Abstract:

Double water-phase polyacylamide(PAM) emulsion has been synthesized by dispersion polymerization of acrylamide(AM) in ethanol/water(90% volume fraction of ethanol) media with poly(vinyl pyrrolidone)(PVP) as the stabilizer, sodium bisulfite and ammonium persulfate as the initiator(I). Influences of polymerization temperature, mass fraction of initiator, AM and stabilizer on monomer conversion, reaction rate, polymer relative molecular mass and emulsion stability have been investigated. The results showed that as the AM mass fraction increased from 10% to 25%, the initial polymerization rate, final conversion of AM, and polymer relative molecular mass also increased. Among them, the initial polymerization rate was increased by 20 times. However, the use of too high monomer mass fraction could cause gelation because of high viscosity and fast reaction rate. With increasing the stabilizer PVP mass fraction, the initial reaction rate and the final conversion of AM decreased, and it was unsuitable for the double water-phase emulsion stability when the mass fraction of PVP was either too high or too low. Increaseof the polymerization temperature resulted in a significant increase of reaction rate and decrease of polymer relative molecular mass from 5.08×105 at 20 ℃ to 0.39×105 at 70 ℃. The monomer conversion increased and polymer relative molecular mass decreased from 4.31×105 to 3.73×105 as the initiator mass fraction was increased from 0.05% to 0.15%. The induction period appeared within about 20~25 min and the maximum rate was postponed until 60 min as the initiator mass fraction was 0.05%. A double waterphase PAM emulsion with the particle size distribution of 10~75 μm and average particle size of 21.94 μm was synthesized at 30 ℃ in 6 h when mass fraction of AM, initiator and PVP was 15%, 0.05% and 6%, respectively. The emulsion had poor stability because of its broad particle size distribution and large particle size. The relationship of polymerization rate at AM conversion 50% with the mass concentrations of the initiator, AM and stabilizer is as follows:rp=kρ0.33Iρ0.84AMρ-2.56PVP. The apparent activation energy of the dispersion polymerization is 40.95 kJ/mol.

Key words: polyacrylamide, double water-phase, dispersion polymerization, kinetics