copolymer(redirected from Alternating polymer)
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, chemical compound with high molecular weight consisting of a number of structural units linked together by covalent bonds (see chemical bond). The simple molecules that may become structural units are themselves called monomers; two monomers combine to form a dimer,
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a polymer whose macromolecules contain several types of monomeric units. In regular copolymers, the different units are arranged in periodic fashion. The simplest examples are copolymers of styrene with maleic anhydride and copolymers of certain olefins with SO2, constructed in the order . . . ABABAB . . . , where A and B are different types of monomeric units. More complicated regular sequences, with an alternating arrangement of units, are characteristic of, for example, the various amino-acid residues in certain proteins, such as the glycine-proline-hydroxyproline sequence in collagen. In irregular copolymers, the distribution of monomeric units is random, which is characteristic for many synthetic copolymers. In nucleic acids and most proteins, the irregular sequences of units are prescribed by a corresponding code, and it is these sequences that determine the biochemical and biological specificities of the corresponding compounds.
Copolymers in which the monomeric units of each type form rather long continuous sequences (blocks) that replace one another within the macromolecule are called block copolymers. One or several chains having a chemical composition different from that of the macromolecular chain may be added to the internal (nonterminal) monomeric units of the chain. Copolymers of this type are referred to as graft copolymers.
Materials with a given set of properties can be prepared by combining chemical units of various types in a single macromolecule. Thus, the synthesis of copolymers is one of the most effective means for modifying the properties of high-molecular-weight compounds.
REFERENCEEntsiklopediiapolimerov, vols. 1–2. Moscow, 1972–74.
V. A. KABANOV