Silane specific forms

Polymeric L-B films fabricated by spreading various polymers at the air/water interface are well-known [6-8], indieating the eapability to take a three-dimensional polymer eoil in dilute solution and form a quasi-two-dimensional array at the air-water interface. By analogy, the adsorption of polymers bearing ehemieally reactive side chains (e.g., thiols, disulfides or silanes) specific for certain interfacial sites, could take advantage of the same organizational principles to yield multipoint attached polymer... 

Silanization of oxidatively activated PDMS surface using functionalized trichloro- or trialkoxysilanes [35, 75-78]. Silanol groups on the activated surface react with the silanes to form stable siloxane bonds. Specific reactive groups introduced by silanes can be used for subsequent grafting. 

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

The plan for a tandem cyclization as the key step in the synthesis of morphine alkaloids has been successfully performed [95]. Three examples are given in Scheme 7.10. Specifically, the initially formed aryl radical, generated by bromine abstraction from compound 74, underwent a tandem cyclization to construct the desired carbocyclic skeleton. Depending on the nature of the Z substituent to the double bond, the product radicals either abstracted hydrogen from silane (Z = C02Me or CN) or eliminated thiyl radical (Z = SPh). 

Under optimum conditions, hydrolysis is rapid, and precedes slower condensation reactions. However, the silanol groups formed in hydrolysis are very reactive, and condensation can be a significant factor even in dilute aqueous solutions. Understanding the kinetics of the hydrolysis and condensation reactions for a specific silane in solution is important because its effectiveness as an adhesion promoter is influenced by the extent of condensation, which, in turn, affects the structure of the interphase in composites. 

The substrate/silane interphase and the silane/matrix interphase are equally important in considering the mechanism of reinforcement by silane coupling agents in composites. The mineral oxide/silane interphase is more well defined than a metal/silane or a silane/matrix interphase. For example, in the case of a metal substrate, surface oxides may dissolve into the silane layer or form a complex. In the case of the silane/matrix interphase, a diffuse boundary layer may exist due to dispersion of physisorbed silanes in the matrix phase or penetration of the matrix resin into chemisorbed silane layers. Many features of the interaction of a silane coupling agent with a polymer matrix are specific to the system, and thus the chemistry of the silane/matrix interphase must be characterized and defined for each system. 

Summarizing, aminosilanes show a fast adsorption on the silica surface. An equilibrium monolayer coating is formed. Modification in aqueous solvent causes polymerization on top of the initial monolayer. For modification from organic solvent, the reactions can be better controlled. With the bifunctional AEAPTS, a secondary silane layer adsorbs on the free primary amine groups of the first monolayer. At high concentration and after long reaction times, for both aminosilane types, a further non-specific deposition occurs. 

We have a specific interest in the self-assembled structures formed by poly(ferrocenylsilane) block copolymers, such as poly(ferrocenyldimethylsilane-Z -dimethyl-siloxane) (PFS-PDMS) and (ferrocenyldimethylsilane-Z>-isoprene) (PFS-PI). The PFS block contains an iron atom in the main chain repeat unit. These polymers are particularly promising for novel applications, since they can be used as charge-transport materials and, by pyrolysis, as precursors to ferromagnetic ceramics [4-6], Moreover, they can by synthesized with a very narrow molar mass distribution, with excellent control over chain length and composition [7], An important feature of PFS is that the polymers bearing two methyl groups on the silane unit are crystalline, whereas polymers with two different substituents on each silane (methyl, ethyl methyl, phenyl) are atactic and remain amorphous. This feature of the polymer composition has a strong influence on the type of self assembled structures that these poly-... 

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