POLYMERIZATION OF STYRENE WITH INITIATOR IONICALLY BOUND TO HIGH-SURFACE-AREA MICA - GRAFTING VIA AN UNEXPECTED MECHANISM

To obtain polystyrene grafted to mica, a free-radical initiator 2,2'-a zobis(isobutyramidine hydrochloride) (AIBA) was attached by ion exchan ge to the surface of an ultrahigh specific surface area (ca. 100 M2/g) muscovite mica powder, and the resulting material was used as an init iator to polymerize styrene. Grafted polymer was indeed obtained, in a mounts 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 mec hanism. Instead of propagation of free radicals from the surface into the bulk monomer (growth from the surface), grafting took place via at tack of growing chains thermally-initiated in the monomer on dispropor tionation products of AIBA attached to the surface (growth to the surf ace). The grafted polymer consisted primarily of high molecular weight chains (M ca. 10(6)) bound by their headgroups to a very small fracti on (less than 1 per 4000) of the surface ion-exchange sites. Consisten t with this mechanism, grafted polymer could also be obtained with ''t hermally-deactivated' AIBA-mica at rates comparable to those obtained with ''fresh'' AIBA-mica. Grafting was accelerated when 2,2'-azobis(is obutyronitrile) was added to the monomer as an additional initiator.