Thermal cure addition silicone

Hydrosilation silicones or addition cure systems utilize a hydride functional crosslinker with a vinyl functional base polymer and a noble metal catalyst. While the cure can be initiated with UV [48,49], thermal cure versions dominate the commercial market [23,50]. In thermal cure systems, inhibitors are necessary for processing and anchorage additives are common. 

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 state-of-the-art silicone systems used in label stock application are normally solventless and thermal curing. Base polymers for these systems are vinyl-functionalized polydimethylsiloxanes having viscosities of around 200 - 600 mPa.s. Cross-linkers normally are hydride-functionalized polydimethylsiloxanes with a viscosity of around 25 mPa.s. These two components are cross-linked by a platinum catalyst, which can be the Karstedt catalyst. Additionally an inhibitor is added to the silicone mixture to prevent curing before it is applied on the substrate. These inhibitors ate... 

The effect of thermally conductive particles on the thermal properties of silicone rubber was studied. Different sized aluminum oxide was blended with addition cured silicone resin at various crosslink densities and filler loading levels. Thermal impedance of each sample was measured. Statistical analysis of the experimental data showed that hardness was not affected by filler type/size or filler amount however, the amount of crosslinker was statistically significant with respect to hardness. 

Fluorosilicones can be compounded by the addition of mineral fillers and pigments. Fillers for such compounds are most commonly silicas (silicon dioxide), because they are compatible with the elastomeric silicon-oxygen backbone and thermally very stable. They range in surface areas from 0.54 to 400 m2/g and average particle size from 100 to 6 nm. Because of these properties, they offer a great deal of flexibility in reinforcement. Thus, cured compounds can have Durometer A hardness from 40 to 80. Other fillers commonly used in fluorosilicones are calcium carbonate, titanium dioxide, and zinc oxide. 

Let s look at silicone gel, a multi-functional material, for electronic applications. This material has excellent physical properties, typical for organopolysiloxanes and also other unique properties which are derived from the low crosslinking density of the gel. Addition reaction type curing mechanism is used for silicone gels, because it offers excellent thermal stability, low shrinkage and ease of molecular design. 

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. 

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