Phosphoranimines

The three steps in equation 3 are carried out in one vessel. This affords a wide variety of disilylaminoorganophosphines (8), including those with vinyl substituents (65), in yields of 40—85%. The oxidation of (8) to (9) and the reaction of (9) with alcohol (eq. 4) are carried out in a second reactor to provide the "monomer" phosphoranimines (10) in overall 30—65% yield based on starting PCl or CgH PCl2. The use of in place of Br2 in the conversion of (8) to (9) makes it possible to carry out all the reactions leading to (10) in one vessel, and this has significantly increased yields of the monomer, with overall yields up to 80% (66). 

The bulk polycondensation of (10) is normally carried out in evacuated, sealed vessels such as glass ampules or stainless steel Parr reactors, at temperatures between 160 and 220°C for 2—12 d (67). Two monomers with different substituents on each can be cocondensed to yield random copolymers. The by-product sdyl ether is readily removed under reduced pressure, and the polymer purified by precipitation from appropriate solvents. Catalysis of the polycondensation of (10) by phenoxide ion in particular, as well as by other species, has been reported to bring about complete polymerisation in 24—48 h at 150°C (68). Catalysis of the polycondensation of phosphoranimines that are similar to (10), but which yield P—O-substituted polymers (1), has also been described and appears promising for the synthesis of (1) with controlled stmctures (69,70). 

In addition to providing fully alkyl/aryl-substituted polyphosphasenes, the versatility of the process in Figure 2 has allowed the preparation of various functionalized polymers and copolymers. Thus the monomer (10) can be derivatized via deprotonation—substitution, when a P-methyl (or P—CH2—) group is present, to provide new phosphoranimines some of which, in turn, serve as precursors to new polymers (64). In the same vein, polymers containing a P—CH group, for example, poly(methylphenylphosphazene), can also be derivatized by deprotonation—substitution reactions without chain scission. This has produced a number of functionalized polymers (64,71—73), including water-soluble carboxylate salts (11), as well as graft copolymers with styrene (74) and with dimethylsiloxane (12) (75). 

Allcock HR, Crane CA, Morrissey CT, Nelson JM, Reeves SD, Honeyman CH, and Manners I. Living cationic polymerization of phosphoranimines as an ambient temperature route to polyphosphazenes with controlled molecular weights. Macromolecules, 1996, 29, 7740-7747. 

Allcock HR, Reeves SD, Nelson JM, Crane CA, and Manners I. Polyphosphazene block copolymers via the controlled cationic, ambient temperature polymerization of phosphoranimines. Macromolecules, 1997, 30, 2213-2215. 

Finally, substituted phosphoranimines seem to be able to avoid substitutional processes carried out on highly reactive polymeric phosphazene inter-... 

Use of polycondensation processes of substituted phosphoranimines to obtain already substituted poly(organophosphazenes)... 

This reaction mechanism is able to account for several characteristics shown by this reaction. First of all the existence of a terminal group (e.g. -PCl3 ) that remains reactive after completing the consumption of the phosphoranimine classifies this reaction in the category of the living polymerization processes. This fact has important consequences that can be summarized below ... 

In the same scheme, moreover, it is evident that, besides phosphazene homopolymers, the substitution of the chlorines with two (or more) different substituents leads to the preparation of substituent phosphazene copolymers [263] containing different homosubstituted and heterosubstituted monomeric units. Moreover, the cationic polymerization of phosphoranimines [215-217] produces polymers with hving reactive ends (vide supra) from which the preparation of chain phosphazene copolymers (block copolymers) [220,223,225, 229,232-235,239, 240] formed by different polymeric backbones linked together in a unique macromolecule could be obtained. 

In this context, phosphoranimine compoimds (both homosubstituted with an unique group or bearing two different groups at the phosphorus) play a fundamental role because their polymerization under different experimental conditions eventually leads to fully substituted polyphosphazenes with no residual chlorines on the phosphazene skeleton. The general scheme of the phosphoranimine polymerization processes is reported in Fig. 10. 

As can be seen, the first example of phosphoranimine polymerization process was proposed by E. P. Flindt and H. Rose [314] in 1977 for tris(trifluoroethoxy)-AT-(trimethylsilyl)phosphoranimine, which could be polymerized to poly[bis-(trifiuoroethoxy)phosphazene] (MW 4000-10,000) by simple heating at 200 °C. 

A few year later (1980) R. H. Neilson and P. Wisian-Neilson started their long term research project on the preparation of alky, aryl, and alkyl/aryl phosphazene polymers and copolymers [55,56,315-334] prepared in the same way by thermal polymerization of a variety of phosphoranimine derivatives [55, 329, 335, 336] to the corresponding phosphazene macromolecules. The polymers obtained by long heating (several days) at high temperatures (160-220 °C) showed relatively low (about 50,000) molecular weight. 

