Siloxanes preparation

Cyclic oligogermanes, synthesis, 3, 788 Cyclic siloxanes, preparation and characteristics, 3, 654 Cyclic sulfonate trienes, in [6+2]- and [6+4]-cycloadditions, 10, 622-623... 

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 ... 

JP 04220431 (Japanese) 1992 Tough polyimides and prepregs and fiber reinforced plastics Toray Industries, Japan M Eno, K Tobukuro Toughened fiber reinforced prepregs Polyimide-siloxanes prepared from BTDA and aminosiloxanes with nadic anhydride termination... 

Fig. 1. Synthesis of monofunctional siloxanes prepared from D3 following the traditional and the new route.

Fig. 25.3. Dipolar-dephasing CP-MAS NMR spectra of the untreated (A) and Hg -treated (B) polysiloxane-immobilized monoamine system and the untreated 3-chloropropylpoly-siloxane, prepared with HCl as catalyst (C). Dephasing period shown in p,s. Ref. 17.

Several independent protocols using a combination of transition metal-catalyzed stereoselective hydrosilylation, such as palladium-catalyzed crosscoupling sequence leading to stereodefined r-conjugated alkene derivatives, have been successfully developed in the last decade (4). Alkenylsilanes or siloxanes, prepared via platinum or rhodium complex-catalyzed intermolecular hydrosilylation of terminal alkynes have been highly stereospecifically cross-coupled with aryl and alkenyl halides to give unsymmetrical stilbenes, alkenylbenzenes, and conjugated dienes (Scheme 24) (4). 

The base polymers are mainly high-molecular-weight linear polydimethyl-siloxanes prepared by the base- or acid-catalyzed polymerization of cyclic dimethylsiloxanes [(CH3)2SiO—] (see Section 2,A). The copolymerization of methylvinylcyclosiloxanes with dimethylsiloxanes afford polymers with methylvinylsiloxy groups that can be rapidly cross-linked by peroxides such as 2,4-dichlorobenzoyl peroxide or other systems as described in Preparation 2-7. 

Liquid crystals are of course of immense importance to the electronics industry. Side-chain liquid-crystalline siloxanes prepared via hydrosilation of mesogens with poly(methylhydrosiloxane) [Eq. (30), e.g.], and their phase behavior studies using DSC, optical microscopy and X-ray diffraction have been reported. 

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