Studies On Structure And Properties Of Water Dispersible Polyisocyanate

At present, the development of polyisocyanates, which is the curing agent of aqueous polyurathane, is very popular, especially the study of water dispersible polyisocyanates. The chemical hydrophilic modification of polyisocyanates were proceeded by the carbamic acid esterification of polyether polyols. This method promoted the development of the modification of polyisocyanates by polyether polyols. But the polyisocyanates synthesized by this method has low average functionality, and the thin film received by polyisocyanates and aqueous polyurethane polyol dispersion has low cross-linking degree and chemical resistance, so the final performances of the materials are not satisfied. Based on the current preparation methods, the water dispersible polyisocyanates were synthesized by isophorone diisocyanate (IPDI) and 3-hexanaphthene amino-1-propane sulfonic acid (CAPS) as the main raw materials in this paper. The hydroxyl component, which were prepared by polyester polyols and dimethylolbutanoicacid (DMBA), and the water dispersible polyisocyanates were used to synthesize the polyurethane hard thin film with water-tolerance, solvent resistance and excellent mechanical properties. The chemical structures of the hard thin film were characterized with the infrared spectroscopy (FI-IR) and nuclear magnetic resonance (1H-NMR). The influences of percentages of CAPS composition on the performances of the water dispersible polyisocyanates,-NCO/-OH equivalent ratio and the percentages of DMBA composition on the performances of aqueous polyurethane polyol dispersion were studied. The Soxhlet extractor, universal mechanical testing machine, pendulum hardness tester, thermal dynamic mechanical analyzer (DMA) and so on were respectively used to characterize the cross-linking density, tensile properties, hardness and glass transition temperature of the polyurethane hard thin film.The results showed that:the hydrophilic sulfonic groups of CAPS were successfully introduced into the molecular chains of polyisocyanates, and the storage time of obtained water dispersible polyisocyanates emulsion was more than half a year. When-NCO/-OH equivalent ratio was 1.8:1 and the percentages of DMBA composition was between 7%～8%, aqueous polyurethane polyol dispersion had excellent comprehensive performances. When the -NCO/-OH molar ratio increased, film-forming property became better, the glass-transition temperature increased, the cross-linking density increased, the water resistance property increased, the tensile strength increased, and the elongation at break decreased. When-NCO/-OH equivalent ratio was 2:1, and the content of carboxyl group (-COOH) was 1.5%-2%, the tensile strength of the thin film was 13.8MPa and the glass-transition temperature was 53℃.