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Polymerization of tetramethylcyclotetrasiloxane monomer by ion-exchanged montmorillonite catalysts

Abstract Montmorillonites ion-exchanged with Li+, Na+, K+, Ca2+, Mg2+ and Ni2+ and acidic clay were used as catalysts for the polymerization of a cyclic siloxane monomer, 2,4,6,8- tetramethylcyclotetrasiloxane. Montmorillonites with Ni2+ and Mg2+ in the interlayer, and acidic clay exhibit a greater ability for siloxane polymerization in both yield and mean molecular weight of products than those containing Li+, Na+ and K+. The difference in catalytic ability of the ion- exchanged montmorillonites is caused by the number of Brønsted acid sites due to the polarization of H2O. This was confirmed experimentally by FTIR analysis of pyridine-treated samples. Therefore, it may be possible to design a catalyst for controlling siloxane polymerization (i.e. mean molecular weight of product) by changing the number of Brønsted acid sites through exchange of the interlayer cations of montmorillonites.