Synthesis of the Ladder Polymers by the Reaction of Catalytic Dehydrocondensation

Abstract The heterofunctional condensation of cis-1,3.5,7-tetrahydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane with dimethylchlorosilane has been studied. It was established that when the reaction proceeds under mild conditions tetraphenylcyclotetrasiloxane incompletely substituted with dimethylsiloxy groups is obtained, i.e., 1,3,5-tris(dimethylsiloxy)-7-hydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane, while under certain conditions 1,3,5,7-tetrakis(dimethylsiloxy)-1,3,5,7-tetraphenylcyclotetrasiloxane is formed. The catalytic dehydrocondensation of 1,3,5-tris(dimethylsiloxy)-7-hydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane both in a dilute and concentrated solutions in the presence of platinochlorohydric acid as a catalyst has been studied. It was shown that the reaction proceeds both by the mechanism of intramolecular cyclization with formation of a bicyclic compound and intermolecularly with formation of a tricyclic compound. The catalytic dehydrocondensation of 1,3,5,7-tetrakis-(hydriddimethylsiloxy)-1,3,5,7-tetraphenylcyclotetrasiloxane with cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane and with oligotetrols (m = 5, 10) was also studied. The reaction order, activation energies and dehydrocondensation rate constants were found. It was established that with an increase in the length (m) of the oligotetrols the degree of catalytic dehydrocondensation is reduced. It was shown that if the platinochlorohydric acid catalyst is replaced by anhydrous powdered caustic potassium a different configuration of the cyclotetrasiloxane skeleton is realized in polymers.