Polyester Polyol Resins
TRiiSO distributes a wide range of polyester 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.
Your TRiiSO Technical Sales Representative is available to assist you in the selection of the appropriate polyester polyol that will provide the specific properties you are trying to obtain. Click here to request a quote.
Polyester-based polyurethane coatings enhanced UV resistance, excellent resistance to oils and fuels, and better abrasion resistance and tensile and tear strength compared to polyether-based polyurethane coatings. However, polyester-based polyurethane coatings are more susceptible to hydrolysis and provide poor resistance to weak acids and bases compared to polyether-based polyurethane coatings.
Polyester polyols are typically formed by the condensation reaction of a glycol with a dicarboxylic acid. The nature of this reaction results in a relatively high polydispersity (broad molecular weight distribution). Consequently, standard polyester polyols are typically quite viscous. However, higher performance polyesters such as polycarprolactones are formed by ring opening of a heterocycle ring (caprolactone monomer) by a glycol initiator. The nature of this reaction results in a low polydispersity. Consequently, polycaprolactones have significantly reduced viscosities, enhanced mechanical properties, as well as enhanced low temperature and high temperature performance properties.
There are several key characteristics which define what performance properties a given polyester 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.