Showing papers in "Macromolecules in 2002"

Micro- and Nanostructured Surface Morphology on Electrospun Polymer Fibers

Abstract: Electrospun fibers were produced using a variety of solvents to investigate the influence of polymer/solvent properties on the fiber surface morphology. Electrospinning is a novel processing techni...

Effects of Clay Content on the Properties of Nanocomposite Hydrogels Composed of Poly(N-isopropylacrylamide) and Clay

Abstract: For two different types of poly(N-isopropylacrylamide) (PNIPA) hydrogels, i.e., nanocomposite type PNIPA hydrogels (NC gel) and conventional chemically cross-linked PNIPA hydrogels (OR gel), the effects of cross-linker contents on various physical properties were investigated. In NC gels composed of a unique organic (PNIPA)/inorganic (clay) network, the inorganic clay acts as a multifunctional cross-linker in place of an organic cross-linker (BIS) as used in OR gels. In NC gels, which generally exhibit extraordinary mechanical toughness, the tensile moduli and tensile strengths are almost proportional to the clay content (Cclay), while the elongation at break tends to decrease slightly with increasing Cclay. On the other hand, in OR gels, which always exhibit weak and brittle natures, there was no detectable change in properties on altering the concentration of BIS (CBIS). The deswelling rate was affected markedly by the cross-linker content in both gels though in opposite directions. On increasing cross-...

Field-Theoretic Computer Simulation Methods for Polymers and Complex Fluids

Abstract: We review a class of new computer simulation methods for polymeric fluids and other soft condensed matter systems that are based on an underlying field-theoretic description. These methods, while still in an early stage of development, show considerable promise for studying the equilibrium properties of many-component systems capable of intricate self-assembly, such as solutions and blends containing block and graft copolymers. Field-theoretic simulation methods also provide a great deal of flexibility in model building and coarse graining, and appear to be particularly well suited to treat systems with soft, long-range interactions, such as polyelectrolytes. We attempt to connect various related theoretical approaches, such as self-consistent field theory and dynamic density functional theory, within a common framework.

Dispersion of Functionalized Carbon Nanotubes in Polystyrene

Abstract: Polystyrene nanocomposites with functionalized single-walled carbon nanotubes (SWNTs), prepared by the in-situ generation and reaction of organic diazonium compounds, were characterized using melt-state linear dynamic viscoelastic measurements. These were contrasted to the properties of polystyrene composites prepared with unfunctionalized SWNTs at similar loadings. The functionalized nanocomposites demonstrated a percolated SWNT network structure at concentrations of 1 vol % SWNT, while the unfunctionalized SWNT-based composites at twice the loading of SWNT exhibited viscoelastic behavior comparable to that of the unfilled polymer. This formation of the SWNT network structure for the functionalized SWNT-based composites is because of the improved compatibility between the SWNTs and the polymer matrix and the resulting better dispersion of the SWNT.

Nanostructures of polyaniline doped with inorganic acids

Abstract: With an average diameter of 150−340 nm and a conductivity of 10-1−100 S/cm, nanostructures (e.g., nanotubes or nanorods) of polyaniline (PANI) were synthesized by a self-assembly method in the presence of inorganic acids (e.g., HCl, H2SO4, HBF4, and H3PO4) as dopants. It was found that the morphology, size, and electrical properties of the resulting nanostructures depended on the dopant structures and the reaction conditions. In particular, all these PANI nanostuctures showed hydrophilic features, and the contact angles with water were measured to be about 27−40° depending on the dopant. The FTIR spectrum, UV−vis absorption spectrum, XPS, and X-ray diffraction were used to characterize the molecular structures of the nanostructures. It was found that their main chain structure and electric structure were identical to those of the emeraldine salt form of PANI. The micelles formed by anilinium cations act as the template like in the formation of PANI nanostructures.

New Polylactide/Layered Silicate Nanocomposites. 1. Preparation, Characterization, and Properties

Abstract: New polylactide (PLA)/layered silicate nanocomposites have been prepared successfully by simple melt extrusion of PLA and organically modified montmorillonite. The d spacings of both the organically modified montmorillonite and intercalated nanocomposites were investigated by wide-angle X-ray diffraction (WAXD) analysis, and the morphology of these nanocomposites was examined by transmission electron microscopy (TEM). Using oligo(e-caprolactone) (o-PCL) as a compatibilizer, the effect of compatibilizer in nanocomposites was investigated by focusing on two major aspects: morphological analysis and mechanical property measurements. The intercalated nanocomposites exhibited remarkable improvement of materials properties in both solid and melt states as compared to that of PLA matrices without clay.

