Polyol

Lore & Background

Polyols are classified by their backbone chemistry, including polyether, polyester, polycarbonate, and acrylic types. Polyether polyols can be further subdivided into polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetrahydrofuran (PTMEG), which have 2, 3, and 4 carbon atoms per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available, and there is an increasing trend to use biobased polyols from renewable sources. Low molecular weight polyols such as glycerol, trimethylolpropane, and pentaerythritol are widely used as crosslinking agents and chain extenders in polymer chemistry. They are key components in alkyd resins, which are used in paints and molds for casting. In polyurethane prepolymer production, low molecular weight diols like 1,4-butanediol serve as chain extenders, increasing molecular weight and viscosity through additional hydrogen bonding. Sugar alcohols are a class of low molecular weight polyols obtained by hydrogenation of sugars, with the formula (CHOH)nH2 where n = 4–6. They are added to foods for lower caloric content and to chewing gum because they do not contribute to tooth decay. Some sugar alcohols, such as myoinositol, pinitol, and mannitol, play roles in maintaining cellular water balance and responding to drought or low temperature stress.

Reader's Guide

Polyols are significant in both industrial chemistry and food science. In polymer chemistry, they are essential building blocks for polyurethanes, which are used to produce flexible foam for mattresses and seating, rigid foam insulation for refrigerators and freezers, elastomeric shoe soles, fibers like Spandex, coatings, sealants, and adhesives. Polyether polyols are major components in polyurethane foam, while polyester polyols are used for rigid foam and are available in aromatic, aliphatic, and mixed versions often made from recycled PET. Acrylic polyols are employed in high-performance coatings requiring UV stability, such as automotive coatings. Caprolactone-based polyols provide enhanced hydrolysis resistance, and polycarbonate polyols, though more expensive, are used in demanding applications like glass coatings and reactive hotmelt adhesives. In food science, sugar alcohols serve as lower-calorie sweeteners and are valued for not promoting tooth decay. The term polyol also applies to molecules like polyvinyl alcohol, which contains many hydroxyl groups, though cellulose, despite having many hydroxyl groups, is not referred to as a polyol. The diversity of polyol chemistries allows for tailored properties in a wide range of products, from industrial coatings to food additives.

Did You Know?

• Polyols containing two, three, and four hydroxyl groups are called diols, triols, and tetrols, respectively.
• Sugar alcohols are added to chewing gum because they are not broken down by bacteria in the mouth or metabolized to acids, and thus do not contribute to tooth decay.
• Polycarbonate polyols are more expensive than other polyols and are used in demanding applications such as glass coatings and reactive hotmelt adhesives.
• Polyols may be based on renewable sources including neem oil, castor oil, and cottonseed oil.