HIGH-MOLECULAR COMPOUNDS

From Big Medical Encyclopedia

HIGH-MOLECULAR COMPOUNDS, polymers — chemical compounds, molecules to-rykh consist of a large number of the repeating groups of atoms or links of identical or various chemical structure.

Century of page divide on natural (proteins, nucleic acids, polysaccharides) and synthetic (polyethylene, polybutadiene, phenolic resins, etc.). Biol, natural V.' value of page is defined by the fact that they make a structural basis of all live organisms and participate practically in all processes of life activity (proteins, nucleic acids, cellulose, starch etc.). Synthetic V. pages find broad application in medicine: incidental materials of sanitation and hygiene, medical tools (syringes, cannulas, catheters), materials to lay down. prosthetics (veins, valves of heart, crystalline lenses and a vitreous of an eye, pins for osteosynthesis, joints, sinews, materials for cosmetic operations, substitutes of a blood plasma, surgical threads and glues, materials for stomatology) etc. Pier. the weight (weight) of V. of page varies from several thousand to several million, and in some cases reaches tens of millions (e.g., proteins). Thousands of atoms connected by forces of the ordinary and (or) coordinate covalencies are molecular composition of V. of page (macromolecules). Atoms or atomic groups B. of page can be located in the following order: 1) an open chain, including linear — linear high-molecular compounds (e.g., polyethylene, natural rubber, cellulose); 2) a chain with branchings — branched high-molecular compounds (e.g., starch); 3) the three-dimensional grid consisting of pieces of a chain structure — the sewed high-molecular compounds (e.g., phenolic resins).

At the same chemical structure of a macromolecule can be constructed of various stereoisomers of a link. Century of page, in macromolecules to-rykh is a certain pattern in an arrangement of stereoisomers, call stereoregular; Century of page, a macromolecule to-rykh contain several types of the repeating links, call copolymers. Depending on the nature of distribution of links in macromolecules of the last distinguish regular and irregular copolymers. In the first case distribution of monomer units is characterized by a certain sequence. The styrene copolymer with maleic anhydride constructed by the principle of ABABAB can be an example of regular copolymer... (And yes In — various monomer units). Also more difficult regular sequences of alternation of links are possible that, in particular, it is characteristic of various amino-acid remains in nek-ry proteins or other natural high-polymer substances — biopolymers, napr, glycine-proline-oxyproline in collagen. In nucleic acids and in the majority of proteins of the sequence of links are set by the corresponding code and define biochemical, specificity of the corresponding connections. In irregular copolymers distribution of links is accidental that is characteristic of many synthetic copolymers.

Depending on structure of a stem nucleus of V. of page divide into two big classes: gomotsepny, stem nucleuses to-rykh are constructed of identical atoms, and geterotsepnye, the atoms containing at the same time and other elements, most often oxygen, nitrogen, silicon, phosphorus (or in itself, or in a combination with carbon). Among gomotsepny V. of page the main place is taken by carbon-chain; their chains consist only of carbon atoms, napr, polyethylene, polymethyl methacrylate, polystyrene, gutta-percha, etc. Heterochain V.' examples of page are polyethers (poly(ethylene oxide), polyethyleneterephthalate, polycarbonates, etc.), polyamides, urea-formaldehyde resins, proteins, cellulose, nek-ry organosilicon polymers. In the polymers containing atoms of polyvalent metals (e.g., zinc, manganese, copper, etc.), usually covalent and ionic bonds can be combined with coordination (intra complex, or so-called chelate polymers).

Depending on molecular shape there are fibrillar and globular V. of page. Fibrillar V. have pages of a molecule representing linear or poorly branched chains, are extended preferential in one direction. Fibrillar V. pages easily form supermolecular structures in the form of asymmetric packs of molecules — fibrilla. Fibrillar V.' examples of page — collagen, fibroin, cellulose fibers, etc. Call globular V. of page, macromolecules to-rykh have the form of compact spherical balls — globul. Strongly branched macromolecule can be a globule, but also education globul from fibrillar V. the page connected with change of a form of a macromolecule under the influence of intramolecular interactions is possible. Globular V.' example of page are nek-ry proteins (albumine, a globin). Reversible transitions of globular structures in fibrillar at change of external conditions are important in biology (e.g., the phenomenon of a denaturation of proteins).

Properties

the complex specific physical is inherent in Polymers. - chemical and mechanical characteristics: ability to formation of high-strength anisotropic high-oriented fibers and films, ability to show big it is also long the developing reversible deformations which are characterized by small values of the module of elasticity; ability to swelling before dissolution and high viscosity of solutions.

This complex of properties is caused high a pier. it is powerful (weight), a chain structure and flexibility, i.e. ability to change the form at preservation of all chemical bonds of linear macromolecules. Upon transition from linear chains to branched rare three-dimensional grids and further to dense nets these properties become less expressed. The pages which are strongly «sewed» by V. are insoluble, not swimming trunks also are not capable to high-elastic deformations.

Century of page exist in crystal and amorphous states. Necessary condition of crystallization — a regularity enough long sites of a macromolecular chain. In crystal polymers emergence of various crystal forms is possible (fibrilla, spheroliths, monocrystals, etc.), the type to-rykh defines properties of polymeric material. Nezakristallizovanny polymers can be in three physical. states: vitreous, high-elastic and plastic.

Century of page can enter the following various chemical reactions: 1) formation of chemical bonds between macromolecules (so-called sewing together), napr, curing of rubbers, a tanning of skin; 2) disintegration of macromolecular chains on separate, shorter fragments (destruction); 3) the reactions of side functional groups with low-molecular substances which are not affecting a stem nucleus (so-called polymeranalogous reactions in chains); 4) the internal reactions proceeding between functional groups of one macromolecule, napr, intramolecular cyclization. When transformations with participation of functional groups (links) of macromolecules take place, the polymeric condition of V. of page influences kinetics and thermodynamics of reactions and a chemical structure of the formed products. Reactivity of a functional group (or the separate link connected with V. page) in comparison with reactivity of a low-molecular analog of this link is defined by the following effects: 1) effect of a polymer chain, napr, due to electronic influence; 2) effect concentration — due to change of microconcentration of reagents near a macromolecule; 3) electrostatic effect, napr, in the polymers containing the loaded links (polyelectrolytes); 4) the effect is configuration, napr, in case of stereoregular polymers; 5) effect of molecular shape in solution when, e.g., transition of a globular form of protein-enzyme to fibrillar changes the speed of catalytic reaction in one million and more time; 6) effect of the supramolecular organization — because of high tendency of macromolecules to aggregation and to structuring even in dilute solutions.

Nek-ry properties B. of page, napr, solubility, ability to frictional flow, stability etc., are very sensitive to action of small amounts of the impurity or additives reacting with macromolecules. So that to turn linear polymer from soluble in insoluble, there is enough formation of 1 — 2 cross bonds on one macromolecule.

Synthetic V. villages receive receiving reactions polymerizations (see) and polycondensation (see. Condensation ). Villages usually receive carbon-chain V. polymerization of monomers with one or several multiple carbon-to-carbon linkages (e.g., vinyl chloride, tetrafluorethylene, acrylic to - that, butadiene, etc.). Villages receive heterochain V. polymerization of the monomers containing multiple bonds carbon — an element (e.g. — With = O — C = N), and also as a result of polyreaction. As monomers at the same time most often use dicarboxylic acids or their derivatives (e.g., anhydrides, acid halides, etc.) in combination with the bifunctional connections containing amino or hydroxylic groups. Reaction of an adipilkhlorid can be an example [Cl — CO — (CH 2 ) 4 COCl] with hexamethylenediamine [NH 2 — (CH 2 ) 6 — NH 2 ], leading to formation of a poligeksametilenadipamid (nylon-6,6). It is possible to receive century of page also polymerization of cyclic connections, napr, a caprolactam with formation of linear polyamide (nylon-6), or the reaction of diisocyanates with diols leading, e.g., to receiving polyurethane. Polycondensation of carboxyanhydrides of alpha amino acids receive the synthetic polypeptides which are models of proteinaceous macromolecules.

Natural V. are formed by page in the course of biosynthesis in cells of live organisms, inorganic — as a result of the geochemical processes happening in crust.

