Tsukasa Miyazaki

Relationships between the chemical structures and the solubility, diffusivity, and permselectivity of propylene and propane in 6FDA‐based polyimides

The solubility, diffusivity, and permselectivity of propylene and propane in 40 different polyimides synthesized from 2,2-bis(3,4-decarboxyphenyl)hexafluoropropane dianhydride (6FDA) were determined at 298 K. The influence of the chemical structures on the physical and gas permeation properties of the 6FDA-based polyimides was studied. The solubility of propylene in an unrelaxed volume of a polymer matrix mainly contributes to the total solubility of propylene for various 6FDA-based polyimides. The diffusivity, the permeability of propylene, and the permselectivity in the propylene/propane mixed-gas system depend on the solubility of propylene. This is thought to be associated with the penetrant-induced plasticization effect. 6FDA-based polyimides, which have a high glass-transition temperature and a large fractional free volume, exhibit a high permeability with a relatively low permselectivity. Changing the number of-CH3 substituents in the phenylene linkage and changing the connectivity in the main chain are good ways of controlling the solubility of propylene and the corresponding permselectivity in the propylene/propane mixed-gas system. Some 6FDA-based polyimides restrict the solubility of propylene through the introduction of a -CONH- linkage between the phenylene linkage; the -Cl substituent in the phenylene linkage at the diamine moiety exhibits a high separation performance in the mixed-gas system. The polyimides are potentially useful membrane materials for the separation of propylene and propane in the petrochemical industry.

Relationships between chemical structures and solubility, diffusivity, and permselectivity of 1,3-butadiene and n-butane in 6FDA-based polyimides

The solubility, diffusivity, and permselectivity of 1,3-butadiene and n-butane in seven different polyimides synthesized from 2,2-bis (3,4-carboxyphenyl) hexafluoropropane dianhydride (6FDA) were determined at 298 K. The influence of chemical structures on physical and gas permeation properties of 6FDA-based polyimides was studied. Solubility of 1,3-butadiene in 6FDA-based polyimides can be described by a dual-mode sorption model. 1,3-Butadiene-induced plasticization is considered to be associated with the increasing permeabilities of 1,3-butadiene and n-butane and the decreasing permselectivity of 1,3-butadiene vs. n-butane in the mixed gas system containing a high concentration of 1,3-butadiene. It was found that controlling the solubility of 1,3-butadiene in an unrelaxed volume in 6FDA-based polyimides is very important to maintain the high permselectivity of 1,3-butadiene vs. n-butane in the mixed gas system. Changing the-C(CF 3 ) 2 - linkage to a -CH 2 -, -O- linkage, removing methyl substituents at the ortho position of the imide linkage, and changing the p-phenylene linkage to an m-phenylene linkage in the main chains in some 6FDA-based polyimides are effective to decrease fractional free volume and restrict the solubility of 1,3-butadiene in the unrelaxed volume of a polymer matrix. The 6FDA-based polyimides restricting the solubility of 1,3-butadiene in an unrelaxed volume exhibit high separation performance in the 1,3-butadiene/n-butane mixed gas system compared with conventional glassy polymers and, therefore, are potentially useful membrane materials for the separation of 1,3-butadiene and n-butane in the petrochemical industry.

Interpretation of d-spacing determined by wide angle X-ray scattering in 6FDA-based polyimide by molecular modeling

Abstract Interpretation of d-spacing determined by wide angle X-ray scattering (WAXS) is of great interest in the study of gas diffusivity or permeability in glassy polymers. Studies of WAXS analysis and of molecular modeling were carried out as a new approach in which to interpret the d-spacings in polyimide synthesized from 2,2-bis (3,4-carboxyphenyl) hexafluoropropane dianhydride (6FDA). The tetramer conformation and the amorphous polymer structure at 25°C were modeled using the semi-empirical molecular orbital method and the molecular dynamics method. The corresponding theoretical X-ray scattering functions were calculated from the atomic coordinates using Debye’s equation and then compared with the experimental data. The amorphous polymer model was found to be superior to the tetramer conformation model in the predicting experimental X-ray scattering function. It was found that the d-spacing for 6FDA-BAAF polyimide was clearly affected by intramolecular distances containing F atoms.

Glassy Dynamics and Heterogeneity of Polymer Thin Films

We review our recent studies on glassy dynamics and glass transition of polymer thin films using neutron and X-ray reflectivity and inelastic neutron techniques. In the last decade extensive studies have been performed on polymer thin films to reveal very interesting but unusual properties such as reduction in the glass transition temperature T g with film thickness and negative thermal expansivity for thin films below about 25 nm, and often some contradictory experimental results have been reported. It is believed that a key to solve the controversial situation is to disclose heterogeneous structure or multi-layer structure in polymer thin films. In the review, therefore, we summarize our recent experimental results by neutron and X-ray reflectivity and inelastic neutron scattering, focusing on the dynamic heterogeneity in polymer thin films.

