P/N-substituted

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). 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibiUty, hydrolytic and chemical stabiUty, and high temperature stabiUty. The abiUty to readily incorporate other substituents (ia addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibiUty of polysdoxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical appHcations can also be envisaged for (3). A third potential appHcation is ia the area of soHd-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

Applications. The P-O- and P-N-substituted polymers have so far shown the greatest commercial promise. The fluoroelastomers possess good rubber properties with the added advantages of being nonhuming. hydrophobic, and solvent- and luel-resistant. In addition lo these, because of flexibility down to about -fi()"C. these polymers have been used in seals, gaskets, and buses in army tanks, in aviation fuel lines and tanks, as well as in cold-climate oil pipeline applications, These polymers have also round application in various types of shock mounts lor vibration dampening. 

The water pressure at the membrane depends on the height of the sea above it, i.e. the depth. P = pgh, and fresh water will begin to pass through the membrane when P = n. Substituting n = P into the equation gives ... 

Figure 4. (A) Structures of the neutral N(n) and polar P(n) (substituted by the strongest acceptor) carotenoids. Molecular geometries were optimized using AM 1 modeP in Gaussian 98 package. Calculations were done for chain lengths of n = 5. 10. 20. and 40 double bonds (B) Variation of the bond-length alternation (top) and total charge Qa (bottom) along the chain in polar P(40) molecule (C) Linear absorption spectra calculated with line width r = 0.2 eV of the N(20) (dashed lines) and P(20) (solid lines) molecules contour plots of electronic modes which domi nate the absorption spectra of N(20) and P(20). Reprinted with permission from ref 81. Copyright 1997 American Chemical Society.

The thermal stability of polymers of types (1) and (2) is also dependent on the nature of the substituents on phosphoms. Polymers with methoxy and ethoxy substituents undergo skeletal changes and degradation above about 100°C, but aryloxy and fluoroalkoxy substituents provide higher thermal stability (4). Most of the P—N- and P—O-substituted polymers either depolymerize via ring-chain equilibration or undergo cross-linking reactions at temperatures much above 150—175°C. 

A general method for malting Camps precursors has been developed/ Treatment of an anthranilic acid 15 with an acid anhydride or chloride in the usual way results in the corresponding benzoxazinone (16). Subsequent treatment with the dianion of an N-substituted acetamide furnishes P-keto amide 17. The reactions were run with crude 16, yields typically 50-80% overall. The effect of substituents on the reaction has not been extensively investigated. 

Prinzbach and Limbach have studied the valence isomerism between N-substituted azepines 14b and benzeneimines 14c (76CB3505) although 14b is much more stable (actually it is the only form detected by NMR), the compound could react, depending on R, as 14c with diazomethane. Later, Prinzbach et al. reported the study of the equilibrium 14b (90% )/14c (10%) in the case of R = p-tosyl [the compound has the following C-substituents 3,6-dichloro-4,5-di(methoxycarbonyl)] in the solid state (X-ray) only 14b is present [86CB616],... 

Pyridinium p-toluenesulfonylmethylide 91 has been used as a formyl anion equivalent for conjugate addition to N-substituted maleimides to give the enol ethers 92, which were readily deprotected to give the aldehydes 93 (80TL705). 

The physical properties of polyphosphazene depend on the nature and the number of substitutes. However, the flexibility of the P-N backbone is the property in common. Because of the weakness of the rotation energy around the N-P bond (3.38 and 21.8 kJ/mol, respectively for... 

R. M.J. Solid-phase syntheses of peptoids using Fmoc-protected N-substituted glycines The synthesis of (retro) peptoids of leu-enkephalin and substance P. Euro. J. Chem. 1998, 4, 1570-1580. 

C-H insertion also occurs in the reactions with acetone and acetophenone, presumably through the rearrangement of transient OH-substituted phosphi-ranes [87]. C-C insertions occur for diketones to give 45 and have been postulated to occur via initial 1,2-addition to the conjugated enol 44 [87]. Diimines 46 also undergo C-C insertions [88]. Based on a theoretical evaluation, the products 47 are considered to result from a 2,3-sigmatropic rearrangement of initial formed P,N-ylids. 

Tervalent organophosphorus compounds containing one single P-N bond with the valency of each atom saturated by protons or carbons (but no other heteroatoms) have been known since their discovery by MichaeUs more than one century ago [ 1 ] and named indistinctly as aminophosphanes, phosphanamines, phosphazanes, or phosphinous amides. This last chemical nomenclature is the one used by the Chemical Abstracts Service (CAS) for indexing these compounds and is also the one that best delimits the scope of this review those species derived from the parent H2P-NH2 (phosphinous amide in CAS nomenclature) by partial or total substitution of protons by hydrocarbon radicals (Table 1). 

Other reactions that resulted in the formation of P=N double bonds are those of NH phosphinous amides with tetrahalomethanes [106-108]. The reaction products, P-halophosphazenes 19, may be further elaborated by substituting the halogen atom with amines or Grignard reagents (Scheme 19). 

The phosphazene backbone has a particularly high resistance to thermal treatment and to homolytic scission of the -P=N- bonds, possibly due to the combination of the high strength of the phosphazene bond and its remarkable ionic character [456]. As a consequence, the onset of thermal decomposition phenomena (as detected, for instance, by TGA) are observed at considerably high temperatures for poly[bis(trifluoroethoxy)phosphazene], [NP(OCH2CF3)2]n [391, 399, 457], for phosphazene copolymers substituted with fluorinated alcohols of different length [391, 399, 457], for polyspirophosphazenes substituted with 2,2 -dihydroxybiphenyl groups [458], and for poly(alkyl/aryl)-phosphazenes [332]. 

Phosphazene polymers can act as biomaterials in several different ways [401, 402,407]. What is important in the consideration of skeletal properties is that the -P=N- backbone can be considered as an extremely stable substrate when fluorinated alcohols [399,457] or phenoxy [172] substituents are used in the substitution process of the chlorine atoms of (NPCl2)n> but it becomes highly hydrolytically unstable when simple amino acid [464] or imidazole [405-407] derivatives are attached to the phosphorus. In this case, an extraordinary demolition reaction of the polymer chain takes place under mild hydrolytic conditions transforming skeletal nitrogen and phosphorus into ammonium salts and phosphates, respectively [405-407,464]. This opens wide perspectives in biomedical sciences for the utilization of these materials, for instance, as drug delivery systems [213,401,405,406,464] and bioerodible substrates [403,404]. 

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