Semibatch RAFT polymerization for branched polyacrylamide production: Effect of divinyl monomer feeding policies

Star and hyperbranched polyacrylamides (s‐PAMs and b‐PAMs) were synthesized via semibatch RAFT copolymerization of acrylamide (AM) and N,N′‐methylenebisacrylamide (BisAM) using four monomer feeding policies. The BisAM to chain transfer agent (CTA) ratios from 1 to 40 at a constant [AM] 0 /[CTA] 0 of 600 were investigated at 60°C. The s‐PAMs with the number of arms of 1.4–12.8 and 1.8–8.4 were, respectively, produced by arm‐first (AF) and core‐first (CF) approaches, whereas the b‐PAMs having the branching density of 1.34–13.1C/1000Cs were synthesized by constant BisAM feeding (semibatch polymerization, SB) and batch (batch polymerization, BA). Soluble b‐PAMs were produced with the four feeding policies at [BisAM] 0 /[CTA] 0 of 5. However, when the [BisAM] 0 /[CTA] 0 was increased to 30, the gelation occurred with the CF and BA approaches while the AF and SB synthesized soluble branched PAMs. The AF and SB approaches appeared to be practical in producing the respective s‐PAM and b‐PAM at high [BisAM] 0 /[CTA] 0 ratios or low CTA usages. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1322–1333, 2013