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Polyimides were synthesized from one-step polycondensation of BPADA and various diamines and were characterized with GPC, FTIR, NMR, DSC, and TGA. Polyimide membranes were prepared, and their hydrophilicity was estimated by contact angles and the free energies of interfacial interactions. Pervaporation properties were investigated for the dehydration of isopropanol, and comparisons were made between BPADA-based membranes and 6FDA-based membranes. The concentration coefficients of BPADA-based membranes were calculated from the linear moiety contribution method based on the results from 6FDA-based membranes, and they were compared to understand the effects of the feed concentration on pervaporation properties. The effects of temperature on permeation flux were studied with permeation activation energies for total flux and water flux in permeates. Moiety contribution factors for activation energies were used to correlate permeation flux and monomer moieties in the polymers, and reasonable results were obtained for BPADA. It is revealed that steric effects of monomers may change the diffusion properties, while functional groups are favorable to the changes in sorption properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The interaction of hydrophobically modified (HM) polybetaines with selected small molecule surfactants in aqueous solution was investigated using rheological and surface tension analyses. The polymers included acrylamide-based, HM polybetaines containing N-butylphenylacrylamide (BPAM) and specified amounts of sulfobetaine, 3-(2-acrylamido-2-methylpropanedimethylammonio)-1-propanesulfonate (AMPDAPS), or carboxybetaine, 4-(2-acrylamido-2-methylpropyldimethylammonio)butanoate (AMPDAB); corresponding control (co)polymers lacking BPAM and/or betaine comonomer(s) were also examined for comparative purposes. Low charge density terpolymers exhibited greater viscosity enhancement with the addition of surfactant compared to the high charge density terpolymers. The addition of sodium dodecyl sulfate (SDS) produced the largest increase in solution viscosity, while N-dodecyl-N,N,N-trimethylammonium bromide (DTAB), N-dodecyl-N,N-dimethylammonio-1-propanesulfonate (SB3–12), and Triton X-100 enhanced polymer solution viscosity to a lesser degree. In most cases, the high charge density carboxybetaine terpolymer exhibited diminished solution viscosity upon surfactant addition. The polymers lacking hydrophobic modification showed no detectable viscosity enhancement in the presence of surfactants. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 658–671, 2004

Hydrophobic poly(ether ether ketone) (PEEK) were modified by sulfonation at different temperatures (22, 36, 45, and 55°C) and varying period of time with concentrated sulfuric acid used as solvent. A kinetic study was carried out based on the assumption that sulfonation reaction is a second-order reaction, which takes place preferentially in the aromatic ring between the two ether (O) links (the first type substitution), and there is only one substituent attached to each repeat unit of the PEEK before the complete substitution of this preferred aromatic ring. More than 100% substitution was observed in experiment. All the data with substitution degree less than 95% agree fairly well with the kinetic behavior of the second-order reaction. The reaction rate coefficient and activation energy for first type substitution were obtained. The sulfonated PEEK samples were characterized in terms of ion-exchange capacity (IEC), 1H-NMR, contact angle, and solubility. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2651–2660, 2001

Crosslinked blended membranes of poly(vinyl alcohol) (PVA) and N-methylol nylon-6 were prepared either by thermal crosslinking at 180°C or by chemical crosslinking with maleic acid. The pervaporation performance for the separation of ethanol–water mixtures of these membranes was investigated in terms of feed concentration, PVA content, and crosslinking agent content. The pervaporation performance of two differently crosslinked membranes was strongly influenced by the nature of the crosslinkage. Significant improvement in the pervaporation separation index can be achieved for chemically crosslinked membranes. From the comparison between the pervaporation and sorption tests, it is suggested that, for hydrophilic membranes, sorption properties dominate the pervaporation performance at feed solutions of higher water content, while diffusion properties govern at feed solutions of higher ethanol content. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 317–327, 1998

