INTERNAL MOTIONS IN POLYLACTIDE AND RELATED POLYMERS

Polylactide(approximately 95% L-isomer), polyglycolide, and a 1:1 copo lymer were studied by differential scanning calorimetry, dynamic mecha nical analysis, and dielectric relaxation. In addition to the previous ly known glass transitions, all of these polymers exhibit a relaxation similar to the beta-relaxation which occurs in many other materials. This relaxation, which occurs near 200 K at 1 kHz, is attributed to no ncooperative local motions. Another new relaxation near 15 K was found in polyactide and the copolymer but not polyglycolide and hence is at tributed to motions of the methyl side groups. The effect of increased humidity on polylactide was also investigated. The weight gain of the samples depends strongly on the relative humidity and continues over extended periods of time. Changes in the dielectric relaxation spectra were consistent with substantial decreases in molecular weight.