High Functionality Polyether Polyols
TRiiSO distributes a wide range of high functionality polyether polyols that allow formulators to produce high quality polyurethane coatings. Polyols contain reactive hydroxyl (OH) groups which react with isocyanate (NCO) groups on isocyanates to form polyurethane coatings.
Polyether-based polyurethane coatings exhibit enhanced hydrolytic stability and excellent resistance to weak acids and bases compared to polyester-based polyurethane coatings. However, polyether-based polyurethane coatings are more susceptible to UV radiation and provide poor resistance to oils and fuels compared to polyester-based polyurethane coatings.
Polyether polyols are formed by propoxylating an initiator (addition of propylene oxide to an initiator). In some cases, the initiator is ethoxylated (addition of ethylene oxide) as well as propoxylated. Ethoxylation can be incorporated in the middle of the polyol, or at the end (tip) of the polyol. When polyether polyols have ethylene oxide tips, the resulting hydroxyl groups are primary hydroxyls; propylene oxide tips yield secondary hydroxyl groups. Secondary hydroxyl groups react slower than primary hydroxyl groups as a result of the increased steric hindrance. Ethylene oxide is more hydrophilic, and thus polyether polyols with ethylene content tend to produce polyurethane coatings that are more hydrophilic than those produced with polyether polyols that are made solely with propylene oxide. The initiator used to produce the polyol can impact reactivity as well as functionality of the polyol. Amine initiated polyether polyols are self-catalyzing and react faster than standard glycol initiated polyether polyols. Sucrose initiated polyols allow for the manufacture of polyols with greater than 7 hydroxyl groups compared to triols formed by trimethylolpropane.
There are several key characteristics which define what performance properties a given high functionality polyether polyol will impart in a given polyurethane coating. These characteristics include: the hydroxyl number or hydroxyl value (OH value), OH equivalent weight, molecular weight, and the functionality of the polyol.
Hydroxyl number (OH ) is the measure of the hydroxyl group content of gram of polyol. Hydroxyl value is measured by titrating a known mass of polyol against potassium hydroxide (KOH), and is expressed as mg KOH/g. Lower hydroxyl values indicates lower hydroxyl content and a higher molecular weight for the overall polyol.
OH equivalent weight is the number of grams of a given product that contains one equivalent of hydroxyl groups (NCO). Equivalent weight = 56100/OH
Molecular Weight is determined by multiplying the equivalent weight by the polyol functionality
Polyol functionality refers to the number of OH groups per molecule. Increasing the number of OH groups results in greater crosslinking. Greater crosslinking yields stiffer, harder products with enhanced chemical and thermal resistance. Polyols that contain 2 hydroxyl groups are called diols, polyols with 3 functional groups are called triols, polyol groups with 4 hydroxyl groups are called tetrols.
Your TRiiSO Technical Sales Representative is available to assist you in the selection of the appropriate polyether polyol that will provide the specific properties you are trying to obtain. Click here to request a quote.