Poly dichlorophosphazene

Poly(dichlorophosphazene), [NPCUjm can be prepared by several routes. The traditional route is the ring-opening polymerization (ROP) of N3P3CI6. Although, as discussed above, Stokes as early as in late 1800 s had observed the formation of crosslinked poly(dichlorophosphazene), it is to the credit of Allcock that he found the correct recipe for isolation of un-crosslinked linear poly(dichlorophosphazene) [21]. He and his co-workers have made the following important and crucial experimental observations. 

Heating N3P3CU at 250 °C in vacuum and by allowing the conversion to proceed only up to 70%, linear poly(dichloro-phosphazene) could be isolated (see Eq. 3.30). This polymer was soluble in a number of organic solvents such as benzene, toluene, tetrahydrofuran etc., to form clear viscous solutions. 

Heating beyond 250 C or allowing the conversion to proceed beyond 70% afforded a crosslinked material similar to what was obtained by Stokes. The crosslinking of the polymer was rapid and the resultant material was totally insoluble. 

The linear polymer prepared by Allcock was truly a high polymer with over 15,000 repeat units representing a of about 1.2x10. The polydis-persity index for the polymer [NPCyn prepared by the ring-opening of N3P3CI6 is greater than 2. 

Hexafluorcyclotriphosphazene, N3P3F6, hexabromocyclotriphosphazene, N3P3Bre and the hexathiocyanato cyclotriphosphazene N3P3(NCS)6 can also be polymerized by the ring-opening polymerization method to the corresponding linear polymers (Fig. 3.27). 

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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 poly(phosphazene) backbone can be made to be part of a fully inorganic polymer by replacing the organic substituents with chlorines, thus generating poly(dichlorophosphazene). However, this is a reactive molecule and is more usually employed as the starting material for the preparation of the various partially organic poly(phosphazenes). 

Preparation of poly(dichlorophosphazene), (NPCl2)n> a polymeric intermediate from which the great majority of POPs have been prepared by nucleophilic substitution of the highly reactive chlorine atoms with carefully selected organic substituents... 

The solution polymerization process for hexachlorocyclophosphazene to poly-dichlorophosphazene is an interesting and attractive alternative to the classic bulk thermal polymerization reaction of this trimer. 

Molecular structural changes in polyphosphazenes are achieved mainly by macromolecular substitution reactions rather than by variations in monomer types or monomer ratios (1-4). The method makes use of a reactive macromolecular intermediate, poly(dichlorophosphazene) structure (3), that allows the facile replacement of chloro side groups by reactions of this macromolecule with a wide range of chemical reagents. The overall pathway is summarized in Scheme I. 

Polymerization and Dilute Solution Characterization of Poly(dichlorophosphazene)... 

Figure 2. Zimm plot for poly(dichlorophosphazene) Sample IL-22...

It is well known that the trimeric phosphonitri-lic chloride can be polymerized, at 200-300°C, to poly(dichlorophosphazene) (1), hereafter this polymer will be referred to as chloropolymer. Since this polymer contains hydrolytically-unstable chlorine groups, these groups are usually replaced with various alcohols, phenols, or amines to import the polymer stability. In our laboratories, the substitution is generally with alcohols or phenols. The reaction scheme is shown in Figure 1. 

Figure 1. Scheme showing the polymerization of the trimeric phosphonitrilic chloride to poly(dichlorophosphazene) and its subsequent substitution with the sodium salts of alcohols or phenols... 

Figure 6. Chromatographs of two samples of poly(dichlorophosphazene) exposed to the atmosphere during polymerization...

Figure 7. Chromatographs of three samples of poly(dichlorophosphazene) prepared by three different polymerization techniques...

Figure 9. Chromatographs of three poly(dichlorophosphazene) samples that showed identical intrinsic visco.%ities in toluene...

Since the initial disclosure by Allcock, workers have sought to answer various questions 1) What is the nature of the polymerization process (mechanism) 2) What is the structure of poly(dichlorophosphazene) that distinguishes it from the insoluble "inorganic rubber (III) 3) The substitution process gives a seemingly endless variety of products. What are the limitations or... 

Figure 1. Synthesis of poly(dichlorophosphazene) and poly(organophosphazenes).

This paper will provide an overview of the polymerization processes and the properties of poly(dichlorophosphazene). This paper will also discuss the various factors which influence the properties of the poly(organophosphazenes) and show how these factors have resulted in a class of polymers with a wide range of properties, including several examples of current commercial importance. 

The elastomeric properties of poly(dichlorophosphazene) have been the subject of various investigations over the years. 

Probably most of these investigators were studying poly(dichlorophosphazene) in the partially crosslinked state. Most of this was summarized by Allcock (.9). More recently, highly purified, uncrosslinked II has been examined in the solid state (21). The unstressed polymer is amorphous at room temperature, but crystallization can be induced by cooling or stretching techniques. The glass transition temperature, measured by Torsional Braid Analysis, is -66°C (22). 

Synthesis-Structure-Properties. Poly(dichlorophosphazene) is important as an intermediate for the synthesis of a wide range of poly(organophosphazenes) (Figure I). The nature and size of the substituent attached to phosphorus plays a dominant role in determining the properties of the polyphospha-... 

Figure 2. GPC studies of melt polymerized poly(dichlorophosphazene). Cumulative C(M) and differential F(log M) MWD of II obtained at 60 and 100 h. Ref. 20.

The grafting from methodology was also utilized for the synthesis of poly(4-methylphenoxyphosphazene-g-2-methyl-2-oxazoline) graft copolymers [187]. The synthetic approach involved the thermal polymerization of hexachlorophosphazene, in the presence of aluminum chloride, to give low molecular weight poly(dichlorophosphazene). The chloro groups were subsequently replaced by 4-methylphenoxy groups, followed by partial bromi-... 

Poly(dichlorophosphazene), 19 56 Polydicyclopentadiene, 8 231 20 432, 433 manufacture of, 20 430 properties of, 20 4221 Polydicyclopentadiene, 26 946-947 Polydime thy lsilane (PDMS). See also Polydimethylsiloxane entries biodegradability of, 22 604-605 lotus effect in, 22 123 pressure-sensitive adhesives and,... 

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