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In the 21st century, both environmental protection and flame retardant have imposed stricter requirements on the use of natural and synthetic polymers. The use of conventional flame retardants to reduce the flammability of polymers is restricted by environmental regulations. In order to meet the flame retardant standards and environmental protection regulations at the same time, the development of new halogen-free flame retardant polymer materials is imperative. Such materials should have excellent thermal oxidation stability, good flame retardancy, no toxicity or low toxicity to human health and the environment, can maintain sufficient strength at high temperatures, the price can be affordable for users, and is relatively easy to process and Recycling and other properties. It can be expected that in the near future, the use of halogen-based flame retardants and their smoldering polymer materials will be reduced due to manufacturers' voluntary actions and related legislation.
Recently, people are working on the research of some halogen-free flame-retardant polymers. This type of polymer does not require flame retardant treatment to meet stringent fire protection requirements and is environmentally friendly. Compared with the conventional flame-retardant polymers, the intrinsically flame-retardant polymer does not have the problems of volatilization, dissolution, migration, and exudation of the flame retardant, and the flame-retardant efficiency is high and long-lasting under the same content of the flame-retardant elements. In particular, the introduction of multiple flame-retardant elements simultaneously in such polymer molecules can produce a synergistic flame-retardant effect within the molecule, which is better than the synergistic flame-retardant effect produced by the physical mixing of various flame retardants. At present, intrinsically flame-retardant polymers are still in the laboratory development stage due to limitations in synthesis, processing, and price, but it represents the development direction of flame-retardant polymer materials.
With regard to the intrinsically flame-retardant epoxy resin, currently there are mainly flame-retardant epoxy resins containing pendant DOPO groups in the molecule and flame-retardant epoxy resins containing phosphate groups in the molecule. The flame-retardant epoxy resin containing pendant groups in the molecule is the key to 'DOPO'. The scientific name for DOPO is 9,10-dihydro-9-oxa-10-phosphaphenanthroline. The DOPO molecule contains active hydrogen. It can act as a reaction center and reacts with a series of functional groups. A series of DOPO-based dihydric phenols can be prepared. When the latter reacts with bisphenol A epoxy resin, the latter can be reacted. DOPO introduces resin side chains to obtain phosphorus-containing intrinsically flame-retardant epoxy resins. This kind of resin can be cured with common curing agents (such as diaminodiphenylmethane, DADPM). The flame retardant effect of phosphorus content of 2% in the cured resin can be comparable to the bromine mass fraction of 16% in the brominated epoxy resin. . Other dibasic acids and diamines synthesized with DOPO can be used as curing agents for epoxy resins. The use of such curing agents to cure common epoxy resins can also impart inherent flame retardancy to the resin, if cured with a phosphorous ring. Oxygen resin, the phosphorus content of the resin, char formation rate and LOI can be further improved.
New Progress in Research on Phosphorus-containing Intrinsic Flame Retardant Polymer
Intrinsic flame-retardant polymers have long-lasting flame-retardant properties, no volatilization, dissolution, and migration issues, and can achieve intramolecular, synergistic flame-retardant effects and compatibility with the environment. Therefore, they have increasingly emerged in recent years. This area continues to make the latest research progress, including intrinsically flame-retardant epoxy resins, polyamides, polyimides, and polyurethanes, all of which are halogen-free polymers with a phosphorus-containing group in the main chain or side chain. How is the synthesis method and performance? A few days ago, it was considered that there has been progress in the 'Research on phosphorus-containing flame retardant polymers'.