| Polymethylsilane (PMS), is once looked upon as an attractive precursor because it is liquid and the C:Si ratio is 1:1. However, PMS suffers from the low ceramic yield and the poor processability. Moreover, the synthesis of PMS is in a very low scale of about 10g/time. In this paper, our work is to make PMS usable as a precursor. The study is in the following aspects: enlarging the scale of the synthesis, modifying PMS to overcome the disadvantages, and then preparing materials with PMS.First, the scale of the synthesis of PMS through Wurtz reaction was enlarged from 10g/time to near 200g/time when the reaction was carried on at 80℃for 24hr, and Dichloromethylsilane (MeSiHCl2, DCMS) : Na: toluene = 1mol: 2 mol: 350 ml. The molecular weight and the ceramic yield of the resulted PMS is 860 and 35%, respectively. Pyrolyzed in N2 at 1250℃, PMS derives ceramic with the Si/C =1.23.A novel SiC precursor, A-PMS, was synthesized through a reaction of polymethylsilane (PMS) with SbCl3, where the Si-H in PMS reacts with Sb-Cl to form Si-Sb bond with HCl evaporated.It is evident that SbCl3 plays a very important role in the promoting chain crosslinking, in the transforming of the Si-Si into Si-C bonds and in the stabilizing PMS from very high oxidation trend of the active Si-H bonds. A-PMS keeps liquid at room temperature that is suitable for the infiltration in the absence of any solvent. When heated, the crosslinking degree increases of A-PMS with the curing temperature. A-PMS can be cured into a fully crosslinked structure at 320℃that leads a very high ceramic yield up to 91%. After pyrolysis, the new precursor resulted in near stoichiometricβ-SiC with the Si/C ratio near 1.12.A-PMS was used as precursor to prepare Cf/SiC and SiCf/SiC composites via polymer infiltration and pyrolysis (PIP) process. The PIP process was modified according to the characteristics of A-PMS. The resulted Cf/SiC samples reaches the density of 1.76g/cm3 and the flexural strength of 381MPa after only 4 pyrolysis cycles, which will be not achieved less than 10 cycles using PCS and the traditional PIP process. A-PMS can also be used preparing SiCf/SiC composites. The resulted composite has the density of 2.05g/cm3 and the flexural strength of 353MPa.PMS and PCS were blended to adjust the C/Si ratio of the derived SiC. Analysis shows that when PMS and PCS are mixed in xylene, there is no reaction between the two precursors and the ceramic yield of the blended polymer is only 48～54%. But when the blended polymer is heated, Si-H groups in PMS and PCS react with each other to give high crosslinked structure. The ceramic yield of PMS/PCS cured at 320℃is 81～83%. The C/Si ratio of PMS/PCS derived ceramics (pyrolyzed at 1250℃) is linear to the content of PMS in PMS/PCS.SiC fibers were obtained from the blended polymers of PMS(8wt%) and PACS (Polyaluminocarbosilane). The diameter and the tensile strength of the resulted fibers are 15.3μm and 1.54GPa, respectively.After the pyrolysis of PMS/PCS at 1250℃, ultra long SiC nanowires with high purity were produced. The length is about 3mm and the diameter is 250nm.
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