PYROLYSIS OF POLY[(SILYLENE)DIACETYLENES] - DIRECT EVIDENCE BETWEEN THEIR MORPHOLOGY AND THERMAL-BEHAVIOR

The pyrolysis of poly[(silylene)diacetylenes] under argon to 1400-degrees-C gives beta-SiC-containing ceramics in high yields (63-87%). All the solid residues contain a large amount of free carbon depending upon the nature of the substituents at silicon, i.e., saturated or unsaturated. Furthermore, the total amount of silicon present in the precursor remains in the final residue. The polymer-to-ceramic conversion has been studied by means of thermal analyses (TGA, TDA and DSC). The polymers primarily undergo low-temperature crosspolymerization through the triple bonds without weight loss which leads to a highly crosslinked carbon network. The mineralization occurs in the temperature range 450-800-degrees-C. The crosslinking step can be related to the morphology of the poly[(silylene)diacetylenes]. As shown clearly by X-ray powder diffraction and transmission electron microscopy studies, steric requirement of the side-groups bonded to silicon (methyl versus ethyl, phenyl and trimethylsilyl) greatly influences the degree of crystallinity of the above polymers. The relationship between this structural observation and the crosspolymerization rate is discussed.