With 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. 

The modification of lignins with chlorophosphazenes results in changes of E that correspond to the degree of substitution and the phosphorous content (Table V). 

Lignin modification with chlorophosphazenes is an example of how this renewable resource may be utilized in special polymeric materials. 

Scheme 2). However, the actual possibility is controlled by a variety of factors, such as chain length, the natime of the reacting group, and the mode of activation of the reacting group. Reactions of difunctional reagents with chlorophosphazenes have been well documented (93). 

Many typical reactions of chlorophosphazenes, R(CO N=PCl3)2 [R = -CCI2- or -CCl2(CH2)5CCl2-] with nucleophiles have been reported ... 

The factors affecting the preparation of the cyclic chlorophosphazenes from phosphorus pentachloride and ammonium chloride continue to receive attention. For example, the yields and reaction times for the preparation of the series, (NPCla) ( — 3—7), varied with the fineness of the ammonium chloride, the nature and volume of the solvent, and added catalysts such as phosphoryl chloride. A procedure, giving due consideration to these factors, was described for the preparation of N3P3CI6 in good yield (88% of cyclic products) and in a relatively short time (2J h). The cyclic chlorophosphazenes can be obtained in even shorter times ca. 10 min) by addition of four moles of pyridine to remove the hydrogen chloride formed ... 

There is little mention in the literature of the use of amide salts in substitution reactions on chlorophosphazene precursors. The anilide anion was shown to be a powerful nucleophile in substitution reactions on various trimer derivatives, but investigations of such reactions with the high polymer have not been reported.22 Where strong nucleophiles (such as amide salts) with low steric requirements are employed, the usual pentacoordinate transition state (Scheme 1), may be a viable reaction intermediate which can undergo alternative modes of decomposition, perhaps involving chain cleavage and/or cross-linking. 

The lignin modifications in solid (C) were carried out using lignins (1.0 g) mixed with corresponding amounts of hydrogen chloride acceptor and chlorophosphazenes. The reaction was carried out by heating at a temperature of 100°C, i.e., above the melting point of chlorophosphazene. The reaction mixture was poured into ice water, and then the solid product was purified as described before (9). 

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 of P-chlorophosphazenes with aziridine are also facilitated by the presence of triethylamine ... 

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... 

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