Precise construction of weather-sensitive poly(ester-alt-thioesters) from phthalic thioanhydride and oxetane

Future materials require improved environmental degradability compared to current state-of-the-art variants while remaining stable under thermal processing conditions. Owing to the chemistry of sulfur, polythioesters could grant such advantages yet their synthesis remains challenging. Here we report the selective ring opening copolymerisation (ROCOP) of oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K catalyst precisely yielding semi-crystalline alternating poly(ester-alt-thioesters) with a high Mn,max = 139 kg/mol which is crucial for maximising thermal stability and tensile strength of the resulting materials. We also find heterometallic cooperativity to be key to achieve productive catalysis. Although the high Mn material shows excellent thermal stability, the regularly distributed thioester-links in the polymer backbone act as photolytic and oxidative breaking points. Investigating its primary degradability as plastic litter in central Europe, artificial weathering experiments reveal improved degradation over current commodity semi-aromatic polyester due to the thioester links in the polymer backbone.