Synthesis of Cyclic Siloxanes by the Thermal Depolymerization of Linear Poly(siloxanes)

A novel method is described for the preparation of cyclic poly(siloxanes) by the thermal depolymerization ("cracking") of linear poly (siloxanes). With use of acidic Zeolite-type fixed bed catalysts at temperatures from 500 to 700 degrees C, it was shown possible to quantitatively convert linear polymers to a mixture of cyclics with ring sizes from 6 to 20. Mixed cyclics having differently substituted siloxy segmers incorporated in the ring could also be readily prepared by the cracking of the appropriate linear poly(siloxane) copolymers. The use of cyclic poly(siloxanes) for the preparation of highly reactive cyclic epoxysilicone monomers is also described.