Preparation And Properties Of Water-dispersible Polyurethane Carrying Sulfonic Acid Groups

Two component waterborne polyurethane coating（2K-WPU）is an environmentally friendly coating with excellent properties comparable to solvent-based polyurethane coating,which is the world’s coating development direction.2K-WPU consists of waterborne hydroxyl resin and water-dispersible polyisocyanate（WDP）,and the latter plays the key role in the film properties and cost.The existing WDP production technology is mainly monopolized by multinational companies.The WDP independently developed by China has the disadvantages of low isocyanate content（NCO%）,high viscosity,poor storage stability and poor compatibility with hydroxy resin.In this paper,a series of sulfamic acid was prepared and used as a hydrophilic modifier to prepare sulfonate WDP products.The effects of sulfamic acid structures and amounts on WDP and film properties were studied.Firstly,cyclohexylsulfamic acid was used as a hydrophilic modifier to synthesize cyclohexylsulfamic acid type WDP by"one-step"process.The reaction rater was faster while the hydrophilic modifier was cyclohexylaminopropanesulfonic acid（CAPS）and cyclohexylaminobutanesulfonic acid.The reaction could be completed at 90℃for 4h,and the prepared WDP product has good appearance;while the reaction of cyclohexylaminoethanesulfonic acid with polyisocyanate was difficult,and the reaction was completed at 90°C for 6 h.The WDP product has a turbid appearance and undesired film properties.Secondly,in order to solve the problems of turbid appearance and poor compatibility between CAPS and polyisocyanate,the"one-step"process was optimized.It was found that increasing the amounts of CAPS could improve the water dispersibility of WDP and the compatibility with waterborne hydroxy resin,and improve the gloss,density and flatness of the film.But it would also cause the problem of increasing the viscosity of WDP as well as the construction difficulty.When the addition of CAPS was 3.5wt%,the prepared WDP had best performance,the NCO%was 20.4%,the viscosity was 6950 mPa·s,the average particle size of the water dispersion was 298 nm,and the gloss of the varnish is90°.The structure of synthesized WDP was characterized with the NMR and FT-IR spectra.A series of N-alkylated sulfonic acids（NSAs）including propyl,isopropyl,isobutyl and phenyl groups were synthesized using primary amines reaction with sultones.The structures of NSAs were characterized by FT-IR,¹H NMR,¹³C NMR,ES-MS,etc.The NSAs were used to prepare WDP as hydrophilic modifiers,and the effects of the structures of NSAs on the properties of WDP and film were studied.The microphase structure of the 2K-WPU film was studied by differential scanning calorimetry（DSC）and dynamic thermomechanical analysis（DMA）.It was found that the molecular weight of WDP increased with increasing of the molecular weight of the substituent of NSAs.Among the NSAs,isobutyl group has smaller molecular weight and lower steric hindrance,isobutyl-based WDP has good water dispersibility and low viscosity,and its coating film has higher degree of microphase separation and better water resistance.When the IBAPS addition was 2.5wt%,the NCO%of the WDP was 20.8%,the viscosity was 4559mPa.s,the average particle size of the water dispersion was 166nm.The gloss of the IBAPS based 2K-WPU film was 92°.However,CAPS has larger molecular weight and steric hindrance effect,and the CAP-WDP has poor water dispersibility.The degree of microphase separation of the film was low,resulting in poor water resistance of the film.Compared with the commercial WDP,the IBAPS-WDP prepared in this paper has advantages in pendulum hardness and water resistance.