Hydrolysis glass silane

W ter ndAlcohols. Silanes do not react with pure water or slightly acidified water under normal conditions. A rapid reaction occurs, however, in basic solution with quantitative evolution of hydrogen (3). Alkali leached from glass is sufficient to lead to the hydrolysis of silanes. 

If hydrolysis in silane precursor-polymer systems is carried out using relatively large amounts of the silane, the silica generated can become the continuous phase, with elastomeric polysiloxane dispersed in it. 395-402 -jjjg resultant composite is a polymer-modified glass or ceramic, frequently of very good transparency. Although thermal stability is inferior to that of the neat ceramic component, there are many applications for ceramic-type materials where reduced thermal stability is not a concern. 

The production of vitreous siUca from chemical precursors was first described in patents filed in 1934, including a fabrication method in which fine, high purity powders were produced by decomposing silanes (39). Forms were then cast from aqueous sHps. More importantiy, a dame hydrolysis process which used SiCl as the chemical precursor was described (40). This latter approach led to a marked improvement in glass purity and served as the basis for the processes used in the 1990s to make synthetic vitreous siUca. 

Ishida, H. and Koenig, J.L. (1980). Effect of hydrolysis and drying on the siloxane bonds of a silane coupling agent deposited on E-glass fibers. J. Polym. Sci. Polym. Phys. Edition 18, 233-237. 

Fig. 5.6. Schematic structure of the silane remnant remaining on the glass fiber surface after extractive hydrolysis with hot water. After Cheng et al. (1993).

Although acid-base effects can be important in adhesion our studies indicate that bonding to metals through silane coupling agents is not by an acid-base mechanism, but probably through Si-O-M oxane bonds. As with glass, the hydrolysis and formation of oxane bonds are true equilibria, but the individual equilibrium constants are not known. 

The kinetics of the hydrolysis and condensation of organic functional trialkoxy silanes has been reported by Pohl and Osterholtz [17-19]. The silane coupling agents used as adhesion promoters [1-3] usually have a trialkoxy silane as one of the functional groups, i.e. (MeO)3Si—(CH,),—0,CC(Me)=CH2. If this attaches to a glass substrate, it will form Si—O—Si bonds or if it attaches to metal substrates, it can form M—O—Si bonds. Thus, the work described here can be applicable to providing additional understanding for those processes. 

Some of the fibers in each batch were aged in humid air, in deionized (DI) water, or in silane solution. All of the aging was carried out at 35°C for 30 days. A commercial (Blue-M) controlled atmosphere chamber held the relative humidity (RH) at 70% and the temperature at 34°C. The silane solutions were prepared by adding the requisite amount (1% by volume) of unhydrolyzed y-APS (A-1100 Union Carbide) to triply distilled water or to acetic acid solution. A hydrolysis time of approximately 8 h was allowed prior to adding fibers to the solution. This yielded solutions at pH 10 and pH 4, respectively. The fibers were suspended in Nalgene containers, where the glass surface area-to-solution volume ratio was fixed at 50 cm1. In all cases, the fibers were dried in air at 75°C and the solutions were analyzed for their Si, Al, Ca, and B contents. Table 1 presents the results of these solution analyses. 

The aminosilane coupling agent 3-aminopropyltriethoxysilane or y-amino-propyltriethoxy silane—also abbreviated as 3-APS, y-APS, APS or A1100 (Union Carbide)—is widely used to promote adhesion between polyimide thin films and mineral surfaces such as native-oxide silica, alumina and various glass ceramics [1, 2]. The structure of APS and the hydrolysis reaction sire shown in Fig. 1. Typically, dilute aqueous solutions of 0.1 vol% or approximately 0.080 wt % are employed to prime the mineral surface. The mechanism for the interaction of the bifunctional aminosilane with the mineral surface is the subject of much speculation, although it is conjectured by Linde and Gleason [3] that the amine end initially forms an electrostatic bond with surface hydroxyls. Subsequently, possibly as the result of elevated temperatures, the silanol end of the molecule proceeds to form a siloxane-like bond with the surface and the amine... 

The organosilane chemicals utilized in glass composites are trifunctional silanes—i.e., they contain three hydrolyzable groups per silicon atom. Upon hydrolysis, the silanol group adheres strongly to the glass surface. The mechanism by which this takes place is inherently difficult. The indirect confirmation is much better documented through mechanical property data. 

The excellent adhesion of MS Polymer sealants to conventional construction substrates such as glass, metal, and plastics (e.g., PVC) is derived finm the widely used silane adhesion promoter V-(P-aminoethyl)-3-aminopropyltrimethoxysilane, DYNASYLAN DAMO-T. Another aspect of using a diaminosilane is the intrinsic change of pH that results in fast hydrolysis and condensation reactions of the MS Polymer . To guarantee a certain shelf life, MS Polymer sealants are generally formulated with vinyltrimethoxysilane, DYNASYLAN VTMO as a water scavenger. 

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