Statistical thermodynamics of polydisperse polymer systems in the framework of lattice fluid model: Effect of molecular weight and its distribution on the spinodal in polymer solution

With the aid of thermodynamics of Gibbs, the expression of the spinodal was derived for the polydisperse polymer-solvent system in the framework of Sanchez-Lacombe Lattice Fluid Theory (SLLFT). For convenience, we considered that a model polydisperse polymer contains three sub-components. According to our calculation, the spinodal depends on both weight-average ((M) over bar (w)) and number-average ((M) over bar (n)) molecular weights of the polydisperse polymer, but the z-average molecular weight ((M) over bar (z)) dependence on the spinodal is invisible. The dependence of free volume on composition, temperature, molecular weight, and its distribution results in the effect of (M) over bar (n) on the spinodal. Moreover, it has been found that the effect of changing (M) over bar (w) on the spinodal is much bigger than that of changing (M) over bar (n) and the extrema of the spinodal increases with the rise of the weight-average molecular weight of the polymer in the solutions with upper critical solution temperature (UCST). However, the effect of polydispersity on the spinodal can be neglected for the polymer with a considerably high weight-average molecular weight. A more simple expression of the spinodal for the polydisperse polymer solution in the framework of SLLFT was also derived under the assumption of upsilon(*)=upsilon(1)(*)=upsilon(2)(*) and (1/r(1)(0))-(1/r(2i)(0))-->(1/r(1)(0)).

Gas transport properties of novel cardo poly(aryl ether ketone)s with pendant alkyl groups

Gas transport of hydrogen, oxygen, nitrogen, carbon dioxide, and methane in four cardo poly(aryl ether ketone)s containing different alkyl substituents on the phenyl ring has been examined from 30 to 100 degrees C. The permeability, diffusivity, solubility, and their temperature dependency were studied by correlations with gas shape, size, and critical temperature as well as polymeric structural factors including glass transition, secondary transition, cohesive energy density, and free volume. The bulky, stiff cardo and alkyl groups in tetramethyl-substituted TMPEK-C resulted in increased H-2 permeability (by 55%) and H-2/N-2 permselectivity (by 106%) relative to bisphenol A polysulfone (PSF). Moreover, the weak dependence of gas transport on temperature in TMPEK-C made it maintain high permselectivities (alpha(H2/N2) in 68.3 and alpha(O2/N2) in 5.71) up to 100 degrees C, exhibiting potential for high-temperature gas separation applications.

Mechanical relaxation time of comblike polymer electrolyte

Using poly(styrene-co-maleic anhydride) as the backbone and poly(ethylene glycol) methyl ether as side chains,three kinds of comblike polymers of different side chain length were synthesized. The Li-salt complexes and their firms were prepared. The dynamic mechanical properties were investigated. It was found that the main chain was rigid and the side chain was flexible in this comblike polymer system. Based on the time-temperature equivalence principle, a master curve was constructed. By selecting T-alpha as reference temperature, Arrhenius plots of shift factor and iso-free-volume plots were attained. The values of WLF parameters C-1 and C-2 increase with increasing salt concentration. By reference to T-0 = 50 degrees C, the relation between the average relaxation time 1g tau(c) and Li-salt concentration C is linear. The master curves are displaced progressively to higher frequencies as the M-w of side chains is increased. The relation between the average relaxation time 1g tau(n) and M-w of side chains is also linear. And the master curves are movable with the change of salts. It shows the effect of different kinds of salt on relaxation time.

Gas and water vapor transport through a series of novel poly(aryl ether sulfone) membranes

The permeation behavior of water vapor, H-2, CO2, O-2, N-2, and CH4 gases in a series of novel poly(aryl ether sulfone)s has been examined over a temperature range of 30-100 degreesC. These polymers include four alkyl-substituted cardo poly(aryl ether sulfone)s and four intermolecular interaction enhanced poly(aryl ether sulfone)s. Their water vapor and gas transport properties were compared to the unmodified cardo poly(aryl ether sulfone) (PES-C). It was found that the bulky alkyl substituents on the phenylene rings were advantageous for gas permeability, while the intermolecular hydrogen bonds and ionic bonds resulted in a considerable increase in gas permselectivity. The causes of the trend were interpreted according to free volume, interchain distance, and glass transition temperature, together with the respective contribution of gas solubility and diffusivity to the overall permeability. Of interest was the observation that IMPES-L, which simultaneously bears bulky isopropyl substituent and pendant carboxylic groups, displayed 377% higher O-2 permeability and 5.3% higher O-2/N-2 permselectivity than PES-C. Furthermore, sodium salt form PES-Na+ and potassium salt form PES-K+ exhibited water vapor permeability twice as high as PES-C and H2O/N-2 selectivity in 10(5) order of magnitude.

