SI-29 NMR INVESTIGATION OF CONDENSATION-REACTIONS OF DIPHENYLSILANEDIOL IN PRESENCE OF TI-ALKOXIDE, ZR-ALKOXIDE, AL-ALKOXIDE, SN-ALKOXIDE AND SI-ALKOXIDE

The investigation of the effects of small amounts of Ti-, Zr-, Al-, Sn - and Si-alkoxides and those of triethylamine and hydrochloric acid on the condensation reaction of diphenylsiloxanediol (DPSD) in molar rat io Si:additive = 1:0.01 and 1:0.04 by Si-29 NMR shows a decrease in th eir activity in the order Ti approximate to HCl > Al > Sn approximate to N(Et)(3) approximate to Zr > Si after 6 h reaction time. The influe nce of the type of alkoxide ligands attached to the metal on the conde nsation rate of DPSD was found relatively low compared to the differen t metals. In presence of Ti-alkoxide the condensation reaction of DPSD leads to di-, tri- and tetrasiloxanediols, the latter of which domina tes and crystallizes from the solution as octaphenyltetrasiloxanediol. The catalysis of DPSD solutions by Al-alkoxide and HCl results prefer ably in tetraphenyldisiloxanediol species even after a few days. The c omplexity of metal alkoxides and the hydrolytic stability of heteromet allic Si-O-M bonds have been discussed as possible reasons for the dif ferences in the catalytic activity of the metal alkoxide.