Linear polymers polycarbosilanes

The first type of polycarbosilane synthesized by using ADMET methodology was a poly[carbo(dimethyl)silane].14c Linear poly(carbosilanes) are an important class of silicon-containing polymers due to their thermal, electronic, and optical properties.41 They are also ceramic precursors to silicon carbide after pyrolysis. ADMET opens up a new route to synthesize poly(carbosilanes), one that avoids many of the limitations found in earlier synthetic methods.41... 

Polycarbosilanes, in their broadest definition, are organosilicon polymers whose backbone is composed of silicon atoms, appropriately substituted, and difunctional organic groups which bridge the silicon atoms, as shown in formula 1. The polycarbosilanes may be linear, or they can be cyclic or polycyclic -... 

In conclusion, the lesson learned from the research carried out to date on the subject of polycarbosilanes is that the general rule that linear, noncrosslinked polymers are not suitable preceramic polymers applies here as well. Crosslinked network-type polymers are needed. Such structures can be generated in more than one way, but in the case of the polycarbosilanes they have, to date, been obtained mainly by thermolytic routes thermal treatment (with or without other chemical additives) in the case of the Yajima polycarbosilanes and the thermolysis of tetramethylsilane in the case of the Bayer process-derived polycarbosilane. 

Linear polycarbosilanes and polycarbosiloxanes-especially those containing arylene units in the chain-have specific physico-chemical properties which can be applicable in heat-resistant materials [29-31]. Phenylene-silylene-ethylene-polymers, which may serve as potential substrates for applications as membrane materials are usually obtained in the presence of platinum catalysts [32], although other transihon-metal complexes have also been tested in this process. 

Acyclic diene metathesis (ADMET) polymerization of dialkenyl-substituted oiganosilicon derivatives occurring in the presence of molybdenum, tungsten, and ruthenium alkylidenes has been commonly used for the synthesis of a wide range of linear unsaturated organosilicon polymers, e.g., polycarbosilanes, polycarbosiloxanes, and related polymers [1-8]. 

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. 

As usual, there are some limitations in attachment of various organic groups to siloxane backbone. In some instances, direct hydrosilylation of an olefin derivative of the intended functional group can lead to serious side reactions it may give poor yield or may simply call for unusual and difficult to prepare intermediates. In any case, hydrosilylation of polymers with Si—H is a good source of preceramic polymeric materials (4,18). A variety of linear polysilanes and polycarbosilanes have been reported, but because they tend to depolymerize on heating and afford little ceramic jdeld, they are not useful as SiC precursors. To increase the... 

Polycarbosilanes are polymers in which organosilicon moieties as silanes, disilanes, and trisilanes and carbon as aliphatic or aromatic units lie in the polymer backbone. The general formula for this class of material may be represented by structure 33. Polycarbosilanes may be linear, cyclic, polycyclic, extended networks, or any combination thereof R and R are the usual substituents found in organo-silanes, and (C) represents difimctional aliphatic (saturated or unsaturated) or aromatic groups that can serve as bridges between the silicon moieties. Consequently, a... 

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