Kinetic and ESR studies on radical polymerization. Radical polymerization of diisopropyl itaconate

Abstract

The polymerization of diisopropyl itaconate (DIPI) initiated with dimethyl 2,2′-azobisisobutyrate(MAIB) was investigated kinetically in benzene. The polymerization rate ( R p) was expressed by R p = k[MAIB] 0.46[DIPI] 1.6 at 50°. The overall activation energy of the polymerization was calculated to be a low value of 60.2 kJ/mol. Rate constants of propagation ( k p) and termination ( k 1) were estimated different polymerization conditions, using the ESR-determined concentrations of the propagating polymer radical. The k p value (2.4–2.9 1/mol · sec) at 50° shows a little increase with monomer concentration. The k 1 value (1.8–4.9 × 10 4 1/mol · sec) was fairly dependent on the chain-length of the propagating polymer radical, which is mainly responsible for the high dependence of R p on the monomer concentration. Activation energies of initiation ( E i), propagation ( E p) and termination ( E t) were also determined; E i = 129.1 kJ/mol, E p = 28.5 kJ/mol, E t, = 66.1 kJ/mol. The large apparent activation energy of termination is a main origin of the low overall activation energy of the polymerization. Copolymerization of DIPI ( M 1) with St ( M 2) was also examined at 50° in benzene. The following copolymerization parameters were obtained according to the Kelen-Tüdős method; r 1 = 0.11, r 2 = 0.56, Q = 0.47, e = + 0.87. Using the above results, the rate constants of cross-propagations in the copolymerization were estimated.