Stability of two-phase polymerization of acrylamide in aqueous poly(ethylene glycol) solution

A poly(acrylamide) (PAM) aqueous dispersion with high solid was successfully synthesized through two-phase polymerization of acrylamide (AM) in aqueous poly(ethylene glycol) (PEG) solution. To prepare stable PAM aqueous dispersion, the effects of initiator, monomer and PEG concentration on the stability of the aqueous two-phase polymerization system were investigated in detail. Dynamic light scattering (DLS) was applied to study the evolution of the size and size distribution of the aqueous PAM droplet in the initial stage of polymerization. A droplet aggregation period was found in the initial stage, in which the PAM coagulum is easy to be generated below the conversion of about 5% due to high polymerization rate. By analyzing the effects of PEG on the stability of this polymerization system, it was found that PEG plays both precipitant and stabilizer role. When PEG concentration ranges from 12 to 24%, increasing its use would promote the droplet stabilization; however, when PEG concentration exceeds 28%, increasing its use may accelerate the droplet formation which does not further favor the droplet stabilization. Furthermore, the viscosity evolution during the polymerization under various reaction conditions was determined by rotational viscometer on line. When monomer concentration exceeded 8%, increasing the initiator or monomer concentration would result in that the polymer produced in the continuous phase could not be separated in time due to the high viscosity. All these results demonstrated that the slower the polymerization rate is, the more stable PAM aqueous dispersion will be.