Synthesis and Characterization of High Molecular Weight Polyacrylamide Nanoparticles by Inverse-emulsion Polymerization

Polyacrylamide (PAM) and its copolymers are of important polymeric materials in petroleum industry, for example in drilling fluids and enhanced oil recovery. High molecular weights of these polymers are needed to have optimum efficiency in the above given applications. High molecular weight polyacrylamide nanoparticles were prepared by inverse-emulsion polymerization of aqueous acrylamide solution in xylene as a continuous phase under various conditions in the presence of a mixture of non-ionic emulsifiers (Tween 85 and Span 80). Monomer conversion, particle size and its distribution in the final emulsion and molecular weight of the polymer product were analyzed appropriately by gravimetry, dynamic light scattering (DLS) and capillary viscometry techniques. The effect of variables such as stirrer speed, temperature, initiator concentration and type, emulsifier concentration and hydrophilic-lipophilic balance (HLB) value of the emulsifier system on the viscosity-average molecular weight, particle size and its distribution and reaction kinetics were investigated. Depending on the reaction conditions, PAM particles with average particle sizes generally smaller than 200 nm in diameter and particle size distribution in the range of 50-400 nm and viscosity-average molecular weights as high as 8×106 g.mol^-1 were obtained.