Combining ring-opening metathesis polymerization and cyclic ester ring-opening polymerization to form ABA triblock copolymers from 1,5-cyclooctadiene and D, L-lactide

ABA triblock copolymers were synthesized by combining ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) with ring-opening polymerization of D, L-lactide. Hydroxyl-functionalized telechelic polyCOD was prepared by taking advantage of chain transfer during ROMP of COD using the acyclic chain transfer agent cis-l,4-diacetoxy-2-butene. These hydroxy-terminated macroinitiators were used as initiators for the polymerization of lactide to form a series of triblock copolymers with compositions in the range 0.24 ≤ f _pla ≤ 0.89 and molecular weights ranging from 22 to 196 kg mol ^-1. The ordered-state morphologies of the triblocks were determined using small-angle X-ray scattering; well-ordered microstructures were observed for several samples, in accordance with the predicted dependence of morphology on composition. The mechanical properties of these materials were also investigated by performing tensile measurements; the triblocks were considerably tougher than poly(D, L-lactide), most markedly in samples with low polyCOD midblock content.