Synthesis of star cationic polyacrylamides using the copolymerization of semi-bath reversible addition-fragmentation chain transfer (RAFT) inverse emulsion

An "arm-first" semi-batch RAFT inverse emulsion copolymerization of acrylamide (AM), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC), and N, N'-methylenebisacrylamide (BisAM) was developed for the first time to synthesize the star cationic polyacrylamides (sCPAM) with cationic chain segments concentrating at the arm ends of the hyperbranched polyacrylamide (PAM) cores. The sCPAMs having various arm lengths, hyperbranched PAM cores, and chain-end cationic segment compositions were synthesized via controlling the AM and BisAM feeding and the molar ratio of AM to RAFT chain transfer agent. The sCPAMs having the number of arms between 2.5 and 6.9 and up to 92.9%(wt) of star structures were successfully produced at a low usage of BisAM with the molar ratios of BisAM to AM and DMC of 2~5 to 1600. The flocculation test with TiO2 particles shows that the sCPAMs comprising larger fraction of star polymer and having high terminal cationic monomer density possess better flocculation performance. The performance of the sCPAM sample was superior to that of the commercial linear cationic PAM sample C535M which has higher cationic density and higher molecular weight.