Synthesis of star-shaped poly(D,L-lactic acid-alt-glycolic acid)-b-poly(L-lactic acid) with the poly(D,L-lactic acid-alt-glycolic acid) macroinitiator and stannous octoate catalyst

Two types of three-arm and four-arm, star-shaped poly(D,L-lactic acid-alt-glycolic acid)-b-poly(L-lactic acid) (D,L-PLGA50-b-PLLA) were successfully synthesized via the sequential ring-opening polymerization Of D,L-3-methylglycolide (MG) and L-lactide (L-LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct(2)) as a catalyst. Star-shaped, hydroxy-terminated poly(D,L-lactic acid-alt-glycolic acid) (D,L-PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization Of L-LA with the SnOct(2) catalyst in bulk at 130 degreesC. For the polymerization Of L-LA with the three-arm, star-shaped D,L-PLGA50 macroinitiator (number-average molecular weight = 6800) and the SnOct(2) catalyst, the molecular weight of the resulting D,L-PLGA50-b-PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) Of L-LA to MG, and the molecular weight distribution was rather narrow (weight-average molecular weight/number-average molecular weight = 1.09-1.15). The H-1 NMR spectrum of the D,L-PLGA50-b-PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio Of L-LA to the macroinitiator. The C-13 NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L-PLGA50 as the first block and poly(L-lactic acid) as the second block. (C) 2001 John Wiley Sons, Inc.