Use of organosilicon polymers

Organosilicon polymers are becoming important in many aspects of device technology. Multilevel metallization schemes require the use of a thin dielectric barrier between successive metal layers (i). Often, these dielectric materials are silicon oxides that are deposited by low-temperature or plasma-enhanced chemical vapor deposition (CVD) techniques. Although conformal in nature, CVD films used as intermetal dielectrics frequently result in defects that arise fi om the high aspect ratios of the metal lines and other device topographies (2). Several planarization schemes have been proposed to alleviate these problems, some of which involve the use of organosilicon polymers (2-4). 

We have described new routes to useful preceramic organosilicon polymers and have demonstrated that their design is an exercise in functional group chemistry. Furthermore, we have shown that an organosilicon polymer which seemed quite unpromising as far as application is concerned could, through further chemistry, be incorporated into new polymers whose properties in terms of ceramic yield and elemental composition were quite acceptable for use as precursors for ceramic materials. It is obvious that the chemist can make a significant impact on this area of ceramics. However, it should be stressed that the useful applications of this chemistry can only be developed by close collaboration between the chemist and the ceramist. 

Marosfoi, B., Szabo, A., Kiss, K., and Marosi, G. 2009. Use of organosilicone composites as flame retardant additives and coating for polypropylene. In Fire Retardancy of Polymers, eds. Kandola, K. and Hull, R. Cambridge, U.K. Royal Society of Chemistry, pp. 49-58. 

Intermediate. A reactive compound containing an essential grouping which, by further processing or reaction, is conveyed to the finished product here, a reactive organosilicon compound of relatively simple structure which is used in the preparation of organosilicon polymers. 

Especially the latter subject is a strongly developing field of research, trying to find answers to such important questions as, e.g., the stereo- and enantioselective synthesis of organosilicon polymer precursors and the use of Si-M compounds for the production of new polymers. In addition, even in widely used industrial processes as, e.g. the hydrosilylation reaction, the respective mechanism is still under discussion and research is focused on the development of more active and less expensive catalysts (compared to the today used nobel metal complexes). 

The surface activity of organosilicon polymers with backbones other than siloxane is not very well known. Interest in varying the backbone in organosilicon polymers does not normally stem from a desire to modify surface properties. Usually, the purpose of backbone variation is to increase thermal stability, as for example, with poly(silphenylenesiloxane) and poly-(carboranesiloxane) copolymers. Because thermal stability is often achieved by increasing TgS by using rigid backbones, most backbone variations will have a detrimental effect on polymer surface activity. 

SiC fiber was produced from polycarbosilane (PCS) by Yajima et al. " in 1975, which is the earliest case of organosilicon polymer utilization for an industrial structural material. In the Yajima process, PCS was mainly synthesized from polydimethylsilane (PDS) by a thermal conversion process using an autoclave or an open reflux system. This is the commonly available PCS. Its melt spinability, solubility in various orgaiuc solvents, and stability for storing at room temperature are critically important for industrial uses. 

For the further increase of toughness, continuous hber reinforcement has been employed. In this category, silicon carbide reinforced with silicon carbide hbers, which is usually fabricated by the densification process using chemical vapor infiltration (CVl) or impregnation and pyrolysis of organosilicon polymers, is one of the most attractive materials. In these materials, the interface is also essentially important. As shown in Figure 9.1.12, appropriate thickness of carbon interface introduced by CVl process leads to a nonlinear fracture. 

Yajima, S., Hasegawa, Y, Okamura, K., Matsuzawa, I. (1978). Development of high tensile strength silicon carbide fibers using an organosilicon polymer. Nature, 273, 525-527. doi 10.1038/273525a0. 

Gas-filled plastics are polymer materials — disperse systems of the solid-gas type. They are usually divided into foam plastics (which contain mostly closed pores and cells) and porous plastics (which contain mostly open communicating pores). Depending on elasticity, gas-filled plastics are conventionally classified into rigid, semi-rigid, and elastic, categories. In principle, they can be synthesized on the basis of any polymer the most widely used materials are polystyrene, polyvinyl chloride, polyurethanes, polyethylene, polyepoxides, phenol- and carbamideformaldehyde resins, and, of course, certain organosilicon polymers. 

Summary Catalytic crosslinking processes of organosilicon preceramic polymers using transition metal complexes as well as stoichiometric reactions between such polymers and transition metal complexes and powders that lead to new ceramic phases are reviewed. 

Watanabe and Ohnishi [39] have proposed another model for the polymer consumption rate (in place of Eq. 2) and have also integrated their model to obtain the time dependence of the oxide thickness. Time dependent oxide thickness measurement in the transient regime is the clearest way to test the kinetic assumptions in these models however, neither model has been subjected to experimental verification in the transient regime. Equation 9 may be used to obtain time dependent oxide thickness estimates from the time dependence of the total thickness loss, but such results have not been published. Hartney et al. [42] have recently used variable angle XPS spectroscopy to determine the time dependence of the oxide thickness for two organosilicon polymers and several etching conditions. They did not present kinetic model fits to their results, nor did they compare their results to time dependent thickness estimates from the material balance (Eq. 9). More research on the transient regime is needed to determine the validity of Eq. 10 or the comparable result for the kinetic model presented by Watanabe and Ohnishi [39]. 

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