Tailoring the Properties of Polyhydroxyalkanoates from Plastics to Elastomers via Stereoselective Copolymerizations of rac‐β‐Butyrolactone and β‐Propiolactone

Comprehensive Summary Poly(3‐hydroxybutyrate), a crucial member of the large biodegradable polyhydroxyalkanoate family, suffers from its brittleness. To enhance its performance, we employed a straightforward approach involving the ring‐opening copolymerization of racemic‐β‐butyrolactone (rac‐β‐BL) and β‐propiolactone (β‐PL) using the syndio‐selective amino‐alkoxy‐bis(phenolate)‐yttrium complex as a catalyst, thanks to the excellent ductility of poly(3‐hydroxypropionate). Control over the rac‐β‐BL/β‐PL feeding ratios and polymerization time yielded random or block copolymers with tunable thermal and mechanical properties comparable to traditional fossil‐based plastics. Furthermore, we achieved one‐pot synthesis of hard‐soft‐hard triblock copolymers by exploiting monomers’ different copolymerization rates and a bifunctional initiator, thus transforming polyhydroxyalkanoates from hard and tough plastics to soft and ductile thermoplastic elastomers.