Polymerization of tetramethylcyclotetra- siloxane monomer by ion-exchanged montmorillonite catalysts

AB S TRACT: Montmorillonites ion-exchanged with Li +, Na +, K § Ca 2+, Mg 2+ and Ni 2+ and acidic clay were used as catalysts for the polymerization of a cyclic siloxane monomer, 2,4,6,8tetramethylcyclotetrasiloxane. Montmorillonites with Ni 2+ and Mg 2+ 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 ionexchanged montmorillonites is caused by the number of Brmasted acid sites due to the polarization of H20. 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 Bronsted acid sites through exchange of the interlayer cations of montmorillonites.