TRiiSO distributes a wide range of polyether diols 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 diols 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 diol. When polyether diols 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 diol can impact reactivity as well as functionality of the polyol. Amine initiated polyether diols are self-catalyzing and react faster than standard glycol initiated polyether diols. Higher performance polyether diols are formed by ring opening of tetrahydrofuran (THF) to form polytetramethylene ether glycol (PTMEG).
There are several key characteristics which define what performance properties a given polyether diol will impart in a given polyurethane coatings. These characteristics include: the hydroxyl number or hydroxyl value (OH value), OH equivalent weight, and the molecular weight of the diol.
Hydroxyl number (OH ) is the measure of the hydroxyl group content of gram of diol. Hydroxyl value is measured by titrating a known mass of diol 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 diol.
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 diol functionality (2).
Your TRiiSO Technical Sales Representative is available to assist you in the selection of the appropriate polyether diol that will provide the specific properties you are trying to obtain. Click here to request a quote.