Effect of 1,1-diphenylethylene on the radical polymerization of di-n-butyl itaconate in benzene

Effect of 1,1-diphenylethylene (DPE) on the polymerization of di-n-butyl itaconate (DBI) with dimethyl 2,2′-azobisisobutyrate (MAIB) was studied at 50°C and 60°C in benzene kinetically and by means of ESR. DPE in the low concentration range (up to 0.03 mol/l) was found to serve as a retarder in the polymerization at 50°C and 60°C. As a result, the polymerization rate and the molecular weight of resulting polymer decreased with increasing DPE concentration. The rate constant of the addition of poly(DBI) radical to DPE was estimated to be 74 l/mol s at 50°C and 97 l/mol s at 60°C, respectively, compared to 9.5 l/mol s at 50°C and 11 l/mol s at 60°C as propagation rate constant of DBI. ESR spectrum of the propagating polymer radicals was observed for the actual polymerization mixtures containing DBI, DPE and MAIB in benzene. ESR-determined apparent kp value decreases with increasing DPE concentration, while the apparent kt value increases with the DPE concentration. This is because the relative concentration of DBI-ended polymer radical to DPE-ended one decreases with increasing DPE concentration.