Explanation

In chain polymerization, the process of inactivating the active center of the growing chain. According to the number of growth chains involved in the termination reaction, chain termination can be divided into bimolecular termination and unimolecular termination. For radical chain polymerization, bimolecular termination can be divided into disproportionation termination termination and coupling termination. The method of chain growth radical seizing the hydrogen atom or other atoms of another chain radical to terminate polymerization is called disproportionation termination. The result of disproportionation termination is that two active chains lose their activity at the same time, the degree of polymerization and the number of structural units in the chain radical are the same, and only one end of each macromolecule is a initiator residue, and the other end is a saturated or unsaturated end, accounting for half of each. The way to terminate polymerization by combining the single electrons of two chain radicals to form covalent bond is called coupling termination. The result of coupling termination is that two active chains lose their activity at the same time, and the degree of polymerization of macromolecule is twice the number of structural units of chain free radicals. When initiator initiates without chain transfer, both ends of macromolecule are initiator residues. Therefore, coupling termination and disproportionation termination can be distinguished according to the number of initiator residues on the macromolecular chain. The way of chain termination is related to the type of monomer and polymerization conditions. The way that chain growth radicals react with other compounds to terminate polymerization is called unimolecular termination. For example, chain growth radicals are coupled with primary radicals, chain growth radicals are coupled with other stable radicals, and chain growth radicals react with chain termination agent to terminate chain polymerization.

Classification