Synthesis of well-defined polyacrylonitrile by ICAR ATRP with low concentrations of catalyst

Acrylonitrile (AN) was polymerized by initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP). The effect of the ligand, tris(2-pyridylmethyl)amine (TPMA) and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), in the Cu-based catalyst, the amount of catalyst, several alkyl halide initiators, targeted degree of polymerization, and amount of azobisisobutyronitrile (AIBN) added were studied. It was determined that the best conditions utilized 50 ppm of CuBr₂/TPMA as the catalyst and 2-bromopropionitrile (BPN) as the initiator. This combination resulted in 46% conversion in 10 h and polyacrylonitrile (PAN) with the narrowest molecular weight distribution (M_w/M_n = 1.11-1.21). Excellent control was maintained after lowering the catalyst loading to 10 ppm, with 56% conversion in 10 h, experimental molecular weight closely matching the theoretical value, and low dispersity (M_w/M_n < 1.30). Catalyst loadings as low as 1 ppm still provided well-controlled polymerizations of AN by ICAR ATRP, with 65% conversion in 10 h and PAN with relatively low dispersity (M_w/M_n = 1.41). High chain end functionality (CEF) was confirmed via ¹H NMR analysis, for short PAN chains, and via clean chain extensions with n-butyl acrylate (BA).