Polymerization of Styrene with Peroxide Initiator Ionically Bound to High Surface Area Mica

Mica powders with ultrahigh specific surface areas (ca. 100 m 2 /g) were treated with aqueous solutions of peroxide radical initiators bearing a single cationic group to exchange the mica surface ions with initiator cations. The stability of the initiators, the adsorption isotherms on the mica, and the adsorption equilibrium constants were measured. The resulting materials initiate the polymerization of styrene at various conditions, forming bound polymer chains in amounts up to ca. 30 wt % polymer (ca. 55 vol %) with respect to the mica. The bound chains could be removed from the surface by extraction with good solvents for poly(styrene) only when the solvent contained ions for ion exchange. On the basis of kinetic evidence, the mechanism of grafting appears to be propagation of free radicals from the surface into the monomer solution, i.e., “growth from the surface”. The results differ strongly from those previously obtained with a dicationic surface-bound azo initiator, where grafting was shown to occur by “growth to the surface”.