Siloxane-1,1 -diols

Keywords Silanediols / Siloxane-1,1 -diols / Condensation / Distribution / Kinetics... 

Summary The acid- and base-catalyzed reaction of some partially water-soluble silanediols XMeSi(OH)2 and siloxane-1,1-diols have been investigated preferably in the two-phase system water/toluene. The diols react in water only whereas the less water-soluble products of the primary reactions are dissolved in the inert toluene phase. The silanediols give condensation only, the siloxanediols also show Si-O-Si-cleavage. The distribution rates of the model compounds and the rate constants of the primary reactions in water have been investigated,... 

The silanediols XMeSi(OH)2 and the siloxane-1,1-diols (Table 1) have been prepared by hydrolysis of the corresponding dichlorosilanes. We succeeded in the preparation of the previously unknown hexamethylcyclotetrasiloxan-l,l-diol, (D3D °" 2 ), (Fig. 1. ). 

Table 2. Differential Scanning Calorimetry data of siloxane-diols 2 - S and copolymers 6 -16.

Linear short-chain dimethylsiloxanes (oligomers) from hydrolysis or methanolysis processes are utilized as the starting material in the manufacture of polydiorganosiloxanes by polycondensation. If linear siloxane polymers are required, dimethyldichlorosilane with a high purity is necessary, since distillalive processing of siloxane diols is not possible due to their tendency to condensation (with cleavage of water). 

Block copolymers with known block lengths were prepared by Bostick (1970) using organocyclosiloxanes with lithium-based catalysts. For example, when hexamethylcyclotrisiloxane is reacted with the lithium salt of diphenyl-siloxane diol, a multistep addition polymerization occurs ... 

The chemistry of silicone sealants is much the same as that discussed above for silicone pressure-sensitive and mbber-based adhesives, with the exception of the MQ taddfier addition. The basic polymer for silicone sealants is that based upon poly (dimethyl siloxane)diol. This material can be cured by any one of a number of polyfunctional curing agents, all of which are based upon tetrachlorosilane. Thus, such materials as methyl triacetoxysilane or methyl trimethoxysilane can be used in conjunction with a poly(dimethyl siloxane)diol to yield a room... 

Zorbax PSM packings are produced in three forms unmodified, trimethyl-silane modified, and diol modified. Modified Zorbax PSM packings are produced by chemically bonding a layer on the silica surface through siloxane bonds (Table 3.1). Silanized Zorbax PSM packings suppress adsorption effects and are the preferred choice when the mobile phase contains organic solvents. Unsilanized and diol modified Zorbax PSM packings should be used when the mobile phase consists of aqueous solvents. 

The same type of reaction has been used just recently by Sonnek and coworkers [17] to get access to di(meth)acrylate structures added to siloxanes via hydrolytically stable silicon-carbon bond formation. 2-Heptamethyltrisiloxanylbut-2-en-l,4-diylbismethacrylate is accordingly prepared in 90 % yield by hydrosilylation of the bismethacrylate of 2-butyne-l,4-diol. 

The formation of the linear cyclic polymers is dependent upon the reaction conditions. Hydrolysis with water alone gives rise to 50-80 per cent linear polydimethyl siloxane a, w-diols and 50-20 per cent polydimethyl-cyclosiloxanes. 

The MTO-catalysed oxidation of silanes to silanols (data reported in Table 10) and epoxidation of olefins (data reported in Table 11) by aqueous H2O2 proceeds in high yields and excellent product chemoselectivities (no siloxane and no diol are observed as byproducts) in the presence of zeolite-Y [64], which are better than those obtained under homogeneous conditions (data in Table 11). For example, only 26% of PhMe2SiH is converted with as low as 20% selectivity towards silanol in 24 h when reacted with 85% H2O2 and catalysed by MTO (entry 5, Table 10). However, in the presence of zeolite-Y, 99% conversion is reached with 99% selectivity (entry 6, Table 10). The confinement of the oxidative species inside the 12 A supercages... 

See under Siloxanes in article on Silanes in this Vol for the definition and a brief description of the basic molecular structure. The name silicone was created by F.S, Kipping as an analogy to ketones. However, his silicane-diols , (Aryl)2Si(OH)2 could not be dehydrated to silicones but always condensed to higher mw Si—0—Si compds. These structures were then (early 1900s) referred to as silicones. In time the name has come to represent any organo-silicon oxide polymer, such as polydimethy-siloxane (see below) ... 

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