Phosphazene rubber

Q, FKM, and EPDM are examples. An example of SEC analysis of these rubbers is seen in phosphazene rubbers (30,31). In the SEC of such rubbers, difficulties arise in finding suitable SEC solvents. In principle, such methods as increasing the temperature to enhance the solubility are needed for these rubbers. In EPDM or EPM (copolymers of ethylene and propylene), for instance, once normal room temperature SEC was used, but today use of a high-temperature SEC is the most common because these may contain some crystalline parts depending on the block of Cj or C3 segments. Choice of other solvents depends on the required sensitivity of the detectors. 

Applications. Among the P—O- and P—N-substituted polymers, the fluoroalkoxy- and aryloxy-substituted polymers have so far shown the greatest commercial promise (14—16). Both poly[bis(2,2,2-trifluoroethoxy)phosphazene] [27290-40-0] and poly(diphenoxyphosphazene) [28212-48-8] are microcrystalline, thermoplastic polymers. However, when the substituent symmetry is dismpted with a randomly placed second substituent of different length, the polymers become amorphous and serve as good elastomers. Following initial development of the fluorophosphazene elastomers by the Firestone Tire and Rubber Co., both the fluoroalkoxy (EYPEL-F) and aryloxy (EYPEL-A) elastomers were manufactured by the Ethyl Corp. in the United States from the mid-1980s until 1993 (see ELASTOLffiRS,SYNTHETic-PHOSPHAZENEs). 

Figure 12.30 Potential uses of polyphosphazenes (a) A thin film of a poly(aminophosphazene) sueh materials are of interest for biomedical applications, (b) Fibres of poly[bis(trifluoroethoxy)phosphazene] these fibres are water-repellant, resistant to hydrolysis or strong sunlight, and do not burn, (c) Cotton cloth treated with a poly(fluoroalkoxyphosphazene) showing the water repellaney eonferred by the phosphazene. (d) Polyphosphazene elastomers are now being manufaetured for use in fuel lines, gaskets, O-rings, shock absorbers, and carburettor eomponents they are impervious to oils and fuels, do not bum, and remain flexible at very low temperatures. Photographs by eourtesy of H. R. Allcock (Pennsylvania State University) and the Firestone Tire and Rubber Company.

S. H. Rose in 1968 [263, 265] first described the reaction of polydichloro-phosphazene with trifluoroethoxy groups coupled with a second fluorinated alkoxy residue of longer chain. During the successive twenty years they were deeply investigated by Horizon Inc. [263, 265, 502-506, 518, 544, 552-554], AMMRC [396, 452, 555-557], NASA [517, 522, 523], The Firestone Tire and Rubber [393,519,528,530,533,558,559], and Ethyl Co. [507,560,561] for the applications described above (vide supra). 

JThe effect of the substituent on the properties of the polyphosphazenes is not fully understood. For instance, [NP(OCH ) ]n and [NP C CH. homopolymers are elastomers (8,29). Synthesis using lithium, in contrast to sodium, salts is claimed to produce rubber-like fluoroalkoxyphosphazene polymers (30). The presence of unreacted chlorine or low molecular weight oligomers can affect the bulk properties (31,32). Studies with phosphazene copolymers both in solution and in the bulk state (29,33-38) indicate a rather complex structure, which points out the need for additional work on the chain structure and morphology of these polymers. 

Figure 6. Phosphazene fluoroelastomers (PNF) were used to prepare various rubber end items, some of which are commercially available.

Elastomers, synthetic -acrylic elastomers [ELASTOMERS, SYNTHETIC - ACRYLIC ELASTOMERS] (Vol 8) -butyl rubber [ELASTOMERS, SYNTHETIC - BUTYL RUBBER] (Vol 8) -chlorosulfonated polyethylene [ELASTOMERS, SYNTHETIC - CHLOROSULFONATED POLYETHYLENE] (Vol 8) -ethylene-acrylic elastomers [ELASTOMERS, SYNTHETIC - ETHYLENE-ACRYLIC ELASTOMERS] (Vol 8) -ethylene-propylene-diene rubber [ELASTOMERS,SYNTHETTC - ETHYLENE-PROPYLENE-DIENE RUBBER] (Vol 8) -fluorocarbon elastomers [ELASTOMERS, SYNTHETIC - FLUOROCARBON ELASTOMERS] (Vol 8) -nitrile rubber [ELASTOMERS, SYNTHETIC - NITRILE RUBBER] (Vol 8) -phosphazenes [ELASTOMERS, SYNTHETIC - PHOSPHAZENES] (Vol 8) -polybutadiene [ELASTOMERS, SYNTHETIC - POLYBUTADIENE] (Vol 8) -polychloroprene [ELASTOMERS, SYNTHETIC - POLYCHLOROPRENE] (Vol 8) -polyethers (ELASTOMERS, SYNTHETIC - POLYETHERS] (Vol 8) -polyisoprene [ELASTOMERSSYNTHETTC - POLYISOPRENE] (Vol 9) -survey [ELASTOMERS, SYNTHETIC - SURVEY] (Vol 8)... 

Zinc complexes are important as additives for rubber polymers. Dithiocarbamate complexes are most commonly used here, but bis(8-hydroxyquinolinato)zinc inhibits the thermal decomposition of poly[(trifluoroethoxy)(octafluoropentoxy)phosphazene]. The zinc is thought to complex residual P—OH groups in the polymer chain, which would otherwise lead to rearrangement and chain scission.126... 

Figure A. Chemical structure and properties of phosphazene fluoroelastomer, PNF gum rubber.

Figure 5. Phosphazene fluoroelastomer (PNF) compounds were used to prepare molded rubber parts for diverse applications. Shown here Include 0-rlngs fuel hoses, shock absorption and vibration damping mounts. Photograph courtesy of the Firestone Tire and Rubber Co.

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. 

Care must be taken to avoid the formation of insoluble poly(dichlorophospha-zene) inorganic rubbers , and in the selection of the proper conditions for conversion into poly(organophosphazene)s. Although problems still exist in the synthetic area, work has progressed to where a wide variety of poly(organo-phosphazene) polymers are now available. ... 

A new route to poly(organophosphazene)s has been reported in which the phosphazene cyclic trimer [NP(OCHjCF3)2J3 is copolymerized with (NPa )3 to yield a new series of rubbers. The copolymers have been characterized by means of substitution reactions and P n.m.r. analysis. The synthesis of resins by the... 

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. 

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