Hydrosilylation addition cure

Typical components of a silicone adhesive based on hydrosilylation addition cure system... 

When formulating a silicone adhesive, sealant, or coating, based on hydrosilylation addition cure, one must consider the following properties of the uncured product pot life, dispensing technique, rheology, extrusion rate, cure performance. These characteristics directly affect the processing properties of the polymer base or crosslinker parts. The degree of cure conversion at the temperature of interest is determined by properties such as tack free time, cure profile and cure time. Once... 

SiHcone mbber has a three-dimensional network stmeture caused by cross-linking of polydimethjlsiloxane chains. Three reaction types are predominantly employed for the formation of siHcone networks (155) peroxide-induced free-radical processes, hydrosilylation addition cure, and condensation cure. SiHcones have also been cross-Hnked using radiation to produce free radicals or to induce photoinitiated reactions. 

There are numerous applications where cure reaction by-products are not acceptable as they may contaminate other sensitive areas of the devices, and where fast deep section cure is required. These constraints have directed the choice to the platinum-catalyzed hydrosilylation addition cure system. The reaction involves the addition of a hydrido silane (SiH) to an alkenyl organic group (-CH=CH2), typically the vinyl or hexenyl groups. The product of the reaction is the ethylenic bridge (-CH2-CH2-). The alkenyl groups are usually placed at the end of the polymer base chains in structures such as The SiH groups are usually placed in a combed structure within the polymeric or copolymeric chains called cross-linker M-D -M or M-D -Dy-M. (The M, D, etc. nomenclature is explained in Silicones structures.) Typical values of n cover a wide range from 100 to 1000, while the values of x and y vary from 3 to 100. 

Thermal cure system. The thermal cure system is based on a hydrosilylation addition reaction between vinyl-functionalized and silicon-hydrido functionalized polysiloxanes [32,33,35], Unsaturated organic groups react with a Si-H functionality in the presence of a platinum-based catalyst (Scheme 10). 

The variation of organo-substituents at the silicon centers performed by Grignard reactions or by hydrosilylation of H-silanes or H-siloxanes with alkenes and alkines, respectively, gives even today materials with new industrially exploitable properties. Thus, besides the classical routes of condensation and addition curing mechanisms to build silicon network structures, new opportunities of photocrosslinking have been put into practice. This counts as well for radical as for cationic systems. 

The addition cure mechanism, known as hydrosilylation reaction cf. Figure 7.2 [38]), involves the transformation of silicon hydride (Si-H) groups to an unsaturated C-C bond (vinyl/alkenyl functionality) in presence of nobel metal catalyst (platinium, palladium, rhodium, etc.) [34, 38]. 

Vulcanisation of conductive silicone rubber compositions is, like conventional silicone rubber, by peroxide. However inhibition of dichlorobenzoyl peroxide by carbon blacks makes it necessary to use an alternative curing technique, i.e. hydrosilylation or addition curing, for hot-air vulcanisation. Applications for conductive or antistatic silicone rubber include ... 

Hydrosilylation (the addition of R3SiH to a double bond) is an important reaction in the silicone polymer industry. It is used for curing silicone rubber, by cross-linking polymer chains. The reaction is catalyzed by Pt and Rh complexes, following the cycle shown in Figure 3.45. 

Hydrosilylation of unsaturated organosilicon compounds has also found several applications in molecular and polymer organosilicon chemistry. In particular, the addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane, catalyzed exclusively by Pt compounds and providing an activated cure for silicon rubber [10], has been of great practical importance. Hydrosilylation of the vinyl group at silicon seems to be effective synthetic method for preparation of oligomers and polymers with a linear or cyclolinear stmcture (polyhydrosilylation), and can occur either via the addition of dihydro-carbosilanes and -siloxanes to divinyl-silanes and -siloxanes [25, 26] or by intermolecular hydrosilylation [4] (eq. (1)). 

Hydrosilylation Cure. The addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane provides cure for silicone rubber. The commonest activated curing method is based on hydrosilylation of polydiorganosiloxanes containing small numbers of vinyl groups and Si—H groups (usually end-blocked by them) (7) (see Scheme 33). 

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