Synthesis and thermal properties of aliphatic copolyesters of L-lactic acid

The copolyesters of L-lactic acid were prepared by direct condensation of two combinations of monomers based on L-lactic acid/ethylene glycol/adipic acid and L-lactic acid/1,4-butanediol/succinic acid. The linear copolyesters obtained by condensation generally yield low molecular weights of less than 30000. Addition of a polyol such as pentaerythritol produced multibranched copolyesters whose molecular weights were remarkably increased upto about 50000. The glass transition temperatures of the linear and multibranched copolyesters were in the range of -17-43°C and 10-23°C, respectively, and which are lower than that of linear poly (L-lactic acid). Initial thermal decomposition temperatures (2% weight loss) of the linear and multibranched copolyesters were in the range of 205-272°C and 194-228°C, respectively, which are higher than that of linear poly (L-lactic acid), 168°C.