Polybenzimidazole solutions solubility

The polymers obtained were soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solutions. The polymers were stable up to 400 °C, but they yielded polybenzimidazoles by eliminating sulfonic acid groups, instead of ring closure. 

Polybenzimidazoles are normally highly soluble in polyphosphoric acid (PPA) which is commonly used as polycondensation solvent. From this solution, phosphoric acid-doped membranes can be obtained directly by casting the crude mixture as a thin film. A sol-gel transition is subsequently induced by hydrolyzing the PPA (good solvent) to orthophosphoric acid (poor solvent) under an atmosphere with carefully controlled temperature and humidity to control the acid content of the membrane [1]. This approach is further reviewed in Chap. 10. 

Various polymers have been successfully electrospun from solution, sol-gel suspension, or melt into ultrafine nanotibers. For example, as listed in Table 13.2, these polymers included nylon-6 [20, 21], polyacrylonitrile (PAN) [22, 23], polyethylene terephthalate (PET) [24], polyvinyl alcohol (PVA) [25], polystyrene (PS) [26, 27], polyvinylidene fluoride (PVDF) [28, 29], polyethersulfone (PES) [30], polyimides (PI) [31, 32], polyethylene oxide (PEO) [33], polyurethanes (PU) [34], polycarbonates (PC) [35], polycaprolactone (PCL) [36], polybenzimidazole (PBI) [37, 38], polyvinylpyrrolidone (PVP) [39], polytrimethylene terephthalate (PTT) [40], polyvinyl chloride (PVC) [41], polymethylmethacrylate (PMMA) [42], hydrox-ypropyl cellulose (HPC) [43], polyglycolic acid (PGA) [44], polyhydroxybutyrate (PHB) [45], cellulose acetate (CA) [46,47] and many more. To be used as filtration membranes, nanoflbers made of water-soluble polymers have to be further cross-linked after the electrospinning process. As polymers having different physical and... 

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