Alkyl alkoxy silane

The different types of admixtures, known to reduce alkali-aggregate reactions, can be divided into two groups those that are effective in reducing the expansion due to the alkali-silica reaction, and those that lower expansions resulting from the alkali-carbonate reaction. For the alkali-silica reaction, reductions in the expansion of mortar specimens have been obtained with soluble salts of lithium, barium and sodium, proteinaceous air-entraining agents, aluminum powder, CUSO4, sodium silicofluoride, alkyl alkoxy silane,... 

Alkyl alkoxy silanes have been found to be very effective in reducing alkali-aggregate expansion [11] (Fig. 6.4). Of the silanes used in the study, hexyl trimethyl siloxane and decyl trimethoxyl silane were found to be more effective in decreasing the expansion than the others. In the same study, Ohama et al. [11] investigated the effect of sodium silicofluoride, alkyl alkoxy silane, lithium carbonate, lithium fluoride, styrene-butadiene rubber latex and lithium hydroxide on compressive strength and the expansion of mortar containing cement with 2% equivalent Na20. The reduction of the level of expansion shown in Fig. 6.4 with the siloxanes was attributed to... 

As a recent trend, there have been a few attempts to use polymer latexes with chemical admixtures such as superplasticizers,alkyl alkoxy silane,and amino alcohol derivativeP I at low polymer-cement ratios of 5.0% or less. A trial to inhibit alkali-aggregate reaction with chemical admixtures and SBR latex has also been done.l When such attempts are completed, new polymeric chemical admixtures for ordinary cement concrete may successfully be developed in the near future. 

As mentioned in Introduction, recently polymer-impregnated mortar and concrete have hardly been used as construction materials except for a few applications. At present, their precast products such as permanent forms are manufactured to order at Materras Oume Co., Ltd. in Japan, which is their only manufacturer in the world. However, a recent great interest has been oriented toward the durability improvement of reinforced concrete structures by the concrete surface impregnation techniques using alkyl alkoxy silane-based barrier (or surface) penetrants, similar to the field polymer impregnation techniques [85]... 

The surface silanols are usually reacted with chloro- or alkoxy silanes, differing in substitution (mono-, di-, and tri-chloro [or alkoxy] silanes) and alkyl chain lengths (C4-C30, dominating C18 and C8). The reaction can be performed in vacuum with the total exclusion of water or in an... 

About this time, it was postulated that the transition state was a trivalent siliconium ion followed by the rapid addition of water. In 1982, this view was supported by Schmidt et al. [15], They studied the hydrolysis of tetra-alkoxy-silanes and various alkoxyalkylsilanes. It was noted that the alkyl-containing silanes reacted significantly faster than the analogous alkoxysilanes. They attributed this result to the stabilizing effect that the electron donating character of the alkyl group (+1 effect) would have on a siliconium ion. 

In recent years, we have been investigating easy and economical functionalization of widely nsed carbon based polymers snch as polybntadienes. The preliminary results of these studies have led our group to discover a highly selective and mild synthetic route to silyl-functionalization of 1,2-polybutadienes (PBD) via Pt-nanocluster catalyzed hydrosilylation of olefin bonds. Unlike other catalytic systems, our system was found to be equally effective with all varieties of functional silanes such as halo-, alkyl-, aryl- and alkoxy- silanes affording high yields and selectivities. In addition, all the hydrosilylation reactions were found to be very clean with the ease of product separation and purifications (Scheme 2). 

A general method for a-hydroxyalkylation involves addition of a Grignard reagent or an alkyllithium to a vinyl(alkoxy)silane. Metal-catalyzed coupling of the resulting a-silycarbanion with an alkyl halide (or epoxide) followed by oxidation results in a secondary alcohol. 

For reverse-phase chromatography purposes, silica sorbents are commonly modified by hydrophobic ligands by means of silanes. These systems are therefore particularly suitable for water intrusion experiments [7]. We studied the influence of the chain nature (perfluorated, alkyl), the chain length and the type of bonding chemistry (mono or trifunctional, chloro- or alkoxy- silanes) on the hydrophobic properties of silica gels. 

Silica gel-based materials for RP chromatography with nonpolar (most often Cg or Cjg alkyls) or moderately polar stationary phases covalently bonded via Si-O-Si-C bonds are prepared by chemical modification of the silanol (Si-OH) groups on the silica gel surface by chloro-silane or alkoxy-silane reagents, and are relatively stable to hydrolysis. The retention in RP increases with increasing surface coverage and length of the bonded alkyl chains, so that Cjg phases show greater retention than Cg-bonded phases. 

The silicon hydrides do not spontaneously add to alkenes either. However, the hydrosilation, or hydrosilylation reaction, of olefins is of significant utility in the preparation of alkyl-subtituted silanes with the use of either radical or transition metal catalysis. The preferred metal catalysts for hydrosilation are platinum complexes. Chloro-platinic acid will catalyze hydrosilations with halosilanes, alkylarylhalosilanes, alkoxy-silanes, and siloxanes that in many cases are quantitative under ambient conditions. Yields and conversions are generally poorer for alkyl,- and arylsilanes. Many other coordination complexes have been found to catalyze the hydrosilation reaction, and these can provide certain advantages, particularly in regiochemistry. Some typical hydrosilation reactions are shown in Table... 

Alkyl, alkoxy, aryl and halogen substituted silanes are referred to by prefixing silane with the specific group present. Hence ... 

Correlations were sought between the structure of external alkoxy silane donors and the microstructure of the obtained polymer chain. Propylene was polymerized in liquid monomer with a heterogeneous high activity Ziegler-Natta catalyst. Fifteen different alkoxy silanes of structure RnSi(OR )4.n, where ns 1-3, R = Ph or alkyl and R = C1.3 alkyl, were used as external donors. Polymers were fractionated by boiling heptane extraction. Microstructures of the polymers were studied by means of C NMR. 

The catalyst was a typical modem supported Zie er-Natta catalyst of type MgCl2/TiCl4/DIBP-AlEt3/ext.donor (DIBPsdiisobutylphthalate). Titanium content of the catalyst was 2.6% b.w. The alkoxy silanes tested, with their abbreviations, are listed in Table 1. Aluminum alkyl was 10% b.w. triethylaluminum (TEA) in heptane firom Schering AG. Propylene was grade 2.5 from Messer Griesheim. 

E. P. Plueddemann (VoiO Coining) 1 agree that covalent bonds are almost certainly formed by reaction of alkoxy silanes with aluminum acetate surface with elimination of alkyl acetate. 

From the above discussion, it becomes obvious that what is needed to impart mobility to backbone-atoms during the gelling of the polymer is to block one substituent of the silicon. Blocking by a less-reactive bulky alkoxy-substituent is undesired since it implies a penalty of an increased contraction due to the increased volume, and yet cracking can start eventually when this group will be hydrolyzed.The better alternative is to select a monomer with a single blocked substituent, which is non-reactive under the mild conditions of the sol-gel reaction. Such monomers are the alkyl-trialkoxy-silanes R -Si(OR)3. This type of monomer is analogous to Al(OR)3, monomers for which successful formation of thin-films by the sol-gel technique has been recently reported (16-18). 

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