(1) polyisocyanateCommonly used are aromatic diisocyanates and aliphatic or aliphatic diisocyanates.(2) polymer polyolsThe commonly used oligomers polyols are generally polyether polyols and polyester polyols.(3) hydrophilic chain extenderIt can make waterborne polyurethane with good water dispersion and self-emulsification, according to the introduction of hydrophilic groups into the type of anion, cationic, non-ionic and amphoteric, more applications, better relative effect is anion reagent.In addition, there are small molecule chain extender, solvent, catalyst, crosslinking agent, salt agent and other additives.2.2 preparation method:(1) emulsification methodTwo emulsifying methods are usually used:First, the prepared organic solvent - based polyurethane was made into polyurethane water emulsion (external emulsification method) by external mechanical force in the high shear force emulsifying equipment with emulsifier. The particle size of polyurethane emulsion prepared by this method is larger than 1 micron.The other is to introduce surfactant group on the prepolymer group, so that the synthesized polyurethane has hydrophilic (internal emulsification method). The surfactant groups are: sulfonate, carboxylate, tertiary amine, amphoteric and non-ionic polyethylene glycol. The polyurethane emulsion prepared by this method has a small particle size and can be used as the emulsion protectant such as carboxymethyl cellulose and polyvinyl alcohol to improve the stability of the emulsion.(2) acetone methodIn the presence of acetone, the hydrophobic prepolymer reacted with hydrophilic monomer to expand the chain to produce a high polymer. At the same time, the reaction mixture was diluted with acetone. Then water was added to the system and stirred to form a continuous aqueous phase and a discontinuous polyurethane particle phase swollen by acetone. The waterborne polyurethane produced by this method has good repeatability, uniform emulsion size and good dispersion, but the method requires a large amount of acetone, the solvent recovery process is complicated and the risk factor is high.(3) protect reactive stream polyurethaneThe isocyanate-terminated polyurethane will undergo chain extension reaction when exposed to water, giving off carbon dioxide and forming urea group at the same time. To this end, we adopt certain compounds to a N CO base closed, made a part of the enclosed double sealing and N C O polyurethane pre polymers, make its can be emulsified in water, chain extender, introducing the group, and then by heating the solution close, make the isocyanate crosslinking reaction regeneration, commonly used sealants are: acids, tertiary alcohols, sulfite and low molecular weight amines and acetic acid esters.(4) melt dispersion methodThe urea-terminated oligomers containing ionic groups were quaternized and methylated in the molten state, and then water was added to form a stable emulsion. This method is simple, easy to control, does not need to use solvent in the preparation process, no pollution to the environment, strong adaptability, but this method reaction temperature is high.