Explanation

polymerization between monomer and monomer, monomer and dimer or polymer and polymer through chemical reaction between functional groups. polymerization is characterized by the gradual reaction in the process of transformation low molecules into macromolecule, that is, the reaction rate constant and activation or conditioning energy of each step are roughly the same. At the beginning of the reaction, most of the monomer quickly polymerized into dimers, trimers, tetramers and other oligomer. The oligomer continued to react, and the molecular weight slowly increased until the degree of reaction was very high, and the molecular weight reached a higher value. Therefore, the conversion of reaction monomer is basically independent of the extension of polymerization time, but the molecular weight of the product gradually increases with the extension of polymerization time. In the process, the system is composed of monomer and a series of intermediate products with increasing molecular weight, and any two molecules of intermediate products can react with each other. Most polycondensation reaction reactions are typical. Other non polycondensation stepwise (reaction) polymerization includes the synthesis of polyurethime, polyphenylene oxide, polysulfone, etc. Since polycondensation reaction is an equilibrium reaction, the molecular weight will be affected by many factors, such as reaction degree, equilibrium constant, equivalence ratio of two monomer and so on. Controlling the molecular weight of the product is the most critical issue. Usually, the molecular weight can be adjusted by adding mono functional group substances or excessive monomer and trying to eliminate low molecular weight by-products. The polymerization heat of stepwise (reaction) polymerization is not large, but its activation or conditioning energy is large, and generally needs to be carried out at a higher temperature. Stepwise (reaction) polymerization can adopt three methods: melt polymerization, solution polymerization and interfacial polymerization, which can be selected according to different reaction types.

Classification