Phosphoranimine monomers

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. 

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). 

The phosphoranimine monomer is readily prepared in two steps from PCI3 in a one-pot procedure [eqn (11.35)]. ... 

Living" polymer end units initiate more of the same monomer, or a different phosphoranimine monomer, or react with a functional chain terminator to give an end-functionalized polyphosphazene. 

The living polymer end unit initiates more of same monomer, a different phosphoranimine monomer, or is coupled to a (1) phosphoranimine-terminated organic polymer. 

It has also been reported that the reaction of N(Si(CH3)3)3 with PCI5 can be manipulated to maximize yields of either the cyclic trimer (76%) or the pure phosphoranimine monomer (40%) through variations in reaction conditions (25). These reactions use milder conditions than previously reported methods, with higher yields. In addition, the major side product, (CHslsSiCl, can be recycled to form one of the starting materials, NlSilCHslsls. 

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). 

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. 

The phosphoranimine route also allows an alternate route to poly(dichlorophosphazene) by using lV-(trimethylsilyl)-/)/)/>-trichlorophosphoranimine as the monomer. The phosphoranimine route not only efficiently produces alkyl and aryl poly(phosphazene)s but also offers... 

This S5mthetic method has been extended to the direct synthesis of poly(organophosphazenes) as well as the development of star and block copolymers. For example, triarmed star-branched polyphosphazenes (eg, 6) can be synthesized through the initiation of trifimctional phosphoranimines (22). It has also been shown that the presence of living active sites at the termini of the poljuner chains allows for addition of a second monomer and the formation of block copolymers (23), such as (7) which is formed through the initiation of a difunctional linear phosphoranimine and the subsequent introduction of two different monomers (24). These developments offer the prospect of improved routes... 

Phosphoranimines, which are of interest as monomers in phosphazene polymer synthesis, may be isolated as cationic structures stabilized by donor ligands. In this example, a chlorinated phosphoranimine carrying a hindered aromatic substituent reacts with N,N-dimethylaminopyridine (DMAP) to yield a donor complex. Scheme 4. The donor complex structure was proposed based on single crystal x-ray analysis that revealed a... 

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