Preparation of Monodisperse Cross-Linked Elastic Silicone Particles

Abstract

Micrometer-sized monodisperse silicone droplets are prepared through a sol–gel process involving 3-methacryloxypropylmethyldimethoxysilane (MPDS) at room temperature for 1.5 h in the presence of NH₃ as a catalyst. The size of the obtained droplets is controlled by changing the stabilizer concentration and solvent polarity. However, the obtained droplets have not maintained their particulate shape in the dry state due to the absence of a cross-linking structure. Thus, radical polymerization is performed on the obtained silicone droplets at 70 °C for 2 h; consequently, spherical particles with high monodispersity are observed in the dry state, indicating the presence of a cross-linked structure. Microcompression tests are conducted to evaluate the mechanical properties of the silicone particles. Initially, the recovery ratio (elasticity) is not high because the molecular weight of the silicone particles is low, ≈600, due to MPDS cyclization (MPDS trimer). Anionic ring-opening polymerization is therefore performed to extend the molecular weight of the MPDS trimer. Benzyldodecyldimethylammonium bromide and tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium chloride are used as catalysts for anionic ring-opening polymerization. These catalysts increased the molecular weight to ≈2000 and 7600, respectively. Furthermore, the silicone particles obtained through anion ring-opening polymerization and radical polymerization have high recovery ratios (elasticity).