Toshiaki Ougizawa

Oxygen permeability and free volume hole size in ethylene-vinyl alcohol copolymer film: temperature and humidity dependence

Abstract Relationship between oxygen permeability and free volume hole size evaluated from ortho -positronium lifetime in ethylene–vinyl alcohol copolymer (EVOH) was studied as functions of temperature and relative humidity. As the relative humidity rises at room temperature, the permeability first decreases and then increases. This behavior is attributed to the effects of pore filling and plasticization by water molecules. Linear correlations are obtained on the plots of logarithmic permeability versus reciprocal free volume hole size for EVOH at different temperatures and humidities as well as for different polymers including EVOH at room temperature, suggesting that the free volume hole size plays a crucial role in the oxygen permeation in EVOH and other polymers.

Phase dissolution in polymer blends. Kinetics of dissolution and related problems in rubber technology

Abstract For a blend of cis -1,4-polybutadiene and poly(styrene- co -butadiene), which has been found to exhibit upper critical solution temperature ( UCST ) behaviour, the kinetics of phase dissolution in the single-phase region above the UCST was investigated by light scattering, using novel specimens with regularly phase-separated structure having a periodic distance of a few micrometres. The apparent diffusion constant for the dissolution was estimated to be of the order of 10 −13 –10 −12 cm 2 s −1 . The rate of phase dissolution was much increased by the presence of a small amount of organic peroxide. The results give a new viewpoint on understanding the mixing and curing process in elastomer blends.

Studies on the free volume and the volume expansion behavior of amorphous polymers

Abstract In order to estimate the free volume contribution on the volume change, we investigated the relationship between the volume expansion behavior by Pressure–Volume–Temperature measurement apparatus and the free volume behavior by Positron Annihilation Lifetime Spectroscopy for some amorphous polymers. From these results, the free volume fraction of the amorphous polymers was calculated by assuming that the core volume increases at a constant rate with temperature. It was found that the amount of free volume was not constant even in the glassy state and it played a very important role in the volume expansion.

Studies on the reactive polysulfone–polyamide interface: interfacial thickness and adhesion

The reactive interface formed between an immiscible polymer pair, amorphous polyamide (aPA) and functionalized polysulfone (PSU), was studied by ellipsometry. Diblock copolymers were formed in situ by an interfacial reaction between the amine-terminated aPA and the end-functionalized PSU, whereas graft copolymers were formed between the amino-chain end groups of aPA and the PSU functionalized in the middle of the chains. It was found that the interfacial reaction significantly increased the interfacial thickness, even reaching the size larger than the coil size of the copolymers formed at the interface. The interface structure and the properties were affected by the position and type of functional groups incorporated to the PSU. The reactive interface resulting in the graft copolymers tended to be thicker than that forming the block copolymers. However, the thinner interface demonstrated a superior adhesion to the thicker interface.

Reactive blending of polysulfone with polyamide: a potential for solvent-free freparation of the block copolymer

Abstract Reactive blending of polysulfone (PSU) and polyamide 6 (PA) was carried out at 20:80 (PSU-PA) wt. ratio using a gram-scale mixer (Mini-Max Molder). Three PSUs with different functional groups were prepared and used: maleic anhydride-grafted PSU (PSU-MAH), carboxylic acid-grafted PSU (PSU-COOH) and phthalic anhydride-terminated PSU (PSU-PhAH), having almost same molecular weight ( M w = ca. 20 k) and functional group content (ca. 90 μmole g −1 ). The change in PSU particle size with mixing time was investigated by light scattering and transmission electron microscopy. As expected, all reactive systems yielded finer particles via faster size reduction process, compared with non-reactive system. Attainable particle diameters were: ca. 1 μm for non-functionalized PSU, ca. 0.6 μm for PSU-MAH, 0.3 μm for PSU-COOH, and ca. 40 nm for PSU-PhAH. The particle size of PSU-PhAH system was comparable to that in a pre-made block copolymer synthesized by solution polymerization, suggesting a potential for the solvent-free preparation of PSU-PA block copolymer when adequate reactivity and molecular architecture are provided in reactive blending.

Polymerization-