From Big Medical Encyclopedia

POLYMERIZATION — the process of formation of a molecule of high-molecular substance (polymer) consisting in consecutive accession of molecules of low-molecular substances (monomers) to an active center (or to the centers) the growing chain; reverse carries the name a depolymerization. Distinguish two main types of reactions, as a result to-rykh polymers are formed: reaction of consecutive accession (actually polymerization) and polyreaction (see. Condensation ). Unlike reaction of consecutive accession polyreaction proceeds with release of low-molecular substance (e.g., waters). As a result of such reaction biopolymers are formed — proteins (see), polysaccharides (see), nucleic acids (see), etc.

Formation of biopolymers is catalyzed by complex enzymatic systems (see. Polymerases ), owing to what reaction biol, polycondensation differs from chemical a little. So, at chemical polycondensation usually there is an accidental combination of two any particles, i.e. the polymerization degree is low. At biol, synthesis of polymers molecules of monomer consistently join the activated end of the growing chain, the polymerization degree considerably increases. Besides, at synthesis of biopolymers in most cases there is a selection of the connected monomers on a matrix owing to what polymer of the set structure (is synthesized see. Gene , Genetic code ). A depolymerization, i.e. splitting of biopolymers, hydrolases catalyze, e.g. Peptide-hydrolase (see), deoxyribonucleases (see), restriktaza (see. Nucleases ), ribonucleases (see), various hydrolases (see).

If the links making polymer are identical, then call polymer homopolymer. If polymer is formed by a combination of two and more constitutional repeating units, it call hetero - or copolymer, and reaction of formation of copolymer — copolymerization (see).

Ability of nek-ry substances to connect with each other, forming polymers, is called polymerism. The connections entering polyreaction shall be bifunctional, i.e. have two fragments which can connect to other links in molecules. If ny connections participate in reaction only biofunctionality, then linear polymers are formed. If the monomer units which are used for polymerization are multifunctional, then the formed polymer may contain branched chains, or «stitchings», between chains. Polyreaction is entered by the substances having functional groups of different type capable to interact with each other (e.g., amino and carboxyl groups, at interaction to-rykh the peptide bond is formed and water is emitted).

The item of monomers happens or by disclosure of multiple bonds between atoms, or by cyclic regroupings.

The structure and structure of a monomer unit in polymer in most cases corresponds to structure and a structure of initial monomer (except for the bonds which are disconnected as a result of reaction). However examples when monomer units differ from initial monomer on structure, and sometimes and on structure, napr, owing to formation of new bonds in a monomer unit, shift of one atom or group of atoms during accession of monomer, allocation as a result of reaction of low-molecular substances are known.

See also Proteins, biosynthesis of proteins ; High-molecular compounds, receiving .

Bibliography: Reactivity, mechanisms of reactions and structure in polymer chemistry, under the editorship of A. Jenkins and A. Ledvis, lane with English, M., 1977; With p and-r and Yu. L N. Polyreactions, Kiev, 1977.

O. D. Lopina.