Abstract
Poly(l-lactide) (PLLA) prepared by ring-opening melt polymerization using tin−octoate as catalyst undergoes a rapid melt degradation. The melt stability of PLLA was evaluated by using a Haake melt rheometer at various temperatures. The degradation rate constants were calculated from the changes in the melt viscosity for as-polymerized, precipitated, and acid treated PLLA. Furthermore, stability measurements were performed for as-polymerized PLLA modified with various types of peroxides (hydroperoxide, dialkyl peroxide, peroxy ester, and diaroyl peroxide). The energy of activation for the melt degradation of as-polymerized PLLA was calculated to 119.4 kJ/mol at temperatures between 180 and 210 °C. Precipitation of PLLA gave a reduction of the tin catalyst content in the polymer, and this also reduced the extent of the melt degradation. A further reduction of the tin content, and accordingly a reduction in the melt degradation, was achieved after acid treatment of the polymer. Addition of peroxide in open a...
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