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Vitrimers are a class of plastics, which are derived from thermosets and are very similar to them. Vitrimers consist of molecular, covalent networks, which can change their topology by thermally activated bond-exchange reactions. At high temperatures they can flow like viscoelastic liquids, at low temperatures the bond-exchange reactions are immeasurably slow („frozen“) and the Vitrimers behave like classical thermosets at this point. Vitrimers are strong glass formers. Their behavior opens new possibilities in the application of thermosets like self-healing or simple processibility in a wide temperature range. Polymer networks other than epoxy resins based on diglycidyl ether of bisphenol A have been utilized in vitrimer technology, such as polylactide,〔 polyhydroxyurethanes,〔 epoxidized soybean oil with citric acid, and polybutadiene. == Background and significance == Thermoplastics are on the one hand easy to process but on the other hand also easy corrodible by chemicals and mechanical stress. The opposite is true for thermosets. Thermoplastics are made of covalent bond molecule chains, which are connected by weak interactions (e.g. Van der Waals forces). Thus they can be easily processed by melting (or in some cases also from solution), but are also susceptible against appropriate solvents creep under constant load. Thermoplastics can be deformed reversibly above their glass-transition temperature or their crystalline melting point and be processed by extrusion, injection molding and welding. Thermosets, however, are made of molecular chains, which are interconnected by covalent bonds to a stable network. Thus they have outstanding mechanical properties and thermal- and chemical resistance. They are an indispensable part of structural components in automotive and aircraft industry. Due to their irreversible linking by covalent bonds molding is not possible anymore as soon as the polymerization is completed. They must be polymerized therefore in the desired shape, which is time-consuming, restricts the shape and is responsible for their high price. If there was a way to create reversible covalent bonds, this would combine good processability, repairability and high performance. There have been already a number of strategies tried that would allow such plastics. Vitrimers combine the desirable properties of both classes: they show the mechanical and thermal properties of thermosets and can be also molded under the influence of heat. Vitrimers can be welded like (silicon) glasses or metals. Welding by simple heating allows the creation of complex objects. Vitrimere like (silicon) glasses or metals are welded. A weld by simply heating allows Customize complex objects. Vitrimers could be therefore a new and promising class of materials with numerous applications. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「vitrimers」の詳細全文を読む スポンサード リンク
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