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The influence of morphology on the hydrolytic degradation behavior of poly(L-lactide) has been studied. High molecular weight and highly crystalline as-polymerized poly(L-lactide) was obtained in high yields through melt polymerization. Poly(L-lactide) fiber with a draw ratio of 5.6 was obtained by hot-drawing solution-spun fiber. During the bulk degradation of as-polymerized poly(L-lactide), a rapid decrease of molecular weight and tensile properties was observed. This could be explained by the morphology of the material and the presence of thermal stresses and subsequent generation of microcracks. The lamellar crystallites in as-polymerized poly(L-lactide) appeared to be very stable towards hydrolysis. The resorption time of high molecular weight as-polymerized poly(L-lactide) in vivo was estimated at 40-50 yr by extrapolation of molecular weight data. Hot-drawn poly(L-lactide) fiber showed exceptional hydrolytic stability under a static load and substantially retained its mechanical properties over a period of more than 5 yr. The high perfection of the crystalline fiber and the elimination of micro-voids obtained by hot-drawing prevented penetration of water and induced surface erosion of the fiber.

Blends of D,L-lactide/glycolide copolymers were synthesized and their properties and in vitro degradation behaviour were evaluated as a function of chain architecture and blend composition. Tensile and impact properties of the blends are hardly influenced by matrix composition and chain architecture, but predominantly vary with the amount of rubber. In vitro degradation showed that hydrolytic degradation is enhanced by the incorporation of glycolide into the poly(D,L-lactide) matrix. Surprisingly, blends based on 6-arm star-shaped poly(D,L-lactide-co-glycolide) retain their mechanical properties for a longer period than blends with linear matrices of comparable composition. Physical aging of the linear copolymers is more severe and faster than that of star-shaped copolymers. (C) 1997 Elsevier Science Ltd.

Copolymers of L-lactide(a)) with D-Lactide(a)), glycolide(b)), epsilon-caprolactone and trimethylene carbonate, and networks with spiro-bis-dimethylene-carbonate (2,4,7,9-tetraoxaspiro[5.5]undecane-3,8-dione) were prepared in bulk at standardized polymerization conditions. The properties of the nascent copolymers were evaluated with respect to the nature of the comonomer. Copolymerization with comonomers entailing low glass transition temperature simultaneously reduces the crystallinity. 300 MHz H-1 nuclear magnetic resonance is shown to be a useful technique for the determination of the average monomer sequence lengths in epsilon-caprolactone and trimethylene carbonate copolymers. The presence of crystallizable L-lactide sequences, due to differences in monomer reactivity, has a large effect on the thermal properties of the copolymer as well as on the long-term degradation characteristics.

The influence of morphology on the hydrolytic degradation behavior of poly(L-lactide) has been studied. High molecular weight and highly crystalline as-polymerized poly(L-lactide) was obtained in high yields through melt polymerization. Poly(L-lactide) fiber with a draw ratio of 5.6 was obtained by hot-drawing solution-spun fiber. During the bulk degradation of as-polymerized poly(L-lactide), a rapid decrease of molecular weight and tensile properties was observed. This could be explained by the morphology of the material and the presence of thermal stresses and subsequent generation of microcracks. The lamellar crystallites in as-polymerized poly(L-lactide) appeared to be very stable towards hydrolysis. The resorption time of high molecular weight as-polymerized poly(L-lactide) in vivo was estimated at 40-50 yr by extrapolation of molecular weight data. Hot-drawn poly(L-lactide) fiber showed exceptional hydrolytic stability under a static load and substantially retained its mechanical properties over a period of more than 5 yr. The high perfection of the crystalline fiber and the elimination of micro-voids obtained by hot-drawing prevented penetration of water and induced surface erosion of the fiber.

Blends of D,L-lactide/glycolide copolymers were synthesized and their properties and in vitro degradation behaviour were evaluated as a function of chain architecture and blend composition. Tensile and impact properties of the blends are hardly influenced by matrix composition and chain architecture, but predominantly vary with the amount of rubber. In vitro degradation showed that hydrolytic degradation is enhanced by the incorporation of glycolide into the poly(D,L-lactide) matrix. Surprisingly, blends based on 6-arm star-shaped poly(D,L-lactide-co-glycolide) retain their mechanical properties for a longer period than blends with linear matrices of comparable composition. Physical aging of the linear copolymers is more severe and faster than that of star-shaped copolymers. (C) 1997 Elsevier Science Ltd.

Copolymers of L-lactide(a)) with D-Lactide(a)), glycolide(b)), epsilon-caprolactone and trimethylene carbonate, and networks with spiro-bis-dimethylene-carbonate (2,4,7,9-tetraoxaspiro[5.5]undecane-3,8-dione) were prepared in bulk at standardized polymerization conditions. The properties of the nascent copolymers were evaluated with respect to the nature of the comonomer. Copolymerization with comonomers entailing low glass transition temperature simultaneously reduces the crystallinity. 300 MHz H-1 nuclear magnetic resonance is shown to be a useful technique for the determination of the average monomer sequence lengths in epsilon-caprolactone and trimethylene carbonate copolymers. The presence of crystallizable L-lactide sequences, due to differences in monomer reactivity, has a large effect on the thermal properties of the copolymer as well as on the long-term degradation characteristics.