MECHANISM OF RADIATION VULCANIZATION OF NATURAL-RUBBER LATEX SENSITIZED BY MONOACRYLATES

The mechanism of radiation vulcanization of natural rubber with 2-ethy l hexyl acrylate (2EHA) monomer was investigated using electron spin r esonance spectroscopy and nuclear magnetic resonance (NMR) spectroscop y. The primary radicals formed in the acrylate molecule were found to abstract the allylic hydrogens of the polyisoprene. Crosslinking may o ccur through the allylic radicals and/or main chain radicals formed on the polyacrylate. Acrylate was found to concentrate in the rigid regi ons of the crosslinked rubber indicating heterogeneity and a nonunifor m distribution of the acrylate in the latex particles. The addition of the acrylate and the irradiation seems to effect the Brownian motion of the latex particles. Both the viscosity and the NMR peak widths are effected by the irradiation. Addition of 5% 2EHA increases the crossl inking by a factor of 3.6. The thermal stability of the rubber first i ncreases with the dose in the presence of acrylate, but drops at highe r doses due to peroxide formation. (C) 1995 John Wiley and Sons, Inc.