacer length between and repeat unit symmetry about the resulting backbone thioether moiety. In addition, the backbone thioethers of some samples were functionalized postpolymerization with methyl triflate to produce polyethylenes containing sulfonium cations. All polymers were then characterized for their thermal stability, crystallinity, and morphology using differential scanning calorimetry (DSC) and X-ray scattering. While the carbon spacer length and repeat unit symmetry had no effect on polymer thermal stability, the incorporation of cationic sulfonium groups reduced the degradation temperature. Most polymers were polymorphic with respect to crystal structure, and increasing the carbon spacer length led to an increase in polymer melting temperature and percent crystallinity. Furthermore, the average carbon spacer length had a larger effect on polymer percent crystallinity and crystal structure than repeat unit symmetry, but the symmetry had a significant impact on polymer crystal melting temperature, as symmetric polymers had higher melting temperatures. Overall, TES polymerization was utilized to fabricate precisely functionalized polyethylenes, where the repeat unit symmetry improved polymer crystal perfection.

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alkyl acrylate),14 expanding the range of available applications for polyethylene. However, the polymerization of ethylene-based monomers presents significant challenges. First, all monomers must be candidates for single-site catalysis or free radical polymerization, the most common approaches used for polymerizing ethylenebased monomers. 11,14 Since not all functional groups coordinate to catalyst centers with the same affinity, altering the moiety on a monomer can significantly impact the reactivity and polymerization rate of each monomer during single-site catalysis polymerizations.11 Furthermore, free radical polymerizations are known to produce vast numbers of irregularities and defects within the polymer structure.1,15 These two methods of polymerizations just mentioned highlight the challenges of synthesizing well-controlled functional polyethylenes, since each monomer would need to have controllable reactivity in order to regulate the incorporation and distribution of the monomers within the polymer.11 Even when copolymerized successfully, the desired functionality is incorporated statistically throughout the polymer backbone, making it difficult to control the architecture, morphology, and crystallinity of the resulting polymer. Therefore, the field remains interested in new methods of synthesizing functional

INTRODUCTION

Polyethylene is one of the most important and widely used polymers today. It has found tremendous success in many industrial applications including, but not limited to, packaging, biomaterials, microelectronics, protective coatings, and adhesion.1 Polyethylene has been successful due to its low cost, ease of processing, resistance to weathering, and excellent physical and chemical properties.2 In addition, the ability to tune the inherent semicrystalline morphology of polyethylene enhances its potential for a variety of applications by influencing the material’s properties.1 To expand the properties of polyethylene and its utility, considerable efforts have been devoted to developing functional polyethylene through the addition of specific side chains or functional moieties.3,4 Incorporation of chemical functionality has led to the improvement of important properties such as adhesion, printability, miscibility in polymer blends, and toughness, and it can also impart new properties, such as ion conduction.3,5−10 Through the addition of reactive functional groups, further modification can be accomplished postpolymerization to better control the materials’ properties.3 The most commonly employed methods of producing functional polyethylenes are the copolymerization of ethylene and a functional comonomer or the homopolymerization of a functional monomer.11,12 Polymerizing ethylene-based functional monomers has produced polymers such as poly(vinyl chloride),1 poly(tetrafluoroethylene),13 and poly(ethylene-co© XXXX American Chemical Society

Received: February 12, 2018 Revised: May 10, 2018

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DOI: 10.1021/acs.macromol.8b00334 Macromolecules XXXX, XXX, XXX−XXX

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simplicity of the thiol−ene reaction. By using commercially available dithiol and diene monomers, the number of carbons surrounding the resulting thioether moiety can be easily controlled, modifying the density and placement of the functional group along the polymer backbone. Here, two series of functional polymers were synthesized to study the effects of both modulating the carbon spacer length between thioethers and the repeat unit symmetry. In addition, the effects of introducing ions along the backbone were studied by methylating the thioethers to produce sulfonium cations. All polymers were characterized for their thermal stability, crystallinity, and crystalline morphology showing the tunability and versatility of TES polymerization.

polyethylene with precise polymer architectures, where the placement of the functional group along the backbone occurs in regular and controlled intervals.7,12,16 The most common method employed to synthesize precisely functionalized polyethylene utilizes acyclic diene metathesis polymerization (ADMET).1,14,17,18 By specifically designing functional diene monomers, polymers can be synthesized where the moiety is incorporated at regular, precise locations along the polymer chain, dictated by the location of the functional group in the monomer.6,7,19,20 This approach has successfully produced precise polymers containing a variety of functional groups including carboxylic acids,14 phosphonic acids,21 halogens,1,22 alcohols,23,24 and sulfones,6 demonstrating a wide range of unique properties and morphologies.7,19 In spite of its success, ADMET has the disadvantages of requiring difficult monomer syntheses, long polymerization times, and high temperatures.25 In addition, the required ruthenium catalyst used in ADMET can be difficult to remove, and the resulting polymer product contains double bonds in the backbone that must be hydrogenated to obtain the desired polyethylene backbone.26 Therefore, developing an approach to include precise functional group placement that complements ADMET would represent a significant advancement toward new functional polyethylenes. The thiol−ene step-growth (TES) polymerization is an excellent candidate to combine controlled functional group placement with synthetic ease for producing precisely functionalized polyethylene. In general, the thiol−ene reaction has undergone a resurgence in use for polymer research due to its versatility and robustness, although it is principally used for postpolymerization functionalization and the synthesis of crosslinked polymer networks, rather than the synthesis of linear polymers.27,28,37,29−36 The photochemically initiated radical thiol−ene reaction presents numerous benefits in the synthesis of functional polyethylenes as it is insensitive to oxygen, proceeds under ambient conditions, is tolerant to a wide range of functional groups, and often uses commercially available starting materials.28,29,44,30,35,38−43 Furthermore, the initiators are entirely organic and can be easily removed after polymerization, and the reaction avoids backbone unsaturation removing the need for hydrogenation.45,46 Despite the potential for its use in synthesizing linear aliphatic poly(thioethers) with rapid and quantitative conversion, only recently has research begun to investigate the thiol−ene reaction for the formation of linear polymers.30−32,47−49 The photoinitiated polymerization of α,ωalkene thiols was reported recently to produce a series of low molecular weight polymers with a precisely controlled number of carbons between thioether units.50 In the past few years, the thiol−ene reaction has been used to produce a variety of novel polymers with precise control over spacer length between functional groups.45,46,51 Given the initial success of the thiol− ene reaction in producing linear polymers, the production of functional polymers utilizing this approach has become popular in recent years. Polymers containing a wide range of functionality have since been produced, including carbonates,46 zwitterions,46 alcohols,46,52 molecular rods,53 and furfurals,52 to name a few. Moreover, the reactivity of the thioether moiety allows for postpolymerization modifications to incorporate a variety of additional functionality into these polymers.45,46,54 Capitalizing on these advantages, this work employed the TES polymerization in an effort to combine the benefits of precisely controlled functional polyethylene with the ease and

