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Preparationof stable, free-standing elastic film with hydrophobicsurface from water-dispersible polyurethanes (WDPUs) is a challengingtask. Here, we have prepared WDPUs from polybutadiene-based diolsand the resulting PU films are satisfying the requisites. Two typesof diols, namely, hydroxyl-terminated polybutadiene (HTPB) and terminal-functionalizedHTPB with dinitrobenzene (DNB) [HTPB-DNB], were used to make WDPUsand the effects of diol structures were investigated. The synthesizedWDPUs displayed particle morphology with size in the range of ∼130–270nm and more than 1 year storage stability. WDPUs yielded stable andfree-standing films upon curing and the resulting films showed highthermal and mechanical stabilities. The contact angle of the filmsis in the range of ∼80–100°, attributing the hydrophobicnature of the surface. Hard segment content of the PU varied from30 to 40% (by weight) to tune the properties of WDPUs and the resultingfilms. [ABSTRACT FROM AUTHOR]

We report a new blend system consisting of an amorphous polymer polybenzimidazole (PBI) and a semicrystalline polymer poly(vinylidene fluoride) (PVDF). A systematic investigation of the blend pair in various compositions using Fourier transform infrared (FT-IR) spectroscopy provides direct evidence of specific hydrogen bonding interaction involving the N−H groups of PBI and the >CF2groups of PVDF. Blending shows a maximum 30 cm-1frequency shift in the N−H stretching band of PBI and also the existence of a partial double bond character in the PVDF chain. Differential scanning calorimetry (DSC) study proves the miscibility of these polymers in a wider composition range. The decrease of the Tgwith increasing PVDF in the blend and also the decrease of both the Tmand Tcwith increasing PBI in the blend attribute the miscibility of the blend systems. The PA doping level of the blend membranes improves significantly as a result of the hydrophobic nature of the PVDF component. [ABSTRACT FROM AUTHOR]

In the present work, a series of novel random polybenzimidazole (PBI) copolymers consisting of m- and p-phenylene linkages are synthesized from various stoichiometric mixtures of isophthalic acid (IPA) and terephthalic acid (TPA) with 3,3‘,4,4‘-tetraaminobiphenyl (TAB) by solution copolycondensation in polyphosphoric acid (PPA). The resulting copolymers are characterized by different techniques to obtain their molecular properties parameters. The monomer concentration in the polymerization plays an important role in controlling the molecular weight of the polymer. Surprisingly, a simple change in the dicarboxylic acid architecture from meta (IPA) to para (TPA) increases the molecular weight of the copolymers, which is maximum for the para homopolymer. The low solubility of TPA in PPA is found to be the dominating factor for obtaining the higher molecular weight polymer in the case of the para structure. FT-IR study shows that the introduction of the para structure enhances the conjugation along the polymer chain. The positive deviation of the copolymer composition from the feed ratio is due to the higher reactivity ratio of TPA than IPA, which is obtained from proton NMR studies. The incorporation of the para structure in the chain enhances the thermal stability of the polymers. The para homopolymer shows 59 °C lower glass transition temperature compare to the meta homopolymer indicating enhancement of the flexibility of the polymer chain due the introduction of the p-phenylene linkage in the backbone. The Tgof the copolymers shows both positive and negative deviation from the expected Tgcalculated by the Fox equation. The enhanced conjugation of the polymer chains also influences the photophysical properties of the polymers in solution. All the PBI polymers exhibit strong fluorescence in dimethylacetamide solution. As expected, that all the polymers are amorphous in nature reveals that the copolymerization does not influence the packing characteristics of the PBI chains. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]