Route to hydrophilic, hydrophobic and functionalized cross-linked polysiloxane microspheres

A new approach to the synthesis of all-polysiloxane functional microspheres is worked out. Simultaneous catalysis of four reactions of polyhydromethylsiloxane (PHMS) by a Pt(0) complex in an aqueous emulsion process is used to synthesize all-polysiloxane microspheres containing a large number of silanol groups. These reactions include (i) hydrosilylation of olefinic bond of a cross-linker with the SiH group on the polymer, (ii) hydrolysis, and in some cases alcoholysis, of the Si–H bond in the polymer and (iii) dehydrogenative condensation of the SiOH group formed in the hydrolysis with the SiH group. A solution of PHMS with divinyltetramethyldisiloxane (DVTMS) cross-linker together with the catalyst is mechanically emulsified with water. The polymer cross-linking and the silanol formation occur in the formed emulsion. In most cases preliminary hydrosilylation is carried out before emulsification, which leads to the grafting of vinylsiloxane on PHMS. In the emulsion process a large number of SiH groups on PHMS may be transformed into SiOH hydrophilic groups. This reaction occurs not only on the surface of microspheres but also in their bulk. The cross-linking of PHMS takes place as a result of hydrosilylation of vinyl groups grafted on the polymer and by dehydrogenative condensation of the SiH groups with the silanol groups which are formed on PHMS. The SiOH content, density of grafting and the particle size depend on the parameters of the process. The obtained microspheres, named here M–OH, are modified by reactions with reactive silanes containing organofunctional groups.