In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively.
Polyols may be classified according to their chemistry. Some of these chemistries are polyether, polyester, polycarbonate and also acrylic polyols. Polyether polyols may be further subdivided and classified as polyethylene oxide or polyethylene glycol (PEG), polypropylene glycol (PPG) and Polytetrahydrofuran or PTMEG. These have 2, 3 and 4 carbons respectively per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available. There is also an increasing trend to use biobased (and hence renewable) polyols.
Polyether polyols have numerous uses. As an example, polyurethane foam is a big user of polyether polyols.
Polyester polyols can be used to produce rigid foam. They are available in both aromatic and aliphatic versions. They are also available in mixed aliphatic-aromatic versions often made from recycled raw materials, typically polyethylene terephthalate (PET).
Acrylic polyols are generally used in higher performance applications where stability to ultraviolet light is required and also lower VOC coatings. Other uses include direct to metal coatings. As they are used where good UV resistance is required, such as automotive coatings, the isocyanate component also tends to be UV resistant and hence isocyanate oligomers or prepolymers based on Isophorone diisocyanate are generally used.
Caprolactone-based polyols produce polyurethanes with enhanced hydrolysis resistance.
Polycarbonate polyols are more expensive than other polyols and are thus used in more demanding applications. They have been used to make an isophorone diisocyanate based prepolymer which is then used in glass coatings. They may be used in reactive hotmelt adhesives.
All polyols may be used to produce polyurethane prepolymers.
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Xylitol is a chemical compound with the formula C5H12O5, or HO(CH2)(CHOH)3(CH2)OH; specifically, one particular stereoisomer with that structural formula. It is a colorless or white crystalline solid that is freely soluble in water. It can be classified as a polyalcohol and a sugar alcohol, specifically an alditol. The name derives from ξύλον, xyl[on] 'wood', with the suffix -itol used to denote sugar alcohols. Xylitol is used as a food additive and sugar substitute. Its European Union code number is E967.
An alkyd is a polyester resin modified by the addition of fatty acids and other components. Alkyds are derived from polyols and organic acids including dicarboxylic acids or carboxylic acid anhydride and triglyceride oils. The term alkyd is a modification of the original name "alcid", reflecting the fact that they are derived from alcohol and organic acids. The inclusion of a fatty acid confers a tendency to form flexible coatings. Alkyds are used in paints, varnishes and in moulds for casting.
Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group (–OH) attached to each carbon atom. They are white, water-soluble solids that can occur naturally or be produced industrially by hydrogenating sugars. Since they contain multiple –OH groups, they are classified as polyols. Sugar alcohols are used widely in the food industry as thickeners and sweeteners.
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