Oxidation Reaction of Polycarbosilane

Abstract

Polycarbosilane(PCS) is organic polymer which consists of the skeleton of Si-C bond. SiC fiber is produced from PCS by the steps of spinning, curing and heat treatment. Curing process of SiC fiber is generally oxidation reaction of PCS by heat treatment in air. Structures and characteristics of SiC fiber is affected by oxidizing conditions of PCS. However, details and mechanism of PCS-oxidation has not yet been clarified. Therefore, the change of PCS after oxidation in air was studied by measurement of weighing, oxygen analysis, mp, GPC, solubility in THF and infrared spectrum. The oxidation of PCS gave the following reaction.1) oxidation reaction of two SiH bonds followed by condensation to give Si-O-Si bond, 2) hydration of SiH bond to give SiOH bond, 3) oxidation reaction of SiCH3 bond to give SiOH bond and formaldehyde, 4) dehydrated condensation of two SiOH bonds to give Si-O-Si bond, (reaction eq. (1)-(4)). PCS became infusible by crass linkage of Si-O-Si bonds. However infusible PCS consisted of more than 7 wt% of oxygen because it had more SiOH bonds than Si-O-Si bonds (Table 2). Condensation reaction of SiOH bonds has also given Si-O-Si bond by heat treatment in nitrogen. By applying this fact, we obtained the infusible PCS which consisted of 3-6 wt% of oxygen (Table 3).