There are many kinds of thickeners, and their preparation methods vary with different varieties. In general, the preparation of low molecular thickener is relatively simple, for example, low molecular inorganic thickener and surfactant are combined to thicken; Ether/amine oxide thickener is prepared by oxidation reaction; Ester thickeners can be obtained by direct esterification. Polymer thickeners occupy a large proportion in the market. Except inorganic polymer thickeners and natural polymer thickeners, most of them are prepared by emulsion polymerization and inverse emulsion polymerization, and a few are prepared by solution polymerization, bulk polymerization and precipitation polymerization.       溶液聚合
       Solution polymerization refers to the polymerization process of monomer and initiator dissolved in a certain solvent, and its components are usually polymerized monomer, oil-soluble and water-soluble initiator, solvent and water.      

     The solution polymerization method mainly focuses on the preparation of polyacrylic acid thickener. The characteristic is that a large amount of solvents are needed to dissolve the polymer in the preparation process, and most of these solvents are insoluble in water, and need to be recycled in the later stage. Therefore, the cost is high, and it is not conducive to environmental protection.    

      bulk polymerization

      Bulk polymerization means that under the action of heat source (light, heat, radiant energy, etc.), no or a small amount of initiator/catalyst is added to initiate/accelerate the polymerization of monomer itself. The method has less requirements on monomers and does not need solvent dissolution, and the obtained product has the advantages of few impurities and high purity. In recent years, some scholars began to prepare associative polyurethane thickener by bulk polymerization (two-step method). First, polyurethane prepolymer was polymerized in bulk, and finally, it was capped with long-chain fatty alcohol to obtain the product.