Core-shell latex particles consisting of polysiloxane-poly(styrene-methyl methacrylate-acrylic acid): Preparation and pore generation

Latexes with a poly(dimethyl siloxane) core and a poly(styrene-methyl methacrylate-acrylic acid) [poly(St-MMA-AA)] shell have been prepared in two steps in order to generate particles that have a core with a very low glass transition temperature. In the first step, poly(dimethyl siloxane) particles were obtained via the ring-opening emulsion polymerization of octamethyl tetracyclosiloxane (D(4)). The polymerization was carried out using either an anionic or a cationic catalyst. In the first case, sodium hydroxide was used as catalyst and sodium dodecylbenzene sulfonate as surfactant, while in the second, the alkylbenzene sulfonic acid (ABSA) was used both as catalyst and surfactant. Using a PD(4) latex as seed, a seeded emulsion polymerization of St-MMA-AA was conducted to obtain PD(4)-P(St-MMA-AA) core-shell particles. Numerous recipes were attempted and the most successful were those in which the seed was prepared with a cationic catalyst (ABSA) at a relatively low temperature (75 degrees C). The core-shell structure of the particles was identified by transmission electron microscopy, but also via wetting angle, water absorption, and T(g) measurements. Finally, pores were generated in the core-shell particles via an alkali-acid treatment. Because PD(4) has a very low glass transition temperature, it cannot be easily handled. However, protected by a shell, it could be used as a constituent of composite materials with enhanced impact strength, even at very low temperatures. (C) 1999 John Wiley & Sons, Inc.