Silane groups

At 165°C and in the presence of chloroplatinic acid as catalyst, isoprene reacts with trichlorosilane, metbyldicblorosilane, ethyldichlorosilane, ben2yldichlorosilane, and diben2ylchlorosilane (72). The addition is 1,4- with the substituted silane group attaching to the first carbon atom. 

Two-part room temperature condensation cure. Silicone can be formulated into two-part systems [3,12,14,33] that prevent the reactive groups from coming into contact before they are needed. The reactions in these systems are based on the condensation of a silanol group with an alkoxy silane group, catalyzed by organo-tin compounds (Scheme 9). 

Similarly, efficient tetracyclization (MeAlCl2-promoted) of the bis-allylic silane/ bis-epoxide 97 constitutes the key step in the synthesis of (+)-a-onocerin. In this case, because of the presence of the bis-allylic silane group, a double bis-annula-tion occurs, with the formation of the ethylene-bridge linked bis-decalin system present in the target compound (Scheme 8.26) [46],... 

Enones and enoates undergo 1,2-reduction [115, 191]. Lipshutz et al. reported the effective protection of carbonyl functions by the triisopropylsilyl acyl silane group (TIPS), which allowed the selective conversion of alkenes or alkynes to the corresponding zirconocene complexes [24]. The aldehyde could subsequently be regenerated by desilylation with TBAF [186]. 

The surface hydroxyl groups can be replaced by silane groups (Micale et al, 1985) or by titanate groups (Hotta et al, 1991) e. g. 

The same 3-si lyl-( )-hex-4-enoates have been transformed into /-lactones 67 and 68 by asymmetric dihydroxylation (Scheme 13).[62 821 After mesylation the remaining hydroxyl was substituted by an azide with inversion of configuration. When the silane group was first eliminated to give the allyl azide 69, reduction of the latter could not be achieved. Therefore, reduction and Boc protection of the resulting amine was performed before silane elimination, to give the Boc-protected dipeptide isostere 70. 

Figure 1. (a) Polymeric aminofunctional silane-carrying dialkoxy silane groups, (b) Multiple sawhorse -type siloxane bonding to the fiber surface. 

A number of types of cyclization reaction have been reported in which the reactivity of the acyl silane grouping is a factor in the transformation. These are discussed below. 

Labile silane groups, e.g., alkoxysilane groups, react through a two-stage mechanism. The first stage is hydrolysis (Eq. (2.54)). The second stage is condensation, either with elimination of water, as in Eq. (2.53), or of an alcohol, as in Eq. (2.55) ... 

The sol-gel chemistry has also been used to prepare inorganic inhomogeneities in an organic matrix. Silane end-capped macrodiols can be used. Hydrolysis and condensation of alkoxy silane groups lead to inorganic hard clusters (Fig. 7.6b). Intramolecular reactions and the miscibility of the soft-segment chains with the relatively polar crosslinks determine the size distribution of the clusters (nanofillers). 

Only little work has been focused on the action of ozone onto non-hydrocarbon polymers. This area of research has been investigated by Karandinos et al. [148] who cross-linked polydimethylsiloxanes (PDMS) bearing silane groups Si-H after ozonization. These workers studied the reaction shown in Scheme 41. 

The 1273 K treated sample (figure 14.9a) shows 2 bands, at 3740 and 2290 cm 1. These may be assigned to surface hydroxyls and silane groups, respectively. Upon thermal decomposition of the alkyl chain, hydrogen gas is formed. The evolved gas may react with the silica surface siloxanes, according to reaction (E). 

A dielectric oxide layer (eg. silica) is useful as a shell material because of the stability it lends to the core and its optical transparency. The classic method of Stober for solution deposition of silica are adaptable for coating of nanocrystals with silica shells.111 This method relies on the pH and the concentration of the solution to control the rate of deposition. The natural affinity of silica to oxidic layers has been exploited to obtain silica coating on a family of iron oxide nanoparticlcs including hematite and magnetite111 Such a deposition process is not readily extendable to grow shell layers on metals. The most successful method for silica encapsulation of metal nanoparlides is that due to Mulvaney and co-workers.114 In this method, the surface of the nanoparticles is functionalized with aminopropyltrimethylsilane. a bifunctional molecule with a pendant silane group which is available for condensation of silica. The next step involves the slow deposition of silica in water followed by the fast deposition of silica in ethanol. Fig. 13 shows the TEM images... 

Evaluation of the degree of conversion On the basis of the NIR data and the calibration curve, the degree of conversion of the silane groups was evaluated using the following equation (Eq. 3)... 

This development was reported in 1995 by T.-M. Feng and B.A. Waldman (1995) of Osi Specialities Inc (now part of Witco). Silane-endcapped urethane polymers generally consist of urethane backbones, prepared at a low NCO.OH ratio, with reactive organofunctional silane groups at the end. 

Probes without a functionalized silane group cannot besuccessfiilly applied in this study because they cannot be localized at a special position in the network. This is important for the study of the swelling process of crosslinked polydimethylsiloxanes. If the probe is not attached it will be completely extracted during the swelling process. 

As a rule, tBLMs refer to architectures in which the lipid bilayer is separated from the support through a monomolecular layer tethered to the support via a sulfhydryl or disulfide group (for gold, silver, or mercury supports) or via a silane group (for... 

Several new developments in silanes have been reported re cently. One deficiency of existing silanes was that they were not applicable to high-temperature polymers such as polyimides, either because they were not thermally stable or because they did not facilitate adhesion. A new aromatic imide silane was synthesized with two silane groups attached to the terminal phenyls in the molecule. A... 

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