Effect of pressure on the precipitation and sol‐phase aqueous polymerization of methyl methacrylate

摘要

AbstractEffect of pressure (atmospheric to 120 kg/cm2) on the K2S2O8–Na2S2O4‐initiated aqueous polymerization of methyl methacrylate has been studied at 25°C. When the concentrations of the redox initiator are so adjusted as to obtain the separating polymer phase as a coarse coagulum, the conversion, rate, and molecular weight of polymerization tend to rise initially with increase of pressure up to a certain value and fall subsequently to a limiting value. However, these parameters fall monotonously with an increase in pressure when the polymer phase separates out as a fine colloid at a lower concentration of the initiator. The initial rise in rate is consistent with an increase inkpand or a decrease inktunder high pressure; the ultimate fall in rate may be due to a decrease in the diffusion of monomer from the aqueous phase to the growing polymer radical site. The fall in the molecular weight with pressure is explained on the basis of enhanced monomer transfer. In the colloidal range the pressure dependence trend is related to the stability of the colloidal phase. The rate is proportional to the square root of the product of K2S2O8–Na2S2O4and varies linearly as the first power of the monomer concentration as also observed under normal pressure conditions. The MWD values of the polymers are ca. 2.5 and do not change with applied pr