Solvent‐free generation of poly(vinyl acetals) directly from poly(vinyl acetate)

Abstract

AbstractThe simultaneous methanolysis and butryalization of poly(vinyl acetate) was conducted via the reaction of methanol and butyraldehyde with polyvinyl acetate under batch conditions at temperatures from 70°C to 90°C at the vapor pressure of the reactants. It was found that use of an acid catalyst allowed for the methanolysis to be the rate limiting step of a simultaneous methanolysis‐butyralization reaction, minimizing the buildup of alcohol repeat units in the polymer during the reaction. As such, use of an excess of aldehyde was counterproductive in that it served to dilute both the methanol and the acetate groups in the polymer phase, lowering the overall rate of the reaction. With 20% stoichiometric excesses of methanol and butyraldehyde, it was possible to produce poly(vinyl butyral) directly from poly(vinyl acetate) with very low residual acetate and overall conversions equivalent to commerical samples. Further, carbon dioxide was evaluated as a reversible plasticizer for polyvinyl acetate during methanolysis. Results at various pressures were consistent with the expectation that the presence of CO2 would lower the reaction rate, primarily because of dilution of reactants in the CO2‐swollen polymer phase. Finally, it was shown that the simultaneous reaction procedure can be used to generate polyvinyl acetals from a variety of aldehydes.