Quantitative Theory for Linear Dynamics of Linear Entangled Polymers

Abstract: We present a new quantitative development of the reptation picture of de Gennes−Doi−Edwards. It is well-known that the original reptation theory is unable to fit linear relaxation spectra (G‘ and G‘ ‘) as it misses several important physical processes: (1) contour length fluctuations, (2) constraint release, and (3) longitudinal stress relaxation along the tube. All of these processes were treated theoretically before; however, the treatment used either uncontrolled approximations or failed to include all of them at the same time. The aim of this work is to combine self-consistent theories for contour length fluctuations and constraint release with reptation theory. First, we improve the treatment of contour length fluctuations using a combined theoretical and stochastic simulation approach. This allows us to obtain an expression for the single chain relaxation function μ(t) without any adjustable parameters and approximations. To include constraint release, we use the scheme proposed by Rubinstein and C...

Comparison of the Structure of Polyelectrolyte Multilayer Films Exhibiting a Linear and an Exponential Growth Regime: An in Situ Atomic Force Microscopy Study

Abstract: We report here on the structural characterization of polyelectrolytes multilayer films formed by poly(l-glutamic acid) and poly(l-lysine) (PGA/PLL). The growth of this system is compared to that of poly(styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) multilayers by means of in situ atomic force microscopy (AFM) and by optical waveguide lightmode spectroscopy (OWLS). In contrary to the (PSS/PAH)i films that are growing linearly with the number of deposited layer pairs i, optical data evidenced that the (PGA/PLL)i films are characterized by an exponential growth. The analysis of the structure of the (PSS/PAH)i films reveals a smooth featureless surface covered by small globules. On the other hand, (PGA/PLL)i films form extended structures that appear with a vermiculate pattern. We propose a new growth mechanism based on polyelectrolyte diffusion in and out of the film coupled to the formation of polyanion/polycation complexes at the surface of the film in order to explain the whole results.

Layered, erasable polymer multilayers formed by hydrogen-bonded sequential self-assembly

Abstract: Robust multilayers can be formed on solid surfaces, and subsequently destroyed by changing the environmental conditions, by the layer-by-layer sequential assembly of monomolecular films of a polyacid and polybase from aqueous solution. Interlayer hydrogen bonding produces stable multilayers up to the point where altered pH or other environmental stimulus introduces an unacceptably large electrical charge within them. This is demonstrated for the polyacids poly(acrylic acid), PAA, and poly(methacrylic acid), PMAA, and for the polybases poly(vinylpyrrolidone), PVPON, and poly(ethylene oxide), PEO, in D2O. The adsorption was quantified by Fourier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR). The ratio between suppressed ionization of the carboxylic groups within the film and their ionization in solution, as directly measured by FTIR-ATR, was used to estimate the fraction of hydrogen-bonded carboxylic groups; this was ∼0.5 in PVPON/PMAA but only ∼0.1 in the PEO/PMAA system, though...

Molecular Weight Dependence of Polymersome Membrane Structure, Elasticity, and Stability

Abstract: Vesicles prepared in water from a series of diblock copolymers“polymersomes”are physically characterized. With increasing molecular weight Mn, the hydrophobic core thickness for self-assembled bilayers of poly(ethylene oxide)−polybutadiene increases up to ∼20 nm, which is considerably greater than any previously studied lipid or polymersome system. Micromanipulation of vesicles demonstrates an interface-dominated elasticity that is independent of Mn. Furthermore, membrane stability as defined by the maximal areal strain increases with Mn, approaching a universal limit predicted by mean-field ideas and set by the interfacial tension. Nonlinear responses and memory effects also emerge with increasing Mn, indicating the onset of chain entanglements at higher Mn. The results highlight the interfacial limits and transitions to bulk responses of self-assemblies.

Reinforcement Mechanism of Nanofilled Polymer Melts As Elucidated by Nonlinear Viscoelastic Behavior

Abstract: Nonlinear viscoelastic properties are reported for composites of fumed silica with various surface treatments and matrices of poly(vinyl acetate) of different molecular weights as well as a copolymer matrix of vinyl acetate and vinyl alcohol. Data above the glass transition temperature are reported here. The increase in the composite storage and loss moduli measured at low strains, and their relative rates of decrease with strain, are found to depend on filler surface treatment. The nonlinear behavior of the loss factor with strain is dramatically altered by filler treatment and quite revealing as to the likely mechanism causing the nonlinearity. In addition, the relative reinforcement and the degree of nonlinearity are found to be the highest for the lowest molecular weight matrices. The effect of copolymer substitution for the homopolymer matrix is equivalent to an increase in molecular weight. The primary underlying mechanism for reinforcement and nonlinear behavior appears to be the filler−matrix inte...

Novel Sulfonated Polyimides as Polyelectrolytes for Fuel Cell Application. 1. Synthesis, Proton Conductivity, and Water Stability of Polyimides from 4,4‘-Diaminodiphenyl Ether-2,2‘-disulfonic Acid

Abstract: A sulfonated diamine monomer, 4,4‘-diaminodiphenyl ether-2,2‘-disulfonic acid (ODADS), was successfully synthesized by direct sulfonation of a commercially available diamine, 4,4‘-diaminodiphenyl ether (ODA), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated polyimides were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), ODADS, and common nonsulfonated diamines. The resulting sulfonated polyimides displayed much better stability toward water than those derived from the widely used sulfonated diamine 2,2‘-benzidinedisulfonic acid (BDSA). This is because ODADS-based polyimide membranes have a more flexible structure than the corresponding BDSA-based ones. Fenton's reagent test revealed that ODADS-based polyimide membranes also had fair good stability to oxidation. Polyimide membranes with good water stability as well as high proton conductivity were developed. NTDA−ODADS/BAPB(1/1) copolyimide membrane (BAPB refers to 4,4‘-bis(4-aminophenoxy)biphenyl)), for ex...

Molecular dynamics simulation of a polymer melt with a nanoscopic particle

Abstract: We perform molecular dynamics simulations of a bead−spring polymer melt surrounding a nanoscopic particle. We explore the effect of the polymer/nanoparticle interactions, surface-to-volume ratio, and boundary conditions on both the structure and dynamics of the polymer melt. We find that the chains near the nanoparticle surface are elongated and flattened and that this effect is independent of the interaction for the range of interactions we study. We show that the glass transition temperature Tg of the melt can be shifted to either higher or lower temperatures by tuning the interactions between polymer and nanoparticle. A gradual change of the polymer dynamics approaching the nanoparticle surface causes the change in the glass transition. The magnitude of the shift is exaggerated by increasing fraction of surface monomers in the system. These behaviors support a “many-layer”-based interpretation of the dynamics. Our findings appear applicable to systems in which surface interactions dominate, including b...

Evidence of elongated polymeric aggregates in Nafion

Abstract: Small-angle X-ray and neutron-scattering techniques have been used to probe the structure of swollen Nafion membranes in the range 10−10000 A. From analyzing the scattering data as a function of the polymer volume fraction and using a contrast variation method for the neutron experiments, we suggest a new structural model of Nafion in the hydrated state. It is based on the aggregation of the ionomer chains into elongated polymeric bundles with a diameter on the order of 40 A and a length larger than 1000 A, surrounded by the electrolyte solution.

Synthesis, Structure, and Properties of PBO/SWNT Composites &

Abstract: Poly(p-phenylene benzobisoxazole) (PBO) has been synthesized in the presence of single-wall carbon nanotubes (SWNTs) in poly(phosphoric acid) (PPA) using typical PBO polymerization conditions. PBO and PBO/SWNT lyotropic liquid crystalline solutions in PPA have been spun into fibers using dry-jet wet spinning. The tensile strength of the PBO/SWNT fiber containing 10 wt % SWNTs is about 50% higher than that of the control PBO fibers containing no SWNTs. The structure and morphology of these fibers have been studied.

Influence of Crystallization on Intercalation, Morphology, and Mechanical Properties of Polypropylene/Clay Nanocomposites

Abstract: Intercalated nanocomposites of polypropylene (PP)/clay (PPCNs) were prepared by a melt extrusion process using maleic anhydride modified PP (PP-MA) and organophilic clay The extent of intercalation of PP-MA chains in the space between silicate galleries increased with crystallization temperature Tc and decreased as clay content increased As compared to matrix PP-MA, the dispersed clay particles in the PP-MA matrix acted as a nucleating agent and lowered the spherulite dimension with increasing clay content as revealed by light scattering experiments and polarizing optical microscopy The PPCN crystallized at high Tc showed that a certain extent of segregation of the dispersed clay particles takes place around the boundary of the spherulites (interspherulite) Extensive intercalation occurred during crystallization, especially at high Tc due to the long time for full solidification of the melt The degree of intercalation of PP-MA chains in the silicate galleries strongly depends on the time in the molte

ATRP of Amphiphilic Graft Copolymers Based on PVDF and Their Use as Membrane Additives

Abstract: The direct preparation of amphiphilic graft copolymers from commercial poly(vinylidene fluoride) (PVDF) using atom transfer radical polymerization (ATRP) is demonstrated. Here, direct initiation of the secondary fluorinated site of PVDF facilitates grafting of the hydrophilic comonomer. Amphiphilic comb copolymer derivatives of PVDF having poly(methacrylic acid) side chains (PVDF-g-PMAA) and poly(oxyethylene methacrylate) side chains (PVDF-g-POEM) are prepared using this method. Surface segregation of PVDF-g-POEM additives in PVDF is examined as a route to wettable, foul-resistant surfaces on PVDF filtration membranes. Because of surface segregation during the standard immersion precipitation process for membrane fabrication, a PVDF/5 wt % PVDF-g-POEM membrane, having a bulk POEM concentration of 3.4 wt %, exhibits a near-surface POEM concentration of 42 wt % as measured by X-ray photoelectron spectroscopy (XPS). This membrane displays substantial resistance to BSA fouling compared with pure PVDF and wets...

Modes of Crystallization in Block Copolymer Microdomains: Breakout, Templated, and Confined

Abstract: We examined the melt and solid-state structures of a series of diblock copolymers containing polyethylene as the minority block, with a rubbery hydrocarbon majority block. When the interblock segregation strength during crystallization is sufficiently high (approximately 3 times the segregation strength at the order−disorder transition), crystallization can be effectively confined within spherical domains formed by microphase separation in the melt; the process is homogeneously nucleated, and the resulting kinetics are first-order (Avrami n = 1). Below this critical interblock segregation strength, crystallization disrupts the spherical microdomains, resulting in sigmoidal kinetics (n > 1). Cylinder-forming materials are more complex: there exists a range of intermediate segregation strength where crystallization is templated but not wholly confined within the nanoscale domains prescribed by microphase separation; while the melt morphology is generally retained on cooling, local distortions and connectio...

Poly(ethylene glycol)-Conjugated PAMAM Dendrimer for Biocompatible, High-Efficiency DNA Delivery

Abstract: We demonstrate a simple and successful synthetic approach to devise a highly efficient DNA delivery system with low cytotoxicity and low cost. Polyamidoamine (PAMAM) dendrimer is a highly efficient DNA delivery agent, when compared to other chemical transfection reagents. Partially degraded, high-generation dendrimers offer even higher efficiency, presumably due to enhanced flexibility of the otherwise rigid dendrimer chains.1 We hypothesized that chemical modification of low generation dendrimer with biocompatible poly(ethylene glycol) (PEG) chains would create a conjugate of PAMAM core with flexible PEG chains, which mimics the fractured high-generation dendrimer and produces high transfection efficiency. Generation 5 PAMAM was modified with 3400 molecular weight PEG. The novel conjugate produced a 20-fold increase in transfection efficiency compared with partially degraded dendrimer controls. The cytotoxicity of PEGylated dendrimers was very low. This extremely efficient, highly biocompatible, low-cost...

Evidence for the Shift of the Glass Transition near the Particles in Silica-Filled Elastomers

Abstract: Filled elastomers exhibit a complex dependence of their viscoelastic modulus as a function of both temperature and frequency. Otherwise, recent observations on thin polymer films have shown that their glass transition temperature depends on their thickness. On the basis of these recent results and on a recent model, we propose that the mechanical behavior of the filled elastomer is strongly influenced by a gradient of the glass transition temperature in the vicinity of the particles. This allows us to suggest a specific temperature−frequency superposition law for filled rubbers. This law seems to apply very successfully on two systems with different dispersion qualities, revealing the existence of a glass transition temperature gradient in the vicinity of the particles.

Synthesis of shell cross-linked micelles with pH-responsive cores using ABC triblock copolymers

Abstract: A series of well-defined poly[(ethylene oxide)-block-2-(dimethylamino)ethyl methacrylate-block-2-(diethylamino) methacrylate] (PEO−DMA−DEA) triblocks were synthesized by successive ATRP polymerization of DMA and DEA monomers using PEO-based macroinitiators of different molecular weights. These triblock copolymers dissolved molecularly in aqueous solution at low pH; on addition of NaOH, micellization occurred at pH 7.1 to form three-layer “onionlike” micelles comprising DEA cores, DMA inner shells, and PEO coronas. Above pH 7.3, dynamic light scattering studies indicated unimodal, near-monodisperse populations, with mean micelle diameters of 27−84 nm depending on block compositions (for PEO113 triblock copolymers) and polydispersities typically less than 0.10. The average hydrodynamic diameter Dh of the micelles decreased as the solution pH was increased from pH 7.3 to pH 9.0, indicating that the micelles become more compact due to deprotonation of the tertiary amine residues in the DMA and DEA blocks. 1H NMR studies supported a three-layer micelle structure and also revealed changes in the hydrophilicity of the DMA chains in the inner shell during cross-linking, which was achieved by adding the bifunctional alkyl iodide, 1,2-bis(2-iodoethoxy)ethane (BIEE). Selective quaternization of the DMA residues by the BIEE leads to increased hydrophilicity and colloid stability for the shell cross-linked (SCL) micelles. The minimum amount of BIEE required to “lock-in” the micellar structure depended on the thickness of the PEO corona: shorter PEO chains led to enhanced cross-linking efficiency. At pH 8.5, the hydrodynamic diameter of un-cross-linked micelles increased rapidly above 40−50 °C due to the LCST behavior of the neutral DMA chains in the inner shell. In contrast, the dimensions of the SCL micelles in dilute aqueous solution are independent of temperature. These SCL micelles exhibit reversible swelling on varying the solution pH. At low pH, the DEA cores become protonated and hence hydrophilic. The effect of varying the block composition and the target degree of cross-linking on the structural stability and pH-dependent (de)swelling of the SCL micelles was systematically studied. Longer DEA blocks and lower target degrees of cross-linking led to increased swellability, as expected.

Synthesis of Polymer Brushes on Silicate Substrates via Reversible Addition Fragmentation Chain Transfer Technique

Abstract: Reversible addition fragmentation chain transfer (RAFT) has been used to synthesize polymer brushes. Styrene, methyl methacrylate, and N,N-dimethylacrylamide brushes were prepared under RAFT conditions using silicate surfaces that were modified with surface-immobilized azo initiators. Films with controlled thicknesses were produced. RAFT was also used to synthesize PS-b-PDMA and PDMA-b-PMMA block copolymer brushes that displayed reversible surface properties upon treatment with block-selective solvents.

Role of Competitive PEO−Water and Water−Water Hydrogen Bonding in Aqueous Solution PEO Behavior

Abstract: The behavior of aqueous solutions of poly(ethylene oxide) (PEO) is studied theoretically by applying a mean field-like approach which includes the effect of the competition of PEO and water as proton acceptors in hydrogen bond formation. Accounting for this effect is of crucial importance for a correct description of all solution properties. We calculate the temperature and concentration dependence of the average fraction of hydrogen bonds between PEO and water and find very good agreement between our predictions and experimental or MD simulation data. We also make predictions concerning the temperature behavior of the second virial coefficient A2 and the effective interaction parameter χeff and compare it with experimental data. We found that the decrease of A2 with temperature is caused by the delicate balance of the opposing effects of water−PEO and water−water hydrogen bonding. The phase diagram for PEO of different molecular weights in water is calculated using experimentally reported data for the en...

Functionalization of Carbon Nanotubes with Polystyrene

Abstract: Single-walled and multiple-walled carbon nanotubes were functionalized with a polystyrene copolymer, poly(styrene-co-p-(4-(4‘-vinylphenyl)-3-oxabutanol)). The functionalization reaction conditions ...

Elasticity of Polymer Networks

Abstract: We develop and solve a new molecular model for nonlinear elasticity of entangled polymer networks. This model combines and generalizes several succeseful ideas introduced over the years in the field of the rubber elasticity. The topological constraints imposed by the neighboring network chains on a given network are represented by the confining potential that changes upon network deformation. This topological potential restricts fluctuations of the network chain to the nonaffinely deformed confining tube. Network chains are allowed to fluctuate and redistribute their length along the contour of their confining tubes. The dependence of the stress σ on the elongation coefficient λ for the uniaxially deformed network is usially represented in the form of the Mooney stress, f*(1/λ) = σ/(λ − 1/λ2). We find a simple expression for the Mooney stress, f*(1/λ) = Gc + Ge/(0.74λ + 0.61λ-1/2 − 0.35), where Gc and Ge are phantom and entangled network moduli. This allows one to analyze the experimental data in the form...

Effective ab Initio Emulsion Polymerization under RAFT Control

Abstract: Emulsion polymerization offers consider-able advantages for such industrial synthesis. Hitherto,attempts to implement RAFT in ab initio (unseeded)emulsion have met with problems such as loss ofmolecular weight control, loss of colloidal stability, and/or formation of an intractable oily layer (e.g., ref 2).Various reasons for these problems have been suggested(e.g., refs 2 and 3), including hydrolysis of the RAFTagent, poor transport of RAFT agent through the waterphase, and formation of oligomers in droplets (i.e.,droplet polymerization) arising from the presence ofRAFT agent therein. On the other hand, it has provedpossible to eliminate all these problems by performingRAFT in a seeded emulsion polymerization using a (78nm diameter) seed and a highly hydrophobic RAFTagent which was transported to the seed particles usingacetone, the acetone being subsequently removed byrotary evaporation prior to polymerization.

The Full Phase Behavior for Block Copolymers in Solvents of Varying Selectivity

Abstract: The phase behavior of six poly(styrene-b-isoprene) (SI) diblock copolymers has been mapped out in the styrene-selective solvents di-n-butyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The polymer molecular weights were chosen to make the melt order−disorder transition (ODT) experimentally accessible, and the styrene compositions f ranged from 0.23 to 0.70, to access the full range of melt morphologies. For each polymer a phase diagram was constructed, with polymer volume fractions, φ, ranging from 0.01 to 1.0 and temperatures, T, from 0 to 250 °C. Phase assignments were based on small-angle X-ray scattering (SAXS), and the ODTs and order−order transitions (OOTs) were located by a combination of SAXS, rheology, and static birefringence. The critical micelle temperatures (cmt) in dilute solution were determined by dynamic light scattering. In this manner the full “phase cube” was mapped out in each solvent, enabling generation of phase maps (φ,f) at constant T and (f,T) at consta...

Synthesis, nanostructures, and functionality of amphiphilic liquid crystalline block copolymers with azobenzene moieties

Abstract: A series of liquid crystalline (LC) homopolymers of poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate}containing an azobenzene mesogen with different degrees of polymerization were synthesized by using the atom transfer radical polymerization (ATRP) method. The homopolymers were prepared with a range of number-average molecular weights from 6100 to 23 500 with narrow polydispersities of less than 1.17. Thermal investigation showed that the homopolymers exhibit monolayer smectic A, smectic C, and an unknown smectic X phases. The transition temperatures increase slightly with the increase of the molecular weights and level off at around 21 500. Novel amphiphilic LC-coil diblock copolymers with a defined length of a flexible poly(ethylene glycol) segment as the hydrophilic coil were also prepared by the ATRP method. The LC-coil diblock copolymers exhibit narrow polydispersities of less than 1.11. Morphologies of the thin films of the block copolymers were investigated by using transmission electron m...

Novel sulfonated polyimides as polyelectrolytes for fuel cell application. 2. Synthesis and proton conductivity of polyimides from 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid

Abstract: A new sulfonated diamine monomer, 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid (BAPFDS), was synthesized by direct sulfonation of the parent diamine, 9,9-bis(4-aminophenyl)fluorene (BAPF), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated polyimides with different sulfonation degrees were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), BAPFDS, and common nonsulfonated diamines. The resulting sulfonated polyimides generally showed good solubility in m-cresol and DMSO. Proton conductivities of these polyimide membranes were measured as the functions of relative humidity and temperature. The resulting homopolyimide, NTDA-BAPFDS, displayed proton conductivities quite similar to those of Nafion 117 in the whole humidity range (RH < 100%). At 100% relative humidity, all the BAPFDS-based polyimide membranes showed proton conductivities similar to or higher than those of Nafion 117. In addition, BAPFDS-based polyimide membranes exhibited much better water sta...