Platinum-cured silicon

The chemistry of silicones is summarized by following the steps necessary to produce a two-part, platinum-cured silicone containing vinyl-stopped polydimethylsiloxane, Si-H-on-chain siloxane, platinum catalyst and catalyst inhibitor. The process begins with silicon dioxide and follows the steps of conversion to sand to elemental silicon. Silicon is reacted with MeCl to make methylchlorosilanes in the methylchlorosilane reaction (MCS). The products from the MCS reaction are separated by distillation and then hydrolyzed and condensed to make the various siloxane polymers. Polymers with methyl, vinyl or Si-H functionality are made as required for the platinum addition-cured silicone product. 

Silicone Good Phenyl-methyl silicones are more stable than are methyl silicones. Platinum cure is superior to peroxide cure full cure during manufacturing can eliminate most postirradiation effects. 

The formulation ofmoisture-ujriiig silicones includes a silicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. A newer class of silicone sealants are known as the silicone latex sealants. These sealants are silicone-in-water emulsions that cure by evaporation of the emulsifying water. Addition-curing silicones in general are two-part systems that cure by the platinum-catalyzed reaction of a silicone hydride with typically a vinyl group attached to silicon. Because no by-products are generated by the cure, there are few volatiles and no shrink in thick sections. 

Only two studies have involved a direct determination of the SiH concentration by IR spectroscopy [5, 10]. The IR measurement of SiH absorption is, however, only suitable for analyzing the reaction in very thin layers or on surfaces. Supplementary to this analysis of the chemical conversion there are also many publications which describe the curing behaviour of industrial platinum-crosslinked silicone rubbers [11,12] (Fig. 1). 

Model Networks. Construction of model networks allows development of quantitative structure property relationships and provide the ability 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 functionality, and controlled molecular weight distribution of cross-linked chains. Silicones 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, co-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

Addition-cured silicones Vinyl-terminated polydimethyl siloxanes DMS-V03-V22, and-V33 (Gelest) Tri- or tetra- functional potysihcon hydride (10-15 phr) Platinum-complex catalysts (2-50 ppm), PCO 72, 73, 74, and 75 (United Chemical Tech.)... 

Heat cured silicone Low and high viscosity chloroplatanic or organo platinum catalyst (1-5 ppm), vinyl resin blend (Polymer VS-50, 100, 90,000 Anders) Dow Coming 3-6605, and 3-6265... 

The silicone elastomers most commonly used for medical applications are the high consistency (HC) and liquid injection molding (LIM) types. The former is most often peroxide cured and the latter platinum cured although there are variations. Both materials are similar in properties. LIM offers greater advantages to the medical device molder and is gaining in popularity. This form of silicone may become the molder s material of choice within the next few years. 

The silicones industry got its start in the late 1930 s (1,2) and became viable after Rochow s 1940 discovery of the direct process which reacts elemental silicon with MeCl to produce methylchlorosilanes (3,4). This chapter attempts to summarize some of the steps which take place in the process of converting sand into silicones. The vignette chosen for this summary is the production of a platinum-cure, so-called addition cured silicone. This brief review will make use of the M, D shorthand wherein an M group is MojSiO- and a D group is -MojSiO-. Substituents on silicon other than Me are represented with a superscript so that M stands for (H2C=CH)Me2SiO- and DH stands for -(Me)(H)SiO- (5). Figure 1 summarizes the entire process covered in this review. 

MDX4 210 MED-42111 40072 40029 Liquid Silicone, 25 Durometer, Platinum Cure Liquid Silicone, 30 Durometer, Platinum Cure... 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

Hirayaina et al. [22] have shown that polyhydrogenmethylsiloxane can bind to aluminum, copper and steel surfaces via activation with a suitable platinum complex. The attached polymer promotes the adhesion of silicone materials whose cure involves SiH/SiVinyl hydrosilylation. Presumably, it would also be effective with other unsaturated organic polymer phases. 

Newer silicone adhesives having solids levels up to 97% are also commercially available [109]. Instead of using silanol condensation reactions, they rely on addition chemistry between vinyl functional silicone oligomers and silicon hydride terminated silicones. This addition reaction is typically facilitated with platinum derived catalysts. This hydrosilation process can be run at reduced oven temperatures, but the finished products typically do not yield the same balance of properties as seen for condensation cure materials. 

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