Conjugated vinyl lactones commonly serve as precursors of polymers with pendant cyclic esters, which can undergo several chem. modifications. They have notably been copolymd. with "more activated monomers" like (meth)acrylates. By contrast, the radical polymn. of nonconjugated methylene lactone analogs has been disregarded as well as their copolymn. with "less-activated monomers" such as acyclic vinyl esters. The present work explores the conventional radical polymn. and the reversible deactivation radical polymn. of γ-methylene-γ-butyrolactone (γMγBL) and its copolymn. with vinyl acetate (VAc). Statistical P(γMγBL-co-VAc) copolymers with predictable molar mass, low dispersity, and precise compns. were notably achieved by organometallic-mediated radical polymn. based on cobalt complexes via both reversible termination, also referred to as reversible chain deactivation, and degenerative chain-transfer pathways. Upon hydrolysis, these γMγBL-contg. (co)polymers release one alc. moiety and one carboxylic group per repeating unit, leading to unprecedented carboxylic acid-functionalized poly(vinyl alc.) derivs. A preliminary study emphasizes the pH responsiveness of the latter in water.