N-methylol nylon 6 membranes were prepared by reacting nylon-6 with formaldehyde. Elemental analysis, used to analyze the composition of modified membranes, showed that the degree of substitution increased with formaldehyde content in the reaction solution. The modified nylon-6 membranes exhibited a high affinity to ethanol. Pervaporation results for the separation of ethanol-water mixtures showed that these membranes were water-selective, indicating that the diffusion property is the dominant factor. An N-methylol nylon-6 membrane with 33% degree of substitution showed the best membrane performance. In order to control the swelling of N-methylol nylon-6 membranes in the feed solutions of high ethanol content, thermal crosslinking was applied at 180°C for different times. It was found that heat treatment of 10 minutes gave the optimal permselectivity. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 855–863, 1997

The characteristics of solvent evaporation and polymer precipitation during the formation of asymmetric aromatic polyetherimide (PEI) membranes via the dry/wet phase inversion method are studied and the results are discussed with reference to membrane preparation. It is shown that the solvent evaporation from the surface of freshly cast films in early evaporation stages can be quantified by an empirical equation with two parameters. Analysis of the evaporation parameters partially explains the interaction effect of membrane preparation variables on membrane performance. The phase separation data for systems PEI/DMAc/H 2 O and PEI/NMP/H 2 O with and without LiNO 3 additive are determined using the turbidimetric titration method. The kinetic data on solvent-nonsolvent exchange and additive leaching during polymer precipitation in nonsolvent water are measured. The results presented here offer a qualitative basis for the development of asymmetric PEI membranes.

Ionically crosslinked latex membrane is prepared by treating the latex membrane containing carboxyl groups with salt solutions. Pervaporation separation with these membranes shows that the ionic crosslinking raises the permeability, with the selectivity being maintained or increased. Ionically crosslinked membranes also have a higher pervaporation separation efficiency than the nontreated membranes. Permeability and selectivity increase with increasing ethanol content in feed. The temperature dependence of permeability can be correlated by the Arrhenius relationship. © 1994 John Wiley & Sons, Inc.

Novel ionically cross-linked blended membranes of nylon 6 and poly(acrylic acid) (PAA) were studied for the pervaporation separation of the binary organic mixture of pentane and methanol. Membranes of composition 25 wt % PAA were used after cross-linking. The experimental data obtained from the pervaporation runs were compared with the theoretical values of the individual permeabilities for binary mixtures predicted by the modified Fels and Huang model. This new model is based on an extension of the free volume theory and the introduction of Flory–Huggins thermodynamics for the calculations of the binary interaction parameters and the diffusion coefficients. The calculated values of permeabilities obtained from this modified model were reasonably close to the experimental values.

A model calculating the diffusion coefficients of liquids in polymeric membranes from the diffusion coefficients at zero concentration was developed. This model is based on Fujita's volume theory and considers crystallinity in the polymer and is tested by using available data in the literature, i.e., n-hexane–polyethylene and benzene–polyethylene systems. The calculated diffusion coefficients were simulated by calculating the pure liquid permeabilities in a pervaporation system. When comparing the predicted pure liquid permeabilities with the experimental values, these calculated values were found to be in fairly good agreement.

Membranes consisting of ionically crosslinked polyacrylic acid (PAA) and Nylon 6 were prepared and tested for the pervaporation separation of acetic acid-water mixtures. The polyacrylic acid (PAA) membranes were crosslinked in aluminum nitrate aqueous solution while the polyacrylic acid (PAA)-Nylon 6 blends were cast from homogeneous PAA-Nylon 6 mixtures to appropriate thicknesses and then crosslinked in aqueous aluminum nitrate solutions. Optimum pervaporation results were obtained from blends of Nylon 6 and PAA in the weight ratio of 60–75 wt% Nylon 6 and 25–40 wt% PAA which have separation factors (water/acetic acid) of over 60 and flux rates higher than 100 g/m2 h at 15°C for the separation of acetic acid-water mixtures. The flux rates and separation factors could be altered by changing the blend composition of the membrane. The effects of the feed composition on the separation factors were investigated.

The transport of gaseous ethylene oxide (EtO) in several polymer films is studied using the carrier gas method of measurement. Permeability, solubility, and diffusion coefficients describing ethylene oxide (EtO) transport in polypropylene, polyvinylchloride, Teflon-FEP copolymer, and polyethylene films have been obtained over a 30 Celsius degree range at a low concentration of EtO using the carrier gas method of measurement. The results indicate that the diffusion of EtO in polyethylene is independent of penetrant concentration over the range of concentrations used. However, concentration-independent diffusion could not be verified directly for the other films studied. Two different techniques of determining diffusion coefficients were used, and within the precision of the data both yield the same result. An excess enthalpy of solution for the solubility of EtO in Teflon-FEP copolymer was calculated, an observation that suggests that dual-mode sorption may be taking place.