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EXPERIMENTAL SECTION

Materials. Dichloromethane (Fisher Scientific) was dried over calcium hydride under N2 gas and then distilled before use. 1,7Octadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 1,2-ethanedithiol, 1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,10-decanedithiol, methyl trifluoromethanesulfonate (methyl triflate), Irgacure 2959, chloroform, methanol, and tetrahydrofuran (THF) were purchased from Sigma-Aldrich, Alfa Aesar, Acros Organics, or Fisher Scientific and were used as received. Instrumentation. A Blak-Ray 100 W B-110 AP/R lamp was used to irradiate samples for photopolymerization. The 1H spectra were recorded using a Bruker 500 MHz Ascend NMR spectrometer retrofitted with a cryo-probe. Polymer molecular weight distributions were measured using gel permeation chromatography (GPC) with THF as the eluent on an Agilent 1260 series system equipped with both a refractive index (RI) and an ultraviolet (UV) detector, a PL Gel 5 μm guard column, two 5 μm analytic Mixed-C columns, and a 5 μm analytical Mixed-D column. All columns were connected in series and incubated at 40 °C with THF as the eluent at a flow rate of 1.0 mL/ min with toluene as the flow marker. X-ray scattering was performed using an Osmic MaxFlux Cu Kα X-ray source with a wavelength of 1.54 Å and a 2-dimensional, gas-filled wire array detector (both from Molecular Metrology, Inc.) set at a distance of 1.476 m from the sample. Thermal properties were characterized using differential scanning calorimetry (DSC) on a Thermal Instruments Q200 DSC with refrigerated cooling and a N2 sample flow rate of 50 mL/min. Thermal stability was obtained using thermogravimetric analysis (TGA) on a Thermal Instruments Q500 TGA using air as the gas. Synthesis of Poly(thioethylenes). General Procedure. The appropriate dithiol was added to a 20 mL scintillation vial, followed by the corresponding diene, and the two were vortexed. Next, Irgacure 2959 and THF were added, and the solution was vortexed again. The vial was tilted at an angle and placed under the UV light to ensure the entire solution was exposed to UV irradiation. The solution was then irradiated with UV light (365 nm) for 1 h. After that, the resulting material was dissolved in a minimal amount of chloroform and precipitated once into methanol to remove any photoinitiator and unreacted monomers. The resulting precipitate was filtered and dried under high vacuum overnight. PTE-8,2. The general procedure was followed using the following amounts: 1,2-ethanedithiol (0.236 g, 2.505 mmol, 1 equiv), 1,7octadiene (0.276 g, 2.505 mmol, 1 equiv), Irgacure 2959 (4−5 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,4. The general procedure was followed using the following amounts: 1,4-butanedithiol (0.267 g, 2.184 mmol, 1 equiv), 1,7octadiene (0.242 g, 2.184 mmol, 1 equiv), Irgacure 2959 (4−5 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,6. The general procedure was followed using the following amounts: 1,6-hexanedithiol (0.300 g, 1.996 mmol, 1 equiv), 1,7octadiene (0.220 g, 1.996 mmol, 1 equiv), Irgacure 2959 (4−5 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,8. The general procedure was followed using the following amounts: 1,8-octanedithiol (0.321 g, 1.797 mmol, 1 equiv), 1,7B

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Scheme 1. Synthetic Procedure for Octadiene-Based Poly(thioethylenes) via Thiol−Ene Chemistry, with Nomenclature Represented below the Structures

Table 1. Thermal Properties for Series 1 Polymers sample

Mna (kg/mol)

Mwa (kg/mol)

Đ

degradation tempb (°C)

peak degradation rate tempc (°C)

Tmd (°C)

ΔHd (J/g)

PTE-8,2 PTE-8,4 PTE-8,6 PTE-8,8 PTE-8,10 PTE-8,12 PTE-8,14

5.7 14.0 13.0 12.0 7.9 9.9 7.7

7.7 24.0 21.0 20.0 10.0 13.1 12.0

1.4 1.7 1.6 1.6 1.3 1.3 1.5

310 308 318 320 314 318 323

346 359 361 366 346 364 372

79.6/85.0 71.7 75.1 82.5 78.5 86.4 88.4

34.7 71.3 82.9 91.2 46.7 98.2 100.0

a

Determined by GPC using THF as the eluent against PS standards. bPolymer degradation temperature determined at 5% mass loss by TGA. cPeak degradation rate temperature, obtained by TGA, was determined from the maximum calculated slope of the thermogram. dPolymer melting characteristics determined by DSC. ramp of 20 °C/min under air, measuring the mass remaining of the sample as a function of temperature. Differential Scanning Calorimetry. For all samples, 1−3 mg was loaded into aluminum pans, hermetically sealed, and run using a heat− cool−heat method. Samples were first heated to 200 °C at a heating ramp of 10 °C/min, then cooled to −50 °C at a cooling ramp of 10 °C/min, and then heated again to 200 °C at a heating ramp of 10 °C/ min. Only the second heating curve was used for analysis. X-ray Scattering. X-ray scattering samples for each of the 11 samples were prepared using the same method. Metal washers were first rinsed with acetone and allowed to dry. Kapton tape was then placed over one side of the washer, covering the opening, and the samples were packed into the opening on the other side using a spatula. A second piece of Kapton tape was used to seal the sample within the open space of the washer. All samples were clamped into the appropriate sample holder and irradiated for a total of 360 s under vacuum at room temperature for each type of scattering experiment: ESAXS, SAXS, MAXS, and WAXS.

