Resorbable and Highly Elastic Block Copolymers from 1,5-Dioxepan-2-one and l-Lactide with Controlled Tensile Properties and Hydrophilicity

Abstract

New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different poly(l-lactide-b-1,5-dioxepan-2-one-b-l-lactide) triblock copolymers and one new poly(l-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and l-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content. The receding contact angle varied from 27 to 44°. The tensile properties of the copolymers were controlled by altering the PDXO block length. The tensile testing showed that all the polymers were very elastic and had very high elongations-at-break (ε_b). The copolymers retained very good mechanical properties (ε_b ≈ 600−800% and σ_b ≈ 8−20 MPa) throughout the in vitro degradation study (59 days).