Kinetic Study of Atom Transfer Radical Polymerization of Methyl Acrylate with Polyvinyl Acetate Macroinitiator
In atom transfer radical polymerization (ATRP) of methyl acrylate (MA) with polyvinyl acetate macroinitiator in bulk at 90°C the plots of Ln [M]0/[M] increased linearly with reaction time. The apparent propagation rate constant (kp app) of the reaction was obtained from the linear curve and used to calculate the free macroradical concentration ([R°]) in polymerization medium. The [R°] and also kp app values decreased with concentration of CuCl2 (deactivator). The slope and extrapolation values of the linear curve of (kp app)-1 versus CuCl2 concentrations and kinetic equations were used to calculate ka and kd/ki constants to be 2.576×10-4 M-1.s-1 and 222. The Mn values of block copolymers obtained by GPC were nearly in agreement with the theoretical values and increased linearly with conversion. Furthermore, PDI decreased with conversion due to the controlled/living behavior of the ATRP with PVAc macroinitiator. The kp app and [R°] values increased with catalyst and macroinitiator concentrations and also decreased with monomer concentration. The polymerization medium undergone termination reactions were attributed to increases of the macroradical concentration. The ratio of kt/Keq = 4.313×1020 was also calculated on the basis of Fischer equation. Furthermore, the Mn values of the block copolymers decreased with free macroradical concentration and the PDI values were also broadened due to termination reaction.
کلیدواژه ها [English]
kinetic constants, atom transfer radicalpolymerization, block copolymers, molecular weight, macroinitiator