Siloxane structures chemistry

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

The following review is concerned with the synthetic and structural chemistry of molecular alumo-siloxanes, which combine in a molecular entity the elements aluminum and silicon connected by oxygen. They may be regarded as molecular counterparts of alumo-silicates, which have attracted considerable attention owing to their solid-state cage structures (see for example zeolites).1 3 Numerous applications have been found for these solid-state materials for instance the holes and pores can be used in different separation techniques.4,5 Recently the channel and pore structures of zeolites and other porous materials have been used as templates for nano-structured materials and for catalytical purposes.6 9... 

Extended siloxane stmctures are in almost all cases formed by the stepwise condensation of silanols. The possibility of following the growth of siloxane structures from molecular units via oligomeric species to two- or three-dimensional extended systems is unprecedented in chemistry. This allows, inter alia, study of the influence of the precursor composition and the synthesis parameters on the stmctures and the properties of the extended systems. 

We have been interested for some time in the chemistry and structure of polysiloxane containing systems. We suggest that some of the important characteristics of siloxane structures, such as their thermal and oxidative stability, low glass transition temperature, hydrophobic character and low surface energies could perhaps render them useful as epoxy modifiers, order to do so, however, one would have to consider the questions of functionality, both with respect to type and concentration and also the miscibility or solubility of such hydrophobic nonpolar materials in the typically aromatic based epoxy precursors. 

The unique surface characteristics of polysiloxanes mean that they are extensively used as surfactants. Silicone surfactants have been thoroughly studied and described in numerous articles. For an extensive, in-depth discussion of this subject, a recent chapter by Hill,476 and his introductory chapter in the monograph he later edited,477 are excellent references. In the latter monograph, many aspects of silicone surfactants are described in 12 chapters. In the introduction, Hill discusses the chemistry of silicone surfactants, surface activity, aggregation behavior of silicone surfactants in various media, and their key applications in polyurethane foam manufacture, in textile and fiber industry, in personal care, and in paint and coating industries. All this information (with 200 cited references) provides a broad background for the discussion of more specific issues covered in other chapters. Thus, surfactants based on silicone polyether co-polymers are surveyed.478 Novel siloxane surfactant structures,479 surface activity and aggregation phenomena,480 silicone surfactants application in the formation of polyurethane foam,481 foam control and... 

Numerous diamines and aromatic dianhydrides have been investigated. Wholly aromatic Pis have been structurally modified by incorporating various functional groups, such as ether, carbonyl, sulfide, sulfone, methylene, isopropylidene, perfluoroisopropylidene, bipyridyls, siloxane, methyl phosphine oxide, or various combinations of these, into the polymer backbone to achieve improved properties. The chemistry and applications of Pis have been described in several review articles (4). 

The entire area of organosilicon chemistry blossomed with Kipping s preparation of such compounds by the more convenient Grignard process. These silanes turned out to be of paramount importance since they hydrolyzed readily to form compounds containing Si-0 bonds, both linear and cyclic.12,22,24 28 These new materials were first called silicoketones or silicones by analogy with ketones in the organic area. Structural studies, however, showed that they did not contain the Si=0 double bond. Thus, the silicone name is a misnomer, but it has persisted, at least in casual usage. However, the terms siloxanes and polysiloxanes are preferred. 

Fig. 104. Schematic structure of hybrid siloxane-metal oxide materials. From (Viana et al., 1995), reproduced with permission from the Royal Society of Chemistry.

The reaction chemistry of the polysilanes (particularly those formed from PhSiH3) have been studied to a limited extent and will only be mentioned briefly here. The polysilanes, H(RSiH)raH, obtained from dehydrocoupling are air-sensitive producing a siloxane-type structure for the polymer... 

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