Preparation Of Anionic Polyacrylamide By Aqueous Two-phase Polymerization

Anionic polyacrylamide dispersed in an aqueous solution was successfully prepared through aqueous two-phase copolymerization of acrylamide (AM) using 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride as initiator. The effect of various parameters like comonomers, salting-out agent and stabilizer on the aqueous two-phase copolymerization was studied. Research was made later on the copolymerization AM/AA/C with the stabilizer poly(acrylic acid sodium) (PAANa) in ammonium sulfate (AS) solution. The effect of monomer concentration, AA/AM ratio, salt concentration and stabilizer concentration on the critical conversion, critical molecular weight and droplet morphologies at phase separation was studied. After the study on the composition of the copolymer chain and droplet granularity, the droplet forming mechanism of aqueous two-phase copolymerization was presented.Research on the Q-e value and reactivity ratio of the monomers and found that introducing the third monomer C as hydrophobic monomer smoothed the reaction. AS was selected as the salting-out agent because of its strong effect with water molecule, and as the amount of AS increased, the reaction speed was enhanced. PAANa was selected as the stabilizer and its amount had minor effect on the reaction speed.By using the spectrophotometer, the phase separation point was determined on-line where the transparence of reaction solution declined suddenly. The effect of various parameters on the critical conversion, critical molecular weight and droplet morphologies after phase separation was measured by bromating method, gel permeation chromatography and optical microscope, respectively. The experimental results showed that the addition of C could decrease the hydrophilicity of the polymer chain, which in accordance made the critical conversion, critical molecular weight and droplet morphologies of phase separation decrease. As the amount of total concentration of AM and AA increased, the critical conversion of phase separation decreased while the critical molecular weight and droplet morphologies of phase separation increased. The salt concentration and the stabilizer concentration had similar effect on the critical conversion and droplet morphologies of phase separation, but different effect on the critical molecular weight of phase separation. In addition, the increase of temperature was unfavorable for phase separation.By using the gas chromatography, the exact monomer residues were detected and the structure of the copolymer chain was determined. The AM and C segments were the main part of the copolymer chain at the initial stage, later AM grew mainly into the copolymer chain, and the AA and AM segments were the main part of the copolymer chain at the last stage. The droplet appearance and growth in the initial stage of the AM/AA/C aqueous two-phase polymerization was detected by dynamic light scattering (DLS). Results showed that the polymer droplet aggregates with each other at the initial stage. Therefore, the droplet size distribution became wide at first, and then turned to narrow again as the polymerization proceeds. The droplet forming mechanism on the aqueous two-phase copolymerization of AM/AA/C with the stabilizer PAANa in AS solution was presented. The negative charge of the AA segment was considered as a significant factor in the stabilization of the aqueous two-phase system.