Viscoelastic, Mechanical, and Glasstomeric Properties of Precision

Mar 28, 2018 - Mechanical and viscoelastic properties of precision polyolefins, poly(4-phenylcyclopentene) (P4PCP) and its hydrogenated analog ...
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Viscoelastic, Mechanical, and Glasstomeric Properties of Precision Polyolefins Containing a Phenyl Branch at Every Five Carbons Robert J. Kieber III, William J. Neary, and Justin G. Kennemur* Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States S Supporting Information *

ABSTRACT: Mechanical and viscoelastic properties of precision polyolefins, poly(4-phenylcyclopentene) (P4PCP) and its hydrogenated analog (H2-P4PCP) containing atactic phenyl branches at exactly every five carbons along the backbone are explored. Both materials are amorphous with a glass transition temperature of ∼17 ± 3 °C. Rheological investigations determined that P4PCP has an entanglement molar mass (Me = 10.0 kg mol−1) much higher and closer to polystyrene than H2-P4PCP (Me = 3.6 kg mol−1). Both materials have elastomeric and shape memory properties at ambient temperatures, which were further explored through strain hysteresis measurements. H2-P4PCP has an elastic recovery of ∼95% at max strain values up to 500% as determined by uniaxial tensile testing. Time−temperature superposition analysis, Williams−Landel−Ferry constants, and further mechanical analysis are discussed and compared to previously reported ethylene−styrene copolymers of similar phenyl-branch content within the microstructure.

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INTRODUCTION Although styrene (S) polymerizes readily through most chaingrowth strategies, it is challenging to copolymerize with other prominent olefin monomers, such as ethylene (E), due to the high discrepancy in comonomer reactivity.1 Ethylene−styrene (ES) copolymers have historically garnered interest due to the large range of material properties possible from combining two ubiquitous yet markedly different homopolymers.2−7 Although traditional Ziegler−Natta catalysts were unsuccessful at ES copolymerizations, the advent of metallocene single-site or molecular catalysts successfully made ES copolymers with varying degrees of control.8−25 The reactivity difference of E and S still presents challenges with homopolymer formation, nonuniform comonomer distribution, necessity for high S content in the feed, and the well-defined yet often complex catalyst systems. In the late 1990s, the Dow Chemical Company patented INSITE technology, which are constrained-geometry catalysts that allowed for superior control over a variety of E copolymerizations, even with S.4,7,26−28 The coined ES Interpolymers (ESIs) were introduced with a broad distribution of E and S composition fidelity and a multitude of potential applications. Varying the S composition allowed for a wide range of tunable polymer properties such as glass transition temperature (Tg), melting behavior, tensile properties, and dynamic mechanical response in addition to many other thorough investigations pioneered by Hiltner and Baer in collaboration with the Dow Chemical Company.7,26,29−35 General trends in material properties were elucidated as the incorporation of S within the ESIs increased. For example, crystallinity is sequestered once the S content exceeds ∼42% w/w S. As the S content is further increased above ∼42% w/w, © XXXX American Chemical Society

the Tg value of the ESI also gradually increases and reaches ambient values (∼25 °C) at ∼70% w/w S.7 ESIs with this high level of S content (termed “Type S”)30 were coined with the name “glasstomers” due to their unique strain rate sensitivity. However, the S-Series were the most synthetically challenging of the ESI systems due to the very high S feeds required, which also produced atactic PS homopolymer within the materials (up to 10% w/w). As with many copolymerizations, varying degrees of microstructural ambiguity can arise and comonomer sequences for Type S ESIs were often termed “pseudorandom” due to the absence of successive head-to-tail S insertions discovered by 13C NMR.30 An alternative method to achieve ES copolymers is through the copolymerization of styrene and butadiene, followed by hydrogenation. Styrene butadiene rubber (SBR) copolymers have widely been studied and produced as synthetic rubbers dating back to WWII. Now it is recognized as the source for more than half of all synthetic rubbers globally.36 Phenyl functionalized butadienes, which can be polymerized through ionic, emulsion, or Ziegler−Natta type methods, allow for synthesis of ES copolymers with greater microstructural control by eliminating statistical comonomer distributions compared to SBR.37−48 However, utilization of these polymerization methods to synthesize ES copolymers also presents challenges. Namely, this polymerization method often results in 1,2 or 3,4 addition rather than 1,4 (especially with 1-phenylbutadiene), Received: December 29, 2017 Revised: March 8, 2018 Accepted: March 22, 2018

