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There are currently five U.S. manufacturers of propylene glycol ether derivatives. The ethers of mono‐, di‐, tri‐, and polypropylene glycol are prepared commercially by reacting propylene oxide with the alcohol of choice in the presence of a catalyst. They also may be prepared by direct alkylation of the selected glycol with an appropriate alkylating agent such as a dialkyl sulfate in the presence of an alkali. The monoalkyl ethers of dipropylene glycol presumably can appear in four isomeric forms. The commercial product Dowanol® DPM Glycol Ether is believed to be a mixture of these but to consist to a very large extent of the isomer in which the alkyl group has replaced the hydrogen of the primary hydroxyl group of the dipropylene glycol; the internal ether linkage is between the 2 position of the alkyl‐etherized propylene unit and the primary carbon of the other propylene unit, thus leaving the remaining secondary hydroxyl group unsubstituted. In the case of dipropylene glycol monomethyl ether, the primary isomer is 1‐(2‐methoxy‐1‐methylethoxy)‐2‐propanol. The monoalkyl ethers of tripropylene glycol can appear in eight isomeric forms. The commercial product Dowanol® TPM Glycol Ether, however, is believed to be a mixture of isomers consisting largely of the one in which the alkyl group displaces the hydrogen of the primary hydroxyl group of the tripropylene glycol and the internal ether linkages are between secondary and primary carbons. The known physical properties of the most common ethers are given. The methyl and ethyl ethers of these propylene glycols are miscible with both water and a great variety of organic solvents. The butyl ethers have limited water solubility but are miscible with most organic solvents. This mutual solvency makes them valuable as coupling, coalescing, and dispersing agents. These glycol ethers have found applications as solvents for surface coatings, inks, lacquers, paints, resins, dyes, agricultural chemicals, and other oils and greases. The di‐ and tripropylene series also are used as ingredients in hydraulic brake fluids. Occupational exposure would normally be limited to dermal and/or inhalation exposure. The toxicological activity of the propylene glycol–based ethers generally indicates a low order of toxicity. Under typical conditions of exposure and use, propylene glycol ethers pose little hazard. As with many other solvents, appropriate precautions should be employed to minimize dermal and eye contact and to avoid prolonged or repeated exposures to high vapor concentrations. The propylene glycol ethers (PGEs), even at much higher exposure levels, do not cause the types of toxicity produced by certain of the ethylene glycol ethers (EGEs). Specifically, they do not cause damage to the thymus, testes, kidneys, blood, and blood‐forming tissues as seen with ethylene glycol methyl and ethyl ethers. In addition, the propylene glycol ethers do not induce the development effects of certain of the methyl‐ and ethyl‐substituted ethylene glycol–based ethers nor the hemolysis and associated secondary effects seen in laboratory animals with EGE. Other propylene glycol ethers also exhibit a similar lack of toxicity. For example, propylene glycol ethyl ether (PGEE) and its acetate do not cause the critical toxicities of testicular, thymic, or blood injury and do not produce birth defects. Propylene glycol tertiary ‐butyl ether (PGTBE) also has been tested and fails to cause these toxicities or birth defects in rats exposed by inhalation to substantial concentrations. The methyl, ethyl, and n ‐butyl ethers of butylene glycol considered herein are prepared by reacting the appropriate alcohol with so‐called straight‐chain butylene oxide, consisting of about 80% 1,2 isomer and about 20% 2,3 isomer in the presence of a catalyst. They are colorless liquids with slight, pleasant odors. The methyl and ethyl ethers are miscible with water, but the butyl ether has limited solubility. All are miscible with many organic solvents and oils; thus they are useful as mutual solvents, dispersing agents, and solvents for inks, resins, lacquers, oils, and greases. Industrial exposure may occr by any of the common routes. The common esters and diesters of the polyols are prepared commercially by esterifying the particular polyol with the acid, acid anhydride, or acid chloride of choice in the presence of a catalyst. Mono‐ or diesters result, depending on the proportions of each reactant employed. The ether esters are prepared by esterifying the glycol ether in a similar manner. Other methods can also be used. The acetic acid esters have remarkable solvent properties for oils, greases, inks, adhesives, and resins. They are widely used in lacquers, enamels, dopes, and adhesives to dissolve the plastics or resins. They are also used in lacquer, paint, and varnish removers. Generally speaking, the fatty‐acid esters of the glycols and glycol ethers, in either the liquid or vapor state, are more irritating to the mucous membranes than those of the parent glycol or glycol ethers. However, once absorbed into the body, the esters are hydrolyzed and the systemic effect is quite typical of the parent glycol or glycol ethers. It should be noted that the nitric acid esters of glycols are highly toxic and exert a physiological action quite different from that of the parent polyols. These materials are covered. The nitric acid esters of glycols are not typical of the esters or ether esters of organic acids and are considered separately in this chapter. They are used as explosives, usually in combination with nitroglycerin, to reduce the freezing point. Industrial exposures of consequence are most likely to occur through the inhalation of vapors, but may also occur through contact with the eyes and skin. With the dinitrate, a serious hazard exists from absorption through the skin.

