Polymers, carbosilane

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Silene-transition metal complexes were proposed by Pannell121 for some iron and tungsten systems, and such species were observed spectroscopically by Wrighton.122,123 Thus intermediates such as 33 have been proposed in the preparation of carbosilane polymers from hydrosilanes,124 both as intermediates in the isotope scrambling observed to occur in similar ruthenium hydride systems125 126 and in the 5N2 addition of alkyllithium species to chlorovinylsilanes.47... 

Title Dental Compositions Containing Carbosilane Polymers... 

Ring-opening polymerization is one of the most important applications of SCBs in organic chemistry. Polymerization of SCBs, which gives rise to carbosilane polymers, has been carried out thermally, by transition metal catalysis, or, most commonly, by anionic initiation. Thermal polymerization is rare, however, and is not covered in this chapter. For leading references into thermal polymerization of SCBs, refer to <1996CF1EC-II(1B)867> and <1995COMC-II(2)50>. 

It is important to end-cap the living carbosilane polymer with 1,1 -diphenylethylene to decrease the reactivity of the living center in order to obtain the block copolymer successfully. The diphenylethylene thus provides a milder carbanion for initiation of the methacrylate monomer. With this modification, efficiency of the end-capping by an electrophile (quenching) has reached 0.95 <2001PSA86, 1998PSA2699>. 

Cyclolinear carbosilane polymers with disilacyclobutane rings in the main-chain structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding l,3-dibutenyl-l,3-disilacyclobutanes in the presence of Grubbs catalyst (Scheme 13) <2003PP789, 2004MM5257, 2004PP118>. 

Table 2 Preparation of star-shape siloxane/carbosilane polymers...

Other examples of cationic HBP are the carbosilane polymers with ammonium groups on the surface synthesized by Gomez and de la Mata. The functionalization of a polycarbosilane matrix was carried out with peripheral allyl groups by two strategies (l) hydrosilylation of allylamines with carbosilane HBPs (PCS) containing terminal Si-H bonds, or (2) hydrosilylation of... 

The resistance of SiC to high-temperature working and oxidation makes it a valuable advanced material. Fibres of p-SiC are produced by CVD using R4 SiCl ( precursors or an alkane and chlorosilane in a reactor similar to that in Fig. 28.26. Fibres marketed under the tradename of Nicalon are produced by a melt-spinning process. This begins with reactions 28.21 and 28.22, the products of which are pyrolysed to give a carbosilane polymer (scheme 28.23). 

Wang L, Weber WP (1993) Synthesis and properties of novel comb polymers unsaturated carbosilane polymers with pendant oligo(oxyethylene) groups. Macromolecules 26 969-974... 

Weber WP, Liao X (1992) CrossUnkable saturated and unsaturated carbosilane polymers and formulations. US Patent 5 171 792... 

Carbosilanes, with their Si—CH2—Si skeletons, are formally analogous to silicones, which have Si—0—Si skeletons (p 135). However, whereas silicones have found wide application, the less usefffi bulk properties of carbosilane polymers and their less readily controlled methods of synthesis have prevented their finding comparable use. Apart from the pyrolytic route already described, they can be prepared directly from silicon and di- or poly-chloro alkanes, by thermal rearrangement of disilane derivatives (Si—Si—C -> Si—C—Si), and by dehalogenation of chloro-methylsilanes, e.g. 

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