Physico-chemical studies on acetaldehyde polymerization at high pressure and low temperature : II. The kinetics of the polymerization of acetaldehyde

Abstract

It has previously been reported that the high pressure polymerization of acetaldehyde with no catalyst at low temperature took place at the liquid-solid transition of acetaldehyde by pressure. In the present paper, the effects of reaction temperature and pressure on the polymerization rate of acetaldehyde have been studied. There is the limiting value on the yield of the polymer in the high pressure polymerization of acetaldehyde at each reaction temperature and pressure. The maximum yield is 27.4 weight per cent. The effect of impurity retarding the polymerization of acetaldehyde is remarkable. For example, when only 0.05 volume per cent of paraldehyde is added to acetaldehyde, the yield of the polymer decreases to only 2.8 per cent of the yield in case of no impurities. From the initial rate, the values of -6.2, -8.0 and -11.1ml/mole are obtained as the activation volumes at temperatures -78℃, -70℃ and -60℃, respectively. The apparent activation energies are negative values of -3.17～4.51kcal/mole. Those values increase with pressure. The effect of temperature on the activation volume and the effect of pressure on the activation entropy are satisfied with the equation (∂S/∂P)_T=-(∂V/∂T)_P. On the other hand, the effect of pressure on the initial rate depends mare strongly on the activation entropy than on the activation enthalpy. The intrinsic viscosity of the polymer is not affected by reaction time and has a constant value at each reaction temperature and pressure. The maximum degree of polymerization of the polymer is about 32, 000. The polymerization of acetaldehyde at high pressure proceeds by the catalytic action of the nucleus of crystal growth of the liquid-solid transition.