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The toxicity of the polymers discussed in this chapter may be generally attributed to the residual monomers, catalysts, and other additives present rather than the polymer per se . The cured polymer itself may be of high molecular weight and, consequently, more or less toxicologically inert. Carefully manufactured, highly refined polymers contain few residual toxic chemicals. However, some of the polymers discussed in this chapter, at least in some applications, go through an intermediate stage consisting of “prepolymers” (sometimes referred to as “resins”) that react further to achieve their final, cured form. An example is a polyurethane system for making foam cushions. To manufacture polyurethane foam for cushions, workers combine diisocyanate molecules with a polyol prepolymer. Such “systems” inherently have more potential for exposure of workers if not the general public to toxic monomers or other reactive chemicals. The exposure potential of glues, paints, and coatings may extend more broadly to the consumer. Thus, examination of the toxicity of the polymers discussed in this chapter focuses on monomers and prepolymers. This is not always so. Some of polymers in this chapter are used in biomedical devices or in a way that puts them in intimate contact with humans. Here, the issue of biodegradation becomes important because of potential toxicity from breakdown products of the polymer, or rejection may ensue if the polymer is incompatible with the surrounding tissues.

There are seven U.S. manufacturers of ethers and other derivatives of ethylene glycol (EG), diethylene glycol (DEG), and higher glycols. Five of them are members of the American Chemistry Council (ACC) Glycol Ethers' Panel. The glycol ethers most commonly encountered industrially are colorless liquids that have mild ethereal odors. Alkyl glycol ethers are manufactured in a closed, continuous process by reacting ethylene oxide with an anhydrous alcohol in the presence of a suitable catalyst. Depending on the molar ratios of the reactants and other process parameters, the product mixtures obtained contain varying amounts of the monoethylene, diethylene, triethylene, and higher glycol ethers. Typically, the products in these mixtures are separated and purified by fractional distillation. The miscibility of most of these ethers with water and with a large number of organic solvents makes them especially useful as solvents in oil–water compositions. Their relatively slow rate of evaporation also makes them useful as solvents and coalescing agents in paints. Other uses include inks, cleaners, chemical intermediates, process solvents, brake fluids, and deicers. The ethers of the higher glycols are used as hydraulic fluids. An estimate of the U.S. production and use of representative ethylene glycol ethers is presented. Production of ethylene glycol ethers (total) in Western Europe amounted to 245 thousand metric tons in 1995. Occupational exposure to glycol ethers occurs dermally and by inhalation. Ingestion is not a concern in industrial exposure, although some cases of intentional ingestion of consumer products containing ethylene glycol ethers have been reported. A number of analytical methods have been published that are suitable for detecting glycol ethers in environmental air samples. Glycol ethers generally have low acute, single‐dose toxicity, and LD 50 values generally range from 1.0 to 4.0 g/kg of body weight. In animals and humans, high‐dose administrations (>350 mg/kg) result in central nervous system (CNS) depression, although the results from many studies show no specific damage to neural tissues. Other toxicological effects attributable to glycol ethers are associated with metabolism to the corresponding alkoxyacetic acids. In the case of EGME, EGEE, and certain other glycol ether derivatives, significant reproductive, developmental, hematologic, and immunologic effects have been associated with the formation of either methoxyacetic acid (MAA) or ethoxyacetic acids (EAA). For other glycol ether derivatives substituted with propyl, butyl, or higher homologues, both developmental effects secondary to maternal toxicity (without teratogenic effects) and hematologic effects are observed. Ethylene glycol ethers and acetates may enter the environment from manufacturing effluents and emissions and as a result of their use in commercial products.