In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (−OH). 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,[1] triols,[2] and tetrols,[3][4] respectively.
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 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.[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 both aromatic and aliphatic versions.[21][22] They are also available in mixed aliphatic-aromatic versions often made from recycled raw materials, typically polyethylene terephthalate (PET).[23]
Acrylic polyols are generally used in higher performance applications where stability to ultraviolet light is required[24] and also lower VOC 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, the isocyanate component also tends to be UV resistant and hence isocyanate oligomers or prepolymers based on Isophorone 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 an isophorone diisocyanate based prepolymer which is then used in glass coatings.[33] They may be used in reactive hotmelt adhesives.[34]
All polyols may be used to produce polyurethane prepolymers.[35][36][37] These then find use in coatings,[38] adhesives, sealants and elastomers.[39]
Low molecular weight polyols are widely used in polymer chemistry where they function as crosslinking agents and chain extenders. Alkyd resins for example, use polyols in their synthesis and are used in paints and in molds for casting. They are the dominant resin 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 are glycerol, trimethylolpropane, and pentaerythritol.[40] In polyurethane prepolymer production, a low molecular weight polyol-diol such as 1,4-butanediol may be used as a chain extender to further increase molecular weight though it does increase viscosity because more hydrogen bonding is introduced.[38]
Xylitol
Sugar alcohols, a class of low molecular weight polyols, are commonly obtained by hydrogenation 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 than sugars; however, they are also, in general, less sweet, and are often combined with high-intensity sweeteners. They are also 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. Maltitol, sorbitol, xylitol, erythritol, and isomalt are common sugar alcohols.
Polyether polyol
(The oxygen atoms of the ether linkages
are shown in blue.)
(The oxygen and carbon atoms
of the ester groups are shown in blue.)
The term polyol is used for various chemistries of the molecular backbone. Polyols may be reacted with diisocyanates or polyisocyanates to produce polyurethanes. MDI finds considerable use in PU foam production.[43] Polyurethanes are used to make flexible foam for mattresses and seating, rigid foam insulation for refrigerators and freezers, elastomeric shoe soles, fibers (e.g. Spandex), coatings, sealants and adhesives.[44]
The term polyol is also attributed to other molecules containing hydroxyl groups. For instance, polyvinyl alcohol is (CH2CHOH)n with n hydroxyl groups where n 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 as plant-based materials including castor oil and cottonseed 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 from chemical 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.
هذه مقالة غير مراجعة. ينبغي أن يزال هذا القالب بعد أن يراجعها محرر مغاير للذي أنشأها؛ إذا لزم الأمر فيجب أن توسم المقالة بقوالب الصيانة المناسبة. يمكن أيضاً تقديم طلب لمراجعة المقالة في الصفحة المخصصة لذلك. (يوليو 2020) معركة فورت واجنر الثانية التاريخ 18 يوليو 1863 البلد ا
Confine tra l'Algeria e il MaliLocalizzazione dell'Algeria (verde) e del Mali (arancione).Dati generaliStati Algeria Mali Lunghezza1359 km Dati storiciIstituito nel1905 Attuale dal1983 Manuale Il confine tra l'Algeria e il Mali ha una lunghezza di 1359 km e parte dal triplice confine con la Mauritania a nord-ovest fino al triplice confine con il Niger a sud-est.[1] Indice 1 Descrizione 2 Storia 3 Insediamenti vicino al confine 3.1 Algeria 3.2 Mali 4 Valichi di frontiera 5 …
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يفتقر محتوى هذه المقالة إلى الاستشهاد بمصادر. فضلاً، ساهم في تطوير هذه المقالة من خلال إضافة مصادر موثوق بها. أي معلومات غير موثقة يمكن التشكيك بها وإزالتها. (مايو 2023) هذه المقالة يتيمة إذ تصل إليها مقالات أخرى قليلة جدًا. فضلًا، ساعد بإضافة وصلة إليها في مقالات متعلقة بها. (سب…
У Вікіпедії є статті про інші значення цього терміна: Воєнний хрест. У Вікіпедії є статті про інші значення цього терміна: Воєнний хрест (Франція). Воєнний хрестCroix de guerre 1939-1945 Країна ФранціяТип ХрестСистема Воєнний хрестВручається: Військовим та цивільним особам, війсь
هذه المقالة يتيمة إذ تصل إليها مقالات أخرى قليلة جدًا. فضلًا، ساعد بإضافة وصلة إليها في مقالات متعلقة بها. (ديسمبر 2021) تشوي تاي جون (بالكورية: 최태준) معلومات شخصية الميلاد 7 يوليو 1991 (32 سنة) سول مواطنة كوريا الجنوبية الزوجة بارك شن هي (2022–)[1] العشير بارك …
American flying ace Charles Barbin DeBellevueCaptain Charles B. Chuck DeBellevueNickname(s)ChuckBorn (1945-08-15) August 15, 1945 (age 78)New Orleans, Louisiana, U.S.AllegianceUnited States of AmericaService/branch United States Air ForceYears of service1968–1998Rank ColonelUnit555th Fighter Squadron Commands held432nd Combat Support Group95th Air Base WingAir Force ROTC Detachment 440Battles/warsVietnam WarAwardsAir Force CrossSilver Star (3)Legion of MeritDistinguished Flying …
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艦歴 発注 起工 1929年11月14日 進水 1930年10月9日 就役 1932年7月7日 退役 その後 1942年11月27日にトゥーロンで自沈 除籍 性能諸元 排水量 基準:10,000トン、満載:12,780トン 全長 196 m 全幅 20 m 吃水 7.3 m 機関 ギョ・ド・タンブル式重油専焼水管缶9基+ラトー・ブルターニュ式ギヤードタービン3基3軸推進、100,000 shp 最大速 32ノット 乗員 773名 兵装 Model 1924 20.3cm(50口径)連装砲4基…
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Mountain range in north central Jamaica This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: Dry Harbour Mountains – news · newspapers · books · scholar · JSTOR (February 2022) (Learn how and when to remove this template message) A view of Dry Harbour in the parish of St. Ann's Jamaica, taken from the West end of th…
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