ESR Study of the Propagating Radicals of Diene Compounds in Frozen State. Conformations, Spin Densities, and Reactivities of the Propagating Radicals

Abstract

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

Functional Monomers and Polymers CLXVII. Asymmetric Inclusion Polymerization of 1-Alkyl-1,3-butadienes in Deoxycholic Acid and Apocholic Acid Canals by Long-Lived Propagating Radicals

“…11 The spectra consist of six or four lines with about 1.4 to 1.8 mT of hyperfine splitting constants, and are well assigned to allylic propagating radicals. 14 The spectrum of (III) (Figure l The apparent four line spectrum is considered due to the fact that hyperfine splittings with AH,, AHs, and AH• were smeared out because of the broad linewidth.…”

Kinetic Studies on the Radical Polymerization of Butadiene Derivatives

“…In order to understand separately the reactivity of the propagating radicals and monomers, the cross propagation rate constants (k 12 and k 21 ) were estimated from the kP values and r 1 or r 2 values. 18 The results are shown in Table IV. Monomer reactivity was estimated from k 12 values which are rate Polymer J., Vol.…”

“…Ms-1 T such as Q values, 18 ionization potentials, and half-wave potentials ( as an inhibitor. The polymerization in the presence of TEMPOL took place at the same rate after induction period as that in the absence of TEMPOL as shown in Figure 2(A).…”

“…Since the propagating radicals of dienes are stabilized through delocalization over three carbon atoms of their chain ends, 18 k 1 values of the dienes are considered to be smaller than those of vinyl compounds. The k 1 values of dienes except for AB seem to be a little smaller than those of vinyl monomers (Table III).…”

“…We previously performed an ESR study on the radical polymerization of dienes and found that the propagating radical ends are allylic radicals whose unpaired electron was completely delocalized over the three carbons of the chain ends. 18 A lot of papers have been published on the radical polymerization of butadiene 2 • 3 and monosubstituted butadienes. 4 -16 However, only a few data are available for the elementary rate constants for dienes.…”