Polysiloxanes organofunctional

Chojnowski, J. Synthesis of Organofunctional Polysiloxanes of Various Topologies. In Organosilicon Chemistry VI. From Molecules to Materials Auner, N., Ed. VCH Weinheim, 2005 pp 620-627. 

Chiral Organofunctional Polysiloxanes Synthesis, Properties, and Applications... 

Fig. 5.3. Functions of a coupling agent (a) hydrolysis of organosilane to corresponding silanol (b) hydrogen bonding between hydroxyl groups of silanol and glass surface (c) polysiloxane bonded to glass surface (d) organofunctional R-group reacted with polymer. After Hull (1981).

Several methods of metal removal from process solutions exist. Some of these approaches include crystallization, distillation and extraction. However, these methods can be very time-consuming and often result in loss of some valuable product. To overcome these shortcomings, Degussa has developed Deloxan Metal Scavengers as an attractive option to solve problems associated with transition metal contamination of process solutions. [3, 4, 5] Two resins are commercially available. Deloxan THP 11 (1) is a thiourea functionalized, macroporous, organofunctional polysiloxane while Deloxan MP (2) is mercapto functionalized. 

Spectroscopic techniques are extremely useful for the characterization of filler surfaces treated with surfactants or coupling agents in order to modify interactions in composites. Such an analysis makes possible the study of the chemical composition of the interlayer, the determination of surface coverage and possible coupling of the filler and the polymer. This is especially important in the case of reactive coupling, since, for example, the application of organofunctional silanes may lead to a complicated polysiloxane interlayer of chemically and physically bonded molecules [65]. The description of the principles of the techniques can be found elsewhere [15,66-68], only their application possibilities are discussed here. 

The introduction of organofunctional groups, i.e. the use of alkoxysilanes of the type (R O Si—X—A, where A is a functional organic group and X is a chemically inert spacer permanently linking Si and A, results in a more extensive chemical modification of the materials76. The properties of the organic functions A supplement the properties of the polysiloxane matrix formed by hydrolysis and condensation of the Si(OR )3 and Si(OR )4 units. 

Some authors combined the IPN concept with the use of compatibi-lizers similar to that mentioned in Section 2. These may be a coupling agent such as epoxy-functionalized polysiloxane, polysiloxane copolymers or an organofunctional grafted polyolefin such as poly(ethylene-co-methacrylate) or MA-g-EPDM (maleic anhydride grafted EPDM) [124,125, 133]. Knaub et al. [150] studied a poly(urethane-ureas)/PDMS semi-IPN in... 

At about this time we became aware of a new product from Degussa, a macroporous organofunctional polysiloxane chemically bonded thiourea (DELOXAN) THP that had a high affinity to precious and heavy metals. The manufacturer claimed that the use of the resin, either in suspension or in a fixed-bed, resulted in removal of metals from aqueous or organic solutions. When a small amount of the Deloxan resin was added to the filtered hydrogenation solution containing high amounts of colloidal palladium, stirred and filtered, the palladium content of the filtrate dropped well below the 10 ppm level (Table II). 

Just as the hydrosilylation reaction is important in the synthesis of silanes, so it also serves as a useful route to functional polysiloxanes. The same variety of chemistry as previously described for silanes is available and two further examples are given in equations 82 and 83. One of the main advantages of this route is that the silicon hydride prepolymers are well characterized and readily available materials, which in turn leads to well-defined organofunctional products. A disadvantage is the low efficiency in the use of the precious metal catalyst and the difficulty of its recovery. This is particularly true for systems containing a low level of functionality but this can be partially overcome by using recyclable platinum catalysts on solid supports216,217. 

Organofunctional polysiloxanes with silanol groups can be cold cured with methyl triacetoxysilane, tetrabutyl titanate, etc. On the other hand, organofunctional polysiloxanes with about 0.2% vinyl groups are hot cured with peroxides. All these silicon rubbers are filled with highly dispersed silica since the unfilled rubber is practically useless as an elastomer. 

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