POLY-BENZIMIDAZOLE

Like polyimide, poly-benzimidazole is obtained upon reacting diamines, but with different proportions. It was developed in 1964 as a premium and 

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Neuse, E. Aromatic Poly benzimidazoles. Syntheses, Properties, and Applications. Vol. 47, pp. 1—42. 

Several routes have been reported for the synthesis of aromatic poly(azole)s such as poly(benzimidazole), poly(benzoaxazole), and poly(benzthiazole) melt polycondensation of dicarboxylic acid diphenyl esters with tetramines21 and high-temperature solution polycondensation of dicarboxylic acids or their derivatives with tetramine hydrochlorides in PPA.22 PPA acts as condensing agent and solvent. Ueda etal.23 developed a modified method for the synthesis ofpolyazoles with the use of PPM A. 

Fluorine-containing aromatic poly(benzimidazole)s are synthesized by direct polycondensation of 2,2-bis(4-carboxyphenyl)-l, 1,1,3,3,3-hexafluoropropane (15) with 3,3 -diaminobenzidine tetrahydrochloride (23) (Scheme 13) and 1,2,4,5-benzenetetramine tetrahydrochloride (24) (Scheme 14) in PMMA or PPA.24... 

Poly(benzimidazole)s possess excellent thermal stability, flame resistance, and outstanding chemical resistance. The solubility of hexafluoroisopropyli-dene-unit-containing poly(benzimidazole)s is remarkably improved.24 They are readily soluble in strong acids such as formic acid, concentrated sulfuric acid, and methanesulfonic acid and in aprotic polar solvents such as DMAc and NMP. The polymer from tetramine (23) is soluble even in m-cresol and pyridine. 

The thermal stability of poly(benzimidazole) is further improved by the introduction of hexafluoroisopropylidene units in the main chain. The DTi0 is 520°C in air and greater than 520°C in nitrogen for the polymer from... 

Transparent, flexible, and tough films with deep orange color are cast from HMPA solution of poly(benzothiazole) from 15 and 29.26 The tensile strength of 69Mpa and the tensile modulus of 2.7 GPa are obtained for aromatic poly(ben-zoxazole) (28) from 15 and 29. These values are higher than those of hexafluoroisopropylidene-unit-containing poly(benzimidazole). 

The series of polymers includes the parent poly(benzobis(imidazole)) (PBBI), poly (benzobis(imidazole)vinylene) (PBIV), poly(benzobis(imidazole)divinylene) (PBIDV), poly(benzobis(imidazole)-l,4-phenylenebis(vinylene)) (PBIPV) and poly(benzimidazole-divinylene) (PBBIDV). The new nonconjugated polymer poly(benzobis(imidazole)(dode-camethylene) (PBIC12) as well as the previously reported poly(p-phenylenebenzobis (imidazole)) (PBZI) were also synthesized for the purposes of comparative studies. The XH NMR spectrum of PBIDV in deuteriated nitromethane containing aluminum trichloride, shown in Figure 7, exemplifies the results. 

One of the first examples of this type of blend was composed of SPEEK or SPES as the acidic component and diaminated PES, poly(4-vinylpyridine) (P4VP), poly(benzimidazole) (PBl), or poly(ethyleneimine) (PEI) as the basic component. " For blend lEC values of 1.0 meq/g, conductivity values were reported to be good, as was H2/O2 EC performance. Thermal stabilities for these blends was also demonstrated to be high (>270°C). Other examples of acid-base PEMs include blends of SPPO and PBI, sulfonated poly(phthalazinone ether ketone) and aminated SPES, SPIs and aminated Pls, and SPEEK with PES bearing benzimidazole side groups, ° as well as an unusual example in which the blend is composed of sulfonated, hyper-branched polyether and pyridine-functionalized polysulfone. ... 

The Tg of hexafluoroisopropylidene-unit-containing poly(benzthiazole) is 327°C, which is almost the same as that of hexafluoroisopropylidene-unit-containing poly(benzimidazole). The hexafiuoroisopropylidene-unit-containing poly(benzthiazole) is stable up to 470°C in both air and nitrogen. The thermal stability of the hexafluoroisopropylidene-unit-containing poly(benzimidazole) is almost comparable to that of the hexafluoroisopropylidene-unit-containing poly(benzimidazole). The DT,o is 527°C in air and 537°C in nitrogen. 

Direct copolymerization of sulfonated monomers has been used to synthesize sulfonated poly (benzimidazoles), poly(benzoxazole)s, and poly(benzothia-zole)s. As an example, Kim et al. synthesized poly-(benzthiazole)s from 2,5-diamino-1,4-benzenedithiol dihydrochloride and either 2-sulfoterethphthalic acid sodium salt, 5-sulfoisophthalic acid sodium salt, or 2,4-disulfoisophthalic acid potassium salt in poly-phosphoric acid (PPA), as shown in Figure 34. Similar sulfonated poly(benzimidazole) and sulfonated poly(benzoxazole) ° structures have also been synthesized. A general synthetic scheme for each is shown in Figure 35. The stability of these polymers in aqueous acidic environments appears... 

Figure 35. Synthesis of sulfonated poly (benzimidazole) and poly(benzoxazole).

