Ether linkage

Condensation of 2,6-bis(hydroxymethyl-4-methylphenol) under neutral conditions leads to polymers with exclusively benzylic ether linkages and with molecular weights between 2,500 and 20,000. Dibenzyl ether formation is probably a catalyzed 8 2 reaction, involving the displacement of a hydroxyl group. These resins do not show hyperacidity, but they have remarkable affinity towards divalent metal ions. 

Recently a more detailed analysis has been performed by Tanno et who synthesized heat-reactive p- -butylphenolic resins under closely controlled conditions (Eqs. 10 and 11). Their overall chemical structures 

Model compounds of high ortho-ortho resoles have been prepared by Kammerer et al from the condensation of p-chloro-substituted phenols followed by subsequent dehalogenation. They also prepared a series of p-methyl-substituted benzylic ether-containing compounds and analyzed their structures by IR and UV. 

As the condensation time increased, more and more phenolic aldehyde was formed, owing to the cleavage of the benzylic ether linkage. Autoxida-tion at the ether linkages has been proposed to account for these side reactions (Eq. 12).  

Smith and Dawson determined traces of polyethylene glycol and polypropylene glycol by reacting the sample with hydrobromic acid then determining the dibromoethane and dibromopropane fission products by gas chromatography. 

Various workers have discussed the fractionation of polyethylene glycols using laser desoiption / Fourier transform ion cycloUxjn resonance mass spectrometry and flow field - flow fractionation techniques. 

Kirkland et al determined the molecular weight distribution of polyethylene oxide in the 10 to 2 x 10 molecular weight range by field flow fractionation. 

Vincenti et al used chemical ionization mass spectrometry to determine the molecular weight distribution of polyethylene glycol. 

Polyethylene glycols have been detected using an indirect conductiometric detector following chromatographic separation.  

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Analysis The ether linkage can be disconnected directly on the alkyl side ... 

In contrast to alcohols with their nch chemical reactivity ethers (compounds contain mg a C—O—C unit) undergo relatively few chemical reactions As you saw when we discussed Grignard reagents m Chapter 14 and lithium aluminum hydride reduc tions m Chapter 15 this lack of reactivity of ethers makes them valuable as solvents m a number of synthetically important transformations In the present chapter you will learn of the conditions m which an ether linkage acts as a functional group as well as the methods by which ethers are prepared... 

Many substances have more than one ether linkage Two such compounds often used as solvents are the diethers 1 2 dimethoxyethane and 1 4 dioxane Diglyme also a commonly used solvent is a triether... 

Just as the carbon-oxygen bond of alcohols is cleaved on reaction with hydrogen halides (Section 4 8) so too is an ether linkage broken... 

Polyester (Section 20 17) A polymer in which individual structural units are joined by ester bonds Polyether (Section 16 4) A molecule that contains many ether linkages Polyethers occur naturally in a number of antibi otic substances... 

Hexamethylolmelamine can further condense in the presence of an acid catalyst ether linkages can also form (see Urea Eormaldehyde ). A wide variety of resins can be obtained by careful selection of pH, reaction temperature, reactant ratio, amino monomer, and extent of condensation. Eiquid coating resins are prepared by reacting methanol or butanol with the initial methylolated products. These can be used to produce hard, solvent-resistant coatings by heating with a variety of hydroxy, carboxyl, and amide functional polymers to produce a cross-linked film. 

The isopropylidene linkage imparts chemical resistance, the ether linkage imparts temperature resistance, and the sulfone linkage imparts impact strength. The brittleness temperature of polysulfones is — 100°C. Polysulfones are clear, strong, nontoxic, and virtually unbreakable. They do not hydrolyze during autoclaving and are resistant to acids, bases, aqueous solutions, aliphatic hydrocarbons, and alcohols. 

Solutions of fluorosihcones impart oil and water repeUent finishes to nylon—cotton fabrics. One series of C-1 through C-9 perfluoroalkyl substituents with varying stmctures were attached to siHcon through amide or ether linkages. The fluorosihcones having perfluorinated straight-chain... 

