Emulsion Polymerization of 2‑Methylene-1,3-Dioxepane and Vinyl Acetate: Process Analysis and Characterization

The development of polymerization methods that install weak links or degradable bonds in the backbone of otherwise all-carbon chains could accelerate the design and commercialization of new classes of recyclable, upcyclable, or biodegradable polymers. Cyclic ketene acetals including widely studied 2-methylene-1,3-dioxepane (MDO) can be used as comonomers in conventional free-radical polymerizations to insert labile ester bonds into addition polymer backbones. However, the key obstacle in deploying MDO in water-borne, industrially relevant processes is hydrolysis of the monomer itself. Optimized conditions including relatively low temperatures, mildly alkaline pH, and consistent radical flux lead to high in-process conversions, a rapid rate of polymerization, and a low degree of MDO hydrolysis. Although MDO hydrolysis competes strongly with copolymerization, degradation can be minimized during aqueous emulsion polymerization with vinyl acetate to give robust incorporations of ∼90% MDO. The methods and quantitative analysis tools reported here provide principles for the copolymerization of MDO in aqueous media and will drive innovations in the circular polymer economy.