Preparation of anisotropic snowman-like poly(ionic liquid) particles via microwave-assisted seed emulsion polymerization with silane coupling agent-modified microspheres as seeds

Anisotropic polymer particles transcend the functional constraints of isotropic materials and exhibit properties distinctly different from those of traditional isotropic ones. However, the anisotropic polymer particles are primarily confined to neutral polymers, and research on charged polymer-based anisotropic particles remains limited. As a novel type of polyelectrolyte, poly(ionic liquid) (PIL) offers structural designability, which enables the creation of diverse ionic functional and smart materials. In this study, we prepared anisotropic snowman-like PIL particles via microwave-assisted seed emulsion polymerization with silane coupling agent-modified PIL microspheres as seeds. First, the seed microspheres were fabricated by adding a mixture of ionic liquid monomers (IL) and 3-(methacryloyloxy)propyltrimethoxysilane (MPS) during the late stage of PIL microsphere preparation. Meanwhile, MPS hydrolyses and polymerizes with IL to form a cross-linked shell composed of PIL and silicon oxide (SiO_x) on the surface of PIL microspheres. Subsequent swelling of these seed microspheres via IL emulsion led to the phase separation and the formation of snowman-like morphology, which was then cured through microwave polymerization to yield anisotropic snowman-like PIL particles. The results showed that the phase separation process and the morphology of the resulting snowman-like particles can be modulated by adjusting parameters such as the amount of MPS/IL and the MPS/IL ratio. Additionally, our results suggested that a cross-linked shell is not a prerequisite for the phase separation and the formation of snowman-like morphology; snowman-like PIL particles can also be prepared using seed microspheres coated with a non-cross-linked SiO_x shell formed by the direct hydrolysis of MPS.