Controlled ring-opening polymerization ofL-lactide and 1,5-dioxepan-2-one forming a triblock copolymer

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Novel elastomeric A-B-A triblock copolymers were successfully synthesized in a new two-step process: controlled ring-opening polymerization of the cyclic ether–ester 1,5-dioxepan-2-one as the amorphous middle block (B-block) followed 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-tetraoxacyclodecane initiator system was utilized and the reaction was performed in chloroform at 60 °C. A good control of the synthesis was obtained, resulting in well defined triblock copolymers. The molecular weight and chemical 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 calorimetry. WAXS investigation of the triblock copolymers showed a crystal structure similar to that of the pure poly(L-lactide).