Chemoselective and controlled ring-opening copolymerization of biorenewable α-methylene-δ-valerolactone with ε-caprolactone toward functional copolyesters

Although alpha-methylene-delta-valerolactone (MVL) as a biorenewable six membered lactone bearing an exocyclic double bond has shown great potential for preparing functional polyesters with a pendent modifiable vinyl group, the copolymerization of MVL with other commercial lactones to produce functional polyesters has been scarcely investigated. In this contribution, we present the chemoselective ring-opening copolymerization (ROCP) of MVL with epsilon-caprolactone (CL) to exclusively produce functional P(MVL-co-CL) copolyesters without the formation of vinyl addition products using an organophosphazene/urea binary catalyst. The kinetic experiment and reactivity ratio determination suggested the much higher reactivity of MVL compared to CL, resulting in the formation of a gradient copolyester with CL repeating units located towards the end of the polymer chain. The pendent double bond of the obtained copolyesters can be facilely post-functionalized by the thiol-Michael addition reaction to afford thiolated copolyesters. A series of copolyesters with various MVL incorporations from 10 to 91 mol% was prepared, which exhibited composition dependent thermal properties.