The effects of physical ageing on crazing of polyphenylquinoxaline films

The effects of physical ageing on the crazing of polyphenylquinoxaline (PPQ-E) films were studied. The DSC endothermic peak at the glass transition region of the samples was interpreted in terms of the cohesional entanglement theory. The free volume cavity size and free volume intensity of the samples were characterized by positron annihilation life spectroscopy. The difference in free volume cavity size and free volume intensity between two samples reflect the strength and density of cohensional entanglement point. The critical strain for craze initiation and craze stability depended on physical ageing of the samples. The relationships between physical ageing and crazing were interpreted initially.

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) has been investigated. Heat flow responses were measured after annealing the amorphous samples obtained by quenching the melt into an ice-water bath close to, but below, the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process, which was estimated by a Williams-Watt expression, is similar in magnitude to that obtained for the cold crystallization for the aged samples. The quenched glass is a metastable glass. The conformation of molecular chains rearranges with physical aging which results in the formation of a denser packing in the amorphous phase. The dense amorphous phase may form an initial nucleus for crystallization. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant n is about 2. An Arrhenius expression was used to evaluate the activation energy of relaxation upon physical aging and the activation energy of transportation upon isothermal crystallization. The activation energy of relaxation is similar in magnitude to that of crystallization for aged samples. Results obtained are interpreted as kinetic effects associated with the glass formation process.

Physical aging and crystallization of amorphous poly(aryl ether ether ketone ketone)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) was investigated. Heat flow responses were measured after annealing the amorphous samples that were obtained by quenching the melt into an ice-water bath at just below the glass transition temperature. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant it is about 2. An Arrhenius form was used to evaluate the relaxation activation energy of physical aging and the transport activation energy of isothermal crystallization. The activation energy of physical aging was similar in magnitude to that observed for the temperature dependence of crystallization under conditions of transportation control. Results obtained were interpreted as purely kinetic effects associated with the glass formation process. (C) 1998 John Wiley & Sons, Inc.

Barrier properties of vinylidene chloride methyl acrylate copolymer

A series of vinylidene dichloride (VDC) copolymers with methyl acrylate (MA) as comonomer (3-12wt%), was prepared by free-radical suspension copolymerization. The permeability coefficients of the copolymers to oxygen and carbon dioxide were measured at 1.0 MPa and at 30 degrees C, and those to water vapor were measured at 30 degrees C and 100% relative humidity. All the VDC/MA copolymers studied are semicrystalline. As the MA content increases, the permeability coefficients of the copolymers to oxygen, carbon dioxide, and water vapor are progressively increased, caused by decrease in crystalline fraction and increase in free volume of VDC/MA copolymers.

Barrier property and structure of acrylonitrile/acrylic copolymers

A series of acrylonitrile (AN) copolymers with methyl acrylate (MA) or ethyl acrylate (EA) as comonomer (5-23 wt%) was prepared by free-radical copolymerisation. The permeability coefficients of the copolymers to oxygen and carbon dioxide were measured at 1.0 MPa and at 30 degrees C, and those to water vapor also measured at 100% relative humidity and at 30 degrees C. All the AN/acrylic copolymers are semicrystalline. As the acrylate content increase, the permeability coefficients of the copolymers to oxygen and carbon dioxide are increased progressively, but those to water vapor are decreased progressively. The gas permeability coefficients of the polymers were correlated with free-volume fractions or the ratio of free volume to cohesive energy.

Ion-conducting polymers based on modified alternating maleic anhydride copolymer with oligo(oxyethylene) side chains

Comb-like polymers (CPs) based on modified alternating methyl vinyl ether/maleic anhydride copolymer with oligo(oxyethylene) side chains of the type -O(CH2CH2O)(n)CH3 were synthesized and characterized, and complexed with lithium salts to form amorphous polymer electrolytes. Maximum conductivity close to 1.38 x 10(-4) S/cm was achieved at room temperature and at a [Li]/[EO] ratio (EO = ethylene oxide) of about 0.066. The temperature dependence of ionic conductivity suggested that the ion transport was controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel-Tammann-Fulcher plots. The ionic conductivity maximum moved to a higher salt concentration as the temperature increased, indicating that a larger number of charge carriers can be transferred through polymer chains, of which free volume is increased at higher temperature. IR results indicated that the ester in CPs might decompose at 140 degrees C and reproduce the maleic anhydride ring.

