Tailored rheology of a metallocene polyolefin through silane crafting and subsequent silane crosslinking

Polymer modification through silane grafting and its subsequent crosslinkin g allows the rheological properties of a polymer to be tuned from those of a viscous melt to those of a crosslinked elastic network. In this study, a metallocene polyolefin resin is grafted with vinyl trimethoxy silane (VTMS) using dicumyl peroxide (DCP) as the initiator and is subsequently crosslin ked in an oxidative environment. Dynamic rheological experiments are conduc ted to elucidate the effects of DCP and VTMS concentrations on the grafting and ensuing crosslinking processes. We find that the addition of VTMS alon e to the polymer produces no grafting. In contrast;, the presence of DCP by itself leads to direct crosslinking between polymer chains as suggested by an increase in elastic modulus and complex viscosity. Samples containing b oth DCP and VTMS undergo silane grafting, with the extent of grafting incre asing with increasing DCP concentration. This conclusion is borne out by bo th rheological and Fourier transform infrared measurements. The grafted sam ples undergo silane crosslinking only in an oxidative environment and at te mperatures equal to or greater than 190 degrees C. During crosslinking, the samples undergo a transition from a viscous melt with frequency-dependent moduli to a gel exhibiting frequency-independent moduli with the elastic mo dulus exceeding the viscous modulus. However, the kinetics of crosslinking and the extent of the modulus increase are a function of the DCP concentrat ion, with both exhibiting a maximum at a specific DCP and VTMS combination. (C) 2000 John Wiley & Sons, Inc.