Oligomers phosphate esters

Synthetic fire-resistant fluids have been developed to replace petroleum-based fluids for many applications. Although there are several types of these less hazardous fluids, the only synthetic fluids discussed in this profile are phosphate esters and polyalphaolefins. The phosphate esters are tertiary esters of orthophosphoric acid, 0=P(0H)3, and may be triaryl, trialkyl, and alkyl/aryl. The polyalphaolefins are usually based on 2-decene and contain a mixture of oligomers (dimers, trimers, etc.). 

Three flame retardants were compared in this study, namely, a brominated polycarbonate oligomer (58% bromine), a brominated polystyrene (68% bromine), and a brominated triaryl phosphate ester (60% bromine plus 4% phosphorus). These are described in Table I. Figures 1 and 2 compare the thermal stability of the brominated phosphate with commercial bromine-containing flame retardants by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The brominated phosphate melts at 110°C and shows a 1% weight loss at 300°C. Brominated polycarbonate and brominated polystyrene are polymeric and are not as volatile at elevated temperatures as the monomeric flame retardants. 

Figure 4. Flame Retarding Polycarbonate/PET Polyester Alloy 1. brominated polycarbonate oligomer 2. brominated polystyrene 3. brominated aromatic phosphate ester...

The hydroxy oligomers with the structural formula given in reaction (21) (compound A) are compatible with hydroxy acrylic copolymers, with which they can be combined to obtain paints with excellent physical properties. Because of the fast reaction between epoxy resins and phosphate ester, leading to an increase... 

The term oligomer refers to a polymer-like material having only a few repeating units. The oligomeric phosphorus esters which are the subject of the present paper are generally viscous liquids having an average of two or more phosphate and/or phos-phonate ester units per molecule. 

Pioneering work on phosphorus ester oligomers has been done by Monsanto in the U.S. (1), by Hoechst in Germany (2), and in the Soviet Union. These "itudies involved synthesis and flame retardant applications. The polycondensation of 2-chloroethyl phosphates as a route to oligomeric phosphorus esters (Equation 1) was first reported by Korshak al. (3). This Russian publication describes the polycondensation of tris(2-chloroethyl) phosphate at 240-280° under non-catalytic conditions. 

Five-membered cyclic phosphate and phosphonate esters have rates of hydrolysis orders of magnitude greater than those of the corresponding acyclic esters (6), therefore such five-membered cyclic esters are undesirable components if the oligomers are used as flame retardants. 

There is some evidence that the reaction of ethylene oxide with the metaphosphonate/phosphate may actuary form some cyclic five-membered esters initially, as shown by P signals at 18.4, 17.4 (phosphates) and 49 (phosphonate) which then are converted to acyclic esters. In another example of this route to oligomeric phosphorus esters, P O q is reacted with tris(l,3-dichloroiso-propyl) phosphate to prepare a metaphosphate which is ethoxylated with ethylene oxide to produce a substantially hydroxy-free phosphate oligomer (12). 

Enzymes which catalyze the hydrolysis of the unit linkage of sequential residues of oligomers or polymers determine their substrate specificity by recognizing the particular unit residue in the sequential chain as well as the direction of the chain. For example, ribonuclease cleaves the 3 -phosphate of a pyrimidine nucleotide residue but not the 5 -phosphate, and trypsin hydrolyzes peptide bonds which involve the arginine or lysine residue at the carbonyl end but not at the amino end. This is also the case for the hydrolysis of a variety of synthetic substrates and quasi-substrates (Sect. 4.1). Synthetic trypsin substrates are ester or amide derivatives in which the site-specific group (positive charge) is contained in their carbonyl portion. 

Various organic plasticizers having boiling points over 300 °C are available, such as di(2-ethylhexyl) phthalate (4a), di(2-ethylhexyl) adipate (8), oligomers formed from dicarboxylic acids and diols with molecular weights ranging up to 3500, esters of tri-mellitic acid, epoxidised fatty acids or organic phosphates, such as tris(2-ethylhexyl) phosphate (9) or (2-ethylhexyl) diphenyl phosphate (10). Most phosphates also function as flame retardants and some, such as 10, are smoke suppressants as well (Meier, 1990). 

Early investigations (30) of the rate of internal transesterification of the 4-nitrophenylphosphate ester of propylene glycol (HPNP) and also on RNA oligomers of adenosine phosphate were carried out using Ln(III) complexes of Hgands 13 (32) 14 (32) ind 15 (29, 33, 34). 

Aso et al and Uyama et al found that crude papain extracts catalyzed oligomerizations of L-glutamic acid diethyl ester (conditions pH 7-8.5, 0.5M, ionic strength 2.0 M phosphate buffer, 25 C and pH 7.0, 40°C, 3 hours) giving oligomers with DP 5 to 9 and DPjvg 9.5 from FAB-Mass spectroscopy and H-... 

C—0 and P—0 ester bonds Phosphate diester is tetrahedral and shows antiperi-planar conformations for the C5 —05 bond. X-ray structural studies of tRNA and DNA oligomers suggest that usually H4 —C4 —C5 —05 — P adopts an extended W-conformation in these structures. 

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