Definition and Uses :
Dipropylene glycol [HO- (CH3-CHCH2O) 2-H] is a clear, colorless, slightly viscous liquid that is much less hygroscopic than other common glycols. It is an excellent solvent that is completely miscible with water and many organic compounds, including ethanol, benzene, toluene, castor oil, carbon tetrachloride, and many others. Dipropylene glycol is also an excellent mutual solvent or cosolvent.
Dipropylene glycol is a dihydroxy alcohol and undergoes reactions specific to this type of compound. Its greatest commercial importance is in the reactions in which various ether and ester derivatives are formed. Dipropylene glycol diesters, prepared by the reaction of dipropylene glycol and acids, can be used as plasticizers, fuel additives, resins and dyes, and cosmetic ingredients. A particularly important reaction of dipropylene glycol is with unsaturated dibasic acids such as maleic acid or fumaric acid. The resulting unsaturated polyester resins can then be cross-linked with styrene.
As a solvent, dipropylene glycol is a component of hydraulic brake fluids, cutting oils, and textile oils. It is an excellent solvent for inks, especially those of the steam-set type, and for those used in food packaging where the absence of deposits and odors is essential.
Dipropylene glycol is noncorrosive. It has a low vapor pressure and a high flash point. Consequently, it is easily processed under ordinary commercial conditions. Mild steel is satisfactory for storage tanks except where color requirements are critical. Resin-lined steel, stainless steel, or aluminum tanks provide protection against discoloration and minor iron contamination. It is generally not necessary to blanket storage tanks with inert gas.
Polyester resins prepared from dipropylene glycol tend to be more flexible and less crystalline than those prepared from ethylene glycol.
Dipropylene glycol polyesters are not as sensitive to water as diethylene glycol polyesters. Urethanes ranging from rubberized plastics to foams are synthesized from diisocyanates and polyesters containing dipropylene glycol. The properties of urethanes are determined by the acid and glycol ratios used in the preparation of the polyester component. Urethanes have end uses as adhesives, elastomers, foams, molding compounds, and surface coatings.