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DOI: 10.1021/acs.iecr.7b05395 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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defined microstructure and absence of S homopolymer allows for a more categorical determination of structure−property relationships. The goal of this study is to compare the mechanical and viscoelastic properties for these new materials before and after hydrogenation of the backbone olefins. In addition, we offer comparisons to prior reports of polymers with similar chemical composition that were made through copolymerization strategies.

samples were performed by annealing overnight in a ThermoScientific vacuum oven at ∼80 °C and a vacuum down to 90 mTorr. Dry polymer was then pressed into sheets using a Carver model 4386 melt press at 60 °C followed by cutting to a dogbone shape using a die obtained from Fremont (style: ASTM D638 Type 5). Specimen dimensions were confirmed using a caliper prior to mechanical testing. Uniaxial stress−strain experiments were performed using a Thumler TH-2730 instrument at a constant 0.5 min−1 strain rate. Young’s modulus (E) was calculated as the slope of the stress/ strain curve within the proportional limit that occurred within the first 30% strain and was averaged from at least three successful trials. Elongation at break (ε) and stress at break (σf) were averaged from at least three successful trials. Hysteresis was conducted by sequentially stretching samples from 50 to 400% strain in 50% increments and at a constant strain rate of 0.02 s−1. During a cycle, the sample was pulled to the maximum strain, and the direction was immediately reversed and strain reduced until a 0 stress value was reached. At this point the sample was again pulled to the next value of maximum strain and the cycle repeated. Creep experiments were conducted at a force of 0.1 N (0.089 MPa) for 10,000 s collecting data throughout. Rheology was performed on an Anton-Parr MCR 302 with a polymer melt stage accessory and 25 mm parallel plate geometry. Data was collected under N2 atmosphere and at temperatures monitored by a thermocouple located directly below the bottom geometry. The band gap setting was automatically adjusted for thermal expansion of the geometries during analysis. Densities were determined using a “sink/float” test by suspending dry, bubble-free pieces of each material within known mixtures of ethylene glycol and water that have known densities.69,70 Density values were also corroborated using a 10 mL glass pycnometer and methanol as the nonsolvent. For each test, a calibrated thermometer was used to monitor the solution temperature, which remained within 24 ± 1 °C.

EXPERIMENTAL SECTION Materials. Poly(4-phenylcyclopentene) (P4PCP) (Mn = 43.8 kDa, Đ = 1.80, 87% trans) and its hydrogenated version (H2-P4PCP) (Mn = 51.5 kDa, Đ = 1.68), shown in Figure 1, were synthesized according to a previous report.68 Butylated hydroxytoluene (BHT) (99%) was purchased from SigmaAldrich. Tetrahydrofuran (THF) (≥99.5%) was purchased from EMD Millipore. Characterization and Methods. Number-average molar mass (Mn) and dispersity (Đ) were determined by an AgilentWyatt combination triple detection size exclusion chromatograph (SEC) containing 3 successive Agilent PL-gel Mixed C columns (THF mobile phase), an Agilent 1260 infinity series pump, degasser, autosampler, and thermostated column chamber. The Wyatt triple detection unit hosts a MiniDawn TREOS 3-angle light scattering detector, Optilab TrEX refractive index detector, and a Viscostar II differential viscometer. Molar masses were determined from conventional column calibration using narrow dispersity polystyrene standards. Differential scanning calorimetry (DSC) was conducted on a TA Instruments model Q100 with a model RCS 90 refrigerated cooling system accessory. Temperature was ramped to 180 °C, at a rate of 10 °C min−1, held isothermal for 5 min, then cooled to −30 °C at a rate of 10 °C min−1. The heat−cool cycle was then repeated and thermal transitions were recorded upon the second heating. Thorough drying of the polymer

