E.s.r. of X-ray produced monomer radicals in esters of acrylic, methacrylic, crotonic and nonenoic acids

Abstract

Electron spin resonance was used to study the stable free radicals formed upon X-irradiation of monomer esters of the type RCHCR′—COOR″, where R and R′ can be either methyl or hydrogen. The esters investigated are n-octyl acrylate, decyl crotonate and lauryl methacrylate. Interaction between molecules of ester was blocked by preparing single crystals of ester (decane)+ urea inclusion compounds. Decane functioned as a spacer between ester molecules in the tubular cavities formed by the urea molecules. The urea and decane prevented the ester radicals from polymerizing, and made the identification of the monomer radicals possible. The crystals were X-irradiated at 77°K and their e.s.r. spectra recorded at room temperature. The stable free radicals observed in the environment of the ester (decane)+ urea inclusion lattice were of the hydrogen addition type RCH₂—ĊR′—COOR″. This type of radical was also observed under the same conditions in single crystals of methyl nonenoate + urea, where the long-chain alkyl groups prevent polymerization.