Dendritic Polyester Polyols
Tri-iso distributes a wide range of dendritic polyester polyols that allow formulators to produce high quality polyurethanes. Polyols contain reactive hydroxyl (OH) groups which react with isocyanate (NCO) groups on isocyanates to form polyurethanes. Dendritic polyester polyols offer a large number of primary hydroxyl groups, densely branched polymer backbone, and extensive formulation possibilities. The dendritic structures are formed by polymerization of the particular core and 2,2-dimethylol propionic acid (Bis-MPA). The base products obtained are hydroxyl-functional dendritic polyesters. Fully aliphatic and consisting only of tertiary ester bonds, they provide excellent thermal and chemical resistance. Extensive branching also improves reactivity, lowers viscosity and results in balanced mechanical properties.
Like all polyester polyols, dendritic polyester-based polyurethanes enhanced UV resistance, excellent resistance to oils and fuels, and better abrasion resistance and tensile and tear strength compared to polyether-based polyurethanes. However, polyester-based polyurethanes are more susceptible to hydrolysis and provide poor resistance to weak acids and bases compared to polyether-based polyurethanes.
There are several key characteristics which define what performance properties a given dendritic polyester polyol will impart in a given polyurethane system. 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.
Your Tri-iso Technical Sales Representative is available to assist you in the selection of the appropriate dendritic polyester polyols that will provide the specific properties you are trying to obtain. Click here to request a quote.