Propylene glycol
<p>45% of propylene glycol produced is used as chemical feedstock for the production of unsaturated polyester resins. In this regard, propylene glycol reacts with a mixture of unsaturated <a href="https://en.wikipedia.org/wiki/Maleic_anhydride" title="Maleic anhydride">maleic anhydride</a> and <a href="https://en.wikipedia.org/wiki/Isophthalic_acid" title="Isophthalic acid">isophthalic acid</a> to give a copolymer. This partially unsaturated polymer undergoes further crosslinking to yield thermoset plastics. Related to this application, propylene glycol reacts with propylene oxide to give oligomers and polymers that are used to produce polyurethanes.<sup id="cite_ref-ullmann_4-1" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-ullmann-4">[4]</a></sup>
Propylene glycol is considered <a href="https://en.wikipedia.org/wiki/Generally_recognized_as_safe" title="Generally recognized as safe">generally recognized as safe</a> (GRAS) by the <a href="https://en.wikipedia.org/wiki/U.S._Food_and_Drug_Administration" title="U.S. Food and Drug Administration" class="mw-redirect">U.S. Food and Drug Administration</a>, and it is used as an <a href="https://en.wikipedia.org/wiki/Humectant" title="Humectant">humectant</a> (E1520), solvent, and preservative in food and for tobacco products, as well as being the major ingredient in the liquid used in <a href="https://en.wikipedia.org/wiki/Electronic_cigarettes" title="Electronic cigarettes" class="mw-redirect">electronic cigarettes</a>. It is also used in pharmaceutical and personal care products.<sup id="cite_ref-ullmann_4-2" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-ullmann-4">[4]</a></sup> Propylene glycol is a solvent in many <a href="https://en.wikipedia.org/wiki/Pharmaceuticals" title="Pharmaceuticals" class="mw-redirect">pharmaceuticals</a>, including <a href="https://en.wikipedia.org/wiki/Oral_administration" title="Oral administration">oral</a>, <a href="https://en.wikipedia.org/wiki/Injectable" title="Injectable" class="mw-redirect">injectable</a> and <a href="https://en.wikipedia.org/wiki/Topical" title="Topical" class="mw-redirect">topical</a> formulations, such as for <a href="https://en.wikipedia.org/wiki/Diazepam" title="Diazepam">diazepam</a> and <a href="https://en.wikipedia.org/wiki/Lorazepam" title="Lorazepam">lorazepam</a> that are <a href="https://en.wikipedia.org/wiki/Insoluble" title="Insoluble" class="mw-redirect">insoluble</a> in water, use propylene glycol as a solvent in their <a href="https://en.wikipedia.org/wiki/Clinic" title="Clinic">clinical</a>, injectable forms.<sup id="cite_ref-svt_7-0" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-svt-7">[7]</a></sup>
Like ethylene glycol, propylene glycol is able to lower the melting point of water, and so it is used as aircraft <a href="https://en.wikipedia.org/wiki/De-icing" title="De-icing" class="mw-redirect">de-icing</a> fluid.<sup id="cite_ref-ullmann_4-3" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-ullmann-4">[4]</a></sup><sup id="cite_ref-8" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-8">[8]</a></sup> It is similarly used as automotive <a href="https://en.wikipedia.org/wiki/Antifreeze" title="Antifreeze">antifreeze</a>.<sup id="cite_ref-SeafitAntifreeze_9-0" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-SeafitAntifreeze-9">[9]</a></sup> Water-propylene glycol mixtures dyed pink to indicate the mixture is relatively nontoxic are sold under the name of <a href="https://en.wikipedia.org/wiki/Recreational_vehicle" title="Recreational vehicle">RV</a> or marine antifreeze. It is also used to winterize a vacant structure.<sup id="cite_ref-10" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-10">[10]</a></sup> The <a href="https://en.wikipedia.org/wiki/Eutectic_composition" title="Eutectic composition" class="mw-redirect">eutectic composition</a>/temperature is 60:40 propylene glycol:water/-60°C.<sup id="cite_ref-11" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-11">[11]</a></sup><sup id="cite_ref-12" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-12">[12]</a></sup> The -50°F/-45°C commercial product is, however, water rich; a typical formulation is 40:60.<sup id="cite_ref-13" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-13">[13]</a></sup>
Propylene glycol is a minor ingredient in the oil dispersant <a href="https://en.wikipedia.org/wiki/Corexit" title="Corexit">Corexit</a>, used in great quantities during the <a href="https://en.wikipedia.org/wiki/Deepwater_Horizon_oil_spill" title="Deepwater Horizon oil spill">Deepwater Horizon oil spill</a>.<sup id="cite_ref-NALCO.2C_Corexit_9527A_Safety_Data_Sheet_14-0" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-NALCO.2C_Corexit_9527A_Safety_Data_Sheet-14">[14]</a></sup><sup id="cite_ref-ProPublica_15-0" class="reference"><a href="https://en.wikipedia.org/wiki/Propylene_glycol#cite_note-ProPublica-15">[15]</a></sup></p>