Polycarbosilane characterization

The cyclotrisilazane (R = Me) produced in reaction (14) is recycled at 650°C [by reaction with MeNHo) the reverse of reaction (14)] to increase the yield of processible polymer. Physicochemical characterization of this material shows it to have a softening point at 190°C and a C Si ratio of 1 1.18. Filaments 5-18 pm in diameter can be spun at 315°C. The precursor fiber is then rendered infusible by exposure to air and transformed into a ceramic fiber by heating to 1200°C under N2- The ceramic yield is on the order of 54% although, the composition of the resulting amorphous product is not reported. The approach used by Verbeek is quite similar to that employed by Yajima et al. (13) in the pyrolytic preparation of polycarbosilane and its transformation into SiC fibers. 

As an alternative approach, polycarbosilanes 42 bearing pendant zirconocene moieties have also been prepared by the ROP of the spirocyclic monomer 41 (Equation (14)). In this case, the materials were structurally characterized but the soluble fraction was of low molecular weight M < ca. 3,000) and the high molecular weight fraction was insoluble in organic solvents. In the presence of activators, both fractions functioned as ethylene polymerization catalysts with moderate activity. 

C(/SiC-BN composites and C(/SiC-ZrC composites were fabricated to improve the oxidation resistance and high temperature performance of C /SiC composites through the modification of matrix. SiC-BN matrix was formed through an in-situ reaction of active filler boron and protective gas N2 in the active-filler-controlled polymer pyrolysis (AFCOP). The oxidation performance of C(/SiC-BN composites was greatly improved when oxidized at 1000°C compared to that of C /SiC composite. Meanwhile, SiC-ZrC matrix was fabricated using the ZrC particles as inert filler. Both C(/SiC-BN composites and Ci/SiC-ZrC composites show non-catastrophie ftaeture behavior. The microstructures were also characterized by SEM and EDS. It was shown that the fiber reinforcement hindered the impregnation of solid particles into the fiber bundles so that most of the fillers remained in the inter-bundle matrix and most of the intra-bundle matrices were composed of Sic that resulted from the decomposition of polycarbosilane (PCS). 

By the way, although a dominant majority of papers concerning the formation of amorphous SiC layers describes appUcations of CVD or PVD techniques, there have also been some attempts to use the polymer route for preparing SiC films. Starting from solutions of various polysilanes or polycarbosilanes, frequently films are formed by spin-coating and pyrolyzed under inert atmosphere [215-218]. Of course, such a procedure does not form a part of this section SiC layers via gas phase reactions . However, in this connection it should be mentioned that polysilanes are also applied to form films via evaporation, not only with the aim to build amorphous and/or crystalline SiC films, but also to use special properties of the polysilane films themselves, i.e. without a subsequent pyrolysis of these films. Such amorphous films are characterized by non-linear optical effects [219, 220] and their properties may be controlled by the uniformity of the orientation of polysilane chains which is susceptible to epitaxial influences [221-223]. 

Linear polycarbosilanes of general formula -[RR Si(CH2)2]- have interesting gas penetration and separation properties [9]. This work was aimed at synthesizing and characterizing polycarbosilanes, mainly silylene-alkenylene(arylene) polymers, as potential membrane materials for the separation of hydrocarbons present in natural and petroleum gas. 

Komuro K, Kawakami Y (1999) Synthesis and characterization of side-chain liquid crystalline polycarbosilanes with siloxane spacer. Polym Bull 42 669-674... 

Lach and Frey have shown that silanes containing multiple vinyl groups such as 53, yield hyperbranched polycarbosilanes (55) in the presence of a Pt catalyst (Scheme A derivative of this product was characterized by the Si NMR spectra and had an of 1800 with a degree of dendritic branching (DB) of 0.5. 

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