Phosphazenes chlorophosphazenes

The modification of lignins with chlorophosphazenes allows the manufacture of products characterized by flame resistance and thermal stability. This can be attributed to the aromatic structure of the lignin-phosphazene polymer as well as to the presence of such flame inhibiting elements as phosphorous, nitrogen and sulfur. Other useful properties may also result from this combination. It has previously been reported (8-13) that the modification provides crosslinked products with suitably low chlorine content. This is a consequence of incomplete substitution of the phosphazenes cycles. Additional modification of the reaction products by chemical compounds with reactive hydroxyl or amine groups reduces the unreacted chlorine content and improves product properties (8-13). Some properties of the derivatives obtained are presented in Table I. 

A great deal of basicity data is available on substituted chlorophosphazenes. None has hitherto been published on fluoro-phosphazenes. A priori, one surmises a greater electron-withdrawing inductive effect for fluorine, which oould be compensated for by the greater potential of fluorine to back-donate by a mesomsric effect. Data is new compared on structurally related chloro- and... 

Also found in Table I are the P—N stretching frequencies obtained from the infrared spectra of the cychc phosphazenes. These values fall in the range 1297-1408 cm . For the chlorophosphazenes, (NPCl2)n n — 3-6), this frequency is observed in the range 1218-1354 cm (3). 

The reaction is general for ammonium salts, but for optimum yields ammonium sulphate is preferred. Further details of the stepwise synthesis of linear oligomeric phosphazenes have appeared. The introduction of each phosphazene unit is accomplished by reaction of a F-chlorophosphazene with hexamethyldisilazane, (Me3Si)2NH, and, subsequently, phosphorus pentachloride. The reactions with A-phosphinothioylphosphazenes are thus ... 

Reactions in which the phosphazene unit is retained also are of interest. It should also be noted than in the course of these reactions, changes of conditions may lead to phosphazene transformation. Replacement of chlorine atoms in acyclic chlorophosphazenes continues to be explored. Sterically hindered phenolates RONa (R=2,6-0120 113) and R ONa (R =2,6-Me2C H3) effect partial substitution OPCI2NPCI3 and OPCI2NPCI2NPCI3 to give OPCl2NP(OR)j and... 

Details of the mechanism of the reaction of chlorophosphazenes with ortho-dinucleophiles such as catechol or o-aminophenol have been discussed. Although it is not possible to isolate the substituted phosphazene (43a), good evidence is available for its initial formation from isolation of the spiro-phosphorane (44) and an imino-intermediate (45). Complete investigation of this system is thus difficult, but further aspects of the reaction paths were elucidated by studying the reaction of o-aminophenol with the tri-catechol derivative (43b). A non-geminal structure has been assigned, on the basis of P n.m.r. measurements, to the disubstituted... 

Phosphazene substituted with glycine has been prepared as a passivation agent for CdSe (green emission) and CdSe/ZnS (red emission) quantum dots. The polymer was prepared by the reaction of ethylglycinate with poly(di-chlorophosphazene), which was then de-esterified by base to reveal the active material. Quantum dots were prepared for passivation by initial treatment with mercaptoethanol, followed by treatment with the phosphazene. Fluorescent CdSe/ZnS quantum dots were found to be encapsulated in the polymer, which acted as a multidentate pendant group. It was found to passivate the dots and provided colloidal stability. Encapulated ZnS exhibited fluorescence stability. 

Compounds that contain alternating phosphorus-nitrogen double bonds in then-skeleton are called phosphazenes. As historical background, Liebig first reported the synthesis procedure of chlorophosphazene (NPCl ), prepared by the reaction between phosphorus pentachloride with ammonia in 1834. Then Gladstone, Besson, Rosset, Couldridge, and Stokes furthered the fundamental chemistry of the phosphazene, i.e., substitution, hydrolysis, polymerization, and so forth, from 1850... 

Derivatives with flat or nearly flat rings have low dipole moments (e.g. p = 0.83 D for (PNC s p = 0.10 D for (PNF2)4). Relatively high values are usually found if the phosphazene rings are puckered (e.g. p = 3.3 D for [PN(OPh)2l3). Dipole moments are useful for distinguishing isomers of partially substituted chlorophosphazenes (see below). 

---