PHOTOPOLYMERIZATION OF MICELLE-FORMING MONOMERS .2. KINETIC-STUDY ANDMECHANISM

The kinetics of the photoinitiated polymerization of aqueous micellar solutions of n-alkyl-dimethyl(vinylbenzyl)ammonium chloride surfactant s (Cn-STY with n = 8 and 16) have been investigated. The rate of polym erization was determined by dilatometry and was found to be proportion al to the first power of the monomer concentration, [M], and to the ha lf-power of the oil-soluble initiator concentration, [1]. A dependence of the polymer molecular weight on [I]-0.6 was observed. These scalin g 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 dif fusion through the aqueous phase. Different situations are discussed d epending upon the degree of reactivity of the polymerizable group, the micelle lifetime, and the fraction of micellized surfactant with resp ect to that of free surfactant. This general mechanism accounts for th e 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.