A series of sustainable aliphatic polyester thermoplastic elastomers (APTPEs), consisting of multi-arm star polymers with arms of poly(L-lactide)-block-poly(γ-methylcaprolactone), were investigated and compared to analogous linear poly(L-lactide)-block-poly(γ-methylcaprolactone)-block-poly(L-lactide) triblock polymers. Linear analogues with comparable arm molar mass and comparable overall molar mass were synthesized to distinguish the impact of architecture from molar mass effects. The star block polymers significantly outperformed their linear analogues with respect to ultimate tensile strength and 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 commercial, petroleum-derived styrenic TPEs. The star polymers also exhibited superior recovery compared to the linear APTPEs when subjected to cyclic strain cycles, suggestive of the impact of architecture towards improved polymer mechanical properties. Upon exploration of the polymer stress relaxation behavior, the star APTPEs demonstrated slower relaxation than their linear analogues, indicating the improved performance at a broader range of operating conditions provided by the star architecture. Dynamic mechanical thermal analysis indicates that the star architecture does not negatively impact processability, an important feature for potential industrial applications. Overall, this work illustrates that simple changes in the macromolecular architecture in sustainable APTPEs results 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.

Improving the mechanical properties of aliphatic polyester thermoplastic elastomers through star architectures

ACS Spring Meeting 2021

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