Polymerization of sodium acrylate in inverse-suspension stabilized by sorbitan fatty esters

This paper is devoted the synthesis of poly(sodium acrylate) by an inverse-suspension polymerization technique. Ammonium persulfate, ethylcellulose and toluene were used as initiator, suspending agent, and continuous organic phase, respectively. Two surfactants, sorbitan monooleate (SMO) and sorbitan monostearate, were used as the suspension stabilizers. The effect of the initiator concentration as well as the type and concentration of the surfactant on the polymer molecular weight and solution viscosity was investigated. Participation of the unsaturated surfactant (SMO) in the free radical polymerization was recognized to be the main reason of enhancement of the average molecular weight and viscosity of the products. A similar effect was observed when the polymerization reactions were run in the presence of air. In the latter conditions, however, an inhibition effect of atmospheric oxygen resulted in substantially decreased solution viscosity. Meanwhile, it was found that higher polymers were obtained when the as-synthesized beads were dewatered and hardened in methanol rather than in acetone.