Synthesis and properties of high-functionality hydroxyl-terminated polyurethane dispersions

High-functionality hydroxyl-terminated polyurethane aqueous dispersions (OH-PUDs) were synthesized with sulfonic polyester diol as hydrophilic chain extender, and alcohol-amine compounds as end-cappers. Two-component waterborne polyurethane (2K-WPU) films based on OH-PUDs were prepared and characterized by ultraviolet-visible spectrophotometer and surface contact angle measurement. The effects of synthesis process, molar ratio of NCO/OH, type and molecular weight of macro-diol, and the category of alcohol-amine capping agents on the properties of OH-PUDs and 2K-WPU films were investigated. OH-PUD obtained from first dispersing then blocking PU prepolymer preparation process displayed the best storage stability. The water-resistance of 2K-WPU film was greatly improved with increasing the average functionality of OH-PUDs, and then OH-PUDs displayed good comprehensive properties with PCL220 as the soft segment, trometamol (Tris) as the end-capper and with 1.5 of NCO/OH molar ratio. The 2K-WPU film prepared from OH-PUD-3 exhibited good water-resistance, good transparency and high hardness.