octadiene (0.198 g, 1.797 mmol, 1 equiv), Irgacure 2959 (4−5 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,10. The general procedure was followed using the following amounts: 1,10-decanedithiol (0.330 g, 1.600 mmol, 1 equiv), 1,7octadiene (0.176 g, 1.600 mmol, 1 equiv), Irgacure 2959 (4−5 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,12. The general procedure was followed using the following amounts: 1,8-octanedithiol (0.260 g, 1.458 mmol, 1 equiv), 1,11dodecadiene (0.242 g, 1.458 mmol, 1 equiv), Irgacure 2959 (2−4 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-8,14. The general procedure was followed using the following amounts: 1,8-octanedithiol (0.248 g, 1.389 mmol, 1 equiv), 1,13tetradecadiene (0.270 g, 1.389 mmol, 1 equiv), Irgacure 2959 (2−4 mg, 0.018−0.022 mmol, 1 wt %), and THF (2 mL). PTE-10,10. The general procedure followed using the following amounts: 1,10-decanedithiol (3.00 g, 14.540 mmol, 1 equiv), 1,9decadiene (2.01 g, 14.540 mmol, 1 equiv). Irgacure 2959 (40−50 mg, 0.18−0.22 mmol, 1 wt %), and THF (20 mL). PTE-14,4. The general procedure was followed using the following amounts: 1,4-butanedithiol (0.390 g, 3.189 mmol, 1 equiv), 1,13tetradecadiene (0.620 g, 3.189 mmol, 1 equiv), Irgacure 2959 (0.008− 0.100 g, 0.036−0.045 mmol, 1 wt %, and THF (4 mL). Synthesis of Poly(sulfonium ethylenes). General Procedure. A polythioether sample (PTE-10,10 or PTE-14,4) was added to a flask containing a stir bar, and the flask was immediately covered with a septum. Dichloromethane was added via syringe and heat was used to dissolve the polymer. Next, the flask was placed over a stir plate, and methyl triflate was added via syringe; the reaction was left to stir for 48 h at room temperature. A brown oil formed and was recovered by decanting off excess solvent. The product was left to dry under high vacuum overnight at 50 °C. PSE-10,10. The general procedure was followed using the following amounts: PTE-10,10 (250 mg, 1 equiv), methyl triflate (0.725 g, 4.418 mmol, 3 equiv), and dichloromethane (25 mL). PSE-14,4. The general procedure was followed using the following amounts: PTE-14,4 (250 mg, 1 equiv), methyl triflate (0.725 g, 4.418 mmol, 3 equiv), and dichloromethane (25 mL). Thermogravimetric Analysis. For all samples, 3−5 mg was loaded onto a tared aluminum pan and inserted into the TGA. The sample was then heated from room temperature to 600 °C at a heating

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RESULTS AND DISCUSSION Series 1: Effect of Carbon Spacer Length. Synthesis of Series 1 Polymers. In order to study the ability of the thiol−ene reaction to produce precisely controlled functional polyethylene, seven distinct poly(thioethylenes) (PTEs) were synthesized (series 1). They were designed to establish structure−property relationships relating backbone thioether functionality and carbon spacer length between thioethers to polymer thermal properties and morphology. The polymers were synthesized either by reacting octadiene with a dithiol containing 2, 4, 6, 8, or 10 carbon atoms or by reacting octane dithiol with a diene containing 12 or 14 carbon atoms, as shown in Scheme 1. Octanedithiol was used for the two largest carbon spacers due to the lack of commercially available dodecane and tetradecane dithiols but resulted in polymers with a repeat unit structure identical to those that would have been synthesized from octadiene and the corresponding dithiols. As the length of the carbon spacer was increased, from 2 to 14 carbons, the density of thioether moieties along

C

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molecular weight may have a slight impact on polymer thermal stability, the overall differences were small. The effect of carbon spacer length on polymer crystallinity was examined using differential scanning calorimetry (DSC). After drying, the samples were heated to 200 °C, cooled to −50 °C, and then reheated to 200 °C, with the results of the cooling and second heating shown in Figure 1. From the peak

the polymer backbone decreased, making the polymers more analogous to polyethylene. Nomenclature for these materials is presented in Scheme 1 and involves the common title PTE [poly(thioethylene)] followed by two numbers. For series 1, the first number is 8, representing the eight carbons contained in the first monomer. The second number represents the carbon spacer length of the other monomer and varies as shown in Scheme 1. For example, PTE-8,4 corresponds to the to poly(thioethylene) synthesized using octadiene and butane dithiol, while PTE-8,12 corresponds to the poly(thioethylene) synthesized using octanedithiol and dodecadiene. The polymerization proceeded via the thiol−ene reaction by mixing the required monomers with photoinitiator in THF and irradiating with ultraviolet light for 1 h. Quantitative conversion was confirmed by 1H NMR, which showed the disappearance of ene peaks and the emergence of thioether peaks, as shown in Figures S1−S3. The 1H NMRs of PTE-8,2, PTE-8,8, and PTE8,14 demonstrate that regardless of monomer size, all reactions appeared to go to quantitative conversion, within the limits detectable by the NMR. The resulting polymers were purified by precipitation into methanol, followed by drying under vacuum. Polymer molecular weights were determined using gel permeation chromatography (GPC) with THF as the eluent. All molecular weights ranged from 7 to 20 kg/mol with Đ values ranging from 1.3 to 1.7 (Table 1 and Figure S4), consistent with what is commonly observed using TES polymerization.45,46 It should be noted that not all polymers were fully soluble in THF, potentially causing higher molecular weight fractions to precipitate out of solution, leading to Đ values below the expected 1.5−2. Thermal Characterization of Series 1. Once this series of polymers had been synthesized, the effect of carbon spacer length on polymer properties, such as thermal stability, crystallinity, and morphology, was determined. First, the thermal stability of the polymers was measured using thermogravimetric analysis (TGA) by heating the polymers from room temperature to 600 °C and measuring the mass of the sample as a function of temperature (Figure S5). Before heating, the polymers were dried under vacuum for at least 24 h to remove residual solvent. The resulting stability was determined using two separate analysis methods, with results shown in Table 1. The first method, which reports the temperature at which each polymer lost 5% of its mass, showed that all polymers degraded between 310 and 325 °C. The challenge with this method was that any residual solvent could have affected this measurement; therefore, a second method was also used. The derivative of the raw TGA curve yielded a peak indicating the temperature at which the maximum degradation rate occurred. Using this method, all polymers had peak degradation rate temperatures measured between 346 and 372 °C. While these two methods show no large differences in degradation temperatures, there were slight differences between different samples. When comparing between samples with similar molecular weights, such as PTE-8,4, PTE-8,6, and PTE-8,8 (or PTE-8,10, PTE-8,12, and PTE-8,14), increasing the carbon spacer length seemed to result in a slight increase in the degradation temperature. Furthermore, for samples with slightly lower molecular weights, such as between PTE-8,8 and PTE-8,10, their degradation temperatures slightly decreased as the molecular weight decreased. While this indicated that carbon spacer length and

