Thermoplastic elastomers (TPEs) are arguably the most industrially successful block copolymers due to a synergistic combination of robust mechanical properties and processability. The prototypical example is a linear ABA triblock copolymer with glassy A blocks flanking a rubbery B segment. However, morphological constraints impose an upper limit on the A-block volume fraction, fA ≈ 0.3, beyond which a cylinder-to-gyroid phase transition renders the material plastic, not elastic. Asymmetric miktoarm star polymers (A(BA')n) can significantly deflect this transition, which could result in stiffer TPEs. Moreover, like most commercial block copolymer TPEs, A(BA')n asymmetric miktoarm star polymers studied to date have been derived from petroleum resources. This talk will discuss a library of polyester-based A(BA')n asymmetric miktoarm star polymers with A, A' = poly(L-lactide) (PLLA) as the semi-crystalline hard blocks and B = poly(4-methylcaprolactone) (PMCL) as the soft segment synthesized using a grafting-through synthetic platform known as µSTAR. Architectural design parameters were systematically investigated, in particular the number of BA' arms (n), while holding the A, A', and B block lengths constant. The value of n has a pronounced impact on the mechanical properties. Tensile toughness increases with n, an effect likely related to bridging, as the modulus drops because the hard-block volume fraction decreases. These insights expand our understanding of architecture effects in sustainable thermoplastic elastomers.

Exploring asymmetric miktoarm star polymers for polyester thermoplastic elastomers

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ACS Fall 2022

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