Design and Synthesis of Biodegradable Multiblock Copolymers Based on Polyisobutylene and Poly(L-lactide) Segments

摘要

Poly(L-lactide) (PLLA) based biodegradable thermoplastic elastomers (TPEs) have attracted attention in recent times because of their important applications in various biomedical and pharmaceutical areas. A typical PLLA possesses high young’s modulus (～1.7 GPa) and ultimate tensile strength (～57 MPa), however, the elongation at break is relatively low (～2.9 %). To improve this property, block copolymerization or blending with various soft segments have been investigated. For example, Hillmyer and coworkers synthesized polyisoprene-b-PLLA-b-polyisoprene triblock copolymers and reported elongation at break up to 700 % by tailoring the length of hard and soft segment. Polyisobutylene (PIB) based TPEs are potential biomaterials because of their excellent biocompatibility.For example, polystyrene (PSt)-b-PIB-b-PSt is employed by Boston Scientific Corp. as a biostable polymer drug carrier in TAXUS~R Express~(2TM) paclitaxel-eluting coronary stents. Recently we have reported the synthesis of HO-Allyl-PIB-Allyl- OH from the corresponding bromoallyl telechelic PIB using basic hydrolysis. These hydroxyallyl telechelic PIBs can be used as initiators for ring-opening polymerization of LLA as reported by Sipos et al. In this preprint, preliminary synthesis of PLLA-b-PIB-b-PLLA triblock copolymer and it’s chain extension with 4,4’- methylenebis(phenylisocyanate) (MDI) to obtain the corresponding multiblock copolymer is reported.