All-Methacrylic Stereoregular Triblock Co-polymer Thermoplastic Elastomers Toughened by Supramolecular Stereocomplexation

Doubly stranded pairs of isotactic ( it -) chains of poly(methyl methacrylate) (PMMA) coiled inside of the helical cavity of syndiotactic ( st -) PMMA chains generate a crystalline triple-helix stereocomplex, but its high brittleness limits its application. Here, we present a strategy to toughen up such stereocomplex via construction of thermoplastic elastomer (TPE)-based all-methacrylic stereoregular triblock co-polymers or toughen up such TPEs via stereocomplexation. Specifically, the stereospecific and living coordination–addition polymerization mediated by a chiral zirconocenium catalyst was utilized for the successful synthesis of isotactic ABA triblock co-polymers ( it -MRM, M n up to 200 kDa, isotacticity [ mm ] > 95%) with it -PMMA as two outer complexing hard blocks and it -PRMA bearing C 4–10 alkyl (R) groups as the center, noncomplexing, low- T g soft block. Physical blending of it -MRMs with st -PMMA in a 1:1 or 2:1 st /it-PMMA ratio, when crystallized from tetrahydrofuran solutions, led to stereocomplexed TPEs self-assembled into phase-segregated soft, elastic ( T g from −10 to −40 °C) and high melting, stereocomplexed ( T m = 192–199 °C) domains, the latter of which serves as reprocessable physical crosslinks. Characterizations of mechanical properties of the resulting stereocomplexed triblock co-polymer materials showed a significant toughening of the polymer network compared to the noncomplexed triblock co-polymer, attributed to the ability of dissipating tensile forces (necking) by the st / it -PMMA domains (tensile toughness up to 29 MJ m –3 ) and strain hardening by the entangled soft it -PRMA domains (elongations from 260 to 800%).