Hexachlorocyclotriphosphazene polymerization

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... 

Phosphazene polymers are normally made in a two-step process. First, hexachlorocyclotriphosphazene [940-71 -6J, trimer (1), is polymerized in bulk to poly(dichlorophosphazene) [26085-02-9], chloropolymer (2). The chloropolymer is then dissolved and reprecipitated to remove unreacted trimer. After redissolving, nucleophilic substitution on (2) with alkyl or aryloxides provides the desired product (3). 

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],... 

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). 

Hexachlorocyclotriphosphazene (3.19) is prepared on an industrial scale by the interaction of phosphorus pentachloride with ammonium chloride in an organic solvent such as chlorobenzene. This compound, after careful purification and protection from moisture, is heated in the molten state at temperatures between 210 and 250 °C to induce polymerization.15-18 The mechanism of this reaction is discussed in a later section. Here it is sufficient to note that the process can also be applied, with minor variations, to cyclic phosphazo-phosphazenes (3.22a, 3.23), to cyclic fluorophosphazenes (3.24,3.25), and to cyclic carbo- (3.26), thio- (3.27), and thionyl (3.28) -phosphazenes. 

Hexachlorocyclotriphosphazene (or simply trimer) can be thermally polymerized in bulk or solution at 200-270°C producing hydrolytically unstable poly-dichlorophosphazene (or simply chloropolymer). 

SYNTFiESis TECFiNiQUES (a) Stokes thermally polymerized hexachlorocyclotriphosphazene via a ring-opening process to provide a cross-linked elastomer, but it was not until 1965 that a high molecular poly(dichlorophosphazene) was isolated and subsequently transformed, via nucleophilic substitution, into thermally stable semicrystalline homopolymers. 

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). 

The poorly reproducible polymerization is presumably initiated by traces of cationic impurities. The poly(phosphonitrile chlorides) or poly(dichloro-phosphazenes), II, mostly have PCI3 end groups. They depolymerize at higher temperatures to hexachlorocyclotriphosphazene, I, and octachlorocyclo-tetraphosphazene and hydrolyze even in moist air. The products obtained at high yield are cross-linked and exhibit all the properties of inorganic elastomers. Consequently, they are also called inorganic rubbers. 

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. ... 

SYNTHESIS TECHNIQUES (a) Stokes thermally polymerized hexachlorocyclotriphosphazene via a ring-opening process to provide a cross-linked elastomer, but it was not until 1965 that a high molecular poly(dichlorophosphazene) was isolated and subsequently transformed, via nucleophilic substitution, into thermally stable semicrystailline homopolymers. This procedure was used widely to synthesize a variety until a few years ago, but it suffered from relatively low conversions (<70% so as to avoid cross-linking), unknown chain-end groups and lack of molecular weight control of the product. These difficulties obstructed its commercialization. 

It was later noticed that the hexachlorocyclotriphosphazene can be polymerized by heating in the melt to yield an uncrosslinked linear high polymer, poly[(dichloro)-phosphazene] (Allcock et al, 1965-1966 Rose, 1968). Further heating results in the formation of an insoluble crosslinked material. This leads in both cases to a transparent, rubbery elastomer which hydrolyzes slowly, when exposed to moisture, forming phosphate, ammonia and hydrochloric acid. At temperatures above 350°C, the polymer depolymerizes to cyclic oligomers. The uncrosslinked species serve as highly reactive polymeric precursor. 

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. 

An unusual templating effect was observed by Zhu et al., who reacted hexachlorocyclotriphosphazene with 4,4 -sulfonyldiphenol in a cross-linking polymerization in the presence of triethylamine. The precipitating triethyl-amine hydrochloride formed nanoscopic rod-like crystals around which the cross-linked polymer was formed. Removing the crystalline core with water gave tubes with inner diameters of 10-20 nm. ... 

---