Kinetic and electron spin resonance studies on radical polymerization of isopropenyl acetate

Abstract

An electron spin resonance (ESR) spectrum of the propagating radical in the photopolymerization of isopropenyl acetate (IpAc) in bulk at 32.5 °C was observed. The propagation rate constant ftp for the bulk polymerization of IpAc at 32.5 °C was determined to be 280 M*1 s"1 by ESR, comparable to that of methyl methacrylate (MMA). The cross propagation rate constants for the copolymerization of IpAc with MMA and with vinyl acetate (VAc) were estimated from ftp's for each monomer and the monomer reactivity ratios. The rate constants suggest that reactivities of IpAc and its propagating radical are large enough to give high-molecular-weight polymers in the homopolymerization. The chain-transfer constants to monomer (Cm's)for IpAc at three temperatures were determined by a Mayo plot to be 2 orders larger than that of VAc. The temperature dependence of Cm shows that the activation energy for the chain-transfer reaction is smaller than that for the propagation reaction, which was supported by ESR observation of allylic radical in the photoinitiated polymerization at -160 °C. The difficulty in preparing high-molecular-weight polymers from IpAc was concluded to be due to considerable chain-transfer reaction to monomer as compared with those of monomers which provide high-molecular-weight polymers. In addition, the temperature dependence of the ESR spectrum shows that the propagating radical has two stable conformations which rapidly interchange at room temperature.

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

“…17 It can be compared favorably with the spectrum of Figure 5(b), which was simulated with a doublet of doublets of quartets due to the unequal ␤-methylene proton and ␣-methyl protons, the hfc's of which are 1.5, 1.36, and 2.3 mT, respectively. As the temperature was lowered from 32.5 to Ϫ50°C, the 4 lines indicated by arrows in Figure 5 (2) a broadening of the 4 lines due to the interchange of COH bonds between the two conformations.…”

“…15,17 The temperature dependence of the ESR spectrum for MMA, nBMA, and tBMA in toluene was investigated from Ϫ30 to 90°C [ Fig. 8(a)].…”

“…17 In 1992, Yamada et al 18 reported well-resolved ESR spectra of propagating radicals of styrene and styrene derivatives with a conventional ESR spectrometer with the aid of computer accumulation. In 1995, highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed in a single scan with conventional ESR spectrometry without the aid of computer accumulation and/or a specially designed cavity and cell as long as optimum conditions were chosen for the initiator concentration and irradiation light intensity.…”

An Alkenyl Boronate as a Monomer for Radical Polymerizations: Boron as a Guide for Chain Growth and as a Replaceable Side Chain for Post‐Polymerization Transformation

“…In contrast to vinyl acetate,IPOAc barely polymerizes under standard radical-polymerization conditions,which was attributed to the aforementioned chain-transfer reaction to the a-methyl group. [9] Indeed, both DCT and chain growth are highly exothermic,w hich would explain the frequently observed side reactions during the polymerization of IPOAc.T his trend is comparable to that for MNon, atypical a-methyl-substituted alkene.However, MMA displays endothermic chain transfer and exothermic chain growth similar to IPBpin. Radical stabilization by the side chain is supported by the C À Hb ond dissociation energy for the methine group adjacent to each side chain ( Figure S29 in the Supporting Information).…”

Electron Spin Resonance Study of Stereospecific Polymerization of Vinyl Esters in Fluoroalcohols

“…7 The only study on the conformation ofpoly(vinyl ester) radicals in relation to a solvent or the bulkiness of a monomer has been done using isopropenyl acetate as the monomer. 8 …”