Low‐molecular‐weight copolymers composed of L ‐lactic acid and various DL ‐hydroxy acids as biodegradable carriers

Biodegradable copolymers of L‐lactic acid (L‐LA) and DL‐α‐hydroxy acids with relatively low molecular weights, for example L‐LA/DL‐lactic acid (DL‐LA), L‐LA/DL‐α‐hydroxybutyric acid (DL‐HBA), L‐LA/DL‐α‐hydroxyisovaleric acid (DL‐HIVA), and L‐LA/DL‐α‐hydroxyisocaproic acid (DL‐HICA), were synthesized by quantitative direct copolycondensation without catalysts at 200°C. The in vitro degradation, which was evaluated by measuring the weight loss of these copolymers in M/15 phosphate buffer solution (pH 7,2) without enzymes at 37°C, is strongly dependent on the kind and molecular weight of these copolymers, resulting in the formation of different degradation patterns such as parabola type (L‐LA/DL‐HBA system), linear type (L‐LA/DL‐LA system), and S type (L‐LA/DL‐HIVA and L‐LA/DL‐HICA systems).