Synthesis and Characterization of Hyperbranched Polyacrylamide Using Semi-Batch RAFT Copolymerization of Acrylamide and N,N'-Methylenebisacrylamide

Abstract Highly branched acrylamido polymers have been widely used in drug delivery systems, catalyst supports, viscosity modifiers, biomedicines, etc. In this work, hyperbranched polyacrylamides (b-PAMs) were prepared via a semi-batch reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide (AM) using N,N’-methylenebisacrylamide (BisAM) as branching agent (BA) and 3-benzyltrithiocarbonyl propionic acid (BCPA) as chain transfer agent (CTA). Water soluble b-PAMs were successfully produced at low [BCPA]/[BisAM] ratios of 1/20 ~ 1/50 in comparison with gel formation in RAFT batch copolymerization of AM and BisAM at the same condition, indicating the crosslinking reaction of BisAM was effectively suppressed at low BCPA concentration using the semi-batch technique.

A systematic kinetic study on the semi-batch RAFT copolymerization of AM with BisAM was conducted. Effect of [BCPA]/[BisAM] ratios and feeding rates on the evolution of molecular weight (MW) and distribution (PDI), branching density (BD), and cyclization density (CD) in the polymerization were investigated. It was observed that the b-PAM samples collected at different time during the RAFT copolymerization had similar BD, suggesting that the b-PAMs prepared via the semi-batch RAFT copolymerization technique having homogeneous branching structure. High BisAM feeding rate or BisAM usage benefitted to branching formation. The cyclization reaction was suppressed at low instantaneous BisAM concentration in the copolymerization system.