Silane polymers

Methanolysis-hydrolysis, 551-552 Methoxy-functionalized silane polymers, 455... 

The recent interest in substituted silane polymers has resulted in a number of theoretical (15-19) and spectroscopic (19-21) studies. Most of the theoretical studies have assumed an all-trans planar zig-zag backbone conformation for computational simplicity. However, early PES studies of a number of short chain silicon catenates strongly suggested that the electronic properties may also depend on the conformation of the silicon backbone (22). This was recently confirmed by spectroscopic studies of poly(di-n-hexylsilane) in the solid state (23-26). Complementary studies in solution have suggested that conformational changes in the polysilane backbone may also be responsible for the unusual thermochromic behavior of many derivatives (27,28). In order to avoid the additional complexities associated with this thermochromism and possible aggregation effects at low temperatures, we have limited this report to polymer solutions at room temperature. 

The high radiation sensitivity of substituted silane polymers is an interesting phenomenon upon which a number of current applications are based. Detailed... 

Zhong X, Yuan R, Chai Y, Liu Y, Dai J, Tang D (2005) Glucose biosensor based on self-assembled gold nanoparticles and double-layer 2d-network (3-mercaptopropyl)-trimethoxy-silane polymer onto gold substrate. Sensor Actuator B 104 191-198... 

Tetravalent silicon is the only structural feature in all silicon sources in nature, e.g. the silicates and silica even elemental silicon exhibits tetravalency. Tetravalent silicon is considered to be an ana-logon to its group 14 homologue carbon and in fact there are a lot of similarities in the chemistry of both elements. Furthermore, silicon is tetravalent in all industrially used compounds, e.g. silanes, polymers, ceramics, and fumed silica. Also the reactions of subvalent and / or low coordinated silicon compounds normally lead back to tetravalent silicon species. It is therefore not surprising that more than 90% of the relevant literature deals with tetravalent silicon. The following examples illustrate why "ordinary" tetravalent silicon is still an attractive field for research activities Simple and small tetravalent silicon compounds - sometimes very difficult to synthesize - are used by theoreticians and preparative chemists as model compounds for a deeper insight into structural features and the study of the reactivity influenced by different substituents on the silicon center. As an example for industrial applications, the chemical vapor decomposition (CVD) of appropriate silicon precursors to produce thin ceramic coatings on various substrates may be mentioned. 

Recently increasing interest is evident in polymers bearing group 14 atoms. Polygermane and germane-silane polymers show properties such as semiconductivity, photoconductivity... 

Polygermanes and germane-silane polymers were prepared similarly. Polygermanes from the electroreduction of dichlorophenylbutylgermane showed typically a molecular weight of Mn = 19900 (10% yield). Germane-silane copolymers showed similar M values. The Ge/Si ratio in mixed polymers was roughly proportional to the ratio of monomers... 

The formation of silyl radicals in the exhaustive photolysis of the silane polymers was indicated by the isolation of disilanes of general structure (HSiRR SiRR H) as shown in Table 1. These materials accumulate in the photolysate and are photostable as they absorb only weakly at the irradiation wavelength (254 nm). Longer chain silanes are presumably continuously degraded under the conditions of the exhaustive irradiation. 

Sander et al. [63] investigated the effect of microparticulate silica pore size on the properties of solution-polymerized Cig stationary phases and observed both an increase in bonding density and shape recognition for wider pore (>120 A) silica. A size-exclusion mechanism was proposed, in which the reaction of the silane polymer on the surface is enhanced for wide pores and reduced for narrow pores. Polymeric Ci8 phases prepared on substrates with narrow pores exhibited monomeric-like chromatographic properties. This effect may be the result of an increase in competitive surface linkage with the less sterically hindered monomers that coexist with the bulkier oligomers that have polymerized in the reaction solution (Figure 5.13). 

FIGURE 5.13 Proposed size exclusion mechanism for the reduced reaction of the silane polymer on narrow pores and an enhanced reaction for wide pores. 

