Polymer Poly benzimidazole

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... 

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. 

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... 

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... 

M. Kawahara, J. Morita, M. Rikukawa, K. Sanui, and N. Ogata. Synthesis and proton conductivity of thermally stable polymer electrolyte Poly(benzimidazole) complexes with strong acid molecules. Electrochimica Acta 45, 1395-1398 2000. 

Poly(benzimidazole) can be used as the reactive polymer for the preparation of side chain-type polyrotaxane via the alkylation on nitrogen. Osakada et al. showed that deprotonation of poly(benzimidazole) followed by N-alkylation with alkyl bromide-terminated pseudorotaxane consisting of 2,3,6-trimethyl-/1-cyclodextrin gave a novel side chain-type polyrotaxane (Scheme 38) [206]. Poly(benzimidazole) having a long -hydroxyalkyl group as the side chain can form an inclusion complex with 2,3,6-trimethyl-/l-cy-... 

MacKnight and coworkers found that several poly(imide)s, such as Ultem poly(ether imide) and XU218 poly(imide), formed miscible blends with poly (benzimidazole) (FBI) [58, 59]. The miscibility of these blends is believed to result from specific interactions between the benzimide ring of the poly(im-ide) and benzimidazole ring of FBI. In a later study, Grobelny et al. [60] reported the CFMAS spectra of several of these blends. Slight changes in the lineshape were observed in the intimate blends, and seen as evidence of the specific interactions between the polymers. In particular, the peak in the spectra, due to the imide carbonyl carbon, was seen to broaden towards... 

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

Aromatic poly(benzimidazole)s (PBI)s were synthesized by Vogel and Marvel in 1961 [1,2]. It was soon discovered that these polymers have excellent thermal and oxidative stability. Therefore a growing interest developed. 

Amino monomers can in general be classihed as those that deliver AA or AA/BB type polymers, i.e., poly(benzimidazole)s or poly(benzobisimidazole)s [3]. This is shown schematically in Figure 16.1. 

Lee HJ, Lee DH, Henkensmeier D, Jang JH, Cho EA, Kim HJ, et al. Synthesis and characterization of H3PO4 doped poly(benzimidazole-co-benzoxazole) membranes for high temperature polymer electrolyte fuel cells. Bull Korean Chem Soc 2012 33(10) 3279-84. 

Toiserkani H, Sheibani H, Saidi K. Preparation and characterization of novel organosol-uble and thermally stable poly(benzimidazole-amide)s bearing phthalimide pendent groups. European Polym J 2010 46(2) 185-94. 

Abdolmaleki A, Bazyar Z. Preparation and characterization of poly(benzimidazole-amide)/ zno nanocomposites using silane coupling agent. Polym-Plastics Technol Eng 2013 52(15) 1542-9. 

Poly(benzimidazoles) are speciality polymers that have found only a few civilian applications outside the military area and in space research. PBI fibers have been used for thermally stable protective clothing and as precursors in the production of graphite fibers. Hollow fibers and films of PBI are used to purify sea and brackish water according to the reverse osmosis process. 

Poly(benzimidazoles) have high thermal stability, and there has been no lack of effort to increase the thermal stability even more through suitable choice of the initial monomers. If the dicarboxylic acids are replaced by tetracarboxylic acids or their anhydrides, and these are then converted with tetramines, then more or less perfect ladder polymers are formed. These ladder polymers all have a thermal stability about 100 K higher than PBI, and so can be used up to about 600° C. Poly(imidazopyrrolone) or pyrron, polypyrrolone, and poly(benzimidazobenzophenanthroline) or BBB may be specially mentioned in this respect. The synthesis of these difficultly soluble polymers must be mostly carried out in solvents such as polyphosphoric acid, zinc chloride, or eutectic mixtures of aluminum chloride and sodium chloride ... 

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