Thuy Dang

Next generation of Proton Exchange Membranes (PEM) for fuel cells were synthesized by polycondensation reaction of sulfonated monomers yielding temp. resistance, highly sulfonated polyarylenethioethersulfone (SPTES) copolymers. These copolymers form tough films (at ambient condition), exhibit excellent proton cond. up to 165 mS/cm (SPTES 70 @ 85 °C, 85%RH) and high thermal-oxidative resistance (250 °C). The high proton cond. and their

A series of high molecular weight, highly sulfonated poly(arylenethioethersulfone) (SPTES) polymers were synthesized by polycondensation, which allowed controlled sulfonation of up to 100 mol %. The SPTES polymers were prepared via step growth polymerization of sulfonated aromatic difluorosulfone, aromatic difluorosulfone, and 4,4 ′-thiobisbenzenthiol in sulfolane solvent at the temperature up to 180 °C. The composition and incorporation of the sulfonated repeat unit into the polymers were confirmed by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Solubility tests on the SPTES polymers confirmed that no cross-linking and probably no branching occurred during the polymerizations. The end-capping groups were introduced in the SPTES polymers to control the molecular weight distribution and reduce the water solubility of the polymers. Tough, ductile membranes formed via solvent-casting exhibited increased water absorption with increasing degrees of sulfonation. The polymerizations conducted with the introduction of end-capping groups resulted in a wide variation in polymer proton conductivity, which spanned a range of 100 –300 mS cm−1, measured at 65 °C and 85 % relative humidity. The measured proton conductivities at elevated temperatures and high relative humidities are up to three times higher than that of the state-of-the-art Nafion-H proton exchange membrane under nearly comparable conditions. The thermal and mechanical properties of the SPTES polymers were investigated by TGA, DMA, and tensile measurements. The SPTES polymers show high glass transition temperatures (Tg), ̃220 °C, depending on the degree of sulfonation in polymerization. SPTES-50 polymer shows a Tg of 223 °C, with high tensile modulus, high tensile strengths at break and at yield as well as elongation at break. Wide angle X-ray scattering of the polymers shows two broad scattering features centered at 4.5 Å and 3.3 Å, the latter peak being attributed to the presence of water molecules. The changes in the scattering features of the water in SPTES−70 membrane were examined as a function of drying time during an in situ drying experiment. The in situ small angle X-ray scattering from water swollen SPTES−70 membrane in a drying experiment exhibited a decrease in the water domain size morphology. AFM studies of SPTES−70 membrane in a humidity range (35 – 65 % RH) revealed an increased size of hydrophilic clusters with increasing humidity. SEM examination of cryofractured dry and swollen SPTES−70 membrane surface indicated a change from a smooth brittle fracture to a fractured surface with plastic deformation, verifying the plasticizing effects of the water molecules in the swollen membrane. Membrane electrode assemblies (MEAs), fabricated using SPTES-50 polymer as proton exchange membrane (PEM) incorporating conventional electrode application techniques, exhibit high proton mobility. The electrochemical performance of SPTES-50 membrane in the MEA was superior to that of Nafion. The SPTES polymers have been demonstrated to be promising candidates for high temperature PEM in fuel cell applications.

Fully conjugated poly[(1,7-dihydrobenzo[1,2-d:4,5-d']diimidazole-2,6-diyl)- 2-(2-sulfo)-p-phenylene], sPBI, has a para-catenated backbone. This rod-like polymer displays superior thermal and solvent stabilities. The stabilities hamper its processing for critical applications. Chemical derivative of the sPBI was achieved using pendants of propane-sulfonated Li^+ ionomer for a water-soluble polyelectrolyte, sPBI-PS(Li^+). sPBI-PS(Li^+) aqueous solutions were cast into freestanding films. Room-temperature direct current conductivity parallel to the film

There is a need for materials with improved thermal stability for uses as fuel cell membrane. PBO (poly(p-phenylene-2,6-benzobisoxazole)) is a candidate for use as structural membranes due to its mechanical properties as well as its chemical and thermal stability. Microporous membranes based on rigid rod PBO have been developed. To infiltrate the PBO membranes with proton conducting polymer, knowledge for

While the solubilization, in org. solvents, of sulfonic acid-pendent rigid-rod polymers such as poly(2-sulfo-1,4-phenylenebenzobisthiazole) (2-sulfoPBT) and poly(2-sulfo-1,4-phenylenebenzobisimidazole) (2-SulfoPBI) via the formation of their org. ammonium salts is a well-known phenomenon, no studies have been known yet of the inherent potential for improved compressive properties of these polymeric fibers by the mechanism of strong lateral stabilization via the inter-chain protonation of the heterocycle by the arom. sulfonic acid pendant. This paper describes the synthesis of 2-sulfoPBT and 2-sulfoPBI in moderate to high mol. wts. by the high temp. polycondensation of 4-carboxy-2-sulfobenzoic anhydride with 2,5-diamino-1,4-benzenedithiol dihydrochloride and 1,2,4,5-tetraaminobenzene tetrahydrochloride in polyphosphoric acid (PPA). Intrinsic viscosities of 11.0 and 12.0 dL/g were obtained for 2-sulfoPBT and 2-sulfoPBI resp. in methanesulfonic acid (MSA) at 30°. Fibers of the rigid-rod polymers could be spun from their lyotropic liq. cryst. phase. An investigation of the fiber diffraction patterns for the two polymers revealed that 2-sulfoPBT showed a much higher orientation than 2-sulfoPBI. [on SciFinder(R)]

