Everything about Polyol totally explained
The name
polyols refers to
alcohols containing multiple
hydroxyl groups. In two technological disciplines polyols have special meaning:
food science and
polymer chemistry. For information as it pertains to food ingredients, please see the article on
sugar alcohols.
Polyols in food science
Sugar alcohols, a class of polyols, are commonly added to foods because of their lower caloric content than
sugars; however, they're also, in general, less sweet, and are often combined with high-intensity
sweeteners. They are also added to
chewing gum because they're not metabolized (broken down) by bacteria in the mouth, so they don't contribute to
tooth decay.
Maltitol,
sorbitol, and
Isomalt are some of the more common types. Sugar alcohols may be formed under mild reducing conditions from their analogue
sugars.
Polyols in polymer chemistry
In
polymer chemistry, polyols are compounds with multiple
hydroxyl functional groups available for
organic reactions. A molecule with two hydroxyl groups is a diol, one with three is a triol, one with four is a tetrol and so on.
The main use of polymeric polyols is as reactants to make other polymers, They can be reacted with
isocyanates to make
polyurethanes, and this use consumes most polyether polyols These material are ultimately used to make
elastomeric shoe soles, fibers (
Spandex for example), foam insulation for appliances (
refrigerators and
freezers),
adhesives,
mattresses, automotive seats and so on.
Monomeric polyols such as
pentaerythritol,
ethylene glycol and
glycerin often serve as the starting point for polymeric polyols. Naturally occurring polyols like
castor oil and
sucrose can also be used to make synthetic polymeric polyols. These materials are often referred to as the "initiators" for the polymeric polyols, but they shouldn't be confused with
free radical "initiators" used to promote other polymerization reactions. The functional group used as the starting point for a polymeric polyol need not be a hydroxyl group; there are a number of important polyols which are built up from
amines. A primary amino group (-NH
2) often functions as the starting point for two polymeric chains, especially in the case of polyether polyols.
The polymeric chains built out from the initiator are usually
polyesters or
polyethers. Polyether polyols are made by reacting
epoxides like
ethylene oxide or
propylene oxide with the multifunctional initiator in the presence of a
catalyst, often a strong base such as
potassium hydroxide or more exotic metal cyanides. Common polyether diols are
polyethylene glycol,
polypropylene glycol, and
poly(tetramethylene ether) glycol. The examples shown below are fairly low molecular weight triols based on
glycerin (a triol) being reacted with
propylene oxide,
ethylene oxide or a combination of the two. In reality, the chains wouldn't be of equal length in any one molecule and there would be a distribution of molecular weight polyols within the material. Polyether polyols account for about 90% of the polymeric polyols used industrially; the balance is polyester polyols.
Another class of polymeric polyols is the
polyesters. Polyesters are formed by condensation or
step-growth polymerization of diols and dicarboxylic acids (or their derivatives), for example
diethylene glycol reacting with
phthalic acid. Alternatively, the hydroxyl group and the carboxylic acid (or their derivatives) may be within the same molecule, as in the case of
caprolactone. The example below is an idealized structure that could be obtained by reacting
pentaerythritol (a tetrol) with
gamma-butyrolactone.
A specialist class of polyol is the
hydroxyl-terminated polybutadienes. These polyols are extensively used in formulations for
polyurethanes.
The production of polyester polyols from
vegetable oils is becoming increasingly important. These materials are known as
natural oil polyols, or NOPs.
Further Information
Get more info on 'Polyol'.
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