Urotropine as a highly effective and versatile promoter for atom transfer radical polymerization

Abstract

Atom transfer radical polymerization (ATRP) is a transition metal complex-catalyzed controlled/‘living’ radical process. Recently, there has been a lot of interest focused on decreasing the catalyst loading and reducing the cost of post-polymerization purification for ATRP. In this work, urotropine was found to significantly enhance the ATRP of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St) catalyzed by CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) and CuBr/tris(2-(dimethylamino)ethylamine) (Me6TREN). With the addition of 25 times the amount of urotropine relative to CuBr, well-controlled polymerizations of MA, MMA and St were obtained at catalyst-to-initiator ratios of 0.01, 0.05 and 0.05, respectively, producing the corresponding polymers with molecular weights close to theoretical values and low polydispersities. The catalyst concentration could even be reduced to ppm level at a catalyst-to-initiator ratio as low as 0.001 in the polymerization of MA. These results indicate that urotropine is a very effective and versatile promoter for both CuBr/PMDETA and CuBr/Me6TREN. In the presence of urotropine, the catalyst loading could be reduced by as much as 1000 times. As PMDETA is one of the cheapest ATRP ligands, the combination of urotropine with CuBr/PMDETA could substantially reduce the catalyst loading and the cost of post-polymerization purification at the industrial scale and thus is promising for potential industrial applications. © 2014 Society of Chemical Industry