Aliphatic polybenzimidazoles

I.K. Varma, Veena, Effect of structure on properties of aromatic aliphatic polybenzimidazoles, J. Polym. Sci. Polym. Chem. Ed. 14 (4)(1976) 973-980. 

The general process used to synthesise aromatic polybenzimidazoles (PBIs) is presented in Section 4.3.3. More detailed information can be found in previously published books [87,88]. During 1960-1970 a number of publications, comparable to those on polyimides, reported the synthesis and properties of all aromatic and aryl-aliphatic polybenzimidazoles. Most of these polymers were prepared by the two-step process illustrated in Fig. 14 with the reaction of 1,3-benzenedicar-boxylic acid diphenyl ester 27 and [l,l -biphenyl]-3,3, 4,4 -tetramine 11 yielding ultimately PBI 29. All the applications - laminates and filament winding resins, adhesives, fibres and foams - used polymer 29, which was produced in semicommercial quantities by the Whittaker Corporation (Narmco Division) under the generic trade mark Imidite . Currently, forty years later, this polymer is manufactured by Hoechst-Celanese and its only commercial success is in the area of heat resistant fibres and fabrics. It is, however, worth noting the adhesive properties of this polymer and the reasons explaining the major obstacles to the development of PBIs as heat-resistant adhesives. 

Aliphatic polybenzimidazoles were first synthesized by scientists in the 1950s. However, it was not until the 1960s that H. Vogel and C.S. Marvel first synthesized aromatic polybenzimidazoles and discovered that these unique, highly stable linear heterocyclic rigid-rod polymers exhibited exceptional thermal and oxidative stability [65]. Poly[2,2 -(m-phenylene)-5,5 -bibenzimidazole], PBI, was prepared by the condensation polymerization of... 

Tsu, Y., Levine, H.H., Levy, M. (1974) Effects of structure on properties of some new aromatic-aliphatic polybenzimidazoles. Journal of Polymer Science Part A Polymer Chemistry, 12, 1515-1529. 

Trischler, F.D., Levine, H.H. (1969) Substituted aliphatic polybenzimidazoles as membrane separator materials. Journal of Applied Polymer Science, 13, 101-106. 

Typically the surface area of the product is very low 2 m and further work is underway to improve the porosity of these species. In an alternative procedure a pre-formed polybenzimidazole prepared in the presence of stabilising polymer to provide aliphatic hydrocarbon graft chains can be dissolved in cone. H2SO4 and the acid solution dispersed, without additional stabiliser, in paraffin oil. Slow addition of methanol to the suspension causes precipitation of the polybenzimidazole within the droplets and eventually solid particulates are formed. These can be collected, washed and dried in the usual way. Materials prepared by this method have better porosity and a surface area of 30 m g ... 

Polybenzimidazoles are synthesized from aromatic tetraamines (bis-o-diamines) and dicarboxylates (acids, esters or amides). Generalized monomers are shown in FIGURE 1 and polybenzimidazoles from those monomers are shown in FIGURE 2. In either figure, R(l) and R(2) can be aromatic or aliphatic and may contain other groups as ether, ketone, sulfone, etc. The structures shown do not exhaust all possible benzimidazole polymers. 

The melting temperatures and thermal stabilities of several polybenzimidazoles are shown in TABLE I. For all aromatic polybenzimidazoies, melting points are over 600 C. Generally, the presence of other structural elements will reduce melting points and thermal stabilities. For example, TABLE I includes polybenzimidazoles condensed from either a tetraamine ether or a diacid ether. Strained polymer structures also reduce polybenzimidazole stability as evidenced by the low melting point of a polymer formed with a biphenyl-2,2 -dicarboxylate. Not surprisingly, the aliphatic, adipic acid forms a much less stable polybenzimidazole than the aromatic examples above it in the table. 

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