An ESR study on the radical polymerization of diene compounds was carried out in frozen aromatic solvents, using benzoyl peroxide as a photoinitiator. The diene compounds were CH2 =CHX-CH=CHY (X=OCH3 and Y=COOCH2CH3, X=CH3 and Y=COOCH2CH3, X= H and Y = COOCH2CH3 , and X= H and Y = OCOCH3). Spectra were observed at-l20°C. The hyperfine splitting constants show that the propagating radical ends are allylic radicals whose unpaired electrons were completely delocalized over the three carbons of their chain ends. The conformation and spin density of the radical ends were estimated from the hyperfine splitting constants of methylene protons adjacent to the radicals and ()(-protons. The conformations could be explained by a single conformation. The reactivity of the propagating radicals was estimated from the propagation rate constants for radical polymerizations and reactivity ratios in the copolymerizations with styrene. The relation between the spin density and reactivity of the propagating radicals is discussed. KEY WORDS ESR I Ethyl 4-Ethoxy-2,4-pentadienoate I Ethyl 4-Methyl-2,4-pentadienoate I Ethyl 2,4-Pentadienoate I 1-Acetoxybutadiene I

A kinetic study on the radical polymerization of diene compounds was carried out at 25±0.00loC. The diene compounds were ethyl pentadienoate and its derivatives CH2 =CX-CH=CHCOOCH 2 CH 3 (EP:X=H, EMP:X=CH 3 , and EEP:X=OCH3), and 1acetoxybutadiene (AB). Elementary rate constants of these diene compounds were determined by the rotating sector method; the values of kP and k, for EP, EMP, EEP, and AB were 30.9 and 1.9x 10 7 , 29.7 and 2.3x 10 7 , 9.9 and 0.93x 10 7 , and 18.0 and 28.1 x 10 7 M-1 s-1 , respectively. These kP values are lower than those reported for styrene, MMA, methyl acrylate, and vinyl acetate. Cross-propagation rate constants (k 12 and k 21) were estimated from the kP values and monomer reactivity ratios in the copolymerizations of these dienes (M2) with styrene (M.). Reactivity of the monomers and the propagating radicals was compared with vinyl compounds and other dienes by using k 12 and k21 , respectively. Lower kP values of these dienes are primarily ascribed to the fact that the decrease in the reactivity of the propagating radical is larger than the increase in that of monomer. Change in radical reactivity among dienes is larger than that in their monomer reactivity. Effects of the resonance stabilization of the propagating radicals on k, were not clearly evident in these radical polymerizations which are discussed oh the basis of the preexponential factor.