Enhanced Mechanical Properties of Aliphatic Polyester Thermoplastic Elastomers through Star Block Architectures

A series of sustainable aliphatic polyester thermoplastic elastomers (APTPEs) consisting of multi-arm star polymers with arms of poly(l-lactide)-b-poly(γ-methyl-ε-caprolactone) were investigated and compared to analogous linear poly(l-lactide)-b-poly(γ-methyl-ε-caprolactone)-b-poly(l-lactide) triblock polymers. Linear analogues with comparable arm molar mass and comparable overall molar mass were synthesized to distinguish architectural and molar mass effects. Overall, the star block polymers significantly outperformed their linear analogues with respect to ultimate tensile strength and tensile toughness, exhibiting more pronounced strain hardening than corresponding linear APTPEs. The stars exhibited high ultimate tensile strengths (∼33 MPa) and large elongations at break (∼1400%), outperforming commercially relevant, petroleum-derived, and non-degradable styrenic TPEs. The star polymers also exhibited superior recovery characteristics during cyclic strain cycles and reduced stress relaxation compared to the linear APTPEs, highlighting the impact of architecture on improved TPE mechanical properties. Dynamic mechanical thermal analysis suggests that the star architecture increases the usage temperature range and does not negatively influence processability, an important feature for future applications. Overall, this work illustrates that simple and convenient changes in the macromolecular architecture in sustainable APTPEs result in materials with greatly enhanced mechanical properties. A comprehensive understanding of the relationship between polymer architecture and mechanical properties can be capitalized on to develop property-specific and industrially relevant sustainable materials.