Synthesis Of Branched Polyacrylamides Using A Semi-bath RAFT Inverse Emulsion Polymerization

Polyacrylamides (PAMs) have been widely used in wastewater treatment, oil recovery, mineral processing, paper making and so on. As one of the most important polymeric flocculants, PAMs possess good flocculation performances at low dosages. Traditional PAM flocculants have high molecular weight, resulting in poor solubility, long dissolution time, and high solution viscosity. Moreover, cationic monomer units in cationic PAMs can’t be fully utilized owing to their random distribution in PAM chains. It is essential to develop novel PAMs for enhancing their efficiencies in applications. Branched cationic PAMs have highly potential to be a best candidate to meet the requirements.In this work, a semi-batch RAFT inverse emulsion copolymerization was developed for the first time to synthesize star PAMs, and star cationic PAMs with hyperbranched PAM cores and cationic arms. The cationic segments mainly located at the arm terminals. The branched PAMs were efficiently produced at a low usage of divinyl monomer using an "arm-first" approach in the semi-batch RAFT inverse emulsion copolymerization. It is innovative to tailor the star cationic PAMs with cationic chain segments at the arm ends, since high cationic density is of benefit to enhance adsorption of cationic segments with anionic particles for better flocculation. The main works include:(1) Stable branched polyacrylamide latexes were synthesized using the RAFT inverse emulsion polymerization of AM with a divinyl monomer BisAM. Star PAMs with hyperbranched cores were successfully produced via controlling the feeding of AM and BisAM. The influences of emulsifier composition and BisAM amount on the polymerizations were investigated. It shows that higher weight fractions of polymeric emulsifier Hypermer B246SF in the emulsifier systems favored in producing stable latexes. The semi-batch operation approaches offered better control on synthesis of star polyacrylamide latexes.(2) The star cationic PAMs having various arm lengths, hyperbranched polyacrylamide cores, and chain-end cationic compositions were synthesized via semi-batch RAFT inverse emulsion copolymerization of AM and2-(methacryloyloxy)ethyl]trimethylammonium chloride. Various AM feeding strategies and molar ratios of monomers to RAFT chain transfer agent were used to synthesize the star cationic PAMs. More arm numbers and higher terminal cationic density in the star cationic PAMs were found to benefit flocculation of TiO2particles.(3) The star cationic PAM possessed comparable or even superior flocculation efficiencies to4commercial linear cationic flocculants having higher cationic density and higher molecular weight.