Figure 1. DSC thermograms for series 1 showing the change in melting temperature as the carbon spacer length was increased.

maximum and peak integration of the melting endotherm, the melting temperature (Tm), and enthalpy of fusion (ΔH), respectively, were determined (Table 1). It should be noted, however, that all samples demonstrated small quantities of cyclic polymers (Figure S4), byproducts that are common in step-growth style polymerizations, such as the TES polymerization performed here. While these cyclic polymers could act as plasticizers in the samples, all samples synthesized here likely had similar numbers of cyclic polymers present due to the similarity of the chemistry used, so the effect they had as plasticizers was likely the same for all samples. This was also corroborated by the correlation described below between the Tm, and ΔH, obtained from DSC and the carbon spacer length. When the Tm of each polymer was plotted against the carbon spacer length (Figure S6), a general trend was observed, where the melting temperature appeared to have a positive correlation with increasing carbon spacer length. This was expected since increasing the carbon spacer length likely led to the polymer being more similar to polyethylene, causing the Tm to approach that of polyethylene, between 120 and 180 °C.1 However, three samples, PTE-8,2, PTE-8,8, and PTE-8,10, presented inconsistencies. For PTE-8,2, two melting temperatures were observed, likely indicating polymorphism (Table 1), common for precisely functionalized polyethylenes with small moieties, where two crystal structures most likely dominated, explaining the two prominent melting temperatures.18,55,56 For PTE-8,10, the Tm was lower than expected as compared to the general trend observed for the other polymers. Perhaps this indicated that PTE-8,10 did not pack into crystals as well as expected, despite having a longer carbon spacer length between thioethers. Interestingly, the symmetric PTE-8,8 had a higher Tm than the linear trend would predict, indicating that perhaps the symmetry of this polymer added to its ability to pack into crystals, forming more perfect crystals than other samples with similar carbon spacer lengths. When the enthalpy of fusion was plotted against the carbon spacer length in Figure 2, a clearer and more consistent trend D

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peaks in the WAXS spectrum, highlighted by inverted black triangles in Figure 3, indicating the presence of polymer crystals. From these scattering profiles, corresponding d-spacing (nm) and q values (nm−1) of the crystalline domains were determined (Table S1). In general, the average d-spacings for each peak, A through E, were 0.46, 0.42, 0.39, 0.36, and 0.33 nm, respectively. Overall, the q values of the scattering peaks identified in the WAXS profiles for series 1 corresponded well to the range of q values that were observed in the WAXS profile for HDPE (Figure 3 and Table S2). Since no specific crystallization procedure was employed here, it was likely that these samples were polymorphic, explaining the multiple, potentially overlapping, peaks in the WAXS profile.18,55−58 A previous report studied the polymorphism of poly(ethylene furanoate) (PEF) and demonstrated that different forms of the PEF crystals, brought about by various crystallization conditions, gave rise to subtle variances in the peak positions and relative intensities in WAXS.58 Since these variances can be brought about by different crystal forms, it was likely that the overlapping peaks found in Figure 3 resulted from different crystalline forms in each sample.57 In addition, variable angle Xray scattering showed apparent small, broad, and weak peaks, which were confirmed by Kratky plots (Figures S8−S18). Series 2: Effect of Repeat Unit Symmetry and Polymer Functionality. Synthesis of Series 2 Polymers. Given that repeat unit symmetry appeared to have an impact on crystallinity for PTE-8,8, a second series was designed to elucidate the importance of having the thioether groups symmetrically, or asymmetrically, placed within the repeat unit structure of the polymer. PTE-10,10 and PTE-14,4 were designed to keep the average number of carbon spacers similar, at 10 and 9, respectively, while changing the symmetry of the polymer repeat unit, as shown in Scheme 2. Symmetric PTE10,10 was synthesized using 1,9-decadiene and 1,10-decanedithiol, while asymmetric PTE-14,4 was synthesized using 1,13tetradecadiene and 1,4-butanedithiol. The polymerization was assessed through GPC and showed a comparable polymer molecular weight for PTE-14,4, consistent with those in series 1, as shown in Figure S19. PTE-10,10 was not assessed via GPC due to total insolubility in THF, although it was expected that it would have a similar molecular weight to all other polymers as no significant effect of monomer size on conversion or polymer molecular weight had been observed from series 1. In addition to exploring the effect of repeat unit symmetry, PTE-10,10 and PTE-14,4 were also converted to poly(sulfonium ethylene) (PSE)-10,10 and PSE-14,4, respectively, via postpolymerization modification by methylating the thioethers into sulfoniums with methyl triflate, using an adaption of a known procedure (Scheme 2).54 This allowed for the exploration of how application-relevant functional groups, such as sulfonium cations, affect the polymer crystallinity and morphology. Methylation of the thioethers was carried out in DCM at room temperature for 48 h and resulted in the phase separation of a brown oil from the reaction solution. The excess solvent was decanted off, and the resulting material was recovered and dried under vacuum at 50 °C for 24 h. PSE-10,10 and PSE-14,4 were characterized by 1H NMR which showed both the expected downfield shift of the proton peak alpha to the thioether as well as the emergence of a single methyl peak, as shown in Figure 4 and Figure S20, respectively. Thermal Characterizations of Series 2. Series 2 was characterized using the same methods as series 1 to understand

Figure 2. Plot of enthalpy of fusion versus carbon spacer length for samples in series 1.

was observed, where the enthalpy of fusion increased and then began to plateau. This was not surprising as better packing of longer carbon spacers should result in an increase in the overall degree of crystallinity within the sample, corresponding to an increase in the enthalpy of fusion. All samples appeared to fit well with the trend, except for PTE-8,10 which had a lower enthalpy of fusion than expected. This data corresponded with the lower Tm value for PTE-8,10, indicating again that this polymer did not pack into crystals as well as the carbon spacer length would indicate, although the reason for this observation remains unclear. Furthermore, the fact that PTE-8,8 fits well with the trend in Figure 2 indicated that the percent crystallinity did not increase above what would be expected for the increased carbon spacer length, meaning that the higher Tm, from Table 1, most likely related to better crystal perfection. This indicated that repeat unit symmetry may play an important role in polymer crystallinity for functional polyethylenes. Morphological Characterization of Series 1. The samples were then characterized using wide-angle X-ray scattering (WAXS) to determine the presence of crystalline domains for all polymers and compared to Kapton and high-density polyethylene (HDPE) (Figure 3). All samples featured multiple

