Leveraging E/Z isomerization to enhance ring opening polymerization thermodynamics of a CO₂/butadiene derived...

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), a δ-lactone with 28 wt% CO₂, has been shown to valorize cheap and abundant waste products into commercially competitive polyester products which are non-toxic and potentially biodegradable. Here, our team reports the photochemical E/Z isomerization of EVP through irradiation with 254 nm light. Selective ring-opening polymerization of (Z)EVP is achieved through ureate-anion catalysis, where unwanted Michael addition reaction is suppressed at low temperature (<-10 °C). Further, competitive ureate-anion catalyzed Z to E isomerization of the monomer is suppressed through high initiator loading where poly(Z)EVP is obtained at 69% yield at -40 °C (98% selective). Importantly, the ceiling temperature (T _c) significantly increased from -141 °C to -60 °C from (E)EVP to (Z)EVP, resulting in a six-fold increase in polymer yield at -10 °C (8 vs. 48%). The increase in T _c is rationalized by leveraging a repulsive non-covalent interaction between the methyl group on the ethylidene functional group and the carbonyl oxygen. A reactivity ratio of r _{( Z )EVP} 1.36 and r _{( E )EVP} 0.73 is measured, resulting in a polymeric material with gradient architecture in copolymerizations of the stereoisomers. The increased insertion rate of (Z)EVP is rationalized by a reduction in the steric hinderance along the Flippin-Lodge trajectory of the lactone.