To obtain polystyrene grafted to mica, a free-radical initiator 2,2'-azobis(isobutyramidine hydrochloride) (AIBA) was attached by ion exchange to the surface of an ultrahigh specific surface area (ca. 100 m²/g) muscovite mica powder, and the resulting material was used as an initiator to polymerize styrene. Grafted polymer was indeed obtained, in amounts up to ca. 10 % by weight (ca. 30 % by volume) of polymer based on mica, but it was found that grafting proceeded by an unexpected mechanism. Instead of propagation of free radicals from the surface into the bulk monomer (growth from the surface), grafting took place via attack of growing chains thermally-initiated in the monomer on disproportionation products of AIBA attached to the surface (growth to the surface). The grafted polymer consisted primarily of high molecular weight chains (M ca. 10⁶) bound by their headgroups to a very small fraction (less than 1 per 4000) of the surface ion-exchange sites. Consistent with this mechanism, grafted polymer could also be obtained with ''thermally-deactivated' AIBA-mica at rates comparable to those obtained with ''fresh'' AIBA-mica. Grafting was accelerated when 2,2'-azobis(isobutyronitrile) was added to the monomer as an additional initiator.
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Meier et al. (1994) studied this question.