Polymerization of hexachlorocyclotriphosphazene

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. 

WClg, and vanadium-based initiators (Eq. 53), and the thermal polymerization of hexachlorocyclotriphosphazene (Eq. 54). (Ringopening polymerizations of ethylene and propylene oxides,... 

The polymerization of hexachlorocyclotriphosphazene (I) has been the subject of numerous investigations (9,10). 

Thermal polymerization of hexachlorocyclotriphosphazene (LXXXIII) (also referred to as phosphonitrilic chloride) yields poly(dichlorophosphazene) (LXXXIV) (IUPAC poly[nitrilo (dichloro-Ls-phosphanetriyl)] or catena-poly[(dichlorophosphorus)- j,-nitrido]) [Allcock, 1976, 1986, 2002 Allcock and Connolly, 1985 Archer, 2001 De Jaeger and Gleria, 1998 Liu and Stannett, 1990 Majumdar et al., 1989, 1990 Manners, 1996 Potts et al., 1989 Scopelianos and Allcock, 1987 Sennett et al., 1986],... 

Allcock, H.R., Gardner, L.E. and Smeltz, K.M. (1975) Polymerization of hexachlorocyclotriphosphazene. The role of phosphorus pentachloride, water and hydrogen chloride. Macromolecules, 8(1), 36-42. 

Figure 5.15. Ring-opening polymerization of hexachlorocyclotriphosphazene, and subsequent reactions to yield functionalized polyphosphazenes.

Scheme 4.1 Proposed cationic mechanism for the polymerization of hexachlorocyclotriphosphazene.

A second reason of interest in cyclophosphazenes has stemmed from the facile ring opening polymerization of the hexachlorocyclotriphosphazene, N3P3CI6, to the linear macromolecule [NPCl2]x [4, 5] (Eq. 1). 

FIGURE 11.2 Synthesis of the prepolymer poly(dichlorophosphazene) (b) via thermal ring-opening polymerization of trimer hexachlorocyclotriphosphazene (a) or living cationic polymerization of a phosphoranamine monomer (c). 

SYNTHETIC TECHNIQUES AND TYPES OF SYNTHESIS (a) Thermal two-stage polymerization (ring-opening of hexachlorocyclotriphosphazene followed by nucleophilic substitution).(b) Mixed nucleophiles have also produced useful elastomers using the same two-step procedure, (c) Now better defined block and random polymers with elastomeric properties have been developed and characterized. ... 

The formation of hexachlorocyclotriphosphazene (V) from phosphorus pentachloride and ammonium chloride or ammonia has been known since the work of Liebig and Wohler in 1834.1 Similarly, the thermal polymerization of V to a rubbery, crosslinked form of poly(dichlorophosphazene)... 

An effective summary of the early state of phosphazene chemistry, and in particular, the ROP of hexachlorocyclotriphosphazene and octachlorocyclotetraphospha-zene (Figure 4.2) was published in 1962 [25]. These studies were dominated by the substitution chemistry of these small rings however a section was dedicated to a summary of the available knowledge in polymerization chemistry in these systems. To this point, the chemistry of these systems is dominated by studies into polymerized intractable inorganic rubber , obtained from the uncontrolled ROP of phosphazene rings. 

Perhaps the most significant breakthrough in practical phosphazene chemistry was the abiUty to polymerize hexachlorocyclotriphosphazene to obtain scAuble hnear poly(dichlorophosphazene) in a somewhat reproducible manner moreover, the polymer could be stabilized by immediate reaction with organic nucleophiles. H. Allcock first reported on the subject of the ROP of hexachlorocyclotriphosphazene and octachlorocyclotetraphosphazene in 1964 [33], when he and Best described the synthesis and studied the mechanism using electrochemical methods and electron spin resonance (ESR). 

Other methods of polymerization have met with mixed results, but are worthy of mention at this point. Studies of the photochemical initiation of hexachlorocyclotriphosphazene polymerization were conducted by Dishon and Hirshberg [39]. The exposure of hexachlorocyclotriphosphazene in solvent to ultraviolet irradiation was found to yield both soluble and insoluble products. Although the solutions... 

Although ROP experiments were performed on all three trimers, only the 3-pyridinoxy trimer failed to polymerize at temperatures as high as 300 °C, even in the presence of hexachlorocyclotriphosphazene, AICI3 or water as catalyst. The... 

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