Phosphazenes ring-opening

The first phosphazene polymers containing carbon (79), sulfur (80,81), and even metal atoms (82) in the backbone have been reported. These were all prepared by the ring-opening polymerization of partially or fully chloro-substituted (or fluoro-substituted) trimers containing one hetero atom substituting for a ring-phosphoms atom in a cyclotriphosphazene-type ring. 

At the same time, ring-opening-polymerization (ROP) processes, which dominated the phosphazene field for decades [38], tend now to be substituted by polycondensation reactions. These seem to be more feasible and reproducible, easier to carry out, and able to guarantee predictable MWs and MW distributions for these materials [10]. 

Work on phosphazene high polymers continues to attract increased interest. Advances in the study of the ring-opening polymerization, and physical characterization in the solid state, of the materials produced by these reactions have been reported. 

The halogen atoms remaining can then be replaced by organic residues such as trifluoroethoxy units. High polymers can also be prepared by ring-opening polymerization of the chlorocyclo-phosphazene, XXVIII. Compounds of this type can be converted to nldo-carboranes in the presence of base, but these do not form metallo-derivatlves, presumably for sterlc reasons (29). 

Acylation of A- vinyl phosphazenes 805 derwed from dehydroaspartic acid esters gwes A-acylated dehydroaspartic acid esters 806 as well as the corresponding unsaturated-5(477)-oxazolones 807. Subsequent nucleophilic ring opening of 807 affords A-acylated dehydroaspartic acid derivatives 808 (Scheme 7.247). ° ... 

Inorganic heterocycles in which other p-block elements are inserted into a phosphazene ring are accessible via a variety of synthetic approaches. The primary interest in these hybrid ring systems is as potential precursors of linear polymers via ring-opening polymerisation (Section 11.4.3). Consequently, recent work has focused on halogenated derivatives. For example, the... 

Two inorganic water-soluble polymers, both polyclcctrolytcs in their sodium salt forms, have been know ll for some time poly(phosphoric acid) and poly(silicic acid). A more exciting inorganic water-soluble polymer with nonionic characteristics has been reported. This family of phosphazene polymers is prepared by the ring-opening polymerization of a heterocyclic monomer (6) followed by replacement of the chlorine atoms in Ihe resultant polymer. 

A fast catalyst for the ring-opening polymerization of D4 in solution or in the bulk has been reported by Molenberg and Moller13. They report the use of a phosphazene base in combination with methanol as the initiator, compound 3. 

Linear poly(organophosphazenes) are now synthesized by six different methods. These are (a) The ring-opening polymerization of (NPC12)3 mentioned above, followed by macromolecular substitution (b) Ring-opening polymerization of organic substituted phosphazene cyclic trimers, usually followed by macromolecular substitution ... 

As discussed in Chapter 3, some other inorganic polymers also contain phosphorus atoms.47 They are derived from the basic phosphazene structure described in Chapter 3, and are obtained by the ring-opening polymerization of heterocyclic compounds in which one of the disubstituted phosphorus atoms is replaced by another moiety. Specifically, introduction of a carbon atom can yield poly(carbophosphazenes), with the repeat unit shown in 6.49. Alternatively, replacement with a sulfur atom can yield a poly(thiophosphazene) (6.50). Relatively little is known about these polymers at the present time 47... 

Graft copolymer, polyclhylene-gra/f-poly(propylcnc oxide) (PE-g-PPG), has been synthesized by ring opening anionic polymerization of propylene oxide with a phosphazene catalyst and hydroxylated polyethylene (Mn = 12400, [OH] = 5 units/chain). Polymerization of propylene oxide was carried out in tetraline at 120 °C for 20 hours. The 13C NMR analysis of PE-g-PPG suggested that all the hydroxyl groups were consumed for propylene oxide polymerization (Fig. 6). 

Poly(phosphazenes) are also synthesized by a ring-opening polymerization of the cyclic trimer followed by substituting the chlorines with nucleophiles as shown below ... 

The adduct 126 of dimethyl acetylenedicarboxylate to the 7V-phenyl-/ -enamino-/l5-phosphazene 124 (Ar = / -MeC6H4) is converted into the /l5-phosphole derivative 127 by the action of butyllithium. The process involves the formation and ring-opening of the transient phosphazetine 125 (equation 54)75. 

The polymeric phosphazenes are treated in chapter (see Polyphosphazenes) A recent monograph covers the chemistry of polyphosphazenes (nomenclature, synthesis of cyclic monomers , ring opening polymerization, condensation polymerization, substitution, polymer properties, and applications more than 1000 literature citations). Other reviews have also been published recently. Sulfur-containing polyphosphazenes have also been described. ... 

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