Synthesis of biodegradable poly( L ‐lactic acid‐co‐ D , L ‐mandelic acid) with relatively low molecular weight

A homopolymer of L‐lactic acid (LA), which was synthesized by direct polycondensation in the absence of a catalyst at 200°C, is crystalline, in contrast to the homopolymer of D,L‐mandelic acid (MA) which is amorphous. Poly(LA‐co‐MA), obtained under the above conditions, is amorphous over a wide range of composition from 15 to 100 mol‐% of monomeric units of MA. The in vitro degradation mechanism of these homopolymers shows a parabola‐type degradation pattern for poly(LA) and no degradation throughout an experimental period of 15 weeks for poly(MA). In poly(LA‐co‐MA) the degradation mechanism leads to a typical S‐type degradation pattern, which may be divided into two processes, initial swelling at the surface of the matrix without degradation (induction period), followed by the erosion of oligomers produced by degradation of the main chain in the swollen state.