SYNTHESIS AND DRUG CONTROLLED-RELEASE OF BLOCK-COPOLYMERS OF POLY(L-LACTIDE) WITH POLY(D,L-LACTIDE) AND RELATED MONOMERS

Four types of new biodegradable block copolymers AB, ABA, AC and AD, w here A is poly(L-lactide) (PLLA), B is poly(D,L-lactide) (PDLLA), C is poly(p-dioxanone) (PDON) and D is poly(epsilon-caprolactone) (PCL) wi th different block lengths were synthesized and characterized by GPC, IR, H-1-NMR and DSC. There are phase-separated and biodegradable block copolymers. Their in vitro biodegradation rates with the change of co mposition ratio were studied as well as the biodegradation rates of ho mopolymers with the series as PDON > PDLLA > PLLA in parallel with the ir crystallinities, i.e. from amorphous to semicrystalline. All these block copolymers were used as matrix to test their controlled release behavior of levo-norgestrel (LNG) in the form of microspheres through solvent evaporation preparation with thoroughly longtime washing to mi nimize the generally occurring bursting effect. As a result all of the m showed almost constant rate of release even from the initial stage.