Studies on the bulk polymerization of aliphatic aldehydes under high pressure

Abstract

The bulk polymerization of propionaldehyde was studied at temperatures of 10-35℃ as a function of pressure. The resulting polymer was amorphous and had a polyacetal structure which depolymerized to the original monomer under normal conditions. The ceiling temperature far the bulk polymerization was determined by extrapolating the yields under various reaction conditions to zero yield (weight measuring method) and also by measuring the temperature rise due to the heat of polymerization (thermal method). The thermal method could follow the polymerization more sensitively than the weight measuring method. The thermodynamic quantities of polymerization were determined by the volume change of the polymerization and the pressure coefficient of the ceiling temperature. The volume change was obtained by measuring. the molar volumes of the polymer and the monomer at 25℃ up to 4000kg/cm^2. At 25℃ and 6400kg/cm^2, the heat of polymerizotion is -4.7 kcal/mol, and the entropy change is -16e.u. The effect of alkyl groups on the bulk polymerization of aliphatic aldehydes is discussed by comparing the present result with the previous ones on butyraldehyde and isobutyraldehyde. The effect of pressure on the ceiling temperature of monomers with poor polymerizability is also discussed in comparison with that on the melting point of some compounds.