Silane cross-linking reaction

The hydrosilation of the double bonds with Karstedt catalyst at 70 °C was quantitative. HSi(OEt)3, HSi(OMe)3 and HSi(CH3)2Cl were used for this reaction to obtain a functionalized polysiloxane block. While the trialkoxy-silane groups can be hydrolyzed and used for cross-linking reactions, the chlorosilanes are able to react with a variety of nucleophiles, such as alcohols, carboxylic acids, etc. 

The cross-linking reaction is facilitated by the use of a cross-linking catalyst, which is typically an organotin compound. There are several variations of the silane cross-linking process. In one process, compounding, grafting, and extrusion onto wire are carried out in the same extruder. 

Such a scaling idea leads to the experimental identification of the gel point from the measurement of the dynamic mechanical moduli. Figures 8.18(b) and 8.19 show a typical example. In the course of the cross-linking reaction of poly(dimethyl siloxane) by tetra-functional silane, there is a time at which the storage and loss modulus exhibit... 

Silane cross-linking - specifically the one-shot system - employs a three-component mix (of peroxide, silane, and tin catalyst, either in the form of liquid of dry masterbatch) that is added separately to the compound during extrusion. The reaction is in two stages, the temperature of extrusion being used to decompose the peroxide in order to react the silane molecule onto the polymer backbone. 

With silane cross-linking processes, the cross-linking reactions occur while the polymer is in the solid state. As such, the polyethylene material exists with both crystalline and amorphous regions being present. There will be differences in the degree of... 

Gross-Linking. A variety of PE resins, after their synthesis, can be modified by cross-linking with peroxides, hydrolysis of silane-grafted polymers, ionic bonding of chain carboxyl groups (ionomers), chlorination, graft copolymerization, hydrolysis of vinyl acetate copolymers, and other reactions. 

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)... 

Model Networks. Constmction of model networks allows development of quantitative stmcture property relationships and provide the abiUty to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionahty, and controlled molecular weight distribution of cross-linked chains. Sihcones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, ffl-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

Solid palladium scavengers, PVPy, QTU were pmchased from commercial somces. The mesoporous silica material, S102-SH, was prepared via reaction of SBA-15 (110 A pore diameter) with 3-mercaptopropyltrimethoxysilane (16). Specifically, a toluene suspension of SBA-15 and 3-mercaptopropyltrimethoxysilane was heated at reflux for two days under Ar. Water was then added to promote the cross-linking and the mixture was heated at reflux for an additional day. The sohds were filtered and washed with copious amounts of toluene, hexanes, and methanol to remove unreacted silanes. The solids were finally Soxhlet extracted with dichloromethane at reflux temperature for 3 days, dried, and stored in a nitrogen dry box. The final solid contained 7.5 wt% sulfur (2.3 mmole S/g solid). 

Silicones can be prepared in such a way that they contain only one percent or less of vinyl groups and silicon hydrides, which undergo a catalytic hydrosilylation reaction to give the desired cross-linking (Figure 18.3). Vinyl silanes are made by Si-H addition to acetylene, and thus two hydrosilylations are involved. 

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

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