Silicone resins preparation

Wachholz and coworkers have used a combination of cryo-GC/FT-IR and GC/MS to study the sUoxane pyrolysis products of a silicone resin prepared from a mixture of MesSiCl (0.34 mol), MeHSiCla (0.56 mol), Me(CH2=CH)SiCl2 (0.56 mol) and PhSiCls (1.56 mol). Heating at 500 °C gave an oil which contained over 30 compounds. FT-IR and MS analysis of three of the major signals allowed the identification of 19, 20 and 21. It is not clear if these species were present in the resin as made or if they result from siloxane bond redistribution during the pyrolysis. 

On the commercial scale silicone resins are prepared batchwise by hydrolysis of a blend of chlorosilanes. In order that the final product shall be cross-linked, a quantity of trichlorosilanes must be incorporated into the blend. A measure of the functionality of the blend is given by the R/Si ratio (see Section 29.3). Whereas a linear polymer will have an R/Si ratio of just over 2 1, the ratio when using trichlorosilane alone will be 1 1. Since these latter materials are brittle, ratios in the range 1.2 to 1.6 1 are used in commercial practice. Since chlorophenylsilanes are also often used, the CH3/CgH5 ratio is a further convenient parameter of use in classifying the resins. 

A patent (FR 2474891 see CA 96 124298c) assigned to B.A. Ashby, GE Company, claims a platinum-siloxane complex which catalyzes hydrosilation of vinylsiloxanes or SiOH groups in the preparation of silicone resins and rubbers. 

Emulsifying agents have been prepared from quaternary ammonium salts with silicon in the cation. There is a large number of alkyd-silicone resins. 

Alkaline hy drolysis of dialkyldialkoxysilanes can sometimes be used for the purpose of preparing silicone resins. 

Added importance centers on the dialkyldialkoxysilanes in view of the fact that they are satisfactory intermediates for the manufacture of silicon resins. These compounds may be made by a modification of the Grignard method without the use of ether as a solvent,58 and many of the alkyltriethoxysilanes listed in the compound index at the end of this chapter also were made this way.69 The allyltri-ethoxysilane so prepared apparently did not polymerize, but the phenylethynylsilanes prepared by the following reactions... 

As in other preparative methods for organosilicon compounds, the direct synthesis produces a mixture of methylchlorosilanes rather than the single compound shown in equation 3. Besides dimethyl-dichlorosilane, the mixture usually contains silicon tetrachloride, tri-chlorosilane, methyltrichlorosilane, methyldichlorosilane, trimethyl-chlorosilane, and even silicon tetramethyl. Under proper conditions, dimethyldichlorosilane is the principal product. Of the other compounds, methyltrichlorosilane usually is next in abundance this substance finds use in the cross-linked methyl silicone resins, or it can be methylated further by the Grignard method to increase the yield of dimethyldichlorosilane. There is no way of recycling it in the direct process, and so supplemental operations are required for the conversion. The interconversion of this and the other minor products of the direct synthesis, involving the exchange of methyl and chlorine groups as desired, has been a special study in itself.10... 

TD Resins. The other important class of silicone resins is TD resins. These materials are simply prepared by cohydrolyzing mixtures of chlorosilanes in oiganic solvents (eq. 36), where R = CH3 or C,H, (407). 

Primary aminoalkylsilanes are important compounds in application fields like adhesion promotion, surface modifying, and crosslinking, but are also used for endcapping of various substrates. Currently in focus is the recently developed endcapper (Fig. 1) which is the key molecule for the preparation of thermoplastic silicone elastomers (TPSE). Modification of silicone resins and fumed silica with 1 leads also to products with interesting economical potential. 

The paint samples were prepared from a high-grade silicone resin emulsion paint [48] with a binder ratio of 10 wt% styrene acrylate to 10 wt% silicone resin emulsion (both 50% solids). The coatings were applied to a mineral substrate and dried at room temperature. Part of each sample was etched for a few minutes in 10% nitric acid so that the organic polymer could be visualized better. 

The elastomers investigated were prepared by curing a silicone resin (supplied by Rhodia Silicones) containing a blend of ingredients polysiloxane-diols, small amounts of hydrogen-methyl polysiloxane, tetraalkoxy silane and fumed silica filler. An organotin ingredient, stannous 2-ethylhexanoate, supplied as a 77% w/w solution in 2-ethyl hexanoic acid, was used as a cure initiator. Typically, 5 wt. of initiator is mixed into the polysiloxane resin. After the initial cure, the material is post-cured at 70°C for 16 h in an air oven. 

In fact, these cyclic trimers may be incorporated into silicone resins of the type employed in surface coatings. In such products, a silanetriol is incorporated to cross-link the resin (this cross-linking reaction has been previously described) and to allow the presence of excess hydroxyl groups after resin preparation. These materials containing excess hydroxyl groups are then applied to a substrate as a surface coating and subsequently cured via a thermal cycle of up to 60 min at 500 °F. When catalyzed, their cure cycle may be reduced to 30-60 min at 400 °F. Some typical catalysts and the levels at which they are usually employed are listed in Table II. 

A wide variety of organosilicone resins containing a combination of M, D, T, and/or Q groups have been prepared and many are commercially manufactured. In addition, resins containing hydrosilation-reactive SiH and SiVi groups or other functionalities, including OH and phenyl groups, are known. Two classes of silicone resins are most widely used in the silicone industry MQ and TD resins. 

Many t3ipes of silicone resins are prepared for many different end uses. Of these, their application in the electrical held, where tiiey impart hi temperature resistance to electrical and electronic parts and equipment, is of particular importance. Silicone-glass laminates retain their strength after, long exposure to temperatures of 600 F (260 C). Certiun reans are capable of being foamed in place at either room temperature or elevated temperature. They have excellent heat-insulating properties, with a heat-distortion temperature of above 700 F (371.1°C). 

A coating prepared by the hydrolysis of an alkytri-alkoxysilane in the presence of an acidic silica sol exhibits a number of new and interesting features. It is soluble in an alcohol-water solution, can be readily applied to transparent plastic articles, and cured at temperatures below the Tg of the plastic to form a clear, hard, chemical and abrasion resistant coating. The cured film consists of small silica particles chemically bonded within a silicone resin matrix. 

The Phenolic Resins Modified with Titanium are Synthesized from a High Ortho Novolac Resin and Tetraisopropyl Titanate. The Phenolic Resin Modified with both Titanium and Silicon is Prepared from 2 Weight Percent Titanium Containing Phenolic Resin and Diphenylsilanediol. (Data from Ref.[l 80])... 

Preparation and Properties of Porous Hybrids Silicone Resin for Interlayer Dielectronic Application... 

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