Preparation And Characterization Of Polycarbosilane From The Residue Of Polydimethylsilane Thermal Decomposition

Polycarbosilane(PCS)is usually synthesized by using polydimethylsilane(PDMS)as a raw material in a two-step process,that is,PDMS is heated and cracked,and the gaseous silane produced after the cracking is condensed to form a liquid polycarbosilane(LPS),and then liquid polycarbosilane is used as a raw material for synthesis PCS.In this method,in addition to generating gaseous silane after PDMS cracking,some solid by-products remain.The recycling and utilization of this solid by-product is difficult,but it has great economic value,and it has important social value because of reducing solid waste pollution.In this thesis,the PDMS cracking solid by-product is dissolved in xylene,and then continuous coarse filtration using diatomaceous earth and ultra-fine filtration are performed.Finally,the xylene solvent is distilled off to obtain PCS with a lower melting point.By further high temperature heat treatment,the melting point of the PCS is increased,and the molecular weight and molecular weight distribution are optimized,so as to obtain high-quality polycarbosilane.Master the chemical structure of PCS by IR analysis and 1H NMR,13C NMR analysis.Obtain molecular weight,molecular weight distribution and dispersion coefficient by GPC analysis.Master elemental composition through elemental analysis.Testing ceramic yield by high temperature heat treatment.Studies show that recovering PCS from cracked solid by-products yields ayield of 96.5%.The chemical structure of directly recovered PCS is similar to that of ordinary PCS,but the softening point is relatively low,only 124.1℃,and the ceramic yield is low(38.9%),which is not suitable as a ceramic precursor.Through further high temperature treatment,the molecular weight of PCS is significantly increased,the miecular weight distribution is optimized,and the softening point is increased to 223.0℃,and the yield of pyrolytic ceramic is increased to 59.5%.It is suitable for the requirement of ceramic precursors.And it is passed the user’s app assessment.