Solution properties of gas-phase-polymerized sodium acrylate microparticles. I. Influence of coinitiators
A partially neutralized sodium acrylate (NaAc) monomer was polymerized in the gas phase in the presence of ammonium peroxydisulfate [(NH4)2S2O8] as the primary initiator and zinc acetate (ZnAc) as the coinitiator. The effect of the coinitiator on the solution properties of the spray-polymerized product was investigated for the conversion percentage as a function of (1) the primary initiator (NH4)2S2O8 concentration, with the concentration (14.8% with respect to the monomer) of the coinitiator kept constant; (2) the coinitiator (ZnAc) concentration, with the primary initiator concentration (4% with respect to the monomer) kept constant; and (3) the reaction temperature. The viscosity of the product as a function of the coinitiator concentration was also investigated. The conversion percentage of gas-phase-polymerized NaAc increased by approximately 8% (i.e., from 91.6 to 99.3%) with an increasing (NH4)2S2O8 concentration (0.5-5% with respect to the monomer). The conversion percentage as a function of the coinitiator concentration (0-15% with respect to the monomer) increased by 25% (from 75 to 100%). When the concentrations of the initiators (NH4)2S2O8 and ZnAc were kept constant at 4 and 14.8% (with respect to the monomer), respectively, the conversion increased from 48 to 83% when the reaction temperature was increased from 100 to 140°C. The viscosity (at 20°C) of sodium polyacrylate decreased with an increasing coinitiator concentration. The relative rate of polymerization, as a function of the pH of the polymer, showed a minimum at pH ≈ 6 and subsequently increased steeply, reaching a plateau at pH ≈ 11; it then decreased again very sharply. © 2002 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 87.