Polypropylene glycol is a viscous, odorless liquid used in household products, cosmetics, and industry. It is made from propylene oxide and has varying molecular units. Production methods using alternative sources are being investigated. PPG is similar to PEG in properties and is used as a moisturizer, thickener, defoamer, and lubricant. It is also used in the manufacture of polyurethane, epoxies, and coatings.
Polypropylene glycol (PPG) is a colorless, odorless, viscous liquid that is a polymer of propylene oxide. It is also known as polypropylene oxide. There are a number of different forms that vary in the number of molecular units in the polymer. It is an ingredient in many household products and cosmetics and is widely used in industry for the manufacture of other products. As of 2011, the main production method of this chemical requires raw materials from the petrochemical industry; however, alternative methods that do not depend on fossil fuels are being investigated.
The chemical composition of polypropylene glycol can be summarized as H(C3H6O)nOH, where C3H6O is propylene oxide and n is the number of occurrences of this molecular unit, commonly between 300 and 4,000. It therefore consists of repeating units of propylene oxide with a hydrogen atom at one end and a hydroxyl group (OH) at the other. There are several forms of PPG commercially available. They are generally named by molar mass, roughly equivalent to the number of Propylene Oxide units in the polymer, such as PPG 425, PPG 1200, and PPG 4000.
In the normal manufacturing process, propylene, a by-product of gasoline manufacturing, is converted into Propylene Oxide. This compound is then polymerized, using a strong base, such as potassium hydroxide, as a catalyst. In an effort to reduce dependence on fossil fuels, alternative means of production are being sought. One proposed method involves converting glucose from corn to lactic acid, which can then be used with a copper catalyst to synthesize PPG.
In many respects, polypropylene glycol resembles polyethylene glycol (PEG) in its properties. The viscosity of the liquid increases and its solubility in water decreases as the molar mass, or molecular weight, increases. The molar mass depends on the number of molecular units in the polymer.
Many of polypropylene glycol’s uses relate to its physical, rather than chemical, properties, although its low toxicity is a factor in many of its applications. PPG polymers are used in many cosmetic and personal care products to absorb and retain moisture and as thickeners. Confusingly, the Cosmetic, Toiletry & Fragrance Association (CTFA) has its own system of acronyms for these compounds: for example, PPG-9 in this system is PPG 425 in terms of molar mass. PPGs are used as defoamers in many industrial processes, including food production, as lubricants, and in the study of rheology. They are also used in the manufacture of some forms of polyurethane, flexible epoxies, and radiation-curable coatings.
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