RESULTS AND DISCUSSION We recently reported 4-phenylcyclopentene as a monomer with sufficient ring strain (ΔHP = −5.1 kcal mol−1) for ROMP that allows high monomer conversions (>80%) at cold temperatures (−15 °C) and high molar mass (>150 kg mol−1) based on reaction conditions.68 The resulting polypentenamer, P4PCP, can also be quantitatively hydrogenated to H2-P4PCP using a catalytic amount of BHT along with tributylamine and ptosylhydrazide.68 An intriguing feature of these systems is their lack of structural ambiguity; the ROMP mechanism and monomer symmetry ensures a five-carbon branch periodicity. Furthermore, these materials have a precision microstructure that is inaccessible from copolymerization strategies (i.e., P4PCP resembles a perfectly alternating styrene-1,4-butadiene copolymer with one less methylene per repeating unit whereas H2-P4PCP is analogous to a perfectly alternating ES copolymer with one additional methylene per repeating unit) (Figure 1). The samples used for this report, P4PCP (Mn = 43.8 kg mol−1, Đ = 1.80) and H2-P4PCP (Mn = 51.5 kg mol−1, Đ = 1.68) are amorphous materials with a nearly identical Tg of 17 ± 3 °C (Figures S7 and S8). P4PCP was determined to have ∼87% trans olefin content through inverse gated decoupling 13C NMR spectroscopy (Figure S13). The Tg for H2-P4PCP is lower than those for previously reported ESIs with approximately the same “S content” (∼71−73% w/w S), which may be attributed to the precise periodicity of the phenyl branches (Table 1).7

which limits the full scope of microstructural possibilities.36−41,45,47,49−54 Furthermore, phenyl functionalized butadiene polymers obtained that contain 3,4 addition can undergo intramolecular cyclization.37,43,45,46 High content of 1,4 cis addition (>99%) of 2-phenylbutadiene has been obtained with emulsion polymerization and with certain Ziegler−Natta catalysts; however, material properties of the hydrogenated polymer were not investigated.42,48 Advances in polymer chemistry over the last several decades have allowed alternative methods to access precise polyolefins through ring-opening metathesis polymerization (ROMP)55−60 and acyclic diene metathesis polymerization (ADMET)61−64 with some of them bearing phenyl substitutents.65−67 Recently, we reported the synthesis of a unique alternating trimethylene− styrene copolymer that is inaccessible from ES systems.68 This system is a precision polyolefin that can be likened to an SBR or ESI (after backbone hydrogenation) with high S content (∼71% w/w) and a phenyl branch on exactly every fifth carbon along a linear backbone microstructure (Figure 1). The well-

Figure 1. Chemical structure of P4PCP and H2-P4PCP.

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B

DOI: 10.1021/acs.iecr.7b05395 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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crossover of the dynamic storage (G′) and loss (G″) modulus at frequencies above the terminal regime (where G′ ∼ ω2 and G″ ∼ ω). Furthermore, tan δ (G″/G′) reaches a minimum within the intermediate frequencies where the rubbery plateau (G″ < G′) is observed. The entanglement modulus (GoN), determined as the value of G′ (Pa) at the point where tan δ reaches a minimum, was determined from the master curves and further used to calculate the entanglement molar mass (Me) of each system according to eq 1:72−74

Table 1. Properties of P4PCP and H2-P4PCP Compared to ESI with Similar S Content

−1 b

Mn (kg mol ) Đb ρ24 °C [ρ90 °C] (g cm−3)c Tg (°C)d Cg1e Cg2e GoN (MPa) Me (kg mol−1)f ε (%)g E (MPa)h σf (MPa)i

P4PCP

H2-P4PCP (71.4% w/w S)

ESI (68−72% w/w S)a

43.8 1.80 1.04 [0.999]

51.5 1.68 1.02 [0.980]

185−389 2.0−3.0 1.01−1.02

17 ± 3 12.7 46 0.30 10.0 2497 ± 75.9 0.85 ± 0.06 1.48 ± 0.65

17 ± 3 13.5 55 0.82 3.62 1149 ± 201 1.61 ± 0.47 5.20 ± 1.47

22−33 8.1−11.1 31−43 1.33 1.76−2.04 292−412 10.6−741 21.2−22.8

Me =

ρRT GNo

(1)

