Stereodefect Strategy Enables Thermally Resilient, Rapidly Crystallizable, High-Performance Aliphatic Polyester Thermoplastic Elastomers

Abstract Stereoblock star aliphatic polyester thermoplastic elastomers (APTPEs) comprised of poly(d-lactide)-b-poly(l-lactide)-b-poly(γ-methyl-ε-caprolactone) ((DLM)4) rapidly crystallize to give strong, tough, and resilient APTPEs. However, the high melting temperature of the stereocomplex formed in these materials (Tm ≈ 220 °C) is close to the onset temperature for thermally induced mass loss (Td,1% ≈ 230 °C). This decomposition of the polyester is likely due to depolymerization from the ends of the polymer chain. Here, we report the synthesis of APTPE stars containing stereodefective poly(lactide) end diblocks, that is poly(l-lactide) covalently bonded to a poly(d-lactide) segment that is intentionally doped with a small percentage of l-lactide defects. Incorporating a low level of stereodefects leads to a modest reduction in Tm, while maintaining high levels of crystallinity and rapid stereoblock crystallization rates. The resultant materials have physical properties that are nearly identical to stereoblock star polymers without defects but allow melt processing below the temperature at which significant mass loss begins to occur. To prepare these star block polymers, we also conducted the synthesis in a one-pot, one-catalyst system, aligning the process with the principles of green chemistry.