Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. I. γ irradiation

Abstract

AbstractMutual irradiation of polyethylene (PE) in methyl acrylate vapor easily forms a poly(methyl acrylate) (PMA) homopolymer layer on the inner graft copolymer layer consisting of both PE and PMA components as a result of the rapidly increasing surface‐graft composition. This growth process of surface grafting has been found to provide some specific kinetic features different from those in other surface‐grafting systems. With formation of the surface homopolymer layer, low‐ and highdensity PE sheets give the same grafting rate, whereas both sheets give different rates in grafting stages or conditions in which the homopolymer layer is not formed. This result indicates that most monomers, penetrating across the surface, are entrapped or consumed in the surface homopolymer layer; accordingly the rate becomes independent of the type of PE sheets that have significantly different diffusion coefficients. The thickness of the inner graft copolymer layer, which is kept constant after homopolymer‐layer formation, increases with decreasing dose rate and with increasing monomer vapor pressure and temperature. This behavior can be qualitatively explained according to an equation for the initial steady‐state grafting depth.