Yoshiharu Tsujita

Gas sorption and permeation of glassy polymers with microvoids

Gas sorption and permeation of physically treated glassy polymeric membranes is studied from the viewpoint of the transport mechanism and the control of microvoids in the membrane. Physical treatments, such as sub-Tg annealing, thermal quenching, and CO2 pressure conditioning were found to be effective for the control of microvoids in the glassy state, as well as gas sorption and permeation. The Langmuir saturation constant C′H of the dual-mode sorption model decreased with a sub-Tg annealing period for the copolymer (vinylidene cyanide-alt-vinyl acetate), copoly(VDCN–VAc). On the other hand, Henrys solubility coefficient kD and Langmuir affinity constant b did not change markedly with sub-Tg annealing. The permeability coefficient of copoly(VDCN–VAc) decreased with the sub-Tg annealing period. Furthermore, the dual-mode parameter C′H and the CO2 permeability coefficient of polyamic acid, polyimide, poly(2,6-dimethyl-1,4-phenylene oxide), and polycarbonate increased markedly upon thermal quenching and CO2 pressure conditioning from the liquid state. The gas sorption isotherm and pressure dependence of the permeability coefficients for the polymers studied here are explained in terms of the dual-mode sorption model and partial immobilization model characteristic to a glassy polymer, respectively. It was found that sub-Tg annealing, thermal quenching, and CO2 pressure conditioning control gas sorption and permeation, as well as the occurrence of microvoids in glassy polymeric membranes.

Study on δ-form complex in a syndiotactic polystyrene/organic molecules system, 1: Preferential complexing behavior of xylene isomers

To investigated the preferential complexing behavior of isomeric xylenes, syndiotactic polystyrene (sPS) membranes are prepared using varying compositions of p- and m-xylene. Complex formation between sPS and xylenes was studied by means of thermogravimetric and FT-IR analyses to determine the exact amounts of solvent molecules present per styrene repeating unit. A preferential complexing ability of p-xylene was revealed due to its favorable interaction with sPS.

Analysis of gas transport properties of PPO/PS blends by 129Xe NMR spectroscopy

Abstract Relationships among variations of microvoids and gas transport properties for miscible poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)/polystyrene (PS) blends in the glassy state have been investigated by Xe sorption, Xe permeation, and 129 Xe NMR measurements. Xe sorption isotherms of the blends can be interpreted successfully on the basis of the dual-mode sorption model. Decrease in the permeability of Xe is attributed to the decrease in the diffusivity of that in the Langmuir site. 129 Xe NMR spectra of 129 Xe in the blends show non-linear low-field shift with increasing sorption amount of Xe because of a fast exchange of Xe atoms between Henry and Langmuir sites. From the analysis of 129 Xe NMR chemical shifts, it is found that the mean volume of individual microvoids varies with a negative deviation against volume fraction of PPO in the blend. For PPO/PS blends, it has been clarified that the contraction of individual microvoids occurs by blending and highly affects gas transport properties.

Control of gas permeability for cellulose acetate membrane by microwave irradiation

Abstract It can be expected that a microwave acts as an accelerator of the mobility of polar functional groups such as hydroxyl groups in polymeric membranes, and then gas permeability improves because of the increasing free volume and/or temperature of the membranes. The permeability coefficients of CO 2 for a cellulose acetate (CA) membrane were measured at 25°C using a hand-made apparatus which can irradiate a microwave (2,450 MHz) to the membrane. Both the permeability and diffusion coefficients of CO 2 for CA membranes are increased by irradiation of the microwave, and degree of enhancement increased with power of the microwave.

Characterization of microvoids in PPO/PS polymer blend by means of 129Xe NMR spectroscopy☆

Abstract Relationships among 129 Xe NMR chemical shift, Xe sorption properties, and density have been investigated for poly(2,6-dimethyl-1,4-phenylene oxide) / polystyrene miscible blend system in order to evaluate the variation of microvoids by blending. Xe sorption isotherms of all samples have been explained successfully on the basis of the dual-mode sorption model. Xe sorption properties and densities of blended samples have indicated the reduction of microvoids by blending. 129 Xe NMR chemical shifts of 129 Xe sorbed in each sample have shown a non-linear low-field shift with increasing total amount of Xe sorption. Estimation of the microvoids by 129 Xe NMR spectroscopy has been consistent with the results of density and Xe sorption measurements.

Study on complexing behavior of the syndiotactic polystyrene-aromatic hydrocarbon system

Guest molecular dynamics related to the stable complexing behavior of syndiotactic polystyrene (sPS)-xylene isomer (m- and p-xylene, abbreviated MX and PX) complexes have been characterized by solid-state 13 C-NMR spectroscopy. Similar chemical shifts are observed for both sPS complexes in the 13 C-CP/MAS spectrum. Interestingly, the solvent resonance of methyl carbon could be observed under CP conditions, indicating the relative rigidity of the solvent. Inversely, the sPS-MX system showed doublet peaks at 21.8 and 23.2 ppm when compared with the atactic PS-MX system, suggesting the orderly arrangement of the methyl group in the complexed system. The mobility of the guest molecule in the system is evaluated using spin-lattice relaxation time (T 1 c). Moreover, the mobility of helical chains of sPS is also inferred from its T 1 c. Hence, the influence of the mobility of the methyl carbon of xylene and the sPS helical chain could be investigated, which helps in studying the complexing behavior of the sPS-xylene system.

Evaluation of thermal stability of syndiotactic polystyrene/toluene complex by spectroscopic analysis☆

Abstract The syndiotactic polystyrene membranes containing the δ-form which is a clathrated crystal with some solvent molecules as a guest and so-called “complex”, were prepared by casting from its toluene solution at 85°C and room temperature. In order to evaluate the thermal stability of the complex in the two membranes, WAXD and time-resolved FT-IR measurements at various temperatures were performed. WAXD profiles suggested that the content of the complex in the membrane cast at room temperature was higher than that in one cast at 85°C. The transformation from TTGG helical to TT planar conformation were observed for the both membranes, but only above 190°C for the membrane cast at room temperature, indicating the retention of the helical conformation at a wide range of temperature.