Use

Mechanical strength, elasticity, electric insulation and other valuable properties caused broad use of V. of page in various industries and in life. The main types of polymeric materials — rubbers and rubbers, fibers, plastic, films, varnishes, enamels, paints and glues.

The following requirements are established, the Crimea V. shall satisfy the pages used in the medical purposes: 1) purity of a product; 2) a possibility of molding in a required product without decomposition of polymer and any harmful changes; 3) existence necessary chemical, physical. and mechanical characteristics for performance of required functions; 4) constancy of a form and properties at sterilization; 5) physical., chemical and mechanical stability at interaction with surrounding biol, Wednesday; 6) lack of toxicological, pyrogenic and cancerogenic properties at contact with an organism. So, polymeric material in contact with blood shall not cause thrombogeneses and not influence the normal mechanism of a blood coagulation; not to change a configuration or stability of any cell or soluble part of blood that could lead to various pathological effects. It is necessary to consider that in a live organism under action biol, Wednesdays can occur changes physical. and chemical characteristics of polymer chains, napr, flexibility owing to a mineralization, chemical degradation etc.

Synthetic and natural V. are applied by page to production of the semi-impenetrable membranes used in the devices «artificial lung» and «artificial kidney». In this case V. of page shall meet all listed above requirements, besides, to have ability to bulk up in water and dividing ability. Membranes for a hemodialysis can be made of the cellophane received from cellulose, copolymers of polyethyleneglycol with polyethyleneterephthalate, the sewed polyvinylpirrolidone, polymer - polymeric complexes — of polyelectrolytes of an opposite sign of a charge (e.g., a complex of polystyrene sulphonate of sodium and polivinilbenziltrimetilammoniya of chloride). As material for the oksigenatorny membranes providing saturation of blood with oxygen and removal of carbon dioxide gas serves, e.g., dimethyl silicone.

Pages apply synthetic and natural V. also in pharmacology (the heparin, starch, pepsin, globulins, protamins and dextrans various a pier. weight entered into a blood channel). Polyvinylpirrolidone and Polyglucinum use as substitutes of a blood plasma, and the first, besides, as an active dezintoksikator of the poisons and toxicants collecting in an organism. Complex compound of polyvinylpirrolidone with iodine as well as Iodinolum (a complex of polyvinyl alcohol with iodine), is an effective bactericide and fungicide. The basis of ointments is made by various non-toxic silicone polymers having hydrophobic properties (see. Hydrophobic substances ). The polymeric component — poly(ethylene oxide) often enters a basis of ointments, tablets or coverings of drugs.

Synthetic polymers can possess and own fiziol, activity. So, poly-N-oxy-2-vinyl-pyridine is used for treatment of a silicosis, polymeric quaternary ammonium salts from a tetrametilgeksametilendiamid and a trimetilendibromid use for binding in an organism of excess heparin. Century of page if they bear on themselves pharmacological an active molecule or group, can prolong effect of medicinal substances. Besides, macromolecules B. of page can serve depot of medicines, promoting their gradual allocation in an organism. Such combinations of V. of page with medicines receive or polymerization of the monomers having a double bond and containing a medicinal fragment (e.g., acryloylnovocaine), or method of polymeranalogous reactions with water soluble polymers (e.g., polyvinyl alcohol, polyvinylpyridine, dextrans, etc.).

See also Polymeric materials .


Bibliography: Losev I. P. and Trostyanskaya E. B. Himiya of synthetic polymers, M., 19 71; Polymers in medicine, the lane with English, under the editorship of N. A. Pla-te, M., 1969; Rabinovich I. M. Use of polymers in medicine, L., 1972, bibliogr.; With and d e of l to about in with to and I am F. P. Himiya of N-vinylpyrrolidone and its polymers, M., 1970; Streiikheev A. And., D e p e in and c to and I am V. A. and the Slonim G. L. Fundamentals of chemistry of high-molecular compounds, M., 1966; Ushakov S. N. Synthetic polymers of medicinal appointment, L., 1962.

N. A. Plate, Yu. E. Kirsch.

Яндекс.Метрика