A Lewis acid surfactant combined catalyst (LASC) was tentatively used in a cationic polymerization in miniemulsion of p-methoxystyrene (pMOS). In a first part, the initiating potential of trisdodecyl sulfate ytterbium (Yb(DS)3, 0.25H2O) was evidenced in the solution polymerization of pMOS initiated by the corresponding chlorinated adduct pMOS-HCl. Miniemulsion polymerizations of pMOS performed using the same initiating system gave rise to oligomers, but experimental conditions chosen could not evidence the expected LASC-mediated cationic polymerization process. Further studies showed that LASC is located at the interface and acts only as a surfactant together with SDS. The polymerization occurred due to the hydrolysis of pMOS-HCl. The resulting acidification of the water phase leads to the transformation of SDS into its sulfuric acid form acting as an inisurf according to an interfacial cationic polymerization process. Latex particles of pMOS incorporating narrowly distributed low molar mass chains were obtained.

The cationic polymerization of p-methoxystyrene in water using dodecylbenzenesulfonic acid as a surfactant and ytterbium triflate as a catalyst was studied in terms of kinetics and physicochemistry. Preliminary stability studies showed that stable inverse (water in monomer) emulsions were obtained using excess catalyst and cocatalyst. Rates of polymerization and molar masses were respectively found slower and larger than for direct emulsion processes, in accordance with previous results published by Sawamoto on similar systems. The presence of the catalyst did not affect the mechanism scheme of ionic polymerization in aqueous dispersion; i.e., the polymerization is interfacial, and physicochemical issues govern molar masses.