Silicone waxes—synthesis via hydrosilylation in homo- and heterogeneous systems

Silicone waxes, i.e. polysiloxanes with a long alkyl chain (>C8) as a pendant group make one of the most important classes of modified polysiloxanes widely applied to many branches of industry. Main methods of synthesis of silicone waxes are based on catalytic processes of hydrosilylation of alkenes with poly(hydro, methyl)siloxanes. Results of studies on syntheses of silicone waxes in homo- and heterogeneous catalytic systems are presented. The most effective catalyst for the reactions studied appeared to be siloxide rhodium complex [{Rh(μ-OSiMe3)(cod)}2]. The immobilisation of this complex in ionic liquids resulted in a highly selective and very active catalytic biphase system that enabled easy product separation and repeated use of the catalytic system. Excellent selectivity was observed also in the case of hydrosilylation of the above alkenes in a typical heterogeneous system in the presence of supported metallic catalysts. In this group of catalysts particularly active was platinum supported on a highly hydrophobic styrene–divinylbenzene resin which enabled to obtain product yield of about 90% in reactions with 1-octene and well over 90% in reactions with 1-hexadecene. When platinum was accompanied by copper on supports such as activated carbon and carbon black, product yields were clearly higher than those obtained on monometallic catalysts. Supported rhodium was either inactive or poorly active in reactions studied.

Graphical abstractSilicone waxes were synthesized using hydrosilylation of alkenes with poly(hydromethyl, dimethyl)siloxane in the presence of transition metal complexes in homogeneous system and immobilised in ionic liquids as well as on supported metal catalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide