Dipropylene glycol monomethyl ether (CAS 34590-94-8) is the technical name for the solvent the coatings and inks industries normally call DPM. It is a colourless liquid of low odour and low toxicity, with a boiling point near 188 °C, a flash point around 75 °C and complete solubility in water. Those three numbers explain almost every application it has: the high boiling point gives slow evaporation and long open time, the high flash point makes it safe to store and pump in ordinary chemical warehouses, and complete water solubility lets it act as a bridge between water and the resins, pigments and oils that do not dissolve in water on their own.
| Property | Value |
|---|---|
| CAS number | 34590-94-8 |
| Molecular formula | C7H16O3 |
| Molar mass | 148.20 g/mol |
| Boiling point | about 188 °C at 101.3 kPa |
| Relative density | about 0.95 at 20 °C |
| Flash point | about 75 °C, closed cup |
| Water solubility | complete |
The product is manufactured by reacting propylene oxide with methanol and then with a further mole of propylene oxide, which produces a small family of isomer structures. They are not separated, because they behave almost identically in formulation and the mixture is easier and cheaper to supply than any single isomer.
Coupling Agent in Water-Based Coatings and Inks
Water-based paints are not simple solutions. They are dispersions of resin particles and pigment in water, and the organic components that give the film its performance do not always mix with the water phase. A coupling agent is the component that reconciles the two. DPM carries out that duty because one end of the molecule is compatible with water and the other with the resin and pigment surface. In practice this produces four effects formulators rely on:
A uniform, lump-free dispersion that does not separate during storage.
Better wetting of pigment, so colour strength develops fully and fewer defects appear in the film.
Controlled drying. DPM leaves the film later than water and faster solvents, so the coating stays mobile long enough to level and to lose brush or spray marks.
Improved film formation at lower baking temperature, because the resin particles coalesce more readily with the solvent still present.
The same principle is used in water-based gravure, flexographic and screen printing inks, where DPM is added to the solvent blend as a coupling agent so the ink wets the substrate evenly and the printed layer stays consistent across the run.
Active Solvent in Solvent-Based Coatings and Printing Inks
In systems that contain little or no water, DPM is not a coupling agent but a genuine active solvent. It dissolves a wide range of acrylic, alkyd, epoxy, polyurethane and cellulose-ester resins, and it is usually blended with faster evaporating solvents so the drying profile is balanced from the wet film to the dry film.
| System | Function of DPM |
|---|---|
| Solvent-based coatings | Active solvent for the resin; controls open time and flow |
| Gravure and flexographic inks | Slow tail solvent that keeps the ink fluid on the press and prevents premature drying in the cells |
| Screen printing inks | Primary solvent that maintains viscosity and stops the ink drying in the screen mesh |
| Resin production | Viscosity control during the reaction, keeping the batch pumpable |
Cleaners, Degreasers and Paint Removers
Cleaning formulations combine two requirements that are hard to satisfy at once: the product must dissolve grease, oil and dried paint, and it must also dilute with water so the user can rinse or build a water-based concentrate. DPM satisfies both. Because it is completely water miscible it can be formulated into aqueous cleaners without a hydrotrope, and because it is an effective solvent for oily soils it does the actual cleaning work. Typical applications include:
Household and industrial multi-purpose cleaners and hard-surface cleaners.
Metal cleaning and degreasing before painting or assembly.
Paint removers and grease strippers, where the slow evaporation rate keeps the active layer wet on the surface long enough to lift the coating.
Textile Dyeing, Cosmetics and Agrochemical Formulations
In textile processing DPM is used as a coupling agent and solvent in dye liquors, particularly for vat dyes, where it helps the dye penetrate the fibre uniformly and keeps the bath stable through the dyeing cycle. In personal care it serves as a mutual solvent and emollient: it brings together fragrance oils, preservatives and active ingredients that would otherwise separate, and it leaves a light feel on the skin. In crop protection it is used as a solvent and stabiliser in emulsifiable concentrates and suspension concentrates, keeping the active ingredient in solution and preventing crystallisation in the pack or in the spray tank. Floor polishes and finishes also use it to keep the polymer dispersion level and uniform during application.
Handling, Storage and Grade Selection
Store in tightly closed containers in a dry, ventilated place away from strong oxidising agents; the product absorbs moisture from humid air.
Because the flash point is about 75 °C, normal chemical warehousing is adequate, but keep drums away from direct flame and hot surfaces.
Use nitrile or neoprene gloves, safety goggles and local exhaust ventilation where mist or vapour can be generated.
Select technical grade material of about 99% purity measured by gas chromatography, and ask for water content and colour on the certificate of analysis, because both affect performance in coatings and inks.
Frequently Asked Questions
Q: What is dipropylene glycol monomethyl ether used for?
It is used as a coupling agent in water-based coatings and inks, as an active solvent in solvent-based coatings and printing inks, in industrial and household cleaners, in paint removers, in textile dyeing, in cosmetics and in agrochemical formulations.
Q: What is the CAS number of dipropylene glycol monomethyl ether?
The CAS number is 34590-94-8, with the molecular formula C7H16O3 and a molar mass of 148.20 g/mol.
Q: What does a coupling agent do in a water-based coating?
It bridges the water phase and the resin or pigment phase, so the dispersion stays uniform, the pigment wets out properly and the film coalesces evenly as it dries.
Q: Does DPM mix with water?
Yes. It is completely water miscible, which is the property that makes it useful in aqueous cleaners and in water-reducible coating systems.
Q: Why is DPM used in printing inks?
Its slow evaporation makes it an effective tail solvent in gravure and flexographic inks and a primary solvent for screen printing inks, keeping the ink fluid and preventing it from drying in the press or screen.
Q: Is DPM the same as dipropylene glycol methyl ether?
Yes. Both names refer to the same substance and both correspond to CAS 34590-94-8; the monomethyl form is the technically correct description of the structure.