Biodegradable brush-like graft polymers from poly(D,L-lactide) or poly(D,L-lactide-co-glycolide) and charge-modified, hydrophilic dextrans as backbone - Synthesis, characterization and in vitro degradation properties

Brush-like graft polylactide (PLA) and poly(lactide-co-glycolide) (PLG) containing water soluble charged dextrans: dextran sulphate sodium (DSS) and diethylaminoethyl dextran chloride (DEAED) as backbones were synthesized in a bulk polymerization reaction using stannous octoate as catalyst. The polymers were characterized by n.m.r., g.p.c., LS, intrinsic viscosity measurement and d.s.c. methods. Brush-like graft PLA and PLG have different physico-chemical properties compared to linear polyesters such as PLA and PLG. Significantly accelerated degradation properties of the graft polymers were observed compared to linear PLG. A rapid decrease in polymer molecular weight and polymer mass demonstrates the influence of charged functionalities in the backbone. The nonlinear chain structure and an increased number of polar end groups accelerate the degradation and the apparent mass loss of the brush-like graft PLG when the weight average molecular weight (M-w) is still higher suggests a different mechanism from that of linear PLG. The polar groups in the polymeric backbone facilitate the cleavage of ester bonds. A discontinuous polymer mass loss in the case of linear PLG was not observed for brush-like graft polyesters. The charged polyelectrolyte backbone may also anew higher drug loading of parenteral delivery system with peptides and proteins due to ironic interactions. (C) 1997 Elsevier Science Ltd.