where T is temperature in Kelvin, R is the gas constant (8.314 × 106 cm3 Pa K−1 mol−1), and ρ is the density of the polymer at Tref. The density of P4PCP and H2-P4PCP at 90 °C (0.999 and 0.980 g cm−3, respectively) was calculated through the general expression for molar volume thermal expansion of rubbery amorphous polymers as a function of temperature as described by Van Krevelen71 (Supporting Information). The Me values of P4PCP (10.0 kg mol−1) and H2-P4PCP (3.6 kg mol−1) are quite interesting considering the similar Mn, Tg, and ρ of the two materials (Table 1). P4PCP has an Me much closer to that of PS (∼13 kg mol−1 determined experimentally and consistent with recent computational methods) than 1,4-polybutadiene (∼1.8 kg mol−1).75−78 The Me for H2-P4PCP is much closer to that of polyethylene (0.8−1.2 kg mol−1) than PS.75−78 However, when compared to each other, a reduction in Me upon hydrogenation can be attributed to the increased degrees of freedom afforded to the backbone through the reduction of the olefins to methylene units. This, in turn, is predicted to increase the chain contour per repeating unit and increase the mean-square unperturbed end-to-end distance, which is inversely proportional to Me.76 This observation is consistent with literature, in which saturation of backbone olefins results in a decrease in Me.76 Chen et al. predicted Me for a perfectly alternating ES copolymer to be ∼2.3 kg mol−1 based on extrapolation of Me values determined from a series of amorphous ESIs of varying S content (50−68% w/w).33 Our results are consistent with the observation that even small dilutions of the polystyrene microstructure with ethylene-like segments will dramatically reduce the Me although our experimental data suggests that this reduction is not quite as steep as predicted. This can likely be attributed to the extrapolation of Me obtained from ESIs and their pseudorandom comonomer arrangement where a larger reduction in Me may be caused by backbone regions more populated in E content.33 Here we acknowledge that the Me values for the ESI systems correspond to a temperature of 23 °C, which may account for some of the difference. However, it is important to note that the TTS plots given in Figure 2 were created with no vertical shifts applied. Given how well the TTS curves overlap without vertical shifts, especially the tan δ curve, is a good indication that the plateau modulus is relatively insensitive to temperature. Logarithmic horizontal shift factors (aT) from TTS analysis (Table S1) were plotted as a function of T and fit to the Williams−Landel−Ferry (WLF) equation (Figure 3). The WLF constants, C1 and C2 for P4PCP (4.9 and 119) and H2P4PCP (5.8 and 128), respectively, reflect Tref = 90 °C. For comparison to other systems, these values were normalized to the Tg (17 °C) through eqs 2 and 3:

a

Values represent a range of data taken from ESIs with 68 to 72% w/w S reported in references 30−33. bDetermined by SEC. cDensity at 24 °C determined by gradient mixtures of ethylene glycol and water and density at 90 °C (within brackets) calculated using the empirical expression for thermal expansion.71 dDetermined by DSC analysis upon second heating at 10 °C min−1. eWLF Constants referenced to Tg (17 °C). fEntanglement molar mass calculated using eq 1. gStrain at break (%) at 23 ± 2 °C. hYoung’s modulus (MPa) taken within the proportional limit up to 30% strain recorded at 23 ± 2 °C. iStress at break in MPa at 23 ± 2 °C.

Oscillatory rheological measurements in the bulk state were performed on P4PCP and H2-P4PCP over a thermal range of 30 to 150 °C under inert (N2) atmosphere. Prior to analysis, the materials were premolded into disks 25 mm in diameter and 1 mm thick to facilitate sample loading onto the 25 mm parallel plate geometry. To ensure higher temperatures did not cause unwanted cross-linking reactions of the P4PCP backbone olefins, a trace amount of BHT was also added to the bulk polymer prior to analysis. Dynamic frequency (ω) sweeps from 100 to 0.1 rad s−1 were taken at 20 °C intervals between 30 and 150 °C (Supporting Information). Dynamic strain sweeps (ω = 10 rad s−1) were performed at each temperature to ensure the strain used during data collection was within the linear viscoelastic regime. Time−temperature superposition (TTS) analysis was applied to the frequency sweeps using a reference temperature (Tref) of 90 °C to generate the master curves for P4PCP and H2-P4PCP shown in Figure 2. Both systems are clearly entangled as evidenced by a rubbery plateau after the

Figure 2. Time−temperature superposition (TTS) master plots of (a) P4PCP and (b) H2-P4PCP (Tref = 90 °C) with storage modulus (G′) (filled symbols), loss modulus (G″) (open symbols), and tan δ (G″/ G′) (stars) plotted as a function of angular frequency (ω) multiplied by horizontal shift factors (aT). No vertical shifts were applied. C

