Explanation

It is also called anionic polymerization. Ionic chain polymerization in which the active center of chain growth is anion. initiator generally use nucleophilic reagents, such as inorganic bases, organic alkali metal compounds, alkali metals and alkaline earth metals, and their complexes with polyaromatic hydrocarbons; Among them, organic alkali metals are the most important, especially alkyl lithium, such as butyl lithium. Suitable monomer include alkene monomer containing electron withdrawing groups (such as methyl methacrylate, acrylonitrile, acrylate), styrene and butadiene monomer with a conjugate system, monomer containing carbonyl groups (such as formaldehyde), and some cyclic monomer containing oxygen, nitrogen, silicon, etc. (such as ethylene oxide, caprolactam, cyclooctamethylsiloxane) can be initiated by alkaline reagents under certain conditions. anion polymerization is characterized by fast initiation, slow growth, no termination and no transfer, so it is also called living polymerization. Compared with free radical polymerization, the reaction temperature is generally lower. The properties of solvent and counter ion affect the reaction rate, molecular weight and the stereoregularity of polymer in polymerization. The growing active centers of β - cyclodextrin all have the same charge, and can only undergo unimolecular termination reaction, or chain transfer reaction to monomer and solvent to interrupt chain growth. chain transfer is more difficult to occur in polymerization of non-polar conjugated olefins, or even chain termination does not occur, becoming active polymerization. In the case of no termination of polymerization, water, alcohol, acid, amine, etc. are often added to terminate polymerization. At the end of active polymerization, carbon dioxide, ethylene oxide and diisocyanate are purposely added to form polymer with reaction groups at the end, which are further used to synthesize block and telechelic polymer. The trace water, carbon dioxide and substances containing active hydrogen in the anion polymerization system are easy to interact with the active center and destroy the polymerization reaction, which adds some difficulties to industrial production.

Classification