Semicontinuous microemulsion copolymerization of vinyl acetate and butyl acrylate: high solid content and effect of monomer addition rate

Vinyl acetate and butyl acrylate were copolymerized in microemulsion under monomer-starved conditions by a semicontinuous process using different monomer addition rates (Ra). A mixture of sodium dodecyl sulfate and polyethylene glycol dodecyl ether (Brij®35) were used as surfactants. Potassium persulfate was the initiator. High copolymer content latexes (around 40 wt.%), average particle diameters (Dp) < 50 nm and polymer-to-surfactant ratios (12 to 14, weight/weight) were obtained with weight average molar masses (Mw) between 180,000 and 760,000. Dp and Mw of the copolymers decrease as Ra is decreased. As Ra increases, a shoulder in the molar mass distribution was observed at high values of Mw, which was ascribed to chain transfer to polymer. Homogeneous copolymer compositions were observed throughout the reaction, which cannot be obtained by the usual batch process.