Anionic emulsion polymerization of siloxanes

Abstract

In 1959, Hyde and Wehrly described an emulsion polymerization of permethylcyclosiloxanes. This unique example of an emulsion polymerization proceeding via an ionic mechanism involved base catalysis with a cationic surfactant. An analogous acid‐catalyzed anionic emulsion polymerization has now been developed which employs dodecylbenzene‐sulfonic acid as the catalyst and surfactant. Polydimethylsiloxane emulsions with particle diameters of 500–5000 Å are obtained on heating aqueous dispersions of permethylcyclosiloxanes with dodecylben‐zenesulfonic acid at 50–100°C. Polymerization is completely arrested by neutralization of the catalytic surfactant. As in the earlier cationic emulsion polymerization, the molecular weight of the polymer is easily controlled by the temperature of polymerization via the equilibrium between siloxane, water, and silanol. Polymers with molecular weights of 49,000 and 172,000 are obtained at 90°C and 25°C, respectively. The use of alkyltrimethoxysilanes in this anionic emulsion polymerization makes available a new system of colloidal silsesquioxanes with extremely small and uniform particle size. Colloidal methylsilsesquioxanes with particle diameters of 70–1000 Å are obtained by the addition of methyltrimethoxysilane to an aqueous dodecylbenzenesulfonic acid solution. Methylsilanetriol and methylsiloxanols were shown to be intermediates in this latter reaction.

Emulsion polymerization of dimethylcyclosiloxane in cationic emulsion: mechanism study utilizing two phase liquid–liquid reaction kinetics

“…Polymerization of silicones in emulsion has been known for 50+ years [1][2]. The various reactions that occur in cyclosiloxane emulsion polymerization are: initiation, polymerization (chain growth), condensation (Step growth), termination, depolymerization and redistribution.…”

Nucleation loci in the ring-opening polymerization of octamethyl- cyclo-tetrasiloxane in Winsor I system with dodecylbenzene sulfonic acid sodium salt and sulfuric acid

“…Weynberg et al [1] proposed the following reaction scheme. The species on the right hand side of eq.…”

“…One production method of poly(dimethylsiloxane) is ring-opening step polymerization of octamethylcyclotetrasiloxane (OTS) in an emulsion system with dodecylbenzene sulfonic acid (DBSA) as emulsifier and initiator [1,2]. During the polymerization, polymer droplets, which are by far smaller than the pre-existing OTS droplets, are generated.…”

Emulsion Polymerization

“…Hyde and Wehrly (1959) described the emulsion polymerization of permethylcyclosiloxanes, which proceeds via an anionic polymerization mechanism involving a basic catalyst with a cationic surfactant. Weyenberg et al (1969) developed an analogous acid-catalyzed anionic emulsion polymerization, which employs dodecylbenzenesulfonic acid (DBSA) as the catalyst and surfactant. The cationic polymerization can be compared with a conventional free-radical emulsion polymerization: The cationic polymerization involves monomer, water, surfactant, and catalyst, and the particle size of the resulting polymer dispersion is normally much smaller than that of the initial monomer droplets.…”