2.2.2- Trifluoroethoxy side groups

Allcock and Smith118 have prepared a series of poly(organophosphazenes) containing siloxane grafts and/or trifluoroethoxy side groups (31-34). Polymers 31 and 32 had critical surface tensions of 16-17 rn N rn 1 and surface layers which were enriched in fluorine. In the case of 32, silicone was not observed at the surface. Polymer 33 had a critical... 

These polymers have the lowest Tgs determined to date from hydrolytically stable polythionylphosphazenes. Upon an increase in the loading of trifluor-ethoxide from 27 a-c, the Tg decreased from -14 °C to - 30°C. This decrease in Tg is expected as lower glass transition temperatures are observed for polyphos-phazenes with trifluoroethoxy side groups [P(OCH2CF3)2N]n, Tg= -66°C than with butylamino side groups [P(NHBu)2N]n, Tg= 8°C. ... 

Polyphosphazene Random and Block Copolymers with Alko t alko] and Trifluoroethoxy Side Groups... 

Additional polyphosphazene hydrogels deal with polymers in which gluco-syl side groups are co-substituted with trifluoroethoxy, phenoxy, methylamino or methoxyethoxyethoxy moieties [646]. 

Figure 6. General structure for phosphazenes with mesogenic side groups. Example is a mixed substituent polymer (VII) where R represents the trifluoroethoxy group and the mesogen with flexible spacer is represented by the curlicue and rectangular box.

The preparation of soluble polymers containing species 1-4 was accomplished by the use of the polar trifluoroethoxy group as co-substituent. The partially substituted trifluoroethoxy polymer, prepared in the first step of the polymer synthesis (see Scheme II), provided a polar environment for the incorporation of the chromophoric side chains. However, the maximum loading of the polymers by the chromophores 1-4 was limited by the solubility of the polymeric products. Hence, the side group ratios for polymers 6-9 represent a maximum incorporation range of the chromophore side group by the use of this synthetic scheme. 

Examples of known phosphazene polymer blends are those in which phosphazenes with methylamino, trifluoroethoxy, phenoxy, or oligo-ethyleneoxy side groups form blends with poly(vinyl chloride), polystyrene, poly(methyl methacrylate), or polyethylene oxide).97 100 IPNs have been produced from [NP(OCH2CH2OCH2CH2OCH3)2] (MEEP) and poly(methyl methacrylate).101-103 In addition, a special type of IPN has been reported in which a water-soluble polyphosphazene such as MEEP forms an IPN with a silicate or titanate network generated by hydrolysis of tetraethoxysilane or tetraalkoxytitanane.104 These materials are polyphosphazene/ceramic composites, which have been described as suitable materials for the preparation of antistatic layers in the manufacture of photographic film. 

The semipermeability behavior of a polymer him can be measured by equipment that permits measurements of the diffusion of a small-molecule dye through the membrane. In the phosphazene systems investigated, the rate of diffusion varied with the polymer side group ratio. A typical polymer with roughly 50% of the side groups as methylamino and 50% as trifluoroethoxy showed a faster transmission of dye molecules in water than did standard cellulose dialysis tubing. 

The principal polyphosphazenes that have been used in hydrogels are those with linear or branched ethyleneoxy side chains, aryloxy groups with carboxylic acid substituents, or mixed-substituent polymers that bear hydrophilic methylamino side groups plus a hydrophobic cosubstituent such as phenoxy or trifluoroethoxy. Cross-linking is usually accomplished by gamma-ray irradiation or, in the case of the carboxylic acid functional species, by treatment with a di- or tri-valent cation. Here, we will consider another example based on MEEP (3.79), a polymer that is well suited to the clean method of radiation cross-linking. 

Elastomers. The most advanced applications from a commercial viewpoint are found in the use of polyphosphazenes as elastomers that remain flexible at low temperatures, are resistant to hot oil and hydrauhc fluids, and resist combustion. Polymers with both trifluoroethoxy and heptafluorobutoxy side groups were originally developed for aerospace and automotive applications, but other elastomers that bear both trifluoroethoxy and organosilicon side groups are now... 

Another recent report (18) Involves the evaluation of phosphazenes with nonmesogen side chains that exhibit NLO activity. Modification of the intrinsic optical response of the P-N chain was achieved through substitution of side groups including chloro, anilino, dimethylamino, and trifluoroethoxy. Cyclic phosphazenes were also included in this study. Results suggest that phosphazenes possess inherent NLO activity which can be enhanced by the suitable selection of substituent groups. 

H.R. Allcock, S.R. Pucher, Polyphosphazenes with glucosyl and me-thylamino, trifluoroethoxy, phenoxy, or (methoxyethoxy)ethoxy side groups. Macromolecules 24 (1) (1991) 23-34. 

Lora et al, did try to enhance the biocompatibility of poly[bis(trifluoroethoxy)-phosphazenes] (PTFP) and poly[bis(phenoxy)phosphazenes] (PPP) by grafting different side groups on the polymer surface (Figpme 28). Graft copolymerization w ith dimethylaminoethylmethacrylate (DMAEM) onto the polyphosphazene surfaces highly enhances their biocompatibility. Subsequent heparinization has a negative effect, which is more appreciable with the PPP-based samples (Lora et al., 1991). Surface modification of poly[bis(trifluoroethoxy)phosphazene] with... 

As mentioned earlier, poly[bis(trifluoroethoxy)phosphazene] is a fiber-forming, microcrystalline polymer that can be fabricated into microfibers by solution extrusion from THF into a nonsolvent such as heptane. Alternatively, it can be electrospun to nanofibers from a solution in THF. The structure-property relationships for this polymer are fairly well understood, and these provide a basis for expanding the understanding to polymers with other side groups. 

Phosphonitrilic fluoroelastomers have a phosphonitrilic backbone with trifluoroethoxy and heptafluorobutoxy side groups. The rubbers are useful in the temperature range from -100 F to 300 F, are solvent-resistant and nonflammable. 

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