Hydrolytic Degradation of Polyisobutylene and Poly-L-Lactide-Based Multiblock Copolymers

The hydrolytic degradation of a series of poly-L-lactide (PLLA)-polyisobutylene (PIB) multiblock copolymers was studied in phosphate buffer solution (pH = 7.4) at 37 degrees C. The multiblock copolymers were synthesized by chain extension of PLLA-b-PIB-b-PLLA triblock copolymers, which were obtained by ring-opening polymerization of L-lactide initiated by hydroxyallyl telechelic PIB. The degradation strongly depended on the PLLA segment length. At constant PIB segment length, the multiblock copolymer with the shortest PLLA segment length (DPn = 10), showed significant weight loss after 8 weeks, whereas weight loss for DPn = 36 was only observed after 24 weeks. The gel-permeation chromatographic analysis showed a similar decrease in the number-average molecular weight (M-n) with time further supporting the weight loss data. Dynamic mechanical analysis showed a decrease in ultimate stress and modulus with time. The crystallinity of multiblock copolymers changed significantly with degradation time as indicated from differential scanning calorimetric analysis. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3767-3774, 2010