Spray processable polyurea formulations: Effect of chain extender length on material properties of polyurea coatings

The increasing usage of polyurea coatings has attracted the attention of researchers worldwide. Commercial polyurea formulations contain chain extenders as an essential ingredient, which increases the possibility of intermolecular H-bonding by bringing the urea linkages closer. In this work, we establish the effect of increasing chain length of chain extender on the material properties of the polymer. Different types of chain extender were blended with a long chain diamine and subsequently reacted with an MDI-based isocyanate prepolymer through a reactive spray processing technique. Polyurea coatings containing aromatic chain extenders were found to exhibit higher tensile strength as compared to their aliphatic analogues. Increasing the chain length of the aliphatic chain extender led to a reduction in the mechanical strength. A suitable combination of aromatic and aliphatic chain extender of short length was found to force the macromolecule to orient in such a fashion so as to result in optimal H-bonding. This manifested in terms of improved processability, as confirmed by chemorheological investigations. Fourier transform infrared spectroscopy was used to understand the H-bonded internal structure of the polymer. Optimum H-bonding resulted in improved mechanical properties of the spray-coated polyurea. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48573.