STANNOUS OCTOATE-INITIATED VERSUS ZINC-INITIATED POLYMERIZATION OF RACEMIC LACTIDE - EFFECTS ON CONFIGURATIONAL STRUCTURES

Racemic lactide (D,L-lactide) was bulk-polymerized comparatively using stannous octoate and zinc metal as initiators. A two-level fractional factorial design was used to assess the influence of selected experimental variables with respect to intermolecular transesterification, whose extent in the resulting high molecular weight poly(D,L-lactide)s (PLA50) was investigated by C-13 NMR. Five variables, namely polymerization temperature, monomer-to-initiator ratio, polymerization time, nature of the initiator and monomer degassing-time, were found significant and were ranked according to their average effect on transesterification. A significant interaction of polymerization temperature and polymerization time was also detected. Zinc led to lower stereoregularity than stannous octoate.