Two-component RTV

Two-component RTV elastomers have been developed, based on a variety of chemical reactions. Three systems will be illustrated here ... 

Two-component RTV formulations involve separate packages for the polysiloxane and cross-linking agent. A typical two-component RTV formulation cures by reaction of silanol end groups with silicate esters in the presence of a catalyst such as tin octoate or dibutyltin dilaurate (Figure 4.38). 

Uses Base polymer in two-component RTV fluids cure moderator or inhibitor in RTV systems... 

Phenylmethyl/dimethylsiloxane copolymer base oil, lubricant jet engine synthetic PEG-3 dipelarqonate base oils, synthetic lubricant Diester oils Trimethylolpropane tripelargonate base polymer, addition cure silicone elastomers Polydimethylsiloxane, vinyl-terminated base polymer, two-component RTV fluids Dimethicone, vinyidimethyl-terminated base, acid resolution Dehydroabietylamine base, act. ingreds. 

In one type of two-component system, the silicone polymer contains vinyl groups, and the cure can be brought on by reactions with hydride functional siloxanes in the presence of a catalyst such as chloroplatinic acid. In another type the curing reaction involves reactions of silanol-terminated silicone polymer, a curing agent such as ethyl silicate, and a catalyst such as dibutyltin dilaurate. These two-component RTV elastomers are used in encapsulating and molding applications [32]. 

Two-component RTVs also have major automotive applications that take advantage of their superior electrical properties. All modem automobiles make use of electronic modules where protection is essential against shock, heat, water and dirt. Clear silicone potting gels serve these needs very well, and are widely used for this purpose they conform to the elec-... 

These are silicones in liquid or paste form that can be transformed into cross-linked elastomers at or near room temperature. There are two basic types, one component and two component. The one-component room temperature vulcanizing (RTV) elastomers cure upon exposure to air. A typical material of this type is synthesized from a dihydroxy-terminated siloxane oligomer and methyltriacetoxysilane (Scheme 2). The resulting tetraacetoxy compound will flow as a paste and so can be molded into shape. Hydrolysis of the acetoxy groups takes place over a period of hours. Condensation of the resulting silanols gives a highly cross-linked end product. 

Summary Two-component room temperature-vulcanizing, condensation-curing systems (RTV-2) are well known in silicone chemistry. Even silicone-based materials caimot fulfill all requirements in diverse applications. It is therefore desirable to combine the curing properties of silicone-based systems with those of other polymer backbones. The use of isocyanatomethyl-dimethylmonomethoxysilane allows the straightforward derivatization of, e.g., hydroxyl-terminated polymers, which yield mono-silanol-terminated polymers upon hydrolysis. 

RTV-2 adhesives are solidified with a curing agent like all two-component adhesives. This reaction is not diffusion-controlled, so that the adhesives are suitable for bonding (and sealing) large adhesion gaps. There are two different reaction types for initiation of crosslinking condensation reaction and addition reaction. The end products differ in their chemical structures. 

If these preconditions are not given due to structural reasons, an alternative is the two-component system (RTV-2) with shorter curing times. 

Silicones Adhesives and sealing compounds with the basic framework based on -Si-O- bonds. Available as one and two-component systems (RTV-1 and RTV-2). They are characterized by high-temperature resistance as well as high ageing resistance. 

Rhodifuse lode was designed to deliver sodium iodide in a source of drinking water continuously over a one-year period. It can be placed in a well to release a therapeutic supply of iodine (100 pg / day / individual) at a nearly constant rate. It is a modular matrix system which is composed of three polypropylene baskets, each of them containing three matrices (Fig. 10). The cylinder-shaped matrices are loaded with 30% Nal by weight. They are prepared by molding a dispersion of Nal powder in a two-component silicone RTV (platinum catalyzed). 

Adrub RTV Molding Rubber. [Adhesive Prods.] Two-component urethane used for molds, gaskets, sealants, caoDdng, embossing rollers. 

In both one-component and two-component silicone sealants, the system is crosslinked by using molecules with multi-reactive sites. Either displacement/condensation or addition reactions are used in commercially important sealants. In addition reactions, (Equation 2), a sily1-hydride, =SiH, reacts with an unsaturated site with no evolved by-product. These reactions are catalyzed by a transition metal complex (i.e., H2PtCl6). One-component addition systems are technically feasible, but generally require a cure retarder and heat activation for cure, and are not considered RTV sealants. In these sealants a C-C bond is introduced into the backbone of the system and this could decrease the thermal oxidative stability. 

Two-component silicone rubber that vulcanizes at room temperature (RTV-2 silicone rubber) was invented in the 1950s. Since that time it has been developed into high-tech materials that have found many different applications. The most important are ... 

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