Structural comparison of products from peroxide-initiated grafting of vinylsilane and silane-functionalized nitroxyl to hydrocarbon and polyolefin substrates

摘要

It has been demonstrated that peroxide-initiated grafting of vinylsilanes to polyethylene results in a nonuniform distribution of silane groups on the polymer chain due to a chain-transfer mechanism, leading to inefficient utilization of silane with respect to gel fraction in a crosslinked material. In this article, we demonstrate that grafting a nitroxyl free radical that contains a silane functional group gives a more uniform distribution of silane functionality. Model compounds were synthesized by grafting a silane-functionalized TEMPO derivative and a vinylsilane to cyclooctane, and their structures were compared. The product grafted with vinyltriethoxysilane consisted of essentially all multigrafted product with an average of 2.26 silane grafts per cyclooctane molecule, which is in close agreement with published data, while the product of grafting the silane-functional nitroxyl consisted of only the monografted. species; no multigrafted product was detected. This confirms that grafting a silane-functionalized nitroxyl occurs via bimolecular combination of free radicals that is not affected by chain-transfer and suggests that the process may lead to more efficient utilization of silane as indicated by higher gel fraction for a given level of grafted silane. Synthetic work to prepare silane-functionalized TEMPO derivatives and preliminary studies to graft them to polyolefins are discussed. (C) 2008 Wiley Periodicals, Inc.