Figure 3. WAXS scattering of poly(thioethylenes) from series 1 as compared to a Kapton blank and HDPE, with peaks indicated by inverted trian. E

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Scheme 2. Synthetic Approach to Symmetric (PTE-10,10) and Asymmetric (PTE-14,4) and Subsequent Methylations to Cationic Poly(sulfonium ethylenes) (PSEs)

hygroscopic nature. They were then studied for their thermal stability using TGA, being heated from room temperature to 600 °C (Figure 5). All samples were analyzed following the same two methods as the first series, which reported the temperature at 5% mass loss and the peak degradation rate temperature, with results shown in Table 2. The first thing to Table 2. Thermal Properties for Series 2 Polymers sample

degradation tempa (°C)

peak degradation rate tempb (°C)

Tmc (°C)

ΔHc (J/g)

PTE-10,10 PSE-10,10 PTE-14,4 PSE-14,4

330 150 258 199

358 279 369 279

84.8

46.3

78.4

46.1

a

Polymer degradation temperature determined at 5% mass loss by TGA. bPeak degradation rate temperature, obtained by TGA, was determined from the maximum calculated slope of the thermogram. c Polymer melting characteristics determined by DSC.

Figure 4. 1H NMR of PTE-10,10 (black) in CDCl3 and PSE-10,10 (red) in DMSO-d6. The downfield shift of A to B as well as the emergence of C demonstrates quantitative, selective methylation to the desired sulfonium product.

note is that the shape of the curve was different between the symmetric PTE-10,10 and asymmetric PTE-14,4, with PTE14,4 demonstrating a more gradual loss corresponding to a 5% mass loss temperature of 258 °C as compared to PTE-10,10, which experienced the sudden onset of mass loss at 330 °C. However, the peak degradation rate temperature was almost identical for the two polymers where PTE-10,10 and PTE-14,4

the effect of repeat unit symmetry and charged moieties on polymer thermal stability, crystallinity, and morphology. The four polymers were first dried under vacuum for at least 24 h, with the PSE polymers also being heated to 50 °C due to their

Figure 5. TGA thermograms comparing the thermal stability of (A) symmetric PTE-10,10 and asymmetric PTE-14,4, (B) symmetric PTE-10,10 and PSE-10,10, and (C) asymmetric PTE-14,4 and PSE-14,4. F

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Figure 6. DSC thermograms comparing (A) symmetric PTE-10,10 and asymmetric PTE-14,4, (B) symmetric PTE-10,10 and PSE-10,10, and (C) asymmetric PTE-14,4 and PSE-14,4.

had degradation temperatures of 358 and 369 °C, respectively. This indicated that the main degradation temperature was not affected by repeat unit symmetry. When comparing PTE to PSE samples, it was clear that addition of cationic functional groups significantly reduced the thermal stability of the polymer. The 5% mass loss degradation temperature decreased to 150 and 199 °C for PSE-10,10 and PSE-14,4, respectively, while the peak degradation rate temperature decreased to 279 °C for both polymers. This indicated that the sulfonium moiety was less thermally stable than the initial thioether. In addition, Figure 5 shows that both PSE polymers show a very slow loss of mass until ∼250 °C, after which a sharp loss of mass was observed. This slow loss in mass was likely related to the loss of absorbed water as opposed to actual degradation of the polymer. Similar to the PTE polymers, however, the degradation temperatures of these PSE polymers were similar, indicating that symmetry did not play a significant role in polymer thermal stability. Taking the results as a whole, it was clear that the identity of the functional group was critically important to the material’s thermal stability. The crystallinity of the series 2 polymers was assessed using DSC. After being dried, the samples were heated to 200 °C, cooled to −50 °C, and reheated to 200 °C, with the cooling and second heating curves shown in Figure 6. The curves were then analyzed in order to determine both the Tm and the enthalpy of fusion for each sample (Table 2). From Figure 6A, it was determined that the Tm decreased from 84.8 °C, for the symmetric PTE-10,10, to 78.4 °C, for the asymmetric PTE14,4, while the enthalpy of fusion remained consistent at 46.3 and 46.1 J/g for PTE-10,10 and PTE-14,4, respectively. This indicated that the overall degree of crystallinity within the sample, which was proportional to the enthalpy of fusion, was more dependent on the average size of the carbon spacer length than on the symmetry of the repeat units, as both samples had similar average carbon spacer lengths between functional moieties of 10 and 9 for PTE-10,10 and PTE-14,4, respectively.59 On the other hand, the Tm for the sample appeared to depend more on the symmetry of the repeat units as PTE-10,10 had a higher melting temperature than PTE-14,4. This data supported the observation from series 1 that symmetric repeat units appeared to have improved crystal perfection, given that both PTE-8,8 and PTE-10,10 had increased melting temperatures when compared to their asymmetric counterparts.60 Since higher melting temperatures are known to arise from better polymer chain packing, this further supports the notion of increased crystal perfection in these fully symmetric PTEs.60 Interestingly, this indicated that in order to increase the melting temperature, without limiting the degree of functionality on the polymer, having an equal

number of carbons between moieties was critical. From Figures 6B and 6C it can be seen that the presences of the sulfonium moieties completely hindered crystal formation, as indicated by a lack of any crystallization or melting peaks in DSC. Morphological Characterization of Series 2. The WAXS profiles (Figure 7) for each polymer in series 2 revealed that the

Figure 7. WAXS scattering profiles from series 2 as compared to a Kapton blank, with peaks indicated by inverted triangles.

asymmetric and symmetric PTEs had defined crystalline domains, whereas the sulfonium versions, PSE-10,10 and PSE-14,4 were amorphous. Repeat unit symmetry of the PTE samples appeared to have no influence on the crystalline structure of the polymer, given that both polymers produced similar scattering profiles. Furthermore, the conversion to the sulfonium cation appeared to completely suppress the crystallinity in the PSE polymers, as only a single, broad peak, consistent with an amorphous halo scattering profile, was observed. This loss of crystallinity could be due to any combination of three factors: the charged nature of the cation, the presence of the bulky triflate counterion, or the presence of water. The presences of the triflate counterion as well as water were the most likely reasons, since these types of species reduce or fully remove crystallinity in other hydrophilic, crystalline polymers, such as poly(ethylene oxide).61−63 From the scattering profiles in Figure 7, the d-spacings and q values were determined (Table S3). In general, peaks A through C had average d-spacings of 0.46, 0.39, and 0.36 nm, respectively, which were very similar to the d-spacings reported for the series 1 polymers and for HDPE (Figure 3). From the appearance of three peaks, it was likely that the series 2 polymers were also G

