Polylactide copolymers: Effect of copolymer ratio and end capping on their properties

Racemic copolymers of polylactic acid were investigated to determine the effect of copolymer ratio on melting point, degree of crystallinity, mechanical properties, and processing behavior. The copolymer ratio was found to have a strong influence on the crystallization behavior of the polymer. In addition to the ratio of the L-form to a random mixture of the D and L forms of the lactic acid in the copolymer, the effect of the polymer's molecular weight was examined. The copolymers were produced from the lactide form of the monomer to achieve weight average molecular weights above 100,000. The molecular weight had a profound influence on processability and rate of crystallization. Other notable factors influencing the properties and processing of the copolymers were the concentration of residual monomer in the polymer, the processing time-temperature history, and the extent of molecular weight degradation during processing. An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end capping, and plasticization. © 2005 Wiley Periodicals, Inc.