The technical production of poly(benzimidazole) (PBI) is also carried out in two steps. In the first step an aromatic tetramine is condensed with the diphenyl ester of an aromatic dicarboxylic acid at 220-260 °C, yielding a poly(amino amid) with elimination of phenol. Ring closure with elimination of water occurs in the second step (solid-phase polycyclocondensation), conducted at 400 °C and yielding the polybenzimidazole (experimental procedure, see Table 2.3). 

Over the years it has been shown that complexes prepared from organophosphorous ligands in combination with peroxotungstic acid or its quaternary ammonium salts exhibit efficient catalytic properties. In order to make an efficient recycling of the catalyst possible and get tungsten-free products and effluents, some of these catalysts were immobilized onto polystyrene, poly benzimidazole and polymethacrylate copolymers modified by the introduction of the phosphorous(V)-containing ligands. 

A side-chain polyrotaxane of Type 10 was also obtained by the reaction of de-protonated poly(benzimidazole) with a long-chain bromide bearing a BG at one end in the presence of / -CD [103], Because the CD was threaded onto the side chain before its reaction with backbone to form a hemirotaxane, the preparation is essentially Method 4. 

A great deal of literature attention has been devoted to polymers in this section as thermally stable polymers (B-80MI11101). While some very elegant syntheses have been conducted, the resulting polymers have been, for the most part, quite intractable materials not conducive to extensive screening for a variety of applications. Thus, aside from their bulk thermal performance, little else besides the conditions of synthesis is known about most of the polymers shown. Three notable exceptions about which considerable characterization and product information are available are poly(imides), poly(benzimidazoles) and poly(quinoxalines), and a short discussion is included concerning properties and applications of these polymers. 

Whereas UL 94 delivers only a classification based on a pass-and-fail system, LOI can be used to rank and compare the flammability behavior of different materials. In Figure 15.2 the increasing LOI values are presented for different polymers as an example POM = poly(oxymethylene), PEO = poly(ethyl oxide), PMMA = poly(methyl methacrylate), PE = polyethylene), PP, ABS, PS, PET = polyethylene terephthalate), PVA = poly(vinyl alcohol), PBT, PA = poly(amide), PC, PPO = poly(phenylene oxide), PSU, PEEK = poly(ether ether ketone), PAEK = poly(aryl ether ketone), PES, PBI = poly(benzimidazole), PEI = poly(ether imide), PVC = poly(vinyl chloride), PBO = poly(aryl ether benzoxazole), PTFE. The higher the LOI, the better is the intrinsic flame retardancy. Apart from rigid PVC, nearly all commodity and technical polymers are flammable. Only a few high-performance polymers are self-extinguishing. Table 15.1 shows an example of how the LOI is used in the development of flame-retarded materials. The flame retardant red phosphorus (Pred) increases... 

PB PBI PBMA PBO PBT(H) PBTP PC PCHMA PCTFE PDAP PDMS PE PEHD PELD PEMD PEC PEEK PEG PEI PEK PEN PEO PES PET PF PI PIB PMA PMMA PMI PMP POB POM PP PPE PPP PPPE PPQ PPS PPSU PS PSU PTFE PTMT PU PUR Poly(n.butylene) Poly(benzimidazole) Poly(n.butyl methacrylate) Poly(benzoxazole) Poly(benzthiazole) Poly(butylene glycol terephthalate) Polycarbonate Poly(cyclohexyl methacrylate) Poly(chloro-trifluoro ethylene) Poly(diallyl phthalate) Poly(dimethyl siloxane) Polyethylene High density polyethylene Low density polyethylene Medium density polyethylene Chlorinated polyethylene Poly-ether-ether ketone poly(ethylene glycol) Poly-ether-imide Poly-ether ketone Poly(ethylene-2,6-naphthalene dicarboxylate) Poly(ethylene oxide) Poly-ether sulfone Poly(ethylene terephthalate) Phenol formaldehyde resin Polyimide Polyisobutylene Poly(methyl acrylate) Poly(methyl methacrylate) Poly(methacryl imide) Poly(methylpentene) Poly(hydroxy-benzoate) Polyoxymethylene = polyacetal = polyformaldehyde Polypropylene Poly (2,6-dimethyl-l,4-phenylene ether) = Poly(phenylene oxide) Polyp araphenylene Poly(2,6-diphenyl-l,4-phenylene ether) Poly(phenyl quinoxaline) Polyphenylene sulfide, polysulfide Polyphenylene sulfone Polystyrene Polysulfone Poly(tetrafluoroethylene) Poly(tetramethylene terephthalate) Polyurethane Polyurethane rubber... 

Figure 6.54. Performance of a PBI-based PEMFC at different operating temperatures [45], (Reprinted from Journal of Power Sources, 172(1), Zhang J, Tang Y, Song C, Zhang J, Poly benzimidazole-membrane-based PEM fuel cell in the temperature range of 120-200°C, 163-71, 2007, with permission from Elsevier.)...

Petschek [4] used heterocyclic rigid-rod polyionomers, including poly(pyr-idinium) salt, (III), and poly(benzimidazole-sulfonate), (IV), for coating directionally onto charged surfaces to impart planar alignment and pre-tilt to the surfaces. 

Kawahara, M. et al.. Synthesis and proton conductivity of sulfopropylated poly(benzimidazole) films. Solid State Ionics, 136/137, 1193, 2000. 

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