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

Abstract

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, Mn up to 200 kDa, isotacticity [mm] > 95%) with it-PMMA as two outer complexing hard blocks and it-PRMA bearing C4–10 alkyl (R) groups as the center, noncomplexing, low-Tg 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 (Tg from −10 to −40 °C) and high melting, stereocomplexed (Tm = 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%).