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Polymerization data (1H NMR, GPC), TGA, DSC, X-ray scattering peak analysis, ESAXS, SAXS, and MAXS profiles and analysis (PDF)

polymorphic, similar to series 1, due to the lack of specific crystallization procedures.57,58

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CONCLUSIONS Precisely functionalized polyethylenes were synthesized via TES polymerization to demonstrate the ease and versatility of this method for producing functional polyethylenes. From the first series, which explored the carbon spacer length between thioether moieties, it was determined that increasing the carbon spacer length led to the functional polymers having characteristics more similar to polyethylene, by increasing both the percent crystallinity as well as the crystal perfection. WAXS profiles indicated that all polymers had similar, polymorphic crystalline domains, which appeared within the same range of q values as seen for HDPE. From DSC, both the enthalpy of fusion, proportional to the percent crystallinity, and the Tm, indicative of crystal perfection, increased with increasing carbon spacer length. Interestingly, despite a similar enthalpy of fusion to the other samples, the symmetric PTE-8,8 demonstrated a greater Tm than would be anticipated for its carbon spacer length, indicating that symmetry likely influenced the polymer’s crystal perfection. Repeat unit symmetry’s effect on crystallinity was further explored using series 2, studying two polymers with similar average carbon spacer lengths. These polymers showed that controlling the repeat unit symmetry provided a handle for increasing the Tm, and thus the polymer crystal perfection, without sacrificing the degree or density of functionalization. WAXS and DSC showed that the average carbon spacer length was the determining factor in the percent crystallinity within the sample, as both PTE-10,10 and PTE-14,4 had near identical scattering profiles and enthalpies of fusion. However, DSC also showed that PTE-10,10 had a larger Tm than PTE-14,4, indicating that repeat unit symmetry was critical to the crystal perfection, accounting for the increased Tm. Overall, using the thiol−ene reaction to produce precisely functionalized polyethylenes presents multiple benefits over other approaches utilized up to this point. The reaction proceeds quantitatively within a short reaction time, allows for the use of commercially available monomers, and does not require the use of difficult-to-remove catalysts. Furthermore, the ability to incorporate a different functional group was demonstrated here by the postpolymerization conversion of thioethers into sulfoniums, although additional functional groups can be incorporated via oxidation to sulfoxides and sulfones, for example.45 In order to fully realize the potential of the thiol−ene approach, however, some limitations will need to be overcome. Currently it is difficult to incorporate more than one type of functional group into the same polymer chain using commercially available monomers. Additionally, monomers with longer carbon spacers than those presented here, or monomers incorporating some types of functional moieties, are not commercially available and thus would require monomer synthesis.46 Solving these challenges, however, would be a significant step toward developing a facile approach for synthesizing precisely functionalized polyethylenes with a myriad of chemical moieties.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (G.N.T.). ORCID

Gregory N. Tew: 0000-0003-3277-7925 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by the NSF NRT program DGE1545399 and the NSF GAANN Fellowship DoED P200A150276. We thank Carolyn Zhao for providing the HDPE WAXS profile. We also acknowledge the X-ray Scattering Laboratory in the Polymer Science and Engineering Department at the University of Massachusetts Amherst and the facility director Md. Arifur Rahman for the use and upkeep of the X-ray scattering equipment.

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REFERENCES

(1) Boz, E.; Wagener, K. B.; Ghosal, A.; Fu, R.; Alamo, R. G. Synthesis and Crystallization of Precision ADMET Polyolefins Containing Halogens. Macromolecules 2006, 39 (13), 4437−4447. (2) Jama, C.; Quensierre, J.-D.; Gengembre, L.; Moineau, V.; Grimblot, J.; Dessaux, O.; Goudmand, P. Characterization of Polyethylene Surfaces Heated after Plasma Fluorination. Surf. Interface Anal. 1999, 27 (7), 653−658. (3) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. Linear Functionalized Polyethylene Prepared with Highly Active Neutral Ni(II) Complexes. J. Polym. Sci., Part A: Polym. Chem. 2002, 40 (16), 2842−2854. (4) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. The Search for New-Generation Olefin Polymerization Catalysts: Life beyond Metallocenes. Angew. Chem., Int. Ed. 1999, 38 (4), 428−447. (5) Doak, K. W. Encyclopedia of Polymer Science and Engineering; John Wiley & Sons: New York, 1986. (6) Gaines, T. W.; Trigg, E. B.; Winey, K. I.; Wagener, K. B. High Melting Precision Sulfone Polyethylenes Synthesized by ADMET Chemistry. Macromol. Chem. Phys. 2016, 217 (21), 2351−2359. (7) Seitz, M. E.; Chan, C. D.; Opper, K. L.; Baughman, T. W.; Wagener, K. B.; Winey, K. I. Nanoscale Morphology in Precisely Sequenced Poly(Ethylene-Co-Acrylic Acid) Zinc Ionomers. J. Am. Chem. Soc. 2010, 132 (23), 8165−8174. (8) Trigg, E. B.; Tiegs, B. J.; Coates, G. W.; Winey, K. I. High Morphological Order in a Nearly Precise Acid-Containing Polymer and Ionomer. ACS Macro Lett. 2017, 6 (9), 947−951. (9) Kostalik, H. A.; Clark, T. J.; Robertson, N. J.; Mutolo, P. F.; Longo, J. M.; Abruña, H. D.; Coates, G. W. Solvent Processable Tetraalkylammonium-Functionalized Polyethylene for Use as an Alkaline Anion Exchange Membrane. Macromolecules 2010, 43 (17), 7147−7150. (10) Noonan, K. J. T.; Hugar, K. M.; Kostalik, H. A.; Lobkovsky, E. B.; Abruña, H. D.; Coates, G. W. Phosphonium-Functionalized Polyethylene: A New Class of Base-Stable Alkaline Anion Exchange Membranes. J. Am. Chem. Soc. 2012, 134 (44), 18161−18164. (11) Boffa, L. S.; Novak, B. M. Copolymerization of Polar Monomers with Olefins Using Transition-Metal Complexes. Chem. Rev. 2000, 100 (4), 1479−1494. (12) 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 (8), 773−781.

