PHOTOPOLYMERIZATION OF MICELLE-FORMING MONOMERS .2. KINETIC-STUDY AND MECHANISM

The kinetics of the photoinitiated polymerization of aqueous micellar solutions of n-alkyl-dimethyl(vinylbenzyl)ammonium chloride surfactants (Cn-STY with n = 8 and 16) have been investigated. The rate of polymerization was determined by dilatometry and was found to be proportional to the first power of the monomer concentration, [M], and to the half-power of the oil-soluble initiator concentration, [1]. A dependence of the polymer molecular weight on [I]-0.6 was observed. These scaling laws are close to those obtained for styrene emulsion polymerization. A mechanism is proposed and discussed in terms of micellar dynamics. Initiation occurs within the micelles, and the polymerizing micelles are fed monomeric surfactants coming from noninitiated micelles by diffusion through the aqueous phase. Different situations are discussed depending upon the degree of reactivity of the polymerizable group, the micelle lifetime, and the fraction of micellized surfactant with respect to that of free surfactant. This general mechanism accounts for the above data as well as for other results reported in the literature. It is concluded that a topological polymerization within a micelle is highly improbable.