Radical Copolymerization of Formaldehyde with Vinyl Acetate: Direct Incorporation of C–O Bonds in Vinyl Polymer Backbones

The carbonyl group is an abundant and fundamental functional group in chemistry. While carbonyl compounds have been polymerized via anionic and cationic mechanisms, their radical polymerization remains challenging. In this study, we report the radical copolymerization of formaldehyde (FA), an abundant and important C1 resource, and vinyl acetate (VAc) to generate novel vinyl copolymers that contain C-O bonds in their backbones. The polymerization of VAc in the presence of commercially available paraformaldehyde (PFA) as an FA source produced poly(FA-<i>co</i>-VAc)s via the addition of VAc radicals to the carbon side of FA and the subsequent addition of alkoxy radicals to VAc, resulting in the -CH₂O- units in the backbone. This reaction pathway was supported by NMR analyses and DFT calculations. The incorporation of FA was increased to 22% when polar solvents with highly protic and hydrogen-donating natures were used, which increased the concentration of FA generated from PFA in situ. Saponification of the poly(FA-<i>co</i>-VAc)s produced novel poly(vinyl alcohol) (PVA) copolymers with main-chain oxygen atoms and unique thermal properties. In addition, the detailed structure of the resulting copolymers was analyzed by reacetylation of the poly(FA-<i>co</i>-VA)s. This study highlighted the potential of radical polymerization of the C═O bond to generate unprecedented polymers with oxygen atoms in the backbones.