Enhanced Activity of ATRP Fe Catalysts with Phosphines Containing Electron Donating Groups

Fe-based atom transfer radical polymerization (ATRP) of styrene (St) with various triarylphosphines containing electron donating methoxy groups was investigated. (FeBr3)-Br-III in the presence of tris(2,4,6- trimethoxyphenyl)phosphine (TTMPP) provided faster ATRP of St than in the presence of tris(4-methoxyphenyl)phosphine (TMPP) and much faster than with triphenylphosphine (TPP) under identical conditions. ATRP of St was carried out with initial ratio of reagents: [St]:[EBiB]:[(FeBr3)-Br-III]:[TTMPP] = 200:1:1:2, in 50% (v/v) anisole at 100 degrees C (EBiB is ethyl 2-bromoisobutyrate). After 21 h, conversion reached 92%, yielding polystyrene with molecular weight M-n = 24 100 and M-w/M-n = 1.25. With TMPP and TPP under the same conditions, the conversion of monomer was only 19% and 9%, respectively. With 1 equiv of TTMPP vs (FeBr3)-Br-III, control was better, M-w/M-n similar to 1.1, but polymerization was slower. The phosphines could directly reduce Fe to Feu but could also act as ligands complexing transition metal and forming efficient ATRP catalysts.