Polyols may be classified according to their chemistry.[5] Some of these chemistries are polyether, polyester,[6] polycarbonate[7][8] and also acrylic polyols.[9][10] Polyether polyols may be further subdivided and classified aspolyethylene oxide orpolyethylene glycol (PEG),polypropylene glycol (PPG) andPolytetrahydrofuran or PTMEG. These have 2, 3 and 4 carbons respectively per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available.[11] There is also an increasing trend to use biobased (and hence renewable) polyols.[12][13][14][15]
Polyether polyols have numerous uses.[16][17] As an example,polyurethane foam is a big user of polyether polyols.[18]
Polyester polyols can be used to produce rigid foam.[19][20] They are available in botharomatic andaliphatic versions.[21][22] They are also available in mixed aliphatic-aromatic versions often made from recycled raw materials, typicallypolyethylene terephthalate (PET).[23]
Acrylic polyols are generally used in higher performance applications where stability toultraviolet light is required[24] and also lowerVOC coatings.[25][26] Other uses include direct to metal coatings.[27] As they are used where good UV resistance is required, such as automotive coatings, theisocyanate component also tends to be UV resistant and hence isocyanate oligomers orprepolymers based onIsophorone diisocyanate are generally used.[28]
Caprolactone-based polyols produce polyurethanes with enhanced hydrolysis resistance.[29][30]
Polycarbonate polyols are more expensive than other polyols and are thus used in more demanding applications.[31][32] They have been used to make anisophorone diisocyanate based prepolymer which is then used in glass coatings.[33] They may be used in reactive hotmeltadhesives.[34]
Low molecular weight polyols are widely used inpolymer chemistry where they function as crosslinking agents and chain extenders.Alkyd resins for example, use polyols in their synthesis and are used inpaints and in molds forcasting. They are the dominantresin or "binder" in most commercial "oil-based" coatings. Approximately 200,000 tons of alkyd resins are produced each year. They are based on linking reactive monomers through ester formation. Polyols used in the production of commercial alkyd resins areglycerol,trimethylolpropane, andpentaerythritol.[40] In polyurethane prepolymer production, a low molecular weight polyol-diol such as1,4-butanediol may be used as a chain extender to further increase molecular weight though it does increaseviscosity because morehydrogen bonding is introduced.[38]
Sugar alcohols, a class of low molecular weight polyols, are commonly obtained byhydrogenation of sugars.[41]: 363 They have the formula (CHOH)nH2, where n = 4–6.[42]
Sugar alcohols are added to foods because of their lower caloric content thansugars; however, they are also, in general, less sweet, and are often combined with high-intensitysweeteners. They are also added tochewing gum because they are not broken down by bacteria in the mouth ormetabolized to acids, and thus do not contribute totooth decay.Maltitol,sorbitol,xylitol,erythritol, andisomalt are common sugar alcohols.
The termpolyol is used for various chemistries of the molecular backbone. Polyols may be reacted withdiisocyanates or polyisocyanates to producepolyurethanes.MDI finds considerable use in PU foam production.[43] Polyurethanes are used to make flexible foam formattresses and seating, rigid foam insulation forrefrigerators andfreezers,elastomeric shoe soles, fibers (e.g.Spandex), coatings, sealants andadhesives.[44]
The termpolyol is also attributed to other molecules containing hydroxyl groups. For instance,polyvinyl alcohol is (CH2CHOH)n withn hydroxyl groups wheren can be in the thousands.Cellulose is a polymer with many hydroxyl groups, but it is not referred to as a polyol.
There are polyols based on renewable sources such asplant-based materials includingcastor oil andcottonseed oil.[45][46][47] Vegetable oils and biomass are also potential renewable polyol raw materials.[48] Seed oil can even be used to produce polyester polyols.[49]
Since the generic term polyol is only derived fromchemical nomenclature and just indicates the presence of several hydroxyl groups, no common properties can be assigned to all polyols. However, polyols are usually viscous at room temperature due to hydrogen bonding.
^Howarth, GA (2003). "Polyurethanes, polyurethane dispersions and polyureas: Past, present and future".Surface Coatings International Part B: Coatings Transactions.86 (2):111–118.doi:10.1007/BF02699621.S2CID93574741.
^WO2011129940A1, Montgomery, Steven; Brown, Shawn & Sonnenschein, Mark et al., "Polycarbonate polyols and polyurethanes made therefrom", issued 2011-10-20
^Abraham, T.W.; Höfer, R. (2012). "10.03 - Lipid-Based Polymer Building Blocks and Polymers". In Matyjaszewski, K; Möller, M (eds.).Polymer Science: A Comprehensive Reference. Elsevier. pp. 15–58.doi:10.1016/B978-0-444-53349-4.00253-3.ISBN9780080878621.
^McAdams, Carina; Farmer, Steven (September 2003). "Stabilization of Rigid Systems Containing Aromatic Polyester Polyol and Water".Journal of Cellular Plastics.39 (September 2003):369–386.doi:10.1177/0021955X03035067.S2CID96795892.
^Boustead, I. (2005)."Polyurethane rigid foam"(PDF).Eco-Profiles of the European Plastics Industry. Brussels: PlasticsEurope. Archived fromthe original(PDF) on 2013-09-25.
Media related toPolyols at Wikimedia Commons