Prepolymer synthesis

Formulation design

Different application fields have different requirements for product performance, and the performance of the product depends on the raw materials and their ratio and processing technology. Therefore, before making CPU products, the qualified raw materials should be selected according to the service environment (such as temperature, stress, contact medium, etc.) and service life, and then the appropriate proportion and molding method should be selected according to the designed hardness. The latter includes the synthesis process of prepolymer, mixing temperature of prepolymer and chain extender, mold temperature, curing and post vulcanization conditions, etc. The two-step process is to synthesize isocyanate terminated prepolymer, and determine the accurate content of NCO group (NCO%) in prepolymer through analysis, and then react with the calculated amount of chain extender to produce products; or directly use commercial prepolymer with known NCO group content and chain extender to produce products. Therefore, NCO group content in prepolymer is a key index. In the actual production process, the feeding amount of isocyanate is calculated according to the design value of NCO group content in prepolymer and the feeding amount of oligomer polyol. The low moisture content of oligomer polyol and high purity of isocyanate (≥ 99.5%) have little influence on the calculation results. Therefore, the micro water and purity of isocyanate in oligomer polyol can be ignored when calculating isocyanate feeding. The NCO content in the prepolymer is based on the final analysis result, rather than the design value to calculate the amount of chain extender and crosslinker. Foreign manufacturers of CPU elastomer products generally do not produce prepolymer, but purchase directly from prepolymer suppliers. The varieties, brands and properties of several main prepolymer production companies at home and abroad will be introduced in detail later.