Preparation of polysiloxazanes and their transformation to silicon oxynitride

Abstract

Cyclic and bicyclic oligosiloxazanes were synthesized by the reaction of 1,3-diamino-1,3-di-t-butoxy-1,3-dimethyldisiloxane with 1,1,3,3-tetraisocyanato- 1,3-dimethyl-1,3-disiloxane (M-TIDS) in 1 : 1 and 1 : 2 molar ratios, respectively. Based on these results, polysiloxazane M-PSZ was prepared by the ammonolysis of M-TIDS in tetrahydrofuran (THF) at 213 K. The structure and stability against the gelation of M-PSZ were found to be dependent on the temperature and polarity of the solvents. The molecular weight of M-PSZ was increased by aging a THF solution of M-PSZ at room temperature. A maximum weight average molecular weight of 70000 was observed for M-PSZ, for which a dilute solution was stable over 6 months. Silicon oxynitride was prepared by the pyrolysis of M-PSZ under an ammonia atmosphere. The ceramization process was monitored by infrared and nuclear magnetic resonance spectra, which showed the replacement of a methyl group with an amino group following a condensation reaction to provide silicon oxynitride at 1173 K.