Chloroalkyl phosphates

Pentabromodiphenyl Oxide. Pentabromodiphenyl oxide [32534-81-9] (PBDPO) is prepared from diphenyl oxide by bromiaation (36). It is primarily used as a flame retardant for flexible polyurethane foams. For this appHcation PBDPO is sold as a blend with a triaryl phosphate. Its primary benefit ia flexible polyurethanes is superior thermal stabiUty, ie, scorch resistance, compared to chloroalkyl phosphates (see Phosphate esters). 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

Phosphoms compounds are effective flame retardants for oxygenated synthetic polymers such as polyurethanes and polyesters. Aryl phosphates and chloroalkyl phosphates are commonly used, although other compounds such as phosphonates are also effective. The phosphoms compounds can promote char formation, thereby inhibiting further ignition and providing an efficient thermal insulation to the underlying polymer. 

Commercially available flame retardants include chlorine- and bromine-containing compounds, phosphate esters, and chloroalkyl phosphates. Recent entry into the market place is a blend of an aromatic bromine compound and a phosphate ester (DE-60F Special) for use in flexible polyurethane foam (8). This paper describes the use of a brominated aromatic phosphate ester, where the bromine and phosphorus are in the same molecule, in high temperature thermoplastic applications. 

Chloroalkyl phosphates such as tris(l,3-dichloro-2-propyl) phosphate (TDCiPP) and tris(chloro-wc>-propyl) phosphate (TC/PP) are more often used in textile backcoatings, in rigid and flexible pol3mrethane foams, which are used for thermal insulation and for furniture and upholstery, respectively [63]. In contrast, tris(2-chloroethyl) phosphate (TCEP) is now more frequently used in PVC, unsaturated polyester resins, and textile backcoatings [63]. 

Polycondensation reactions of 2-chloroalkyl phosphates or phosphonates to obtain products having a controllable degree of condensation and low acid or latent acid contents were accomplished in our laboratory using catalysts such as quaternary ammonium salts, amines, amides, sodium carbonate, or lithium chloride (5). Reduction of the temperature diminished the... 

Additive flame-retardants may be more easily incorporated in polyurethane formulation. Several class of compounds have been used to improve flame retardancy of PU foams such compounds are halogen- (very often chloroalkyl-phosphate) or phosphorous-based compounds, although also other substances, like as EG, melamine, aluminum trihydrate and magnesium hydroxide, may be used. 

These mechanisms, however, are not as effective in limiting the rate-of-mass loss, energy release or total mass consumption as is the formation of a monolithic, insulating char barrier. Those organophosphorus compounds most commonly used today, the chloroalkyl phosphates and the aryl phosphates, or even the inorganic ammonium polyphosphates and elemental red phosphorus are not very effective char formers in these polymer systems. 

Environmental concerns are not just limited to the flame retardant molecules themselves or their decomposition products. The implementation of RCRA and the Clean Air Act have also taken their toll of the manufacturing processes for flame retardants. In the last year, one major flame retardant, tetrakis (2-chloroethoxy)ethylene bisphosphate (Figure 3) was withdrawn from the market because of environmental problems stemming from its manufacturing process. Similar manufacturing concerns may threaten other chloroalkyl phosphates if current government scrutiny of their chronic toxicity data doesn t do them in first. 

A more recent addition is Reofos NHP, a low-fogging additive for hot-moulded pol5mrethane (PU) foam for automotive seats. This material offers an alternative to chloroalkyl phosphates to meet the MVSS 302 standard. 

Dimethyl Propylphosphonate (DMPP) [18755-43-6]. This liquid additive was recently introduced by Bayer as LEVAGARD DMRR, an alternative to the chloroalkyl phosphates for flame-retarding rigid polyurethane foams. 

Compared to the foregoing chloroalkyl phosphates, this product has a greatly reduced volatility, much lower water solubility, and high stability toward the... 

A critical review of the toxicity of the haloalkyl phosphates and the potential metabolic products is available (175). The flame retardant tris (tris-2,3-dibromopropyl) phosphate was found to be mutagenic in laboratory tests its production and use were discontinued in the 1970s. Tris(2-chloroethyl) phosphate and tris(dichloroisopropyl) phosphate have voluntary R40 labels (limited evidence of carcinogenicity in animal tests). Tris(chloroisopropyl) phosphate does not require special classification. The chloroalkyl phosphates are undergoing (as of 2004) an EU risk assessment. They have been detected at various locales in mimicipal waste water (176), indoor dust, or indoor air (177,178). 

Tests in pure water, river water, and activated sludge showed that commercial triaryl phosphates and alkyl diphenyl phosphates imdergo reasonably facile degradation by hydrolysis and biodegradation (215,216), the chloroalkyl phosphates less so. 

Melamine is most commonly used in flexible polyurethane foams in combination with chloroalkyl phosphates and in intumescent coatings in combination with ammonium polyphosphate and pentaerythritol. Nevertheless, there is extensive patent literature on the use of melamine in thermoplastics and elastomers, which was reviewed by Weil and Choudhary. The review gives good insight into the mechanism of flame retardant action of melamine. It is known that melamine does not melt, but sublimes at about 350°C (actual volatilization starts at a lower temperature). Upon sublimation, significant energy is absorbed, which decreases the surface temperature of the polymer. This is especially important for polyurethane foams having very low thermal inertia. In a hot flame, melamine may decompose further, with creation of cyanamid, which is also a very endothermic process. 

Chemical Name chloroalkyl phosphate/oliqomeric phosphonate Physical Appearance Dark gray liquid Phosphorus Content Wt% 10.2 Chlorine Content Wt% 37.0 Applications ... 

Chemical Name oligomeric chloroalkyl phosphate Physical Appearance Colorless liquid Phosphorus Content Wt% 14.0 Chlorine Content Wt% 26.0 Applications ... 

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