Polylactide-poly(6-methyl-ε-caprolactone)-polylactide thermoplastic elastomers

Amorphous ABA type block aliphatic polyesters can be useful as degradable and biorenewable thermoplastic elastomers. These materials can be prepared by sequential ring-opening transesterification polymerization (ROTEP) reactions and can exhibit a range of physical properties and morphologies. In this work a set of amorphous polylactide-poly(6-methyl-ε-caprolactone)-polylactide aliphatic polyester ABA triblock copolymers were prepared by consecutive controlled ring-opening polymerizations. Ring-opening polymerization of neat 6-methyl-ε-caprolactone in the presence of 1,4-benzenedimethanol and tin(II) octoate afforded α,ω-hydroxyl-terminated poly(6-methyl-ε-caprolactone). High conversions of 6-methyl-ε- caprolactone (>96%) afforded polymers with molar masses ranging from 12 to 98 kg mol^-1, depending on monomer-to-initiator ratios, polymers with narrow, monomodal molecular weight distributions. An array of polylactide-poly(6-methyl-ε-caprolactone)-polylactide triblock copolymers with controlled molecular weights and narrow molecular weight distributions were synthesized using the telechelic poly(6-methyl-ε-caprolactone) samples as macroinitiators for the ring-opening polymerization of d,l-lactide. The morphological, thermal, and mechanical behaviors of these materials were explored. Several triblocks adopted well-ordered microphase-separated morphologies, and both hexagonally packed cylindrical and lamellar structures were observed. The Flory-Huggins interaction parameter was determined, π(T) = 61.2T^-1 - 0.1, based on the order-to-disorder transition temperatures of two symmetric triblocks using the calculated mean field theory result. The elastomeric mechanical behavior of two high molecular weight triblocks was characterized by tensile and elastic recovery experiments.