Emulsion Polymerized Polydimethylsiloxane

The observations are consistent with the formation of grafts of hydrophilic silicates to the silanol chain ends at the surface of the PDMS emulsion particles prior to removal of the water. The silicates may be introduced into the system directly or through the alkaline colloidal silica, which contains appreciable amounts of dissolved silicates. Monomeric, or possibly dimeric, silicate grafted to more than one chain end could migrate to the interior of the PDMS emulsion particle to form further crosslinks. Grafts to higher molecular weight silicates and silicate grafts bearing anionic change would be solvated with water and tend to remain at the oil-water interface. These grafts can provide additional stabilization to the cured particles. The dialkyltin carboxylate is pictured as playing a role in the grafting and crosslinking process. Evaporation of the water would eventually cause collapse of the stabilizing elements surrounding the PDMS particles to allow contact between particles of silica and the silicate grafts coating the particles of PDMS. The ensuing formation of interparticle hydrogen bonds and siloxane bonds, which can occur readily at room temperature under alkaline conditions, completes the formation of the elastomer network. This is represented in Figure 8. The resulting elastomeric network thus consists of the original emulsion particles, now crosslinked, which are surrounded by a hydrophilic hard phase of silicates and silica. In some aspects, this resembles the morphology proposed for films from dried natural latex.