Clarification of Cross-Linkage Structure in Boric Acid Doped Poly(vinyl alcohol) and Its Model Compound As Studied by an Organized Combination of X-ray Single-Crystal Structure Analysis, Raman Spectroscopy, and Density Functional Theoretical Calculation

When boric acid (BA) is added to poly(vinyl alcohol) (PVA), a chemical reaction occurs to form the cross-linkages between the amorphous PVA chains. The local structural change caused by this reaction has been clarified concretely from the microscopic level on the basis of the X-ray-analyzed crystal structure, Raman spectra, and ab initio density functional theory using a model compound produced by the reaction between pentanediol (PENT) and boric acid (PENT-BA). The PENT-BA compound was found to take the TT and TG conformations in the methylene segmental parts depending on the stereoregularity of the PENT molecule itself, meso and racemo configurations, respectively. These two conformations give the Raman bands at the different positions. By comparison of the Raman spectra between the PVA-BA and PENT-BA model compounds, the local structures of PVA chains connected to BA molecules have been derived concretely: the syndiotactic PVA parts in the amorphous region form the TG-type ring structure with the 3-coordinate boron atom, where T and G are trans and gauche conformers, respectively. On the other hand, the isotactic PVA part takes the TT conformation when it forms a ring with boron atom. The thus-created rings are hydrogen-bonded to form a dimer, which plays a role as cross-linkage between the neighboring PVA chain segments in the amorphous region.

Perpendicular orientation of sub-10 nm channels in polystyrene-b-poly(4-hydroxyl styrene)/PEG oligomer blend thin films

Vertically oriented cylinders via the directional coalescence of the spheres embedded in the blend thin films from polystyrene-b-poly(4-hydroxyl styrene) (PS-b-PHS) and PEG induced by solvent annealing were achieved. Removal of PEG water led to the formation of nanochannels throughout the films. The diameter of these channels could be as small as 9 nm which might enhance the applicability of the nano-porous films as size-selective membranes and controllable drug delivery systems for the objects less than 10 nm.

X-Ray reflectivity study of polyimide thin films swollen by 1,3-butadiene and n-butane

X-ray reflectivity measurements were performed on two different polyimide thin films synthesized from 2,2-bis(3,4-carboxyphenyl)hexafluoropropane dianhydride (6FDA) in 1,3-butadiene and n-butane. In 1,3-butadiene at 2.3 atm, the film thickness increased by 24–30%. However, the film thickness increased by only 10% in n-butane at 2.3 atm. Excessive increases in film thickness were shown in 1,3-butadiene, but the decreases in film density were minor. The probability of the condensation of 1,3-butadiene in the films is indicated.

High-precision spin coater for a synchrotron radiation in situ GISAXS system: for the investigation of formation mechanisms of self-assembled structures in polymer thin films

A high-precision spin-coater system has been developed for the investigation of formation mechanisms of self-assembled structures in polymer thin films. The spin coater was designed to have small axial deflection (<2.6 µm at the maximum speed of 2000 r min−1) during rotation in order to maintain the relative position with respect to the incident X-ray beam, and to be compact (70 mm) in height to facilitate incorporation into an in situ synchrotron radiation grazing-incidence small-angle X-ray scattering (GISAXS) system. The first results of simultaneous measurements on the morphology and film thickness of a triblock copolymer with time resolution of 64 ms during thin-film formation at 2000 r min−1 provide indispensable information for understanding the vertically grown lamellar structure on the film surface.

Surface adsorption of propane, propylene and propane/propylene mixed gas on polyimide observed with X-ray and neutron reflectivity

We observed the surface adsorption layer of propylene, propane and propane/propylene mixed gas on a polyimide film as a function of pressure using X-ray (XR) and neutron (NR) reflectivity. It was initially confirmed by NR that the surface layer is an adsorption layer of propylene using deuterated gas. We have determined by XR the adsorption isotherms of these gases and found that the thickness of the surface adsorption layer of propane and propane/propylene mixed gas is much larger than that of propylene and the isotherm of propane/propylene mixed gas is similar to that of propane. The former and the latter findings predict that the affinity of propane to the polyimide is greater than propylene and the content of propane is much higher than that of propylene in the adsorption layer. We also evaluated the permeability coefficients of these gases as a function of the applied pressure, and found that the permeability coefficients begin to increase at a pressure corresponding to the onset of the adsorption layer. This suggests that the surface adsorption layer of the gas plays an important role in the hydrocarbon gas permeation mechanism in a polymer membrane, while a swelling of the polyimide film is the basis for the increase in the permeability with pressure.

Development of a simultaneous measurement system for SAXS-WAXD and the thickness of coating films during film formation by solvent evaporation

A system for the simultaneous measurement of small-angle X-ray scattering and wide-angle X-ray diffraction (SAXS–WAXD) and the thickness of a coating film, obtained with an automatic coater, during film formation has been developed. The system was installed on beamline BL03XU at SPring-8. As model specimens, poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymers with different compositions were used to investigate the film formation process during solvent evaporation. First of all, the data correction methods were examined for the coating films during solvent evaporation. Since the scattering invariant was affected by the scattering volume and the absorption of X-rays by the solvent and the copolymer during drying, the scattering invariant should be corrected for the film width and the X-ray absorption of the sample. The polymer concentration was estimated from the thickness of the coating film during solvent evaporation, while the X-ray absorption was evaluated by using the X-ray linear absorption coefficients of the solvent and the copolymer. The results showed that the correction of the scattering invariant is crucial for an exact description of the film formation process during solvent evaporation.