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Macromolecules (13) Anton, D. Surface-Fluorinated Coatings. Adv. Mater. 1998, 10 (15), 1197−1205. (14) Baughman, T. W.; Chan, C. D.; Winey, K. I.; Wagener, K. B. Synthesis and Morphology of Well-Defined Poly(Ethylene-Co-Acrylic Acid) Copolymers. Macromolecules 2007, 40 (18), 6564−6571. (15) Yang, H.; Islam, M.; Budde, C.; Rowan, S. J. Ring-Opening Metathesis Polymerization as a Route to Controlled Copolymers of Ethylene and Polar Monomers: Synthesis of Ethylene-Vinyl Chloridelike Copolymers. J. Polym. Sci., Part A: Polym. Chem. 2003, 41 (13), 2107−2116. (16) Grady, B. P. Review and Critical Analysis of the Morphology of Random Ionomers across Many Length Scales. Polym. Eng. Sci. 2008, 48 (6), 1029−1051. (17) Gaines, T. W.; Nakano, T.; Chujo, Y.; Trigg, E. B.; Winey, K. I.; Wagener, K. B. Precise Sulfite Functionalization of Polyolefins via ADMET Polymerization. ACS Macro Lett. 2015, 4 (6), 624−627. (18) Trigg, E. B.; Stevens, M. J.; Winey, K. I. Chain Folding Produces a Multilayered Morphology in a Precise Polymer: Simulations and Experiments. J. Am. Chem. Soc. 2017, 139 (10), 3747−3755. (19) 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 (22), 9003−9012. (20) Middleton, L. R.; Trigg, E. B.; Schwartz, E.; Opper, K. L.; Baughman, T. W.; Wagener, K. B.; Winey, K. I. Role of Periodicity and Acid Chemistry on the Morphological Evolution and Strength in Precise Polyethylenes. Macromolecules 2016, 49 (21), 8209−8218. (21) Opper, K. L.; Markova, D.; Klapper, M.; Müllen, K.; Wagener, K. B. Precision Phosphonic Acid Functionalized Polyolefin Architectures. Macromolecules 2010, 43 (8), 3690−3698. (22) Boz, E.; Nemeth, A. J.; Ghiviriga, I.; Jeon, K.; Alamo, R. G.; Wagener, K. B. Precision Ethylene/Vinyl Chloride Polymers via Condensation Polymerization. Macromolecules 2007, 40 (18), 6545− 6551. (23) Valenti, D. J.; Wagener, K. B. Direct Synthesis of Well-Defined Alcohol-Functionalized Polymers via Acyclic Diene Metathesis (ADMET) Polymerization. Macromolecules 1998, 31 (9), 2764−2773. (24) Thompson, D.; Yamakado, R.; Wagener, K. B. Extending the Methylene Spacer Length of ADMET Hydroxy-Functionalized Polymers. Macromol. Chem. Phys. 2014, 215 (12), 1212−1217. (25) Caire da Silva, L.; Rojas, G.; Schulz, M. D.; Wagener, K. B. Acyclic Diene Metathesis Polymerization: History, Methods and Applications. Prog. Polym. Sci. 2017, 69, 79−107. (26) Middleton, L. R.; Tarver, J. D.; Cordaro, J.; Tyagi, M.; Soles, C. L.; Frischknecht, A. L.; Winey, K. I. Heterogeneous Chain Dynamics and Aggregate Lifetimes in Precise Acid-Containing Polyethylenes: Experiments and Simulations. Macromolecules 2016, 49 (23), 9176− 9185. (27) Fairbanks, B. D.; Love, D. M.; Bowman, C. N. Efficient Polymer-Polymer Conjugation via Thiol-Ene Click Reaction. Macromol. Chem. Phys. 2017, 218 (18), 1700073. (28) Adzima, B. J.; Bowman, C. N. The Emerging Role of Click Reactions in Chemical and Biological Engineering. AIChE J. 2012, 58 (10), 2952−2965. (29) Hoyle, C. E.; Lowe, A. B.; Bowman, C. N. Thiol-Click Chemistry: A Multifaceted Toolbox for Small Molecule and Polymer Synthesis. Chem. Soc. Rev. 2010, 39 (4), 1355−1387. (30) Hoyle, C. E.; Bowman, C. N. Thiol-Ene Click Chemistry. Angew. Chem., Int. Ed. 2010, 49 (9), 1540−1573. (31) Reddy, S. K.; Cramer, N. B.; Bowman, C. N. Thiol−Vinyl Mechanisms. 1. Termination and Propagation Kinetics in Thiol−Ene Photopolymerizations. Macromolecules 2006, 39 (10), 3673−3680. (32) Reddy, S. K.; Cramer, N. B.; Bowman, C. N. Thiol−Vinyl Mechanisms. 2. Kinetic Modeling of Ternary Thiol−Vinyl Photopolymerizations. Macromolecules 2006, 39 (10), 3681−3687. (33) Reddy, S. K.; Okay, O.; Bowman, C. N. Network Development in Mixed Step-Chain Growth Thiol−Vinyl Photopolymerizations. Macromolecules 2006, 39 (25), 8832−8843.

