Polyurethane systems are widely used in a variety of coatings applications. Apart from their decorative aspects, these systems are extraordinarily resistant against chemicals and have very good mechanical properties. In addition, aliphatic polyurethanes possess high weather resistance. Therefore, they are widely used in outdoor and/or topcoat applications.
Actually, there are many alternatives to classical solventborne systems. They are based on waterborne and/or hydrophilic products and are used in wood coatings1, plastic coatings for OEM interior2 and some general industrial applications for metal3. The decision whether to use a solvent- or waterborne system does not only depend on legislation but is influenced by public opinion as well.
When we compare both monomers, differences in their final behavior become evident. HDI is a chain of CH2 groups, which can rotate around the axis of the molecule and will result in a flexible product. The homopolymer has a glass transition temperature of 63 deg C. IPDI, with its cycloaliphatic structure, represents a more rigid form, which results in a glass transition temperature of 105 deg C for the homopolymer.