Rate enhancement in controlled radical polymerization of acrylates using recyclable heterogeneous Lewis acid

The rate enhancement in nitroxide-mediated polymerization (NMP) and reversible addition-fragmentation transfer (RAFT) polymerizations in the presence of catalytic amount of solid acidic alumina as Lewis acid was investigated. The Lewis acid coordinated the ester carbonyl group of the acrylate monomer and reduces the electron density in the conjugated carbon-carbon double bond thereby increasing the reactivity of the radical generated. A significant deviation from linearity was observed at longer reaction times and the polydispersity (PDI) of the resultant polymers was high. The sample of alumina was used for successive n-butyl acrylate homopolymerizations. It was observed that the polymerization rate increased with increasing amount of added alumina. It was also observed that the addition of insoluble acidic alumina to controlled radical NMP and RAFT polymerizations of acrylate monomers results in significantly higher reaction rates and conversions.