SYNTHESIS OF THE LADDER POLYMERS BY THE REACTION OF CATALYTIC DEHYDROCONDENSATION

The heterofunctional condensation of tetrahydroxy-1,3,5,7-tetraphenylc yclotetrasiloxane with dimethylchlorosilane has been studied. It was e stablished that when the reaction proceeds under mild conditions tetra phenylcyclotetrasiloxane incompletely substituted with dimethylsiloxy groups is obtained, i.e., )-7-hydroxy-1,3,5,7-tetraphenylcyclotetrasil oxane, while under certain conditions 1,3,5,7-tetrakis(dimethylsiloxy) -1 ,3,5,7-tetraphenylcyclotetrasiloxane is formed. The catalytic dehyd rocondensation of y)-7-hydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane b oth in a dilute and concentrated solutions in the presence of platinoc hlorohydric 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 forma tion of a tricyclic compound. The catalytic dehydrocondensation of eth ylsiloxy)-1,3,5,7-tetraphenylcyclotetrasiloxane with tetrahydroxy-1,3, 5,7-tetraphenylcyclotetrasiloxane and with oligotetrols (m = 5, 10) wa s also studied. The reaction order, activation energies and dehydrocon densation rate constants were found. It was established that with an i ncrease in the length (m) of the oligotetrols the degree of catalytic dehydrocondensation is reduced. It was shown that if the platinochloro hydric acid catalyst is replaced by anhydrous powdered caustic potassi um a different configuration of the cyclotetrasiloxane skeleton is rea lized in polymers.