Segmented multiblock SPTES polymers contg. hydrophilic disulfonated and hydrophobic unsulfonated blocks were successfully synthesized by two steps polycondensation reaction. The multiblock SPTES polymers were evaluated as proton exchange membranes for proton exchange membrane fuel cells. The multiblock SPTES membranes cast from DMAc soln. which showed water uptake in a range from 40 to 80%. The membranes showed proton cond. up

The liquid crystalline compositions are prepared by the in-situ polycondensation of diamines and diacid monomers in the presence of single wall carbon nano tubes (SWNT). Processing of the new compositions into fibers provide hybrid materials with improved mechanical properties. The in-situ polymerizations were carried out in polyphosphoric acid (PPA). Carbon nano tubes as high as 10 wt.polymer weight have been

Accelerated longitudinal shrinkage has been found to occur in several rigid-rod, polymeric systems at elevated temperatures. Results show that this shrinkage occurs upon reaching temperatures at which pendent cleavage, or the initial stages of carbonization, takes place. Atomistic simulation and WAXD would suggest that this shrinkage is initiated by strains occurring at the crystalline lattice level, resulting from the formation

There is increasing technological interest in polymers reinforced by nanoparticles because of their potential to provide enhanced mechanical properties, decreased permeability and flammability, as well as increased conductivity. Emulsion polymerization offers a viable, flexible route for nanocomposite fabrication from nanoscale spheres, rods, and plates. Combining emulsion generated poly(methyl methacrylate) (PMMA) particles that are ionically stabilized in aqueous solution with a

In an attempt to evaluate the effect of intermolecular hydrogen bonding on compression and transverse properties of rigid-rod polymeric fibers, methyl pendant poly (p-phenylene benzobisimidazole) (MePBI) was synthesized and spun into fibers. The hydrogen bonding in MePBI, as measured by infrared spectroscopy, is present at temperatures as high as 400 C. The fiber crystal structure has been determined, using WAXD and molecular simulation, which also shows significant hydrogen bonding within the system. The compressive strength of both as-spun and heat-treated fibers, measured from the recoil test, was found to be 800 MPa. MePBI also shows an increase in torsional modulus and loop strength, as compared to other methyl-pendant, rigid-rod systems. The temperature dependence of fiber tensile, torsional and bending properties will be reported. A correlation between intermolecular bonding strength, as measured by ab initio simulations, and compressive strength will also be presented.

The crystal structure of poly(2,6-naphthalenebenzobisthiazole) (Naph-2,6-PBT) was studied using X-ray and molecular modeling methods. The X-ray pattern of the annealed Naph-2,6-PBT fiber showed several Bragg reflections as well as streaks along the layer lines indicating that the registry between adjacent chains exists in the crystal with a great deal of axial disorder. Disordered structure in the crystal was fitted into

We have successfully prepd. conducting composites of the conjugated ladder polymer BBL and graphene. An inspection of the TEM image of the Graphene/BBL composite showed that the Graphene layers were distributed homogeneously in the BBL polymer matrix. The mech. properties of the composite were also improved with 50% to Graphene loading. TGA showed that the onset degrdn. temp. was decreased with 50% loading. The elec. resistivity of the composite was obsd. at 50% Graphene reached 6.546x101 Ω cm from the original value of 107 Ω cm for neat BBL. [on SciFinder(R)]

ABSTRACT A systematic investigation of properties and nanostructure of sulfonated polyarylenethioethersulfone (SPTES) copolymer proton exchange membranes for fuel cell applications has been presented. SPTES copolymers are high temperature resistant (250 °C), and form tough films with excellent proton conductivity up to 170 ± 5 mS/cm (SPTES 70 @ 85 °C, 85%RH). Small angle X-ray scattering of hydrated SPTES 70 revealed the presence of local water domains (diameter ∼5 nm) within the copolymer. The high proton conductivity of the membranes is attributed to the formation of these ionic aggregates containing water molecules, which facilitate proton transfer. AFM studies of SPTES 70 as a function of humidity (25–65%RH) showed an increase in hydrophilic domains with increasing humidity at 22 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2813–2822, 2007

Novel nanocomposite membranes based on sulfonated poly(arylenethioethersulfone) and polysiloxane-network were prepared via an in situ sol–gel process. The polysiloxane-network (PSIN) as nanostructure was formed by dimethyldimethoxysilane (DMDMS), tetraethoxysilane (TEOS), and N,N-diethylaminopropyltrimethoxysilane (DAPMS). Sulfonated poly(arylenethioethersulfone) (SPTES-100) polymer was modified to reduce its water absorption by the in situ formation of polysiloaxane-network. DAPMS was introduced as a bonding agent to improve the interaction between the two phases: hydrophilic phase (SPTES-100 polymer) and hydrophobic phase (PSIN) in the nanocomposites. PSIN/SPTES-100 nanocomposite membranes with 5wt% PSIN content had lower water uptake compared with SPTES-100 polymer and exhibited controlled swelling up to 75°C. TGA studies indicated that nanocomposite membranes established the good thermal stability. Proton conductivity of the nanocomposite membranes with 5wt% PSIN was measured under 85% relative humidity conditions up to 85°C, which shows proton conductivity is higher than that of SPTES-50 copolymer and Nafion 117. SEM cross-sectional features showed that the PSIN particles were uniformly embedded in the membrane matrix and the average domain size was ∼500nm. It is noticeable that the improvement in proton conductivity was mainly due to the uniform dispersion of the PSIN particles throughout the membrane matrix, thus establishing continuous conduction pathways in the nanocomposite membranes.

The structures of extruded (counter-rotating die) polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT) membranes wer examined with atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray scattering. The results for PBO indicate that (i) nanofibrils are oriented parallel to the surface, (ii) the nanofibrils are oriented in opposite directions (±22º) on both surfaces due to the counter rotating die extrusion, (iii)