Thermal Conversion of Various Methylsilazane Oligomers into Thermoplastic Polysilazanes

Abstract

Methylsilazanes prepared by the methods reported previously have multifunctional amino groups in a molecule, and show self-condensing character, and were possible to give several forms. Methylsilazane oligomers undergo polymerization and change their states gradually from oily liquid to gelous solid and finally transform into insoluble and infusible solid. Methylsilazane oligomers are easily polymerizable, and therefore it is very difficult to find optimum conditions for preparation of specific forms. In order to resolve these problems, thermal conversions of methylsilazane oligomers were, r investigated. From the resulting diagrams, the thermally converted methylpolysilazanes were divided into three stages according to their heat treatment temperature. In the first stage, heat-treatment temperature was lower and therefore thermally converted methylsilazanes showed only increasing their viscosity, but yet fluid. In the second stage, the converted methylpolysilazanes became gelous solid at room temperature, and showed various softening temperatures. Thermoplasticity of them were controllable by heat treatment. In the third stage, the converted methylpolysilazanes became rigid mass, and they are no longer soluble and fusible. Among three stages, the most applicable one seems to be the second, in wnicn tnermaily converted methylsilazanes, so-called thermoplastic methylpolysilazanes are involved, which have characters defined by the softening temperature. Such a defined thermoplastic methylpolysilazane as a precusor can be useful following preparation of ceramic fibers and films as well as binders. PassibilityasPrecursorstoCeramic.IV.