Telechelic all- <i>cis</i> polycyclooctene <i>via</i> catalytic stereoretentive ROMP for the synthesis of polylactide-based ABA triblock copolymers

Polylactide (PLA) is a commercial and sustainably sourced aliphatic polyester but its applications have been limited by its low toughness. The insertion of a rubbery segment within the PLA backbone is among the promising strategies to enhance the mechanical properties of PLA while retaining sustainability. Herein, we disclose a catalytic stereoretentive ring-opening metathesis polymerization process to access high molar mass (<i>M</i>expn up to 127.9 kg mol^-1) all-<i>cis</i> telechelic polycyclooctene (PCOE) at low catalyst loadings. The use of <i>cis</i>-1,4-diacetoxy-2-butene as a chain-transfer agent in the presence of stereoretentive dithiolate Ru carbenes afforded precise control over the <i>cis</i> content, the molar mass, and the introduction of acetoxy chain ends. Subsequent hydrolysis of the acetoxy motifs followed by chain extension <i>via</i> ring-opening polymerization of D,L-lactide yielded high molar mass (<i>M</i>expn up to 105.0 kg mol^-1) all-<i>cis</i> PLA ABA triblock copolymers. The influence of the molar mass of the all-<i>cis</i> PCOE over the thermal and mechanical properties of the ABA triblock was investigated.