Synthesis and Characterization of New Organic Phosphonates Monomers as Flame Retardant Additives for Polymers

A Crystalline Three-Dimensional Covalent Organic Framework with Flexible Building Blocks

The construction of three-dimensional covalent organic frameworks (3D COFs) has proven to be very challenging, as their synthetic driving force mainly comes from the formation of covalent bonds. To facilitate the synthesis, rigid building blocks are always the first choice for designing 3D COFs. In principle, it should be very appealing to construct 3D COFs from flexible building blocks, but there are some obstacles blocking the development of such systems, especially for the designed synthesis and structure determination. Herein, we reported a novel highly crystalline 3D COF (FCOF-5) with flexible C-O single bonds in the building block backbone. By merging 17 continuous rotation electron diffraction data sets, we successfully determined the crystal structure of FCOF-5 to be a 6-fold interpenetrated pts topology. Interestingly, FCOF-5 is flexible and can undergo reversible expansion/contraction upon vapor adsorption/desorption, indicating a breathing motion. Moreover, a smart soft polymer composite film with FCOF-5 was fabricated, which can show a reversible vapor-triggered shape transformation. Therefore, 3D COFs constructed from flexible building blocks can exhibit interesting breathing behavior, and finally, a totally new type of soft porous crystals made of pure organic framework was announced.

Synthesis of a novel flame retardant based on DOPO derivatives and its application in waterborne polyurethane

An intumescent flame retardant (DOPO-DAM) containing phosphorus and nitrogen was synthesized via a two-step process and then, it was incorporated into waterborne polyurethane to serve as a reactive flame retardant for preparing flame-retarded WPU (FR-WPU). The chemical structures of DOPO-DAM and FR-WPU were confirmed by ¹H NMR, ³¹P NMR, and FTIR studies. The thermal stability, flame retardancy and mechanical properties of FR-WPU were investigated by TGA, TGA-FIR, Py-GC-MS, limiting oxygen index (LOI) test, SEM-EDS analysis, cone calorimeter test and a universal testing machine. The results showed that the conjugation of DOPO-DAM into WPU induced a slight decline in the thermal stability of FR-WPU. However, the incorporation of DOPO-DAM into WPU significantly enhanced the flame retardancy by reducing the heat release rate (HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP). In addition, the morphology, elemental composition and content of the residual char of the flame-retarded WPU indicated the important function of DOPO-DAM in the condensed phase. Thus, DOPO-DAM exhibited gas-phase and condensed-phase flame retardant effects on the WPU films.

An intumescent flame retardant (DOPO-DAM) containing phosphorus and nitrogen was synthesized via a two-step process and it was incorporated into waterborne polyurethane to serve as a reactive flame retardant for preparing flame-retarded WPU (FR-WPU).

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

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 and characterization of novel post-chain extension flame retardant waterborne polyurethane

Flame-retardant waterborne polyurethanes with a phosphorus-containing flame retardant diamine (AWPUs) were synthesized and characterized by the method of post-chain extension technology.