Polyol Resins
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.
Classification
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 carbon atoms 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]
Uses
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]
Polyols from recycled or renewable sources
There are polyols based on renewable sources such as plant-based materials including neem oil, castor oil, and cottonseed oil.[46][47][48][49] Vegetable oils and biomass are also potential renewable polyol raw materials.[50] Seed oil can even be used to produce polyester polyols.[51]
Properties
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.
See also
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