(34) Lee, T. Y.; Roper, T. M.; Jonsson, E. S.; Guymon, C. A.; Hoyle, C. E. Thiol−Ene Photopolymerization Kinetics of Vinyl Acrylate/ Multifunctional Thiol Mixtures. Macromolecules 2004, 37 (10), 3606− 3613. (35) Hoyle, C. E.; Lee, T. Y.; Roper, T. Thiol-Enes: Chemistry of the Past with Promise for the Future. J. Polym. Sci., Part A: Polym. Chem. 2004, 42 (21), 5301−5338. (36) Cramer, N. B.; Davies, T.; O’Brien, A. K.; Bowman, C. N. Mechanism and Modeling of a Thiol−Ene Photopolymerization. Macromolecules 2003, 36 (12), 4631−4636. (37) Cramer, N. B.; Bowman, C. N. Kinetics of Thiol-Ene and ThiolAcrylate Photopolymerizations with Real-Time Fourier Transform Infrared. J. Polym. Sci., Part A: Polym. Chem. 2001, 39 (19), 3311− 3319. (38) Arnold, R. M.; Patton, D. L.; Popik, V. V.; Locklin, J. A Dynamic Duo: Pairing Click Chemistry and Postpolymerization Modification To Design Complex Surfaces. Acc. Chem. Res. 2014, 47 (10), 2999− 3008. (39) Claudino, M.; Jonsson, M.; Johansson, M. Utilizing Thiol−ene Coupling Kinetics in the Design of Renewable Thermoset Resins Based on D-Limonene and Polyfunctional Thiols. RSC Adv. 2014, 4 (20), 10317−10329. (40) Dondoni, A. The Emergence of Thiol-Ene Coupling as a Click Process for Materials and Bioorganic Chemistry. Angew. Chem., Int. Ed. 2008, 47 (47), 8995−8997. (41) Kharkar, P. M.; Rehmann, M. S.; Skeens, K. M.; Maverakis, E.; Kloxin, A. M. Thiol−ene Click Hydrogels for Therapeutic Delivery. ACS Biomater. Sci. Eng. 2016, 2 (2), 165−179. (42) Roper, T. M.; Guymon, C. A.; Jönsson, E. S.; Hoyle, C. E. Influence of the Alkene Structure on the Mechanism and Kinetics of Thiol-Alkene Photopolymerizations with Real-Time Infrared Spectroscopy. J. Polym. Sci., Part A: Polym. Chem. 2004, 42 (24), 6283− 6298. (43) Cramer, N. B.; Reddy, S. K.; O’Brien, A. K.; Bowman, C. N. Thiol−Ene Photopolymerization Mechanism and Rate Limiting Step Changes for Various Vinyl Functional Group Chemistries. Macromolecules 2003, 36 (21), 7964−7969. (44) Kade, M. J.; Burke, D. J.; Hawker, C. J. The Power of Thiol-Ene Chemistry. J. Polym. Sci., Part A: Polym. Chem. 2010, 48 (4), 743−750. (45) Sarapas, J. M.; Tew, G. N. Poly(Ether−thioethers) by Thiol− Ene Click and Their Oxidized Analogues as Lithium Polymer Electrolytes. Macromolecules 2016, 49 (4), 1154−1162. (46) Sarapas, J. M.; Tew, G. N. Thiol-Ene Step-Growth as a Versatile Route to Functional Polymers. Angew. Chem., Int. Ed. 2016, 55 (51), 15860−15863. (47) Reddy, S. K.; Cramer, N. B.; O’ Brien, A. K.; Cross, T.; Raj, R.; Bowman, C. N. Rate Mechanisms of a Novel Thiol-Ene Photopolymerization Reaction. Macromol. Symp. 2004, 206 (1), 361−374. (48) Chiou, B.-S.; Khan, S. A. Real-Time FTIR and in Situ Rheological Studies on the UV Curing Kinetics of Thiol-Ene Polymers. Macromolecules 1997, 30 (23), 7322−7328. (49) Marvel, C. S.; Chambers, R. R. Polyalkylene Sulfides from Diolefins and Dimercaptans. J. Am. Chem. Soc. 1948, 70 (3), 993−998. (50) Deubel, F.; Bretzler, V.; Holzner, R.; Helbich, T.; Nuyken, O.; Rieger, B.; Jordan, R. Polythioethers by Thiol-Ene Click Polyaddition of α,ω-Alkylene Thiols. Macromol. Rapid Commun. 2013, 34 (12), 1020−1025. (51) Walker, C. N.; Sarapas, J. M.; Kung, V.; Hall, A. L.; Tew, G. N. Multiblock Copolymers by Thiol Addition Across Norbornene. ACS Macro Lett. 2014, 3 (5), 453−457. (52) Zhang, D.; Dumont, M.-J. Synthesis, Characterization and Potential Applications of 5-Hydroxymethylfurfural Derivative Based Poly(β-Thioether Esters) Synthesized via Thiol-Michael Addition Polymerization. Polym. Chem. 2018, 9 (6), 743−756. (53) Wessig, P.; Schulze, T.; Pfennig, A.; Weidner, S. M.; Prentzel, S.; Schlaad, H. Thiol−ene Polymerization of Oligospiroketal Rods. Polym. Chem. 2017, 8 (44), 6879−6885. (54) Tang, J.; Xie, D.; Yin, H.-Y.; Jing, J.; Zhang, J.-L. Cationic Sulfonium Functionalization Renders Znsalens with High FluoresI

DOI: 10.1021/acs.macromol.8b00334 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules cence, Good Water Solubility and Tunable Cell-Permeability. Org. Biomol. Chem. 2016, 14 (13), 3360−3368. (55) 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 (14), 4738−4749. (56) 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 (1), 236−245. (57) Woo, E. M.; Wu, M. C. Thermal and X-Ray Analysis of Polymorphic Crystals, Melting, and Crystalline Transformation in Poly(Butylene Adipate). J. Polym. Sci., Part B: Polym. Phys. 2005, 43 (13), 1662−1672. (58) Tsanaktsis, V.; Papageorgiou, D. G.; Exarhopoulos, S.; Bikiaris, D. N.; Papageorgiou, G. Z. Crystallization and Polymorphism of Poly(Ethylene Furanoate). Cryst. Growth Des. 2015, 15 (11), 5505− 5512. (59) Arua, U. N.; Blum, F. D. Disruptions in the Crystallinity of Poly(Lauryl Methacrylate) Due to Adsorption on Silica. J. Polym. Sci., Part B: Polym. Phys. 2018, 56 (1), 89−96. (60) Jariyavidyanont, K.; Williams, J. L.; Rhoades, A. M.; Kühnert, I.; Focke, W.; Androsch, R. Crystallization of Polyamide 11 during Injection Molding. Polym. Eng. Sci. 2017, 47, 21−25. (61) Sarapas, J. M.; Saijo, K.; Zhao, Y.; Takenaka, M.; Tew, G. N. Phase Behavior and Li + Ion Conductivity of Styrene-Ethylene Oxide Multiblock Copolymer Electrolytes. Polym. Adv. Technol. 2016, 27 (7), 946−954. (62) Walker, C. N.; Versek, C.; Touminen, M.; Tew, G. N. Tunable Networks from Thiolene Chemistry for Lithium Ion Conduction. ACS Macro Lett. 2012, 1 (6), 737−741. (63) Walker, C. N.; Bryson, K. C.; Hayward, R. C.; Tew, G. N. Wide Bicontinuous Compositional Windows from Co-Networks Made with Telechelic Macromonomers. ACS Nano 2014, 8 (12), 12376−12385.

J

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