At the beginning of the nineties K. Matyjaszewsky [337-353] re-investigated this field and discovered that phosphoranimine polymerization processes could be induced in an anionic fashion by the action of tetrabutylammonium-... 

Finally, in 1995, the room temperature polymerization approach put forward by I. Manners and H. R. Allcock [217,221,227] allowed the cationic polymerization of variably substituted phosphoranimines, according to Fig. 10. The substituents exploited for the polyphosphazenes synthesized are also reported in the same scheme. 

Three other MEEP-type polyphosphazenes were synthesized by Allcock [622]. Polymers XIII and XIV were prepared via the cationic living polymerization of phosphoranimines, and polymers XV by ring opening polymerization. 

Based on the synthesis of polyphosphazenes and of diblock copolyphosp-hazenes by the living cationic polymerization of phosphoranimines [237,241], the triblock poly(phosphazene-ethylene oxide) copolymer XVIII was synthesized by Allcock [223]. 

A variety of synthetic procedures have been described based on the ringopening polymerization processes of (NPCl2)3 to (NPCl2)n followed by the nucleophilic replacement of the reactive chlorines with carefully selected nucleophiles, and on polycondensation reaction processes of new monomers and of substituted phosphoranimines. 

An alternative method of synthesis of N3P3Cl6 has been developed recently, based on the reaction of tris (trimethylsilyl) amine and phosphorus pentachloride (40). This reaction either preferentially leads to the formation of N3P3C16 or to an N-silylated phosphoranimine intermediate C13P - NSiMe3, depending on the reaction conditions used. Thus the reaction between tris (trimethylsilylamine) and PC15 in methylene chloride at 40° C affords a mixture of cyclo and linear phosphazenes, which has been shown by an NMR analysis to contain up to 76% of N3P3C16 (Eq. 2). 

Fig. 15. (A) Cyclization reaction to afford a metallocyclophosphazene (20) (B) thermolysis of N-silyl-P-(fluoro)phosphoranimine (21) to afford alkyl cyclophosphazenes.

Acyclic phosphazenes (phosphazo derivatives, phosphine imines, phosphoranimines) continue to attract interest. A review of the three coordinate materials, RN=PR =X has appeared. " Several molecular orbital calculations have been reported. An ab initio treatment of the PN energy surface suggests that this species is best regarded as having a dative phosphorus-nitrogen double bond rather than a triple bond and the phosphonitrene, once formed,... 

We report here the results of our recent studies of poly(alkyl/arylphosphazenes) with particular emphasis on the following areas (1) the overall scope of, and recent improvements in, the condensation polymerization method (2) the characterization of a representative series of these polymers by dilute solution techniques (viscosity, membrane osmometry, light scattering, and size exclusion chromatography), thermal analysis (TGA and DSC), NMR spectroscopy, and X-ray diffraction (3) the preparation and preliminary thermolysis reactions of new, functionalized phosphoranimine monomers and (4) the mechanism of the polymerization reaction. 

On heating at ca. 160-200°C for 2-12 days, these phosphoranimines readily eliminate Me3S iOCH2CF3 (eq2) to form the polymeric phosphazenes, e.g., 1-4. Copolymers... 

The possibility of incorporating unsaturated groups into the polymers, as potential sites for crosslinking, is also being explored. For example, the vinyl (7, 8), ally (9), and butenyl (10) substituted phosphoranimines have been prepared and subjected to the usual thermolysis and cothermolysis conditions (eq 3). In these cases, all of which have a terminal... 

The basic reaction which is employed in the derivatization of the phosphoranimine monomers is the deprotonation of 11 with n-BuLi followed by quenching with various electrophiles (eq 4). 

A number of copolymers 14 have been prepared by cothermolysis of the new derivatives, 12 and 13, with the simplest phosphoranimine precursors, MegSiN = P(OCH2CFg)(Me)R (11). The copolymers 14 derived from the Peterson olefination products 13 are soluble, non-crosslinked materials with molecular weights in the 30,000 -100,000 range. This implies... 

Well-defined phosphazene block copolymers were prepared by the cationic polymerization of phosphoranimines [57]. Block copolymers of the type [N = PCl2]n[N = PR(R )]m were prepared using a wide variety of phos-... 

Figure 2 The structure of the magnesium bis(phosphoranimine) CH(Ph2PNSiMe3)2Mgl(THF) 2, with a long Mg- -C interaction. 

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