Bifunctional and Recyclable Polyesters by Chemoselective Ring-Opening Polymerization of a δ-Lactone Derived from CO2 and Butadiene

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 intermediate. However, chemoselective ring-opening polymerization (ROP) of EVP is hampered by unfavorable thermodynamics and the competitive polymerization of highly reactive C=C double bonds. Herein, we report the first chemoselective ROP of EVP using a phosphazene/urea binary catalyst, affording exclusively a linear unsaturated polyester poly(EVP)ROP, with a molar mass (Mn) up to 6.5 kg·mol-1 and narrow distribution (Ð = 1.24), which can be fully recycled back to the pristine monomer, thus establishing a monomer-polymer-monomer closed-loop life cycle. Remarkably, 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. This methodology provides a facile access to bifunctional and recyclable polyesters from readily available feedstocks. In these polyesters, the carbon dioxide content reaches 33 mol% (29 wt%). The reasons for the remarkable chemoselectivity observed were investigated by Density-functional theory (DFT) calculations.