Polypropylene glycol is an addition polymer of propylene glycol and water. It is represented by the formula HO(C3H6O)nC3H6OH in which n represents the average number of oxypropylene groups. Polypropylene glycol is soluble in water and in certain organic solvents as aliphatic ketones and alcohols and insoluble in ether and in most aliphatic hydrocarbons.