Kinetic and ESR studies on radical polymerization. ESR and kinetic evidences for the penultimate effect in the radical‐initiated copolymerization of N‐cyclohexylmaleimide and bis(2‐ethylhexyl) itaconate in benzene

Abstract

AbstractThe copolymerization of N‐cyclohexylmaleimide (1) (M1) and bis(2‐ethylhexyl) itaconate (2) (M2) with dimethyl 2,2′‐azoisobutyrate (3) as an initiator was carried out at 50°C in benzene. Monomer reactivity ratios were estimated as r1 = 0,34 and r2 = 0,38. The copolymerization rate (Rp) and the molecular weight of the resulting copolymer increased with increasing concentration of 1 when the total concentration of comonomers was fixed at 1,00 mol. L−1. Rp was proportional to [3]0,5, indicating a usual bimolecular termination in the copolymerization. An electron spin resonance (ESR) spectrum of the propagating polymer radicals was observable in the actual copolymerization system at 50°C. The spectrum of the copolymerization system is inexplicable in terms of any superposition of spectra observed in the corresponding homopolymerization systems, revealing that some penultimate monomeric unit causes a change in the ESR spectrum, that is, the structure of propagating polymer radical. The apparent rate constant of propagation (kp) and termination (kt) were estimated by ESR. The kp values (1,5–50 L · mol−1 · s−1) are fairly higher than those estimated on the basis of the terminal model, affording another piece of evidence for the penultimate effect. The kt value (1,8–5,4·103 L · mol−1 · s−1) shows a behaviour similar to that of the intrinsic viscosity of the resulting copolymer on varying the monomer feed composition, which seems to reflect diffusion‐control of termination reactions.