Effect of chain extender on phase mixing and coating properties of polyurethane ureas

Structural effects of chain extender on phase mixing and coating properties of polyether-based moisture-cured polyurethane ureas (MCPUs) were determined with a polytetramethylene glycol (PTMG-1000), trimethylol propane (TMP), and isophorone diisocyanate (IPDI)-based system. The reaction of PTMG/TMP/IPDI was carried out using a NCO/OH ratio of 1.6:1. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols and 4: 1 with different aromatic diamines just before the coating application. The viscoelastic properties of the cross-linked films were evaluated with a dynamic mechanical and thermal analyzer (DMTA). The mechanical film properties such as tensile strength, adhesion strength, and hardness were measured and related to chemical composition and cohesion of the hard segment. Surface properties were evaluated through angle resolved X-ray photoelectron spectroscopy (AR-XPS). The degree of phase mixing was found to be dependent on the chain extender structure. The results indicate that the combined analysis of the hard segment cohesion helps in correlating the structure-to-property relationship.