Bifunctional and recyclable polyesters by chemoselective ring-opening polymerization of a δ-lactone derived from CO₂ and butadiene.

Abstract

When aiming at the direct use of CO₂ for the preparation of advanced/value-added materials, the synthesis of CO₂/olefin copolymers is very appealing but challenging. The δ-lactone 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), synthesized by telomerization of CO₂ with 1,3-butadiene, is a promising monomer. However, its chemoselective ring-opening polymerization (ROP) is hampered by unfavorable thermodynamics and the competitive polymerization of highly reactive C=C double bonds under usual conditions. Herein, we report the chemoselective ROP of EVP using a phosphazene/urea binary catalyst, affording exclusively a linear unsaturated polyester poly(EVP)_ROP, with a molar mass (M_n) up to 16.1 kg·mol^-1 and a narrow distribution (Ð < 1.6), which can be fully recycled back to the pristine monomer, thus establishing a monomer-polymer-monomer closed-loop life cycle. In these polyesters, the CO₂ content reaches 33 mol% (29 wt%). The reasons for the unexpected chemoselectivity were investigated by Density-functional theory (DFT) calculations. The poly(EVP)_ROP features two pendent C=C double bonds per repeating unit, which show distinct reactivity and thus can be properly engaged in sequential functionalizations towards the synthesis of bifunctional polyesters. We disclose here a methodology providing a facile access to bifunctional and recyclable polyesters from readily available feedstocks.