DOI: 10.1021/acs.iecr.7b05395 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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consistent with literature.79 When compared to ESIs of comparable S content, the material properties of H2-P4PCP are also notably different. The ESIs were found to have ε < 300% and σf > 20 MPa.30,35 However, when comparing ESIs with lower S content (between 62 and 69%) but with similar Tg to our system, the ESIs were found to have only a slightly higher E (≥3.9 MPa), shorter ε (≤707%), and comparable σf.30,32 We again attribute these differences to the pseudorandom comonomer arrangements of ESIs.30−32 Therefore, precision periodicities of the phenyl branch can provide notably different properties as a result of the finite microstructure and these properties are predicted to be consistent from batch to batch at similar Mn values. This consistency is important because, as shown in Table 1, small differences in S content of ESIs from 68−72% can create large differences in material properties, which stem from the sensitivity of Tg being below or above ambient temperature within this composition range. When manipulated by hand, H2-P4PCP has a noticeable elasticity at ambient temperatures and will recover from subtle deformations (e.g., stretching, bending, and folding). Furthermore, ESI materials with high styrene (i.e., the S-series) were categorized as “glasstomers” due to their ability to behave as a glass at short strain rates and rubbery at longer strain rates.30 Therefore, we investigated the elasticity of this material, in addition to P4PCP, through hysteresis experiments shown in Figure 5. The sample was sequentially pulled to strains from 50

Figure 3. Williams−Landel−Ferry (WLF) plots of (a) P4PCP and (b) H2-P4PCP (Tref = 90 °C). Logarithmic horizontal shift factors (aT) were plotted as a function of temperature (solid symbols). Solid lines are fitted to the data using WLF constants, C1 and C2 for P4PCP (4.9 and 119) and H2-P4PCP (5.8 and 128), respectively.

C1g = C1C2(C2 + Tg − Tref )−1

(2)

C2g = C2 + Tg − Tref

(3)

Cg1

Cg2

to provide and as the WLF constants referenced to Tg shown in Table 1. The constants for both systems fall within the typical range of most polymers.75 P4PCP and H2-P4PCP were subjected to uniaxial tensile testing of 3 and 8 individual dogbone specimens, respectively (Figures S1 and S2). Figure 4 displays a representative stress−

Figure 5. Cyclic deformation (hysteresis) experiments of (a) P4PCP and (b) H2-P4PCP at 24 °C conducted with uniaxially applied stress at a rate of 0.02 s−1. Sample was subjected to max strains of 50 to 400% in increasing increments of 50% each cycle. Cycles were ended when stress returned to 0 MPa and the next cycle was immediately began to the next max strain value.

Figure 4. Uniaxial stress vs strain curves of P4PCP and H2-P4PCP performed at a rate of 0.5 min−1. Data shown is a representative analysis based on the average of three P4PCP and eight H2-P4PCP dogbones tested at 24 °C.

to 400% in 50% increments and a constant rate of 0.02 s−1. Elastic recovery (ER) was calculated using ER = ((εmax − ε(0, εmax))/εmax) × 100, where εmax is the maximum strain for the cycle and ε(0, εmax) is the strain where stress reaches zero upon compression.80,81 For H2-P4PCP, ER for the first cycle to 50% strain was a modest 65%; however, as the maximum strain was increased with each successive cycle, the ER raised dramatically and plateaued at ∼95%. P4PCP exhibited a similar yet reduced ER that recovered to only 18% after the first cycle and plateaued ∼90% at higher strains. The reduced elasticity of P4PCP can be more easily interpreted in the ER profiles as a function of maximum strain plotted in Figure 6. Creep experiments for H2-P4PCP shown in Figure 7 show quite a significant increase in strain as a function of time, especially compared to observed creep in an ESI with similar S content at similar applied stress.32 This likely relates to the greatly increased viscous contribution to the material at room temperature formulated from the rubberlike fluid behavior.

strain curve within the average of the specimens tested. Both materials display elastomeric behavior with no discernible yield point and monotonically increasing stress until break. Elongation at break (ε), stress at break (σf), and Young’s modulus (E) of P4PCP and H2-P4PCP, averaged over all dogbone specimens, is provided in Table 1 with standard deviations values. Though H2-P4PCP has almost double the modulus of P4PCP (E = 1.61 and 0.85 MPa, respectively) and over three times the stress at break (σf = 5.20 and 1.48 MPa, respectively), the latter withstands over twice the elongation (ε = 1149 and 2497%, respectively) before failure. Therefore, when comparing P4PCP and H2-P4PCP, the transformation of rigid olefin groups into more flexible methylene units within the backbone microstructure effectively reduces Me and ε while increasing E and σf. The effect of reduced Me on the mechanical properties of two polymers with similar molar mass is D

DOI: 10.1021/acs.iecr.7b05395 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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content (∼72%), H2-P4PCP was found to have a lower Tg (and therefore a lower E and higher ε) and a higher Me. This study further illustrates the influence of precision microstructure on the properties of polymeric systems and a new contribution to fundamental understanding of structure−property relationships.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b05395. Full tensile data, additional rheology data, and further characterization of synthesized polymers (PDF)

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Figure 6. Elastic recovery (%) as a function of maximum unaxial strain (%) for each elastic deformation cycle of P4PCP (open circles) and H2-P4PCP (closed symbols) performed at 0.02 s−1 and 24 °C.

