Composition and Structure Characterization of Polycarbosilane Synthesized from Polydimethylsilane under High Pressure

CHENG Xiang-zhen,XIAO Jia-yu,XIE Zheng-fang,SONG Yong-cai,WANG Ying-de (Coiiege of Aerospace and Materiais Engineering,Nationai Univ. of Defense Technoiogy,Changsha 410073,China) Abstract:The poiycarbosiiane(PCS),the precursor of SiC fiber,is synthesized at 450C for 6h in an autociave by thermai decomposition of poiydimethyisiiane(PDMS). The composition and structure of the PCS are characterized by softening point,eiement anaiysis,IR,moiecuiar weight distribution,and NMR. Structure modei of PCS is therefore proposed. IR and NMR show the presence of SiC4 and SiC3H structure units containing Si-CH3,Si-CH2-Si,and Si-H groups. Eiementai anaiysis provides an empiricai formuia of SiC1.87H7.13O0.03 . Compared with the PCS with ciose softening point synthesized at normai pressure,the PCS synthesized in the autociave has a approximate eiementai composition,higher Si-H bond content,higher moiecuiar weight,but iower ratio of SiC3H and SiC4 .