Soluble Polysilane Synthesis And Characterization And Thermal Decomposition Characteristics

The organosilicon polymer route offers an innovative approach to the preparation of continuous SiC fiber, in which steps involving synthesis of polycarbosilane(PCS), melt-spinning, curing and firing are usually required. However, the PCS precursor derived from insoluble polydimethylsilane(PDMS) are much carbon-rich and difficult to be purified. Therefore, to prepare soluble near-stoichoimetric preceramic polymer, focus was placed upon the synthesis, composition and structure of soluble polymethylsilane(PMS) as well as its pyrolysis properties.In the paper, polymerization of metyldiclorosilane(MDCS), co-polymerization of dimetyldiclorosilane and methlydiclorosilane and co-polymerization of dimetyldiclorosilane and metyltriclorosilane were thoroughly studied. Synthesis mechanisms and the introduction of unexpected oxygen were primarily proposed, and characterizations of so-obtained soluble PMS, P(MS-DMS) and P(DMS-TMS) were also performed by using IR, 'HNMR, GO-MS and GPC analysis.Cross-linking of the soluble PMS could be achieved through heating and ethyldiamine ammonolysis respectively and those cross-linked PMSs were discussed in view of their composition and structure. In addition, adjusting the ratio of carbon/silicon was investigated by co-polymerization of low molecular weigh PDMS (LPS) and PMS as well as the copolymer. Finally, pyrolysis, ceramic yield and structure evolution of the soluble PMS and modified PMS were studied through IR, TG-DTA and XRD analysis.Results reveal that soluble PMS derived from MDCS are the main product, whose yield, with a maximum value close to that of literature, could be increased by lowering the reaction temperature and properly increasing the amount of monomer. The soluble PMS, with a molecular weight in the range of 300 to 500, are composed of much amount of linear polymers and somering-like polymers. However, the PMS are much sensitive to oxygen due to its much content of Si-H bond and the contaminated oxygen formed Si-O-Si bond in the PMS. Results also confirmed the cross-linking of PMS by heat treatment; in addition, co-polymerization of LPS and PMS could successfully reduce the reactivity and adjust the carbon/silicon ratio of the modified PMS. Pyrolysis process of PMS is similar to that of common PCS and both contain 0 -SiC microcrystalline after high temperature pyrolysis.