A series of poly(vinyl alcohol) membranes were modifed by radiation-induced graft copolymerization with acrylic acid and methacrylic acid monomers. These grafted poly(vinyl alcohol) membranes were then tested for their separation and permeability characteristics in vacuum permeation and dialysis experiments. The permselectivity of the membranes toward methanol and water was studied on a vacuum permeation apparatus at 30, 40, and 50°C. The permeation process was found to be a temperature-activated process. The logarithm of the permeation rate varied linearly with the reciprocal of the absolute temperature. The permeability of the grafted membranes was found to increase with the degree of grafting, with no appreciable selectivity toward water in binary mixtures. The acrylic acid-grafted membranes generally showed greater improvement in permeability than the methacylic-grafted membranes. The permeability of the grafted membranes toward methanol, sodium chloride, urea, creatinine, and uric acid was studied in a dialyzer. In all cases, the grafted membranes showed an improved permeability toward these solutes over the commercial poly(vinyl alcohol) membranes. The dialysis results were then compared with those obtained for dialysis-grade cellophane membranes. For the case of sodium chloride, urea, and methanol, the permeability of the grafted membranes was comparable to that of cellophane. A comparison of commercial and grafted poly(vinyl alcohol) membranes in their permeability toward ionic solutes exhibited somewhat anomalous behavior in that the permeability of the commercial membranes was higher than that of the grafted membranes. This related to the ionic nature of the modified membrane. The permeability coefficients determined in the dialysis experiments were found to be directly related to the degree of hydration of the grafted membrane. This behavior was attributed to changes in the size and shape of voids within the membrane structure.

The composite gel permeation chromatography (GPC) chromatogram of a mixture of polystyrene and poly(methyl methacrylate) has been successfully resolved into its component chromatograms by using a newly developed technique. This technique has made possible the calculation of Mw and Mn values of these polymers in the conjugate phases of the ternary systems with toluene as the solvent. Calculated Mw and Mn values of the two polymers indicated that the larger polystyrene molecules tend to stay in the top polystyrene-rich phase while its smaller molecules tend to stay in the bottom phase to interact with the other polymer. The reverse is true with the poly(methyl methacrylate) molecules. This tendency strongly suggests that interactions among the two polymers were accomplished mainly by their smaller molecules.

Shifts have been observed in the elution volumes of solutions of polystyrene, polybutadiene, and mixtures of the two in gel permeation chromatography using tetrahydrofuran as solvent. Such shifts are examined in terms of the effect on the hydrodynamic volumes of concentration, of molecular weight, and of the presence of an incompatible polymer. Suitable concentration ranges to minimize these shifts have been found.

Several test methods were employed to determine polymer fracture toughness (Ic, the opening-mode strain energy release rate) at room temperature. The materials used included DGEBA epoxies and those modified by the addition of CTBN elastomers. Double-cantilever beam specimens were used to determine the fracture toughness both of bulk resins and of an adhesive layer bonded between two aluminum half-beams. The adhesive fracture toughness of a 0.025-cm bond was slightly less than the bulk Ic value, attributed to the bond thickness effect. Fracture toughness of bulk resins was also evaluated by using both rectangular and round compact tension specimens. The results, when compared with those obtained with the bulk double-cantilever beams, are quite acceptable. The thickness of compact tension specimens, ranging from 0.64 to 1.0 cm, might not give pure plane-strain conditions, and thus some plane-stress contribution to Ic should be expected for the tougher materials. Izod impact tests were also carried out to determine sample fracture toughness at high loading rate.

The synthesis of sulfonated poly(phenylene oxide) polymer was investigated. The poly(phenylene oxide) was synthesized through oxidative coupling from 2,6-dimethyl-phenol with copper (I) chloride-pyridine catalyst and sulfonated using chlorosulfonic acid. The effects of catalyst concentration, solvent, and other experimental variables on the kinetics of the polymerization of poly(phenylene oxide) and its subsequent sulfonation are reported in detail.