Controlled ring-opening polymerization of L-lactide and 1,5-dioxepan-2-oneforming a triblock copolymer

Novel elastomeric A-B-A triblock copolymers were successfully synthesized i n a new two-step process: controlled ring-opening polymerization of the cyc lic etherester 1.5-dioxepan-2-one as the amorphous middle block (B-block) f ollowed by addition and polymerization of the two semicrystalline L-lactide blocks (A-block). A 1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacy clodecane initiator system was utilized and the reaction was performed in c hloroform at 60 degrees C. A good control of the synthesis was obtained, re sulting in well defined triblock copolymers. The molecular weight and chemi cal composition were easily adjusted by the monomer-to-initiator ratio. The triblock copolymers formed exhibited semicrystallinity up to a content of 1,5-dioxepan-2-one as high as 89% as determined by differential scanning ca lorimetry. WAXS investigation of the triblock copolymers showed a crystal s tructure similar to that of the pure poly(L-lactide). (C) 2000 John Wiley & Sons, Inc.