Copolycondensation of regular functional silane and siloxane in aqueous emulsion using B(C6F5)3 as a catalyst a

Abstract

The copolycondensation of siloxane and silane bearing hydrido and methoxy groups, respectively, was carried out in a surfactant-free aqueous emulsion, at room temperature and using B(C6F5)3 as a water-tolerant Lewis acid. Several characterization techniques, including triple detection SEC, 29Si NMR and MALDI-TOF, confirmed the generation of linear polymers (no macrocycles), of average molar masses ranging between 30 and 80 000 g.moll-1, and bearing silanol end-groups. Colloidal evolution with time showed that a stable surfactant-free emulsion was generated before some coalescence occurs by decreasing the content of silanol groups suspected to stabilize the emulsion. The kinetics of reaction was followed by SEC, and revealed the generation of small cycles, along with linear oligomers, before converting them to poly(dimethylsiloxane) chains. A tentative mechanism, where ring-opening polymerization of the most stranded cyclosiloxane and polycondensation of polymer chains are considered, is proposed. © 2007 WILEY-VCH Verlag GmbH &Co. KGaA.