Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly( l ‐lactide) (PLLA) and the soft segment B is poly( ε ‐caprolactone‐ stat ‐ d , l ‐lactide) (P(CL‐ stat ‐DLLA)). The P(CL‐ stat ‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature ( T g = approximately −40 °C). Successive polymerization of l ‐lactide afforded PLLA‐ block ‐P(CL‐ stat ‐DLLA)‐ block ‐PLLAs, which exhibited melting temperature ( T m = approximately 150 °C) for the crystalline PLLA segments and still low T g (approximately −30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐ block ‐P(CL‐ stat ‐DLLA)‐ block ‐PDLAs (PDLA = poly( d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐ block ‐P(CL‐ stat ‐DLLA)‐ block ‐PLLA was blended with PDLA‐ block ‐P(CL‐ stat ‐DLLA)‐ block ‐PDLA, stereocomplex crystals were formed to enhance their T m as well as tensile properties.