Synthesis and thermal properties of copolymers of L-lactic acid and epsilon-caprolactone

Abstract

Copolymers of L-lactic acid with epsilon-caprolactone were prepared to provide poly (L-lactic acid) with flexibility and thermal stability. L-Lactic acid and epsilon-caprolactone were "one-pot" polymerized in the presence of Sb2O3 as a catalyst and dipentaerythritol (DIPET) as an initiator. Molecular weights of the copolymers were remarkably increased by the addition of DIPET. The copolymers were amorphous when the L-lactic acid composition was in the range of 20 similar to 90%, while the homopolymer of L-lactic acid and epsilon-caprolactone were semicrystalline. The glass transition temperatures(T-g) of the copolymers were in the range of -48 degrees C similar to 43 degrees C and decreased as the content of epsilon-caprolactone was increased. Initial thermal decomposition temperatures(T-d) of the copolymers were 212 degrees C similar to 289 degrees C, which were higher than the T-d of poly(L-lactic acid), 168 degrees C.