@article { ISI:000242988100022, title = {Enhancement of gas permeation properties of polybenzimidazoles by systematic structure architecture}, journal = {Journal of Membrane Science}, volume = {286}, number = {1-2}, year = {2006}, month = {DEC}, pages = {161-169}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Systematic structural variations in thermally stable polybenzimidazole (PBI) are explored that led to a substantial improvement in gas permeation properties. Physical property determinations revealed that incorporation of hexafluoroisopropylidene and tert-butyl groups led to amorphous polymers with slightly lowered thermal stability and decreased chain packing. PBI based on 4,4{\textquoteright}-(hexafluoroisopropylidene)bis(benzoic acid) and 5-tert-butyl isophthalic acid exhibited 10-40 times higher permeability, while changes in selectivities for industrially important pairs ranged from modest decrease of 75\% or less than that of PBI based on isophthalic acid. The O-2/N-2 selectivity was almost doubled in case of PBI based on 5-tert-butyl isophthalic acid. Gas diffusion coefficients were estimated from solubility and permeability coefficient determinations. These, along with dual-mode sorption parameters estimated from sorption isotherms provided an insight towards variations in permeation behavior. The permeability predictions for heavier gases in isophthalic acid based PBI correlated well with physical properties. The occurrence of permeation characteristics (especially P-H2 and P-H2/P-N2) near Robeson{\textquoteright}s upper bound, high thermal stability and good solvent solubility achieved by these structural modifications depicted the potential of this family of polymers as gas separation membrane materials. (c) 2006 Elsevier B.V. All rights reserved.

}, keywords = {Diffusion, Gas permeation, Polybenzimidazole, Sorption, thermal stability}, issn = {0376-7388}, doi = {10.1016/j.memsci.2006.09.030}, author = {Kumbharkar, Santosh C. and Karadkar, Prasad B. and Kharul, Ulhas K.} } @article { ISI:000250122000026, title = {Gas sorption and transport in polyarylates: effect of substituent symmetry and polarity}, journal = {Journal of Membrane Science}, volume = {303}, number = {1-2}, year = {2007}, month = {OCT}, pages = {244-251}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The gas sorption properties of polyarylates based on bisphenol-A possessing symmetric/asymmetric substitution by nonpolar -CH3 group and symmetrically linked terephthalic acid were examined. The effects of substitution of polar bromine on terephalic acid moiety of polyarylate based on asymmetrically substituted bisphenol were also studied for physical, sorption and transport properties. The estimation of dual mode sorption parameters, solubility and diffusion coefficient revealed that nature of the substituent and substitution type plays a crucial role in depicting permeation properties. An asymmetric substitution by -CH3 group increased solubility coefficient of pure gases (N-2, O-2, CH4 and CO2) up to 27\% and symmetric substitution increased the same up to 106\%. This was coupled with 7-35\% increase in solubility selectivity in both cases of substitution, which ascertained the usefulness of methyl group substitution in polyarylates based on terephalic acid. The pressure dependency of solubility coefficients and solubility selectivity was also investigated for these polyarylates. The sorption and transport properties of these polyarylates correlated well with physical properties of polyarylates and gases studied. The sorption/desorption kinetics of symmetrically substituted TMBisA-T was performed in order to deduce time dependent sorption behavior and to evaluate diffusivity coefficient. The apparent diffusion coefficients from sorption kinetics, desorption kinetics and from steady-states permeation-sorption were compared. The diffusion coefficients of CH4 and N-2 deduced by these methods correlated well with each other. (C) 2007 Elsevier B.V. All rights reserved.

}, keywords = {Diffusion, kinetics, permeation, polyarylates, Sorption}, issn = {0376-7388}, doi = {10.1016/j.memsci.2007.07.018}, author = {Karadkar, Prasad B. and Kharul, Ulhas K. and Bhole, Yogesh S. and Badhe, Yogesh P. and Tambe, Sanjeev S. and Kulkarni, Bhaskar D.} } @article { ISI:000246347900035, title = {Nitration and amination of polyphenylene oxide: synthesis, gas sorption and permeation analysis}, journal = {European Polymer Journal}, volume = {43}, number = {4}, year = {2007}, month = {APR}, pages = {1450-1459}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

A high degree of nitration of polyphenylene oxide (PPO) was successfully achieved by carefully optimizing synthetic protocol. The reduction of nitro group to amino could be done quantitatively. The physical properties of formed polymers were investigated and correlated with gas sorption and permeation properties. The formed polymers were amorphous in nature as revealed by wide angle X-ray diffraction spectra. An increase in the packing density in comparison to unsubstituted PPO as a result of induced polarity was indicated by lowering of fractional free volume and d-spacing. The substitution by either nitro or amino group increased the chain stiffness as revealed by the dynamic mechanical analysis. Though both, nitro and amino group substitution on PPO led to a decrease in pure gas permeability, the selectivity of various gas pairs was increased by these substitutions. The gas sorption analysis revealed that both, solubility selectivity and diffusivity selectivity were increased by these polar group substitutions. The nitro group substitution was more effective in improving solubility selectivity, while amino group substitution was more effective in improving diffusivity selectivity. (C) 2007 Elsevier Ltd. All rights reserved.

}, keywords = {Amination, nitration, permeation, polyphenylene oxide, Sorption}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2007.01.017}, author = {Bhole, Yogesh S. and Karadkar, Prasad B. and Kharul, Ulhas K.} }