Enantiomeric A‐B‐A tri‐block copolymers of polylactides (A) and aliphatic polycarbonates (B) were mixed to prepare stereo mixtures that are applicable as thermoplastic elastomers having high thermal resistivity.
An oligomer of poly(hexamethylene carbonate) (PHMC) that is synthesized by ester‐exchanging polycondensation of ethylene carbonate and 1,6‐hexanediol is chain‐extended by using diphenyl carbonate as chain extender. The resultant PHMC, dihydroxyl‐terminated, is then subjected to tin‐catalyzed ring‐opening polymerization of L‐lactide to prepare ABA tri‐block copolymers consisting of poly‐L‐lactide (PLLA: A) and PHMC (B), which retain significantly high molecular weights even at increased contents of PHMC. Polymer films of these block copolymers exhibit high elongation, reaching 700% at a high PHMC content. It is therefore suggested that the present block copolymer system can be a novel thermoplastic elastomer, which is partly bio‐based.
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