The capability of three chain-transfer agents, O-alkyl-S-(1-ethoxycarbonyl)ethyl xanthates (CH3CHCO2C2H5)S(CS)OZ′, to control the free-radical polymerization of styrene and ethyl acrylate by the MADIX process was examined. The reactivity of the xanthates varied according to the following trend: Z′ CH2CH3 < CH2CF3 < CH[P(O)(OEt)2]CF3. This change in reactivity allowed a lowering of the polydispersity index from 2.0 for Z′ CH2CH3 to 1.15 for Z′ CH[P(O)(OEt)2]CF3 in the case of the polymerization of styrene.
Evolution of Mw/Mn with conversion during the polymerization of ethyl acrylate in the presence of xanthates X1, X2 and X3. Reaction conditions: [EA]0 = 4.6 M, [X]0 = 5.75 × 10−2M, [AIBN]0 = 1.72 × 10−3M ; T = 80 °C ; solvent: toluene.