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