Aqueous Two-phase Polymerization Of Acrylamide

Polyacrylamide (PAAm), an important water-soluble polymer, is widely used as a flocculant, paper-making additive and so on in industry. The concept of aqueous two-phase system was presented in the 1950s, which has been applied in the field of the separation of biomacromolecules. The techniques of aqueous two-phase separation were mature. However, the studies about the combination of the preparation of water-soluble polymers and aqueous two-phase techniques are still few. In this thesis, the concepts of aqueous two-phase polymerization and a new polymerization method for water-soluble polymer are presented.Aqueous two-phase polymerization is that the water-soluble monomers, initiator and another water-soluble polymer are dissolved to form a homogeneous aqueous solution, then polymerize to form a heterogeneous polymer dispersion aqueous solution, two polymers enriched in dispersed and continuous phase respectively. It may be used to prepare the water-soluble (co)polymer with higher molecular weight which can be directly diluted to use. It overcomes the problems of mixing and heat transfer of polymerization system. Aqueous two-phase polymerization is performed in water without using any organic solvent. It also overcomes the pollution and recycle problems of organic solvent for inverse phase suspension polymerization, water-in-oil inverse phase emulsion polymerization and precipitation polymerization. It's a new polymerization method for preparing the water soluble (co)polymer.Polyethylene glycol (PEG) aqueous solution was selected as the dispersed medium of the aqueous two-phase polymerization for acrylamide based on the hydrophobic interaction among water-soluble polymers, the viscosity of polymer aqueous solution and the stability of the polymerization system. The interactions between PAAm and PEG were measured using FTIR and DSC. The phase diagrams of PAAm-PEG-water aqueous two-phase system were obtained by GPC and turbidity titration. The effects of PAAm and PEG concentration and temperature on the partition coefficient of AAm were studied.According to the morphology and droplet size and distribution of dispersed droplet, the mechanisms of the formation and stability of droplets were presented. Three facts promotedthe droplets of PAAm aqueous solution to disperse in the PEG aqueous solution phase, which include the high viscosity in the droplet, the viscosity of continuous phase and charged surface due to the ionic sulfate end group in polymers prepared with S₂O₈²- as the initiator. The results of the partition coefficient of the AAm during the polymerization showed the polymerization took place in the two phases at the same time.The kinetics of aqueous two-phase polymerization for acrylamide was also studied. For the system initiated by ammonium persulfate (APS), the effects of APS, monomer, PEG concentration, the types of dispersed medium, emulsifiers with various HLB value and polymerization temperature on the polymerization rate, monomer conversion and polymer molecular weight were studied. For the polymerization initiated by APS/ triethanal amine (TEA) redox initiator, the effects of polymerization temperature, APS and TEA concentration on the kinetics were also studied.Keeping low viscosity of the polymerization system during the aqueous two-phase polymerization of acrylamide, it's an important advantage to other polymerization methods. The effects of dispersed medium concentration, monomer concentration, initiator concentration, emulsifier concentration, polymerization and ambient temperature on the viscosity of the final products were studied in the last chapter.