Polyetherimide synthesis has been achieved by reaction of a dianhydride containing an ether linkage with a diamine, reaction of a diamine containing an ether linkage with a dianhydride, or nucleophilic displacement of halo or nitro groups of a bisimide by bisphenol dianion (19,20). Such Pis exhibit good thermal stabiUty and melt processibiUty. 

One class of aromatic polyethers consists of polymers with only aromatic rings and ether linkages ia the backbone poly(phenylene oxide)s are examples and are the principal emphasis of this article. A second type contains a wide variety of other functional groups ia the backbone, ia addition to the aromatic units and ether linkages. Many of these polymers are covered ia other articles, based on the other fiinctionahty (see Polymers containing sulfur, POLYSULFONES). 

Ultraviolet radiation causes cleavage of the aryl ether linkage (23). DMPPO undergoes oxidation when exposed to ultraviolet light and oxygen by direct attack on the aromatic ring to produce a variety of ring-cleaved and quinoidal stmctures (24). 

Halogen Displacement. Poly(phenylene oxide)s can also be prepared from 4-halo-2,6-disubstituted phenols by displacement of the halogen to form the ether linkage (48). A trace of an oxidizing agent or free radical initiates the displacement reaction. With 4-bromo-2,6-dimethylphenol, the reaction can be represented as in equation 10 ... 

In addition to the two main reactions, ie, methylolation and condensation, there are a number of other reactions important for the manufacture and uses of amino resins. For example, two methylo1 groups may combine to produce a dimethylene ether linkage and Hberate a molecule of water ... 

In the presence of sulfide or sulfhydryl anions, the quinonemethide is attacked and a benzyl thiol formed. The P-aryl ether linkage to the next phenylpropane unit is broken down as a result of neighboring-group attack by the sulfur, eliminating the aryloxy group which becomes reactive phenolate ion (eq. 2). If sulfide is not present, a principal reaction is the formation of the stable aryl enol ether, ArCH=CHOAr. A smaller amount of this product also forms in the presence of sulfhydryl anion. 

Sulfonates with Ester, Amide, or Ether Linkages. 

Sulfonates with ether linkages include ring-sulfonated alkylphenol ethoxylates and a disulfonated alkyldiphenyl oxide, Dowfax 2A1, and 3B2 (Dow Chemical Company). This surfactant is characterized by high solubiUty in salt solutions, strong acids, or bases. It is used in industrial and institutional cleaners. 

Polyoxyethylene Surfactants. Polyoxyethylene-solubilized nonionics (ethoxylates) were iatroduced ia the United States as textile chemicals shordy before 1940. The solubiUty of these compounds derives from recurring ether linkages ia a polyoxyethylene chain... 

Poly(hydroxyethyl methacrylate)-dye copolymers —The color additives formed by reaction of one or more of the foUowiag reactive dyes with poly(hydroxyethyl methacrylate), so that the sulfate group (or groups) or chlorine substituent of the dye is replaced by an ether linkage to poly(hydroxyethyl methacrylate) (see Dyes, reactive). The dyes that may be used alone or ia combination are... 

When exposed to heat, cotton fabrics, like most substances, increase in temperature to an extent that is proportional to their specific heats. Altering the chemical composition of the fabrics such that large amounts of heat are absorbed and released in repeatable cycles of controllable temperature ranges produces fabrics that are described as temperature adaptable. The process insolubili2es poly(ethylene glycol)s cross-linked with methylolamides in the cotton fabric (78). As with flame-retardant cellulose, attachment is through an ether linkage to the cellulose at a relatively low DS. 

The principal mechanism of polymer degradation during aging is the acid-catalyzed cleavage of the ether linkage in the backbone. The acid acceptor. 

Polysulfone Resins. Commercially important polysulfones are aromatic, ie, in the generalized formula for the repeating unit R and R both contain aromatic rings (see Polymers containing sulfur, polysulfone resins). They all possess ether linkages as weU, so that use of the designations polysulfone, polyarylsulfone (PAS), and polyethersulfone (PES) is somewhat arbitrary. 

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