According to the synthesis process of CPU elastomer, it can be divided into one-step method and two-step method, the latter is also called prepolymer method, and prepolymer method can be divided into prepolymer method and semi prepolymer method.

Prepolymer method is to synthesize prepolymer from oligomer polyol and diisocyanate under certain conditions. Then the prepolymer is mixed with the chain extender to form. TDI CPU elastomer products are mostly produced by this method. The CPU elastomer with regular structure can be obtained by prepolymer process.

If the isocyanate index (NCO / OH) is greater than 2, there will be excess isocyanate monomer in the prepolymer. If NCO / Oh ≫ 2, the product is actually a mixture of isocyanate terminated prepolymer and isocyanate monomer. This mixture is called a semi prepolymer.

The one-step method is to mix, pour and form the oligomer polyol, polyisocyanate, chain extender and catalyst at one time. One step process is mainly used in the production of low modulus products.