Polyphosphazenes polymerization

Routes to prepare substituted polymer directly were pioneered with the polymerization of /V-trimethy1si1y1phosphoranamines to form low to moderate molecular weight polyphosphazenes (6) where R is alkyl or aryl (8). 

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. 

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. 

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. 

Process III Preparation of Polyphosphazenes by Ring Opening Polymerization Processes of Substituted or Partially Substituted Cyclophosphazenes... 

Polyphosphazenes are intrinsically fire-resistant materials because of the presence of phosphorus and nitrogen in the polymeric chain. A low flammability is thus one of the most important properties of polyphosphazenes, particularly of the polyaryloxyphosphazenes I, in which R may be H, halogens, and alkyl or alkoxy groups. 

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]. 

On this basis, five classes of different polyphosphazenes are considered as outstanding examples of this type of macromolecules, in which skeletal and substituent features overlap to the highest extent. The reported materials are elastomers, flame retardants and self-extinguishing macromolecules, polymeric ionic conductors, biomaterials, and photosensitive polymeric compounds all of them based on the polyphosphazene structure. 

The thermal polymerization of N-trimethylsilylphosphoranimines 2215 to 2216 with elimination of CF3CH20SiMe3 2217 is the prototype for formation of inorganic polymers [5, 23, 24]. Polyphosphazene 2216 is also prepared from bromodimethyl(tri-... 

Three approaches have been developed for the synthesis of polyphosphazenes. These are (1) The macromolecular substitution route (2) The cyclic trlmer or tetramer substitution/polymerization route, and (3) Direct synthesis from organosllylphosphazene monomers. This last method Is described In detail In another Chapter and will not be considered further In this review. 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

Polyphosphazene-Phthalocyanlne Structures. Thus, a related study was carried out with copper phthalocyanine units linked covalently to a poly(aryloxyphosphazene) (44). Non-polymeric copper phthalocyanine forms ordered stacked structures in the crystalline state. When... 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

This effect has also been observed in polyphosphazenes containing alkyl- or phenyl-carborane as pendent groups.12 A typical synthetic route to poly(phenyl-carboranyl-di-trifluoroethoxy-phosphazene) having pendent phenyl-carborane groups is shown in scheme 4. A substantial improvement in the thermal stability of the polymer was observed. This is attributed to a retardation of the ring-chain de-polymerization mechanism due to steric hindrance effects of the carborane units, inhibiting helical coil formation. 

N-Silylphosphinimines. Until recently, no general method has been available which allows complete incorporation of the desired substituents before polymerization. The synthesis of polyphosphazenes with direct phosphorus-carbon bonds has been possible only in a few cases (25,60). A new method which holds promise involves the synthesis of suitably constructed N-silylphosphinimines which upon heating, eliminate substituted silanes to give polyphosphazenes (61). This procedure was... 

In another report polyphosphazene copolymers were synthesized from bis (2-methylphenoxy) phosphazene, which was sulfonated after polymerization. Polymers such as polyvinylidene fluoride, polyhexa-fluoropropylene, and polyacrylonitrile were used to produce a blended membrane system. Polymer blends, cross-linking, and other means of re-enforcement are... 

However, separation of the carborane cage from The phos-phazene ring or chain by a methylene spacer group allows metals to be Inserted into the open face of the carborane. These syntheses were accomplished by the reaction routes shown in Schemes 3 and A. High polymeric analogues of these transformations have also been accomplished following polymerization of XXX. The rhodium-bound cyclophosphazenes and polyphosphazenes are catalysts for the hydrogenation of 1-hexene. In this, they show a similar behavior to metallocarboranes linked to polystyrene... 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

The versatility of water-soluble polyphosphazenes is in the variations in the structures that can be prepared. Structures with a low glass-transition temperature backbone can be modified with a variety of versatile side units. These may find use in solid polymeric ionic conductors, as a means to entrap and immobilize enzymes with retention of enzymic activity, and in biological functions as hydrogels with the capability of exhibiting biocompatibility and... 

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