The Study Of Structure Of Polycarbosilane

Polycarbosilane (PCS) is an excellent precursor for silicon carbide (SiC) ceramic materials and the structural characteristic of which is the key factor of the properties of SiC. Up to now, there some reports about the study of the structure of PCS in the domestic. In this paper, the structure of PCS which contain the structure of polymer chain, average molecular weight, molecular weight distribution snd the structure of non-crystalline was studied in detail by means of ACC, IR, NMR, LLS, VPO, GPC, WAXS, RDF. And by improving the craftwork of precipitation of PCS, the narrow molecular weight distribution of PCS was got.It was found that the structure of PCS is represented by two structural elements (SiC4, SiC3H), at least in part with hexagonal cycles of alternating silicon and carbon atoms, more or less saturated hydrogen atoms. And the chemical structure of PCS is not influnced by the precipitation of PCS, which influnces the average molecular weight and molecular weight distribution. Besides the existence of the molecule of the low molecular weight and size of the content in PCS are the importment factors for average molecular weight, molecular weight distribution, especially for M n.In this paper, the Mark-Houwink constant of PCS is confirmed, and K is 0.191,αis 0.278. When it is 25℃and THF is the solvent. And the molecular weight distribution of PCS can be tokened by molecular weight distribution function.By using Wild angel X-ray scatter and RDF (Radial distribution function ) method, the structure of the short-range order for PCS has been studied successfully at first in domestic.The results have shown that polycarbosilane is amorphous polymer ,and the nearest atom distance is about 1.86×10-10m, to which is the diatance of silicon and carbon probably contributed. So the main-bond tructure of PCS is probably built with silicon and carbon atoms and that is the key factor for PCS to become the precusor of SiC ceramic. Furthermore,It is made up of medium range ordering domains with approximate preriodicity(r1)of 12～14×10-10m and that the distance of short-range order(rs) is about 5.2×10-10m, because r1 equal to 2 rs, it conclused that the structure of PCS is coming to out-of-order.