5‑Methylene-1,3-dioxane-2-one: A First-Choice Comonomer for Trimethylene Carbonate

5-Methylene-1,3-dioxane-2-one (exTMC), a six-membered ring cyclic carbonate bearing an exocyclic methylene group, has been investigated as comonomer for trimethylene carbonate (TMC) with the aim to prepare functionalized polycarbonates. Using methane sulfonic acid (MSA) as an organocatalyst, exTMC and TMC copolymerize in a controlled manner to lead to copolymers of adjusted composition and high randomness (the corresponding reactivity ratios have been determined by the Beckingham–Sanoja–Lynd (BSL) method as 0.93–0.95 and 1.04–1.07 for exTMC and TMC, respectively). Subsequent thiol-ene reaction on the exomethylene group with thioglycolic acid or thioglycerol provides aliphatic polycarbonates with adjustable amounts of COOH or OH groups randomly distributed along the polymer chains.