Waterborne polyurethane thickening agent and preparation method thereof

The waterborne polyurethane thickening agent is prepared from the following raw materials in parts by weight: 200 to 500 parts of polyester type dihydric alcohol, 1 to 3 parts of an antioxidant, 0.5 to 1 part of a catalyst, 10 to 15 parts of isocyanate, 1 to 5 parts of a chain extender, 8 to 15 parts of an end-capping reagent, 10 to 20 parts of a post-treatment agent, 180 to 220 parts of a separating agent and 180 to 220 parts of water. The composition of 1, 4-butanediol, 1, 5-pentanediol and 2, 2-dimethyl-1, 3-propylene glycol is adopted as the alcohol mixed chain extender, so that the chain length of a cross-linked network of the polyurethane thickening agent can be prolonged, a polymer with high molecular weight is formed, generation of oligomers is reduced, and damage to a thickening system is avoided. And C12-C18 fatty acid modified epoxidized p-hydroxyacetophenone is adopted as an end-capping reagent, so that the side chain hydrophobicity of a polyurethane chain is improved, the thickening effect is gre