Method of preparing high molecular weight cationic polyacrylamide

This invention relates to a method to prepare cationic polyacrylamide with high molecular weight. Acrylamide and DAC are adopted as raw materials and aqueous copolymerization takes place in an oxygen-free initiating system with the existence of auxiliary reagents and nitrogen. The auxiliary reagents is one of urea, isopropanol, sodium formate, EDTA, dodecanethiol, OP-10 and polyether AD4074 and weighs 0.5~5% of monomers. The composite initiating system comprises oxidant, reductant, chain extender, and azo compounds, where the oxidant is persulphate weighing 0.001~0.15% of monomers, the reductant is organic amine weighing 0.01~0.20% of monomers, the chain extender weighs 0.01~0.20% of monomers and the azo compounds weigh 0.005~0.20% of monomers. In the end, instant product with high molecular weight and high cation proportion can be obtained.