Platinum-catalyzed cross-linking

The transition metal-catalyzed addition of the Si-H bond of a hydrosilane across a C=C or C=C bond is a transformation of considerable importance in both large-scale industrial processes and in small-scale organic synthesis.Perhaps the most common industrial application of catalytic hydrosilylation is the platinum-catalyzed cross-linking of vinylsilane polymers with hydrosilanes. The interest in catalytic hydrosilylation in organic synthesis... 

Catalysis. Platinum-catalyzed hydrosilation is used for cross-linking siUcone polymers and for the preparation of functionally substituted silane monomers (250). The most widely used catalyst is chloroplatinic acid (Spier s catalyst), H2PtCl3. Other compounds that catalyze the reaction include Pt(Il)... 

Thicker sections can be cross-linked by hydrosilylation addition. This is the same chemistry used to produce fluorosilicone monomers with the vinyl functionality present on silicon. The catalyst reaction occurs between a vinyl group and silicone hydride.66 The advantage of this system is that it does not produce volatile by-products. On the other hand, the disadvantage is that it is available only as a two-part system.67 Recently, however, one-part, platinum-catalyzed products have been developed.66 The reaction is very rapid and at room temperature it is completed in 10 to 30 minutes. It is accelerated with increasing temperature and at 150°C (302°F) it is completed within a few seconds. This makes the compounds ideal for fast automated injection molding operations.68 One-part systems use the chemical complexing of the catalyst, which is activated at elevated temperatures, or its encapsulation into an impermeable shell, which is solid at room temperature and melts at elevated temperatures68... 

A hyperbranched polycarbosilane (hb-P22) was prepared by platinum-catalyzed polyhydrosilylation of methyldiethynylsilane 22 (Scheme 11) [43]. The tacky, highly soluble and stable polymer underwent thermo- and photo-induced cross-linking reactions through the peripheral ethynyl groups. 

A polymer-supported rhodium catalyst modified with Diop attached to non-cross-linked polystyrene, first used in the asymmetric hydroformylation of styrene, gives 95 % branched aldehyde, however with only 2% ee9. Further developments in the preparation and use of cross-linked polymers with attached chiral phosphane ligands (Diop, DIPHOL, BPPM) in rhodium- and platinum-catalyzed asymmetric hydroformylation have led to good to excellent results with respect to the asymmetric induction62-124 157,159 and arc described in Section 1.5.8 2.2.3.2. The results arc integrated in Table 4. 

Another two-pack RTV formulation cures by hydrosilation, which involves the addition reaction between a polysiloxane containing vinyl groups (obtained by including methylvinyldichlorosilane in the original reaction mixture for synthesis of polysiloxane) and a siloxane cross-linking agent that contains Si-H functional groups, such as Si[OSi(CH3)2H]4. The reaction is catalyzed by chloroplatinic acid or other soluble platinum compounds. 

Atomic spectroscopy (including atomic absorption spectrometry, atomic emission spectrometry, and atomic fluorescence spectrometry) is of use across the span of reactive adhesive technologies. For example, the cure of anaerobic adhesives on non-reactive surfaces is usually assisted by the use of an active metal-based primer. Similarly, the cross-linking of silicone adhesives is promoted by the use of organometallic salts of cobalt, tin, iron, lead, and platinum. In the case of polyurethane adhesives, the key condensation reactions are catalyzed by tin salts (e.g., dibutyl tin dilaurate and stannous octoate). 

Class Two. The use of cross-linked PDMS coatings on paper and plastic substrates avoids this thermal variation difficulty. There is also the advantage that such materials are readily available as commercial products primarily to provide release liners for the facile delivery of PSA-coated labels, decals and tapes. Two types of well-understood cross-linking technology are utilized tin-catalyzed systems based on the condensation of silanol and alkoxysilyl functionalities, and platinum-catalyzed systems based on hydrosilylation addition of SiH to vinyl functional siloxanes. 

Figure 12.9 Formation of linear and cross-linked polydimethylsiloxane networks. Room temperature vulcanization (RTV) is performed by reacting methoxysilyl-terminated polymer 75 and methyltrimethoxysilane 76. Hydrolysis produces transient silanols 77 and 78 whose dehydration yields silicone precursor 79. Two-part systems are based on the platinum-catalyzed addition reaction between vinyl-terminated polysiloxane 80 and polydimethylsiloxane carrying either only terminal 81 or multiple silane (Si—H) pendent groups. Silicone main chains of the resulting polymer 82 are linked through silicon—carbon bonds.

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