Studies of the synthesis and characterisation of some polyacrylamides

Polyacrylamides have been synthesised by a solution polymerisation process using water as the solvent. The radical polymerisation performed under a nitrogen blanket was initiated by the thermal decomposition of potassium persulphate. The influence of monomer and initiator concentrations, temperature and reaction time on the polymerisation conversion of monomer into polymer and on polymer molecular weight has been investigated. Average molecular weights of the polymers were determined by solution viscometry and membrane osmometry. A procedure for obtaining reproducible viscosity data.has been developed using the Ubbelohde capillary type viscometer. Because of a degassing problem with water as a solvent and membrane breakdown with formamide as a solvent, it was found that reliable osmotic pressure results were only obtained with difficulty for polymers dissolved in formamide/water (1:3) mixtures. Polyacrylamide samples have been separated by analytical gel permeation chromatography with silica packings. Various modified silicas and several eluents were investigated with the aim of reducing the adsorption of polyacrylamide onto the chromatographic packing. Studies were performed with physically coated phases such as polyethylene oxides, Aerosol OT, with chemically bonded phases such as hexamethyldisilazane and n-propylamine, and with eluents such as distilled water, formamide/water (1:5), 1% 880 and ammonia/formamide. Experimental results have shown that satisfactory separations of polyacrylamide dependent solely on a permeation mechanism were only obtained with a porous silica having a covalently bonded aminopropyl phase at the pore surfaces and with a mixed eluent of formamide/ water (1:5). This GPC system was calibrated with polyacrylamide fractions prepared by fractional precipitation. Molecular weight distributions were determined from the chromatogram for a fraction and a whole polymer. The distribution for the unfractionated polyacrylamide was in reasonable agreement with distributions predicted from the mechanism of polymerisation.