Polyols are hydroxyl functional polymers.
Depending on the composition they can be polyether or polyester polyols.
This indicates that their backbone contains ether or ester groups.
Polyether type polyols are the largest group of
polyol used in urethanes, they are resistant to alkali (base), low viscous
and have low temperature flexibility. Polyethers can have primary (more
reactive) or secondary hydroxyl groups (slower reactive). Polyether
polyols can have functionality from as low as 2 to as high as 8, depending
on what starting polyol was used in their manufacture. Typically they are
prepared by reaction of ethylene oxide or propylene oxide with water a
starting diol or polyol. Ethylene oxide produces primary hydroxyl
functional polyols and propylene oxide predominately secondary hydroxyls.
Ethylene oxide containing polyols are lower in viscosity and more water
sensitive. Polypropylene glycol is only water soluble at a low molecular
weight, only ethylene oxide containing polymers are water soluble at a
high MW. If
primary hydroxyl functional polymers are desired often propylene oxide is
first reacted with the starting polyol and the ethylene oxide is grafted
onto the polypropylene oxide polymer.
More hydrophobic and polyethers with
improved properties are obtained from tetrahydrofuran (THF).
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+ |
R'OH |

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R= CH3, H |
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polyol |
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polyether polyol |
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polypropylene glycol with ethylene glycol end
groups |
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Tetrahydrofurane
(THF) |
Polytetramethylene glycol
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