Nanopolymers refer to organic/inorganic nanocomposites in which inorganic fillers are dispersed in a nanometer-sized organic polymer matrix. Below we summarize methods for obtaining nanopolymers.
1. Intercalation compound method
Layered inorganic substances (such as clay, mica, vanadium pentoxide, layered metal salts with manganese trioxide, etc.) can be broken into nanoscale structural microdomains under action of a certain driving force, and distance between plates is usually nanoscale. and can accommodate monomerically printed polymer molecules.
The composite intercalation method uses layered organic matter as main body, and organic monomers as guests are inserted into interlayers of inorganic materials for in-situ polymerization, or polymers are directly inserted into interlayers to form composites. According to different forms of intercalation, it can be divided into following types:
(1) Intercalation polymerization The monomer is first incorporated into sheet, and then polymerized by heat, light, initiator, etc. For example, clay and caprolactam are melted and mixed, clay/nylon (PA) embedded composites are prepared under action of initiator ; monomers such as aniline, pyrrole, thiophene, and pyran are embedded in inorganic sheets and then chemically oxidized. or electrochemically polymerized, conductive composite materials were prepared.
(2) Solution or emulsion intercalation Polymeric monomers are incorporated into sheet through a solution or emulsion. For example, clay-styrene-butadiene-rubber nanocomposites are obtained by mixing a solution of styrene-butadiene-rubber in toluene and styrene-butadiene latex with clay, respectively. But key to this method is finding right monomer and compatible polymer clay and ore solvent system.
(3) Melt Intercalation The polymer is melt-incorporated into sheet. For example, mixing alkylammonium montmorillonite with polystyrene (Ps) powder, pressing it into pellets, and heating pellets at a glass transition temperature higher than that of Ps can result in nanoclay/polystyrene. This method does not require solvents and is suitable for most polymers.
2. Sol-gel method
Sol-gel technology consists in hydrolysis of a precursor in a co-solution system to obtain a sol in presence of a polymer, and then in gelation and drying to obtain a nanomaterial. This method can be divided into:
1) The precursor is dissolved in polymer solution, then in sol and gel. For example, use of this technology to produce nano-SiO2/polyimide plastics through sol-gel reaction of ethyl silicate in an N,N-dimethylacetamide solution of polyimide;
2) After sol is formed, it is mixed with polymer and then gelled. For example, an aluminum isopropoxide sol is mixed with polyvinyl alcohol (PVA), gelled, and dried in vacuo to form nano-Al2O3/PVA plastics.
3) In presence of a precursor, monomer polymerizes first and then gels, first TiO2/methyl methacrylate sol coated with oleic acid is prepared, and benzoyl peroxide is used as an initiator for nanoparticle polymerization. -TiO2/PMMA plastic.
4) Precursors and monomers are dissolved in solvent to allow hydrolysis and polymerization to occur simultaneously, allowing some insoluble polymers to be incorporated into inorganic network by in situ formation. In addition, groups capable of forming chemical compounds can be introduced into polymers or monomers.ic bonds with inorganic components.
3. Direct scatter method
This method is simplest method for preparing nanocomposite materials and is suitable for nanoparticles of various shapes. To prevent particle agglomeration, surface of nanoparticles should be treated before mixing. Currently used surface treatment methods include surface coating modification, partially active modification, film outer layer modification, mechanochemical modification, etc.; In terms of mixing methods, there are solution mixing methods, emulsion mixing methods, melt mixing methods. Mixing, mechanical mixing, etc. The mixing technology synthesizes nanoparticles and materials step by step, and can control particle shape and size. The difficulty lies in particle dispersion, and key to success is control of phase size and particle size distribution of microdomains. When mixing, in addition to complex treatments such as dispersants, binding agents and surface function modifiers, ultrasonic dispersion should also be used to achieve uniform dispersion.
This structure includes SiO2 nanopolypyrrole plastic obtained by dispersing SiO2 in polypyrrole. In process of preparation, a colloid of dispersed SiO2 microparticles (characteristic particle size 20 nm) is added to monomer, which, under action of an oxidizing agent, polymerizes at a certain temperature by means of electromagnetic stirring.
4. In situ dispersion polymerization branch method
The original technology of dispersion polymerization is to first uniformly disperse nanoparticles in monomer, and then carry out polymerization reaction. The use of seed emulsion polymerization to obtain nanoplastics consists in using nanoparticles as seeds for emulsion polymerization. When there is emulsification, on one hand, it can prevent particles from agglomeration, and on other hand, make each particle evenly dispersed in micelles. The PVA/A12O3 nanocomposite system can be obtained by emulsion polymerization of ethyl acetate using nano-A12O3 as a seed. This method is similar to mixing method, which requires surface treatment of nanoparticles, but its effect is stronger than that of mixing method. This method can not only realize uniform dispersion of particles, but also keep stability of nanoparticles, and can be polymerized and shaped at same time, avoiding heat-induced degradation, so as to maintain stability of drug characteristics.
Source: Public account Polymer Learning Research, Suo