Microcapsules derived from Pickering emulsions as thermal latent curing accelerator for epoxy resins

Organic-inorganic hybrid microcapsules encapsulating 2-phenylimidazole (2-PhIm) were prepared by Pickering emulsion polymerization of styrene and divinyl benzene using methacryloyloxy silane-modified silica particles as the stabilizer, and served as a thermal latent curing accelerator for diglycidylether of bisphenol A epoxy/anhydride system. The one-component curing composition containing 5 wt% of the microcapsules exhibited an excellent storage stability. The pot life at room temperature was as long as 30 days, while which of 2-PhIm curing system was only 2 days. At elevated temperature, the encapsulated 2-PhIm could be released from microcapsules effectively, and instantly accelerated the curing reaction. Meanwhile, the addition of microcapsules did not cause an adverse effect on the thermomechanical performance of the epoxy thermosets. In addition, the latency and curing behavior could be facilely regulated at a wide range of temperature by adjusting monomer ratios of the polymer matrix, to match different process temperatures. The microcapsules with robust cross-linked polystyrene matrix structure also showed good resistance to shearing forces, indicating their feasibility for high-speed mixing or kneading process in practical applications. It is suggested that the novel latent curing accelerator is potential for high-performance one-pot epoxy formulations, particularly recommended for application in electronic packaging fields.