In this post, I am going to tell you about polymeric polyol used in foam production. And also, polyol and it's forms. So take a seat and read it carefully, gently and repeatedly.
First, I will start by telling you what a polyol is.
Polymeric Polyol
Polyols are compounds with multiple hydroxyl functional groups available for organic reactions. Polymeric polyols are the second component for polyurethanes and are reacted with isocyanates.
Although there are relatively few marketable isocyanates, there are a whole host of polyols, polyethers, polyesters, polyether polyols and other substances. This results in a wide variety of polyurethane materials. The properties of polyurethane can be customized by choosing the right polyol components.
ALSO
The term ‘polyol’ describes compounds with hydroxyl groups which react with diisocyanates to produce polymers polyol with isocyanates to generate polyurethanes used to produce construction insulation panels, foam insulation for appliances (refrigerators and freezers), upholsteries, mattresses, elastomeric shoe soles, and adhesives and etc...
Polymeric polyols are usually polyethers or polyesters. 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 a double metal cyanide catalyst such as the zinc hexacyanocobaltate-t-butanol complex. 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 would not 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 onsists of polyester polyols.
The technological discipline of the term "polyol" from a polymer chemistry approach.
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.
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.
Monomeric polyols such as glycerin , pentaerythritol, ethylene glycol and
sucrose often serve as the starting point for polymeric polyols. These materials are often referred to as the "initiators" and reacted with propylene oxide or ethylene oxide to produce polymeric polyols. However, they should not 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 often functions as the starting point for two polymeric chains, especially in the case of polyether polyols.
- Polymeric polyols are generally used to produce other polymers. They are reacted with isocyanates to make
polyurethanes used to make
mattresses, foam insulation for appliances (refrigerators and freezers), home and automotive seats,
elastomeric shoe soles, fibers (e.g.
Spandex ), and adhesives .
polyurethanes used to make
mattresses, foam insulation for appliances (refrigerators and freezers), home and automotive seats,
elastomeric shoe soles, fibers (e.g.
Spandex ), and adhesives .
- Polymeric polyols are usually
polyethers or polyesters . 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 a double metal cyanide catalyst such as zinc hexacyanocobaltate-t-butanol complex.
polyethers or polyesters . 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 a double metal cyanide catalyst such as zinc hexacyanocobaltate-t-butanol complex.
- 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 would not 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.
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.
caprolactone . The example below is an idealized structure that could be obtained by reacting pentaerythritol (a tetrol) with gamma-butyrolactone.
POLYURETHANES
Polyurethanes are made by the exothermic reactions between alcohols with two or more reactive hydroxyl (-OH) groups per molecule (diols, triols, polyols) and isocyanates that have more than one reactive isocyanate group (-NCO) per molecule (diisocyanates, polyisocyanates). For example a diisocyanate reacts with a diol:
The group formed by the reaction between the two molecules is known as the 'urethane linkage'. It is the essential part of the polyurethane molecule.
The group formed by the reaction between the two molecules is known as the 'urethane linkage'. It is the essential part of the polyurethane molecule.
Polymer polyols
Polymer polyols are based around graft copolymers of olefins. In these polymer polyether functional groups are grafted onto the olefin backbone. Important copolymers are acrylonitrile, styrene and mixtures of the two are used. Vinyl acetate, vinyl acetate and also esters of acrylic acids can also be used. Polyol blends with polymer polyols are specialised products.
Polymer polyols based on polyether polyol s often contain three types of polymer: unmodified polyether polyol, some graft polymer with vinyl attached to the polyether chains and some vinyl polymer. The graft component helps to keep the liquid polymer polyol stable. It is possible to make stable, low viscosity polyester polyol solutions by reacting styrene with acrylonitrile. Sometime polyether polyols that are modified to make graft polymerisation easier can stabilise high concentrations of polyvinyl components and to make high-polystyrene polymer polyols.
Other specialty polyether polyols include:
Polyurea modified polyether polyols which contain dispersed particles of polyurea. Such polyurea-modified polyester polyols are designed to react with isocyanates to give increased levels of cross linking in the final polymer.
Amine-terminated polyether polyols react very quickly and they are often used in Reaction Injection Moulding systems.
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