The bulk ring-opening polymerization of renewable δ-decalactone using 1,5,7-triazabicyclo[4.4.0]dec-5ene was carried out at temperatures between 7 and 110 °C. The equilibrium monomer concentration for reactions within this temperature range was used to determine the polymerization thermodynamic parameters (ΔH p = −17.1 ± 0.6 kJ mol −1 , ΔS p = −54 ± 2 J mol −1 K −1 ) for δ-decalactone. The polymerization kinetics were established and high molar mass poly(δ-decalactone) was prepared with a glass transition temperature of −51 °C. Poly(δ-decalactone) samples with controlled molar mass and narrow molar mass distributions were realized by controlling the monomer conversion and initiator concentration. A high molar mass poly(lactide)-poly(δ-decalactone)-poly(lactide) triblock copolymer with a low polydispersity index was prepared by simple sequential addition of monomers. The product triblock exhibited two distinct glass transitions temperatures consistent with microphase segregation.

The mechanical properties of thermoplastic elastomers (TPEs) consisting of 6-arm star block polymers with glassy, crystalline, or composite crystalline–glassy physical cross-linking (hard) domains were investigated and compared to the analogous linear triblock or pentablock polymers. The 6-arm stars exhibited qualitatively similar solid-state morphologies and phase behavior to their linear counterparts, as demonstrated by small-angle X-ray scattering and differential scanning calorimetry. Consequently, the architecture had minimal impact on the small-strain behavior in uniaxial extension at room temperature. As the applied strain increased, the star polymers exhibited more pronounced strain hardening than the corresponding linear TPEs, resulting in an increase in the ultimate strength of 20% for the polymers with crystalline end blocks and 30% when the end blocks were glassy. Each of the three star polymers exhibited superior recovery (i.e., lower residual strain) and lower hysteresis than the corresponding linear TPEs when subjected to repeated strain cycles. The enhancement in the recovery was most significant for the polymers with glassy hard domains. The TPEs with crystalline or crystalline–glassy domains recovered more rapidly than the corresponding linear block polymers but showed only modest improvements in the recovery measured after the specimens were allowed to rest for 5 min. These results indicate that the covalent junction at the core of the star strengthens and accelerates the recovery of the network but does not greatly suppress plastic deformation of the crystallites. Overall, this work demonstrates that the mechanical performance of block polymer TPEs can be improved by using a star macromolecular architecture.

Bottlebrush polymers consist of a linear backbone with densely grafted side chains which impact the rigidity of the molecule. The persistence length of the bottlebrush backbone in solution is influenced by both the intrinsic structure of the polymer and by the local environment, such as the solvent quality and concentration. Increasing the concentration reduces the overall size of the molecule due to the reduction in backbone stiffness. In this study we map out the size of a bottlebrush polymer as a function of concentration for a single backbone length. Small-angle neutron scattering (SANS) measurements are conducted on a polynorbornene-based bottlebrush with polystyrene side chains in a good solvent. The data are fit using a model which provides both the long and short axis radius of gyration (R g,2 and R g,1 , respectively), providing a measure for how the conformation changes as a function of concentration. At low concentrations a highly anisotropic structure is observed (R g,2 /R g,1 ≈ 4), becoming more isotropic at higher concentrations (R g,2 /R g,1 ≈ 1.5). The concentration scaling for both R g,2 and the overall R g are evaluated and compared with predictions in the literature. Coarse-grained molecular dynamics simulations were also conducted to probe the impact of concentration on bottlebrush conformation showing qualitative agreement with the experimental results.

Block copolymers with crystalline, glassy, and rubbery blocks were synthesized by anionic polymerization of butadiene, styrene, and isoprene followed by chlorosilane coupling and hydrogenation. The performance of two pentablock copolymers, with the block sequence crystalline−glassy− rubbery−glassy−crystalline, as thermoplastic elastomers (TPEs) was evaluated against triblock copolymers having either crystalline or glassy end blocks. Judicious choices of block lengths yielded homogeneous melts for both pentablocks; consequently, the low-shear-rate viscosities of the pentablocks were more than 2 orders of magnitude lower than that of the glassy−rubbery−glassy triblock, which remained microphaseseparated in the melt. In the pentablocks, physical cross-linking was achieved by crystallization of the end blocks followed by vitrification of the adjacent glassy blocks, forming composite crystalline−glassy hard domains. All of the polymers studied exhibited desirable mechanical behavior for TPEs, including low Young's modulus, high extensibility, and low permanent set. Increasing the glassy block fraction (at constant hard block content and molecular weight) systematically improved the mechanical performance by reducing the Young's modulus and increasing the ultimate strength; however, the strain recovery was still limited by the crystalline component. Taken in the context of prior work on semicrystalline TPEs, this work highlights the influence of the crystalline morphology on the mechanical properties.

The ever‐growing catalog of monomers being incorporated into block polymers affords exceptional control over phase behavior and nanoscale structure. The segregation strength, χN, is the fundamental link between the molecular‐level detail and the thermodynamics. However, predicting phase behavior mandates at least one experimental measurement of χN for each pair of blocks. This typically requires access to the disordered state. We describe a method for estimating χN from small‐angle X‐ray scattering measurements of the interfacial width between lamellar microdomains, tx, in the microphase‐separated melt. The segregation strength is determined by comparing tx to self‐consistent field theory calculations of the intrinsic interfacial width, ti, as a function of the mean‐field χN. The method is validated using a series of independent experimental measurements of tx and χN, measured via the order–disorder transition temperature, TODT. The average absolute relative difference between χN calculated from tx and the value calculated from TODT is a modest 11%. Corrections for nonplanarity of the interfaces are investigated but do not improve the agreement between the experiments and theory. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J. Polym. Sci., Part B: Polym. Phys. 2019 © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 932–940