Recent Developments in Organophosphorus Flame Retardants Containing P-C Bond and Their Applications

Abstract

Organophosphorus compounds containing P-C bonds are increasingly developed as flame retardant additives due to their excellent thermal and hydrolytic stability and ease of synthesis. The latest development (since 2010) in organophosphorus flame retardants containing P-C bonds summarized in this review. In this review, we have broadly classified such phosphorus compounds based on the carbon unit linked to the phosphorus atom i.e., could be a part of either an aliphatic or an aromatic unit. We have only considered those published literature where a P-C bond was created as a part of synthetic strategy to make either an intermediate or a final organophosphorus compound with an aim to use it as a flame retardant. General synthetic strategies to create P-C bonds are briefly discussed. Most popular synthetic strategies used for developing P-C containing phosphorus based flame retardants include Michael addition, Michaelis–Arbuzov, Friedels–Crafts and Grignard reactions. In general, most flame retardant derivatives discussed in this review have been prepared via a one- to two-step synthetic strategy with relatively high yields greater than 80%. Specific examples of P-C containing flame retardants synthesized via suitable synthetic strategy and their applications on various polymer systems are described in detail. Aliphatic phosphorus compounds being liquids or low melting solids are generally applied in polymers via coatings (cellulose) or are incorporated in the bulk of the polymers (epoxy, polyurethanes) during their polymerization as reactive or non-reactive additives. Substituents on the P atoms and the chemistry of the polymer matrix greatly influence the flame retardant behavior of these compounds (condensed phase vs. the gas phase). Recently, aromatic DOPO based phosphinate flame retardants have been developed with relatively higher thermal stabilities (>250 °C). Such compounds have potential as flame retardants for high temperature processable polymers such as polyesters and polyamides. A vast variety of P-C bond containing efficient flame retardants are being developed; however, further work in terms of their economical synthetic methods, detailed impact on mechanical properties and processability, long term durability and their toxicity and environmental impact is much needed for their potential commercial exploitations.

Synthesis of Resorcinol-Based Phosphazene-Containing Epoxy Oligomers

“…[14]. Aryloxyphosphazenes, for example, in comparison with other phosphorus-based flame retardants have, as a rule, higher thermal stability and chemical resistance [6,11,13,15]. Organophosphazenes are effective flame retardants.…”

Triple‐faced polypropylene: Fire retardant, thermally stable, and antioxidative

“…Such a dual functionality would be expected in view of a report suggesting that N‐alkoxy‐hindered amines can play the role of flame retardant and has synergistic effect between the developed precursor and conventional flame retardants due to free‐radical quenchability and high flame‐retardant efficiency of the developed precursor . Besides, recently, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) is presented as a new and effective flame retardant, and several papers reported the use of DOPO in PP . Overall, there is evidence that the presence of 1.5–2 wt% phosphorus element in the system is adequate to reach an acceptable level of flame retardancy.…”

Performance comparison of epoxy resins modified with diphenylphosphine oxide and DOPO

“…The synthesis and application of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) have been widely studied, since its synthesis was originally reported by Sanko Chemical in 1972 . Now, DOPO has been industrially commercialized, and one of its main applications is as a reactive flame retardant for epoxy resins (EPs).…”

“…The synthesis and application of 9,10-dihydro-9-oxa-10phosphaphenanthrene-10-oxide (DOPO) have been widely studied, since its synthesis was originally reported by Sanko Chemical in 1972. [1][2][3][4] Now, DOPO has been industrially commercialized, and one of its main applications is as a reactive flame retardant for epoxy resins (EPs). It is especially suitable for epoxy resins in the fields of electrical and electronic materials due to its high flame-retardant efficiency and relatively environmentally friendly characteristics.…”