Block copolymer thermoplastic elastomers with composite crystalline-glassy hard domains

We report the synthesis and behavior of thermoplastic elastomers (TPEs) containing both crystalline and glassy hard segments, with the aim of capturing the mechanical properties of conventional all-amorphous triblock TPEs, while forming the solid-state structure by crystallization from a single-phase melt. Living ring-opening metathesis polymerization and subsequent hydrogenation generate pentablock copolymers with the architecture crystalline-glassyrubbery- glassy-crystalline. Analogous crystalline-rubbery-crystalline triblocks show a high initial modulus, yielding, and poor recovery, resulting from plate-like crystalline hard blocks. In the pentablocks, crystallization from a single-phase melt causes a layer rich in the glassy block to form around the crystallites, limiting their lateral growth and generating composite hard domains. The pentablocks show the low initial modulus, strain-hardening behavior, and small permanent set desired for TPEs, while retaining an easily-processed single-phase melt.