Silanes, carbo

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... 

Figure 8.14 Classes of poly[carbo(dimethyl)silanes] produced by ADMET.

TABLE 8.2 Characterization Data for Poly[carbo(dimethyl)silane]s... 

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

It should be remarked here that trimethylsilane 84 a or triethylsilane 84 b and most other known silanes, for example tetramethyldisiloxane 1788, are quite expensive for any large-scale reduction, whereas the subsequently described poly-methylhydrosiloxane 1856 (cf. reductions of an azide moiety in 1855 and a carbo-benzoxy moiety in 1859) is available as large-scale orders for ca 15 kg , which is only a fraction of the cost of any other silane. 

Both Si-H and C—H compounds can function as hydride donors under certain circumstances. The silicon-hydrogen bond is capable of transferring a hydride to carbo-cations. Alcohols that can be ionized in trifluoroacetic acid are reduced to hydrocarbons in the presence of a silane. 

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

Siloxanes, prepared in 1989 as representatives of silicon-based dendritic molecules ( silicodendrimers ), were the first dendrimers to contain heteroatoms other than the usual ones (N, O, S, halogens) [68]. As with the phosphodendri-mers (Section 4.1.10), their readily modifiable architecture and their pronounced thermostability hold promise of applications, for example, in the form of carbo-silanes as liquid-crystalline materials and catalyst supports. They can be subdivided into a number of basic types and their properties are presented below with the aid of characteristic representatives ... 

An examination of all papers describing the synthesis of hyperbranched poly(carbo-silanes) reveals that only two reactions have been used in the polymerization step nucleophilic substitution and hydrosilylation. 

During the course of our research project on asymmetric catalysis of the carbo-nyl-ene reaction, we have found that the BINOL-Ti complexes (1) catalyze rather than promote stoichiometrically the carbonyl addition reaction of allylic silanes and stannanes [11,71]. The addition reactions to glyoxylate of ( )-2-butenylsi-lane and -staimane proceed smoothly to afford the sj -products in high enantiomeric excess (Scheme 27) [71]. The sjn-product thus obtained could readily be converted to the lactone portion of verrucaline A [72]. 

This does not, however, explain the preferential formation of cyclic carbo-silanes, such as Si-hexamethylcyclocarbosilane. The isolation of 1,3-disila-cyclobutane (compound 2, Table III) appears to be especially significant in this connection. Its formation may be thought of as associated with Eq. (2) ... 

Fritz, G., J. Grobe and D. Kummer, Adv. Inorg. Chem. Radiochem., 1965, 7, 349 (carbo-silanes). 

After establishing the elemental compositions of the carbon fiber surfaces by ESCA, wet chemical derivatizations were carried out to determine the number of -COOH, -COH and -C=0 functional groups on the very outer fiber surface[24]. It is posible to use pentafiuorophenylhydrazine for detecting carbonyl, chloro silanes for alcohol and carbo lic acid groups by pentafluorobromotoluene(fig. 11). 

Wagener, K. B. and Smith, D. W. (1991) Acyclic diene metathesis polymerization synthesis and characterization of unsaturated poly[carbo(dimethyl)silanes]. Macromolecules 24, 6073-6078. 

Poly(propyleneimine), poly(amidoamine), siloxane, carbo-silane, and other derivatives are most often used as initial polymer matrices. Spacers are usually aliphatic chains of various lengths, and mesogenic fragments cover the whole arsenal of classical low-molecular-mass liquid crystals. 

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