Photochemical [2 + 2] Cycloaddition Enables the Synthesis of Highly Thermally Stable and Acid/Base-Resistant Polyesters from a Nonpolymerizable α,β-Conjugated Valerolactone.

We report a simple strategy to transform a nonpolymerizable six-membered α,β-conjugated lactone, 5,6-dihydro-2-pyran-2-one (), into polymerizable bicyclic lactones via photochemical [2 + 2] cycloaddition. Two bicyclic lactones, and , were obtained by the photochemical [2 + 2] cycloaddition of tetramethylethylene and . Ring-opening polymerization (ROP) of and catalyzed by diphenyl phosphate (DPP), La[N(SiMe)], and 1--butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris (dimethylamino) phosphoranylide-namino]-2λ, 4λ-catenadi(phosphazene) (Bu-P) were conducted. is highly polymerizable, either DPP or La[N(SiMe)] could catalyze its living ROP under mild conditions, affording the well-defined with a predictable molar mass and low dispersity. could only be polymerized with Bu-P as the catalyst, also generating the same polymer . has high thermal stability, with a being up to 376 °C. Ring-opening copolymerization (ROcP) of and δ-valerolactone (δ-VL) catalyzed by La[N(SiMe)] afforded a series of random copolymers with enhanced thermal stabilities. Both and the copolymer containing 10 mol % exhibited excellent resistance to acidic and basic hydrolysis. Our results demonstrate that direct photochemical [2 + 2] cycloaddition of α,β-conjugated valerolactone is not only a strategy to tune its polymerizability, but also allows for the synthesis of highly thermally stable aliphatic polyesters, inaccessible by other methods.