Aggregation Behavior of Polybenzimidazole in Aprotic Polar Solvent

Abstract

We report a study of aggregation behavior of polybenzimidazole (PBI) in polar aprotic solvents such as dimethylacetamide (DMAc). The photophysical studies of the PBI solution at various concentrations show concentration quenching and reveal that aggregated structures are formed when the polymer concentration is increased. The decay profiles obtained from time-resolved fluorescence study for low (0.00154 g/dL) and high (0.154 g/dL) concentrations of PBI in DMAc solution fit into a triexponential decay, surprisingly high concentration shows a growth (negative pre-exponential factor) in the decay profile, providing a support for excimer formation. The excited-state life time for the aggregated/excimer structure is found to be 4.14 ns, longer than that for the free polymer chains for which the life time is 502 ps. The concentration dependence emission spectra attribute that the aggregation/excimer formation is an intermolecular process. An abrupt decrease of Huggins constant and reduced viscosity with increase in concentration indicate the conformational transition of polymer chains of PBI from compact coil to an extended helical rodlike structure. The NMR and viscosity studies demonstrate that the intra-and intermolecular interactions (interchain hydrogen bonding) play an important role for the conformational transition and aggregation process. Transmission electron microscope images support the conclusion drawn from other studies; show helical rods for high concentration and featureless morphology for low concentration. The circular dichroism spectrum is also in agreement with the helical characteristics of aggregated structure. The temperature-dependent NMR and viscosity studies show that the disruption of interchain hydrogen bonding with increasing temperature destabilizes the aggregated structure at higher temperature.

Solution polymerization of polybenzimidazole

“…21 Synthetic knowledge of these procedures can be applied to polymeric systems when di-functional monomers are incorporated, however, challenges arise when considering polymer solubility and degree of polymerization. Although PBI is a basic polymer (pKa 5.25) 22 with both proton donor and acceptor sites that allow for specific interactions with polar solvents, [23][24][25] fully aromatic…”

Formation of core (polystyrene)–shell (polybenzimidazole) nanoparticles using sulfonated polystyrene as template

“…Poly [2,2 0 -(m-phenylene)-5,5 0 -benzimidazole] (PBI) was obtained by polymerizing 3,3 0 ,4,4 0 -tetraaminobiphenyl (TAB) and isophthalic acid in poly phosphoric acid medium (115%) in the laboratory using our standard method described earlier [37,42]. Styrene (Sisco, India), sodium dodecyl sulfate (SDS, Merck), sodium bicarbonate (Sisco, India), and ammonium per sulfate (APS, Merck) as the monomer, surfactant, buffer, and initiator, respectively, were used as received from the suppliers.…”

“…Phosphoric acid doped PBI is being used in high temperature direct methanol fuel cell as well as H 2 /O 2 fuel cells because of its very high thermo chemical stability and low gas permeability [38][39][40][41]. PBI possesses both proton donor (ANHA) and proton acceptor (AN@) hydrogen bonding sites, which exhibit specific interactions with polar solvents [42][43][44][45] and upon blending with a variety of polymers [12,[46][47][48][49][50]. A wide range of polymers with variety of polar functional groups such as carbonyl, sulfonyl in their backbone form miscible blend with PBI and the miscibility arises due to the specific hydrogen bonding interaction between the functional groups of these polymers.…”

Fluorinated Polyazoles

“…PBI has both proton donor (-NH-) and acceptor (-N]) hydrogen bonding sites that interact with both protic and aprotic polar solvents [17][18][19]. The PBIs were all colored polymers, varying from deep golden yellow to black.…”