Wedge test results suggest that the curing process (e.g., percent crosslinking) of the epoxy-polyamide primer system is not affected by the addition of organosilanes, but may be affected by NTMP. The results of substrate surface characterization, adsorption behavior of applied films, and evaluation of candidate inhibitors by chemical, mechanical, and electrochemical test methods are presented. Mechanisms to explain the observed behavior of the various phosphonate and silane polymer systems are discussed. 

Twenty-five years later, Burhard reported the preparation of permethylated. polysilane (2). These materials were, however, highly crystalline, insoluble white solids which evoked little scientific interest until recently when it was discovered that silane polymers could be used as thermal precursors to / -silicon carbide fibers (3-5). In this regard, Yajima and co-workers reported that poly (dimethyl) silane could be converted by the two-step process shown below to / -silicon carbide, a structural material of considerable industrial importance. 

Examination of the absorption spectra of the new polysilane materials reveals a number of interesting features (14). As shown in Table III, simple alkyl substituted polymers show absorption maxima around 300-310 nm. Aryl substitution directly on the silicon backbone, however, results in a strong bathochromic shift to 335-345 nm. It is noteworthy that 4, which has a pendant aromatic side group that is buffered from the backbone by a saturated spacer atom, absorbs in the same region as the peralkyl derivatives. This red shift for the silane polymers with aromatic substituents directly bonded to the backbone is reminiscent of a similar observation for phenyl substituted and terminate silicon catenates relative to the corresponding permethyl derivatives... 

To resolve this dilema, we propose that the polymer is interacting with the additive in the excited state, (27) perhaps via electron transfer, and that this interaction leads to the irreversible degradation of the polymer. The direct interaction of photoexcited monomeric polysilanes with halogen derivatives resulting in the cleavage of Si-Si bonds had been reported (28). In a similar fashion, we must conclude either that this interaction does not occur with the alkyl silane polymers or that it does not result in rapid polymer degradation. 

Conformational calculations are carried out on poly(di-n-hexylsilanes). The most significant finding from the energy calculations is that the a -trans conformation is not the lowest energy structure for the symmetrically alkyl-substituted silane polymers. A helical structure is preferred for the isolated molecule. 

In addition to pure thermal stability, if the polymer is to be heated in air, one must also consider oxidative stability. In the carbon series oxidation always leads to more stable species and tends to occur, blit in the silicon series there is a much higher tendency towards reaction with oxygen. This is the principal reason for the low utility of the silane polymer. Finally, a third factor in polymer stability is the ease of attack by solvents, acids, bases, etc. This is largely determined by the ionic nature of the bonds involved. The silica based polymers should be more susceptible to such attack than carbon, since they have a higher percent of ionic nature. 

The polymers which have been used to illustrate problems of inorganic polymer formation have been lieteroatomic. that is, their chains are built from different atoms alternating with each other. The other structure mentioned has been homoatomic—all the atoms in the chain are the same. There aie only a few homoatomic polymers of airy promise. Most elements will form only cyclic materials of low molecular weight if they polymerize at all. In addition to the silane polymers, black phosphorus, a high-pressure modification of the element, forms in polymeric sheets. 

When a metal substrate was cleaned with oxygen-argon plasma followed by a thin layer (100-500 nm) of plasma silane polymer deposit, the coated substrates showed good humidity and corrosion resistance. Samples were prepared and placed either in a humidity chamber (85% RH and 60°C) or immersed in a salt solution (5% NaCI) for 5 days. The plasma-coated samples showed little or no pitting on the surfaces, while severe corrosion appeared on the uncoated sample. 

Plasma surface cleaning (Ar-02) of the metal substrate is critical for good interfacial bonding with the subsequent coating. XPS and IR analyses show that the plasma-deposited silane polymers are essentially polyorganosiloxane in nature. 

The bonding environments surroundir alkyl. Si—CH3, Si—CH2, Si—H, and Si ing is believed to be a typical oxane I sitions of deposited silane plasma pob C/Si and O/ Si atomic ratios increas Organofunctional silane polymer coati silane polymers. Corrosion performar to be excellent. The results were partic silane polymer and organofunctiona phosphated steel substrates. 

Figure 8. Schematic diagram of coating on a zinc-phosphated steel substrate. Thin plasma polymer is first deposited on the phosphate crystal surface, followed by an organofunctional silane polymer coating.

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