Structural characteristics Functional polymers generally have groups that show certain functions on the main chain or side chain, and the display of their functions is often very complicated, which depends not only on the primary structure of polymer chains, such as chemical structure, the order of structural units, molecular weight and its distribution, branching and stereoscopic structure, but also on the conformation of polymer chains and the advanced structure when polymer chains are aggregated. The latter is more important for the function of biological activity.
The classification of photopolymer (see photopolymer), also known as photopolymer, undergoes structural chemical or physical changes (such as cross-linking reaction, changing solubility) after light absorbs light energy. Widely used in printing plates, photoresists, photosensitive inks, photosensitive coatings, etc. After some polymers absorb light, the molecular structure changes, which leads to the change of absorption spectrum. This kind of polymer is called photochromic polymer and has been used in color-changing glass, color-changing window glass and information materials.
Electrically functional polymers Some polymers with * * * yoke double bond system, such as polyacetylene, have semiconductor properties and are called polymer semiconductors. If the intermolecular orbital interaction between electrons is strong, these solid polymers will show stronger electrical properties because carriers can be easily generated and transferred, such as conductive polymers obtained by forming charge transfer complexes with tetracyanomethylbenzoquinone to improve conductivity. The charge transfer complex of polyvinyl carbazole and trinitrofluorene can produce photovoltaic effect after illumination, which is called photoconductive polymer and is widely used in xerography, electrophotography and information materials. Polyvinylidene fluoride and its polymers can produce piezoelectric effect and thermoelectric effect under heating and pressure, which is called piezoelectric polymer or thermoelectric polymer.
Catalytic polymers, which have catalytic effect on chemical reactions, mainly include natural and synthetic polymer catalysts. Enzymes are natural polymer catalysts existing in organisms. Its characteristic is that the reaction can be carried out at high speed, high efficiency and high selectivity at normal temperature and pressure. A fully synthetic polymer catalyst with high catalytic activity for some hydrolysis reactions, such as the polymerization of vinyl imidazole and vinyl phenol, can be obtained by introducing constitutive enzyme active center groups into the polymer. Some enzymes contain metals. If metal is complexed with polymer ligand, polymer metal catalyst can be obtained, which can make some reactions proceed at high speed and high efficiency under mild conditions. A high-activity and high-selectivity catalyst synthesized by imitating natural enzyme in this way and referring to the active center of enzyme and combining with polymer effect is called mimetic enzyme. One of the disadvantages of natural enzymes is their water solubility. In order to overcome this shortcoming, the polymer used for enzyme is limited in a certain space, which is called immobilized enzyme.
Bioreactors are called bioreactors by immobilizing bioactive substances such as bacteria instead of traditional catalysts in chemical reactors. This will bring great changes to the classical chemical reactor.
Polymer ion exchange resin with selective separation function is a kind of polymer with separation, purification and purification functions, but its selective separation performance is not high. If ethylenediamine tetraacetic acid and hydroxylamine are introduced into the polymer, the selective separation performance can be further improved. This polymer is called chelating resin. Macroporous resin developed from ion exchange resin has a surface area of hundreds of square meters and a suitable pore size per gram, which can be used as a polymer adsorbent to adsorb nonpolar or polar solutes from polar or nonpolar solutions and trace impurities of ppb level from water. Selective separation membranes developed from ion exchange membranes are widely used in separation, purification and medical fields.
The application of medical functional polymers in medicine should not only have medical functions, but also have safety and reliability, which are generally used in medical materials and polymer drugs. Medical materials can also be divided into: ① soft tissue materials with good histocompatibility and blood compatibility and certain mechanical strength, such as polyether polyurethane and poly (β-hydroxyethyl methacrylate); ② Hard tissue materials represented by polymethyl methacrylate. The former is used for implant materials, repair materials and artificial organs; The latter is used in dentistry and bone cement. Polymer drugs can be divided into two categories: polymer itself has pharmacological activity and small molecule drugs are combined with polymer carriers. The latter can control the release of drugs and achieve long-term effect, thus reducing the number of administration and reducing the toxicity of drugs. If a ligand (such as antibody) with specific affinity to the lesion site is attached to the polymer carrier in addition to the drug, targeted drug delivery can be realized. This drug is called polymer affinity drug, which is particularly meaningful for drug delivery with great toxicity or side effects.
Other functional polymers that can convert chemical energy into mechanical energy (such as artificial muscles), information transmission functional polymers, drag reduction functional polymers, etc. , are exploring and developing.
Synthetic polymerization is used to prepare functional polymers by addition polymerization or polycondensation of monomers containing specific functional groups. Its advantage is that the distribution and arrangement of functional groups in the polymer chain can be adjusted by * * * polymerization or * * * polycondensation, for example:
① Polycondensation of hydroquinone with formaldehyde
(2) The polymerization of vinyl hydroquinone needs protecting groups to ensure the smooth progress of polymerization because hydroquinone is a polymerization inhibitor;
Polymer chemical reaction method introduces groups with specific functions into polymer chains through chemical reactions (see polymer chemical reaction). The polymer chain should contain active groups that can react further, such as hydroxyl, carboxyl, amino, amino, anhydride, carbonyl, acyl chloride, epoxy, hydroxymethylimine, active halogen atom, isocyanate, thioisocyanate, sulfhydryl, active ester, active amide, etc. Their activities are different, and the choice depends on the functional groups to be introduced. This reactive polymer can be obtained by polymerization of reactive monomers or chemical modification of ordinary polymers. Its advantage is that it can basically ensure the polymerization degree of the original polymer chain. However, the number and distribution of functional groups are limited by the steric hindrance of polymer chains, the activity and diffusion of active groups.