Bulk Ring Opening Polymerization of <scp>L</scp>‐Lactide with Calcium methoxide

Abstract

Abstract Summary : Bulk ring opening polymerization (ROP) of L‐lactide (LA) initiated by calcium methoxide (Ca(OMe) 2 ) was investigated in LA/Ca molar ratio from 100 to 5000 and reaction times up to 3h at 180 °C. Ca(OMe) 2 showed good activity as ROP catalyst, particularly at high catalyst concentration. The polymerization shows a linear relationship between $\overline {{\rm M}} $ n and reaction time, typical of a controlled process. The increase of LA/Ca molar ratio decreases the conversion which was maximum (66%) when the polymerization was carried out at 180 °C and LA/Ca = 100. Semicrystalline poly(L‐lactic acid) (PLLA) with moderate $\overline {{\rm M}} $ n varying from 8,500 to 19,500 and polydispersities from 1.20 to 1.44 were obtained. The increase of LA/Ca molar ratio decreased $\overline {{\rm M}} $ n , increased the degree of crystallinity and decreased racemization processes which can be controlled by the polymerization condition. Racemization could be reduced by using low catalyst concentration.