Electron beam induced structural modification of a fluorocarbon elastomer in the presence of polyfunctional monomers

The influence of polyfunctional monomers-tripropyleneglycol diacrylate (TPGDA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA), tetramethylolmethane tetracrylate (TMMT) and triallyl cyanurate (TAC)-on the structural changes of fluorocarbon terpolymer (F content 68%, H 1.4%) in the presence of an electron beam has been investigated with the help of IR spectroscopy (in the ATR mode) and sol-gel analysis. The absorbances at 1397, 1021, 672 and 504 cm(-1), due to the C-F group, decrease on irradiation of the mixtures of fluoroelastomer and TMPTA, indicating dehydrofluorination and scission. The concentration of the double bond decreases both in the polyfunctional monomer and its blends with the polymer as a result of grafting and crosslinking. The concentration of the carbonyl group increases with radiation dose in the fluoroelastomer due to aerial oxidation. The effect of trimethylolpropane triacrylate (TMPTA) is to lower the amount of oxidation, especially at relatively higher levels. At a particular radiation dose, the behaviours of TPGDA, TMPTMA, TMMT and TAC based systems are similar to that of the TMPTA based one. The gel content increases with radiation dose. The influence of polyfunctional monomer on gel fraction is more prominent at higher concentrations, where distinct changes are observed at lower doses. At a particular level of multifunctional monomer, the gel fraction is lower for systems based on TPGDA. The ratio of chain scission to crosslinks calculated using the Charlesby-Pinner equation indicates a much higher crosslinking efficiency with poly functional monomer-fluorocarbon rubber matrix as compared to the control rubber. (C) 1998 Elsevier Science Ltd. All rights reserved.