Editing Polyurethane (section)

===Polyols===
{{main|Polyol}}
[[Polyols#Polyols in polymer chemistry|Polyols]] are polymers in their own right and have on average two or more hydroxyl groups per molecule. They can be converted to polyether polyols by co-polymerizing [[ethylene oxide]] and [[propylene oxide]] with a suitable polyol precursor.<ref>{{cite journal|title=Polyurethanes from Vegetable Oils|first=Zoran S. |last=Petrović |journal=Polymer Reviews |volume=48 |issue=1 |date=2008|pages=109–155 |doi=10.1080/15583720701834224 |s2cid=95466690 }}</ref> Polyester polyols are made by the polycondensation of multifunctional [[carboxylic acid]]s and polyhydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products.

Polyols for flexible applications use low functionality initiators such as [[dipropylene glycol]] (''f''&nbsp;=&nbsp;2), [[glycerine]] (''f''&nbsp;=&nbsp;3), or a sorbitol/water solution (''f''&nbsp;=&nbsp;2.75).<ref>{{cite patent|title=Polyether polyols suitable for flexible polyurethane foam prepared by co-initiation of aqueous solutions of solid polyhydroxyl initiators|pubdate=1997-01-29|inventor1-last=Hager|inventor2-last=Knight|inventor3-last=Helma|inventor1-first=Stanley L.|inventor2-first=James E.|inventor3-first=Gregory F.|inventor4-last=Argento|inventor4-first=Ben J.|country=EP|number=0755955|assign=[[ARCO#ARCO Chemical|ARCO Chemical Technology]]}}</ref> Polyols for rigid applications use higher functionality initiators such as [[sucrose]] (''f''&nbsp;=&nbsp;8), [[sorbitol]] (''f''&nbsp;=&nbsp;6), [[toluenediamine]] (''f''&nbsp;=&nbsp;4), and [[Mannich base]]s (''f''&nbsp;=&nbsp;4). [[Propylene oxide]] and/or [[ethylene oxide]] is added to the initiators until the desired molecular weight is achieved. The order of addition and the amounts of each oxide affect many polyol properties, such as compatibility, water-solubility, and reactivity. Polyols made with only propylene oxide are terminated with secondary hydroxyl groups and are less reactive than polyols capped with ethylene oxide, which contain primary hydroxyl groups.  Incorporating carbon dioxide into the polyol structure is being researched by multiple companies.

Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed [[Copolymer|styrene–acrylonitrile]], [[acrylonitrile]], or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load-bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. Initiators such as [[ethylenediamine]] and [[triethanolamine]] are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. A special class of polyether polyols, [[poly(tetramethylene ether) glycol]]s, which are made by polymerizing [[tetrahydrofuran]], are used in high performance coating, wetting and elastomer applications.

Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. Polyester polyols are usually more expensive and more viscous than polyether polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification ([[glycolysis]]) of recycled [[Polyethylene terephthalate|poly(ethyleneterephthalate)]] (PET) or [[dimethylterephthalate]] (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring low cost and excellent flammability characteristics to [[polyisocyanurate]] (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include [[polycarbonate]] polyols, [[polycaprolactone]] polyols, [[polybutadiene]] polyols, and [[polysulfide]] polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. [[Natural oil polyols]] derived from [[castor oil]] and other [[vegetable oils]] are used to make elastomers, flexible bunstock, and flexible molded foam.

Co-polymerizing [[chlorotrifluoroethylene]] or [[tetrafluoroethylene]] with vinyl ethers containing hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two-component fluorinated polyurethanes prepared by reacting FEVE fluorinated polyols with polyisocyanate have been used to make ambient cure paints and coatings. Since fluorinated polyurethanes contain a high percentage of fluorine–carbon bonds, which are the strongest bonds among all chemical bonds, fluorinated polyurethanes exhibit resistance to UV, acids, alkali, salts, chemicals, solvents, weathering, corrosion, fungi and microbial attack. These have been used for high performance coatings and paints.<ref>{{cite web |author=Bob Parker |title=FEVE Technology for Higher Performance Coating Systems on Bridges |url=https://www.paintsquare.com/library/articles/(038-47)BridgeResins01-15.pdf#:~:text=The%20FEVE%20polyol%20resins%20play%20an%20integral%20part,coating%20systems%20across%20the%20globe%20since%20its%20introduction |url-status=dead |archive-url=https://web.archive.org/web/20210815112712/https://www.paintsquare.com/library/articles/(038-47)BridgeResins01-15.pdf |archive-date=15 August 2021 |access-date=5 March 2022 |website=Paintsquare.com}}</ref>

[[Phosphorus]]-containing polyols are available that become [[Chemical bond|chemically bonded]] to the polyurethane matrix for the use as [[flame retardants]]. This covalent linkage prevents migration and leaching of the [[organophosphorus compound]].