Pure silicone resins

Modified or pure silicone resin with aluminum Zinc silicate... 

Modified or pure silicone resin with aluminum These silicone-based aluminum paints can be used for temperatures between 260° and 540°C. They require a minimum temperature for curing (usually about 260° C) and in general have poor corrosion and weather resistance. 

Pure silicone resins are poly(organosiloxanes) with a high proportion of branching, i.e. tri-or tetra-functional siloxy groups together with di- and optionally mono-functional siloxy groups. 

Most silicone resins are copolymers of methyl and phenyl substituted monomers. Based on the type of organic substitution, the two main types of pure silicone resins are high-methyl silicone resins and high-phenyl silicone resins. 

Silicone alkyds These are alkyds modified with silicone resin. They have superior resistance to weathering (particularly gloss retention) than pure alkyds but are generally significantly more expensive. They are useful for exterior use where appearance is important. 

Silicone resins can be made from pure polyorganic siloxanes with a high percentage of tri- and tetrafunctional siloxy groups, which are crosslinked in the presence of a catalyst by heating at 250 °C for a long time. They can also be made from a mixture of polyorganic siloxanes with polyesters. 

As a group, the methyl silicone resins are characterized by excellent thermal stability and good resistance to oxidation. Samples have been heated to 550° in vacuo and to 500° in hydrogen without disintegration, decomposition, or melting a transparent piece heated in air to 200° C. for one year looks the same as another piece of the same disk kept at room temperature.18 Above 300° C. the resins will oxidize slowly if they have free access to air, but for analytical combustions it has been found necessary to heat the samples to 550° C. or more in pure oxygen. The residue from oxidation under these conditions is a white mass of silica. 

It would be interesting at this point to predict from the present uses of the silicone materials the future trends of application. However, it is doubtful that present experience gives any dependable basis at all for such predictions. When research on silicone resins began, interest centered in their high-temperature performance, and it could not have been predicted at that time that some oily polymers would become important, purely for their Zow-temperature performance, or that some types of silicone resin would be valued purely for their electrical characteristics, or that some intermediates required for methyl silicone production would render many different kinds of surfaces water-repellent. Neither can it be expected that these unrelated and unforeseen outcomes of research have all appeared and that the flow of discoveries will now cease it is more likely that new developments will appear more rapidly as more people become interested and research in the field accelerates. Extrapolation of the present trend would therefore seem to be idle and misleading. 

Silicones pure silicon, fumed silica, silanes, silicone resins and rubbers Materials advanced ceramics, boron compounds, surface treatments and silicon carbide. 

Silicone resins contain, in addition to the D integral parts —O—Si(R2)—O—, some T parts —O—Si(R)(0)—O—, and on both ends of the chains they have OH or OR residues. Pure methyl silicone resins are comparatively brittle and moderately heat resistant. Industrial silicone resin solutions consist of cross-linked methylphenyl polysiloxanes. The heat resistance of the resins is increased by halogenating the phenyl residues. For the manufacture of moulded plastics and laminates, silicone resins may be mixed with filler, such as glass fiber, quartz powder, glimmer, pigments, etc. 

There are numerous types of paints based on silicone which are combined either with alkyd or acrylic resin. Pure silicone resists temperature up to 600°C and has excellent weathering properties. The copolymer is obtained by reaction between the hydroxyl groups in the alkyd resins with the hydroxyl groups in the silicon intermediates. 

In the first step, decomposition of PU and volatilisation of silicone oligomers occur, while in the second one the organic bonds in the silicone resin are broken, with release of methane (ceramisation). The data showed that PU decomposition leaves a carbonaceous residue (about 8 wt%) within the SiOG material, while the ceramic yield of a pure trimethylolpropane trimethacrylate material is about 84 wt% at 1200 °C. Calculated... 

Silicone resins consist of branched polymers, production of which is based on the hydrolysis of trichlorosilanes. If pure trichlorosilanes are hydrolysed, the products are highly cross-linked and intractable and are unsuitable for normal applications. In order to reduce the degree of cross-linking, it is usual to subject a blend of tri- and dichlorosilanes to hydrolysis. A convenient measure of the functionality of a blend is given by the R/Si value, which is the ratio of the numbers of organic groups and silicon atoms. (Thus pure dimethyldichlorosilane and methyltrichlorosilane have R/Si values of 2 and 1 respectively.) For the preparation of commercial resins, R/Si values in the range 1.2-1.6 are usual. Most commercial silicone resins contain both methyl... 

---