SET-LRP of NIPAM in water via in situ reduction of Cu(ii) to Cu(0) with NaBH4

Abstract

The direct and quantitative reduction of the air-stable Cu(II)Br₂/Me₆TREN to Cu(0) by NaBH₄ represents a new method for the aqueous single electron transfer-living radical polymerization (SET-LRP) of water soluble polymers. By changing the stoichiometry of NaBH₄ to Cu(II)Br₂, any desired ratio of Cu(II)Br₂ to Cu(0) could be obtained with no evidence of Cu(I) species. This quantitative reduction to Cu(0) in combination with rapid disproportionation of Cu(I)Br/Me₆TREN in water resulted in activation by Cu(0) initially and during the polymerization. Polymerizations of NIPAM produced polymer within minutes and with controlled and narrow molecular weight distributions in agreement with ideal ‘living’ radical behavior. The direct in situ thio-bromo ‘click’ reaction produce polymers with stable chain-end functionality, eliminating the concern of hydrolysis of the halide end-group (i.e. Br). It was found that the end-group functionality was greater than 95%, and for the very rapid polymerizations close to 100%.