AUTHOR INFORMATION

Corresponding Author

*J. G. Kennemur. Email: [email protected]. ORCID

Robert J. Kieber III: 0000-0001-5232-1111 Justin G. Kennemur: 0000-0002-2322-0386 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This contribution was identified by Prof. Andrew Magenau (Drexel University) as the Best Presentation in the “Dynamic Chemistry in Polymer Materials” session of the 2017 ACS Fall National Meeting in Washington, D.C. We thank the Florida State University Energy and Materials Hiring Initiative and the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. We also thank Prof. Subramanian Ramakrishnan for use of his rheometer purchased through AMSRD-ARL-RO-SI proposal number: 62885-MSREP from the Department of Defense (ARO) and is located in the National High Magnetic Field Laboratory supported by the National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida. We thank Prof. Albert Stiegman for use of his DSC and Prof. Joseph Schlenoff for use of his mechanical tensile tester. 1H and 13C NMR were performed in the FSU Department of Chemistry and Biochemistry NMR Facility under supervision of Dr. Banghao Chen.

Figure 7. Creep measurement (strain % as a function of time (s)) of H2-P4PCP using a constant force of 0.089 MPa for 10,000 s at 24 °C.

The near-ambient Tg and intriguing shape recovery behavior of H2-P4PCP presents a variety of ways to deform and reshape this material. As an example, a rectangular strip of the material was coiled around a small rod and dipped into an ice bath at 0 °C for 1 min to vitrify the polymer in the coiled shape. Upon removal and warming to ambient temperatures above Tg the strip uncoiled and returned to the original shape (Figure S14). Therefore, these materials serve as interesting possibilities for thermally responsive shape memory materials with changes triggered by the ambient temperature ranges experienced within environmental conditions.

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REFERENCES

(1) Scheirs, J.; Priddy, D. Modern Styrenic Polymers: Polystyrenes and Styrenic Copolymers; John Wiley and Sons, Inc: Chichester, West Sussex, England, 2003. (2) Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. Living alkene polymerization: New methods for the precision synthesis of polyolefins. Prog. Polym. Sci. 2007, 32 (1), 30−92. (3) Rodrigues, A. S.; Carpentier, J. F. Groups 3 and 4 single-site catalysts for styrene-ethylene and styrene-alpha-olefin copolymerization. Coord. Chem. Rev. 2008, 252 (18−20), 2137−2154. (4) Klosin, J.; Fontaine, P. P.; Figueroa, R. Development of Group IV Molecular Catalysts for High Temperature Ethylene-α-Olefin Copolymerization Reactions. Acc. Chem. Res. 2015, 48 (7), 2004− 2016. (5) Galdi, N.; Buonerba, A.; Oliva, L. Olefin−Styrene Copolymers. Polymers 2016, 8 (11), 405. (6) Pellecchia, C.; Oliva, L. Ethylene-styrene copolymerization. Rubber Chem. Technol. 1999, 72 (3), 553−558. (7) Cheung, Y. W.; Guest, M. J. Ethylene-Styrene Copolymers. In Modern Styrenic Polymers: Polystyrene and Styrenic Copolymers; Scheirs,

CONCLUSION This study investigated the mechanical and viscoelastic properties of P4PCP and H2-P4PCP, which contain a precise five-carbon phenyl branch spacing along the microstructure. Both materials were found to be amorphous with a Tg ≈ 17 °C and therefore at ambient conditions these materials are just barely above Tg and exhibit interesting elasticity and shape recovery properties. Although Mn, Đ, Tg, and ρ of P4PCP and H2-P4PCP were similar, it was discovered that these materials have significantly different Me (10.0 versus 3.6 kg mol−1), E (0.85 versus 1.61 MPa), and ε (2500 versus 1150%), respectively. Hysteresis was used to probe the elastic properties of both polymers, and after an initial plastic deformation, both materials recovered ≥90% up to 500% strain. H2-P4PCP can be likened to precision ESI system with exactly 71.4% w/w S content. When comparing our materials to ESIs of similar S E

DOI: 10.1021/acs.iecr.7b05395 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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