Synthesis and properties of water-dispersible polyisocyanates carrying sulfonate

A series of N-alkylated aminosulfonic acids (NASAs) were synthesized with 1,4-butane sultone and primary amines and then reacted with hexamethylene diisocyanate trimer to obtain water-dispersible polyisocyanates (WDPs). Two-component waterborne polyurethane (2K-WPU) coatings were finally prepared by the reaction of WDPs and aqueous hydroxyl resins. The structures and properties of WDPs and 2K-WPU coatings were characterized. The effects of the categories and amounts of NASAs on the properties of WDPs and 2K-WPU coatings, including viscosities, water resistance and transparency, were investigated. The results showed that the average molecular weights and viscosities of the WDPs increased with the increase in the amounts and molecular weights of NASAs. 3-(Cyclohexylamino)-1-propanesulfonic acid possesses a high molecular weight, resulting in low-concentration –SO₃ per mass, so a high concentration up to 3.5 wt% was needed to meet water-dispersible requirements. On the other hand, 3-isobutylamino-1-propanesulfonic acid (IBAPS) has high-concentration –SO₃ per mass and only a low concentration (2.5 wt%) was required to offer satisfactory water dispersibility. 2K-WPU film cured by IBAPS-WDP displayed high gloss, good transparency and excellent water resistance owing to suitable steric hindrance and high content of –SO₃H per mass.