Synthesis and characterization of novel biodegradable block copolymer poly(ethylene glycol)‐block‐poly(L‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylene carbonate)

An amphiphilic block copolymer, poly(ethylene glycol)‐ block ‐poly( L ‐lactide‐ co ‐2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate) [PEG‐ b ‐P(LA‐ co ‐MBC)], was synthesized in bulk by the ring‐opening polymerization of L ‐lactide with 2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate (MBC) in the presence of poly(ethylene glycol) as a macroinitiator with diethyl zinc as a catalyst. The subsequent catalytic hydrogenation of PEG‐ b ‐P(LA‐ co ‐MBC) with palladium hydroxide on activated charcoal (20%) as a catalyst was carried out to obtain the corresponding linear copolymer poly(ethyleneglycol)‐block‐poly( L ‐lactide‐ co ‐2‐methyl‐2‐carboxyl‐propylenecarbonate) [PEG‐ b ‐P(LA‐ co ‐MCC)] with pendant carboxyl groups. DSC analysis indicated that the glass‐transition temperature ( T g ) of PEG‐ b ‐P(LA‐ co ‐MBC) decreased with increasing MBC content in the copolymer, and T g of PEG‐ b ‐P(LA‐ co ‐MCC) was higher than that of the corresponding PEG‐ b ‐P(LA‐ co ‐MBC). The in vitro degradation rate of PEG‐ b ‐P(LA‐ co ‐MCC) in the presence of proteinase K was faster than that of PEG‐ b ‐P(LA‐ co ‐MBC), and the cytotoxicity of PEG‐ b ‐P(LA‐ co ‐MCC) to chondrocytes from human fetal arthrosis was lower than that of poly( L ‐lactide).