Novel poly(aryl ether ketone)s containing various pendant groups .2. Gas-transport properties

The gas transport of hydrogen, oxygen, nitrogen, carbon dioxide, and methane gases in a series of poly(aryl ether ketone)s was examined. These polymer membranes have a wide range of permeability coefficients and permselectivity coefficients, showing excellent gas-transport properties. The enhanced interchain interaction in the polymers due to intermolecular hydrogen bonds and ionic bonds results in a considerable increase in permselectivity but a decrease in permeability. On the contrary, the polymers with bulky arkyl substituents show significantly increased permeability. The causes of this trend are interpreted in terms of the free volume, interchain distance, and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall permeability. Of interest is the observation that the ionomer IMPEK-K+, which simultaneously contains bulky isopropyl substituents and pendant carboxylate groups, exhibits over twice higher CO2 permeability and 15% higher CO2/CH4 permselectivity than those of bisphenol-A p'olysulfone (PSF). The possibility of using the new synthesized poly(aryl ether ketone)s in gas separation membrane application is also discussed. (C) 1997 John Wiley & Sons, Inc.

Gas transport property of homo- and copolyimides from isomeric thiaphthalic dianhydride and oxydianiline

Gas transport properties of home- and copolyimides prepared from 3,3',4,4'- and 2,2',3,3'-thiaphthalic dianhydride (p-TDPA and m-TDPA, respectively) with 4,4-oxydianiline (ODA) were investigated. The fractional free volume of m-TDPA-ODA is larger than that of p-TDPA-ODA, and the chain segmental mobility of the former is lower than that of the latter. The permeability coefficients of m-TDPA-ODA to H-2, CO2, and O-2 are more increased by 48, 69 and 75%, at 30 degrees C and 10 atm, respectively, than those of p-TDPA-ODA; but the permselectivities of m-TDPA-ODA for H-2, CO2, and O-2 toward N-2 are more decreased by 33, 77, and 26%, respectively, than those of p-TDPA-ODA. The permeability coefficients and the diffusion coefficients of the copolyimides can be described by the following equations: log P = Phi(p) log P-p + Phi(m), log P-m and log D-a = D-a = Phi(p) log(D-alpha)(p) + Phi(m) log(D-a)(m), respectively. The variation of the permselectivity is controlled predominantly by diffusivity selectivity. These observations are interpreted in terms of variations in the fractional free volume of polyimides. (C) 1997 John Wiley & Sons, Inc.

Study on diffusion of electroactive species in polyelectrolyte polyethylene glycol lithium perchlorate by chronoamperometry at a microdisk electrode

The mass transport dynamics of Ferrocene in polyelectrolyte polyethylene glycol lithium perchlorate (PEG . LiClO4) was studied by using chronoamperometry at a microdisk electrode. Chronoamperometry is a powerful method for the study of mass transport in polyelectrolyte, it has many advantages over the conventional methods at a microelectrode and the steady-state method at an ultramicroelectrode. By using this method the apparent diffusion coefficient D-app and concentration C-a of the electroactive species, can be estimated from a single experiment without previous knowledge of either one. We have estimated D-app and C-a of ferrocene in PEG . LiClO4 polyelectrolyte from 25 degrees C to 75 degrees C. The dependence on the concentration of electroactive species was observed. The diffusion coefficients decrease with increasing ferrocene concentration and decreasing temperature. The mass transport mechanism is explained, by using a free volume model.

Gas permeation properties of copolyimides from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride

A series of aromatic copolyimides was prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride (6FDA) with 3,3'-dimethyl-4,4'-methylene dianiline (DMMDA) by a chemical imidization. The gas permeability coefficients of the copolyimides to H-2, CO2, O-2, N-2 and CH4 were measured under 7 atm. pressure. The fractional free volume of 6FDA-DMMDA is larger than that of HQDPA-DMMDA, while the chain segmental mobility of 6FDA-DMMDA is lower than that of HQDPA-DMMDA. The gas permeability of 6FDA-DMMDA is much higher than that of HQDPA-DMMDA but the permselectivity of 6FDA-DMMDA for H-2, CO2, O-2, N-2 over CH4 is lower than that of HQDPA-DMMDA. The experimental values of the gas permeability coefficients of the copolyimides are in satisfactory agreement with the values estimated from the gas permeability coefficients of the constituent homopolyimides and their weight fractions.

A study of the dependence of ferrocene diffusion on chain length in polymer electrolytes

The diffusion rates of ferrocene have been estimated in five kinds of poly(ethylene glycol) solution, containing the electrolyte LiClO4, by using non-steady-state chronoamperometry. The D-app of ferrocene increases with increasing temperature, and the dependency of D-app on temperature obeys the Williams-Landel-Ferry equation. The D-app of ferrocene decreases with increasing polymer chain length. Both the chain length and temperature dependence conform to a simple free volume model. A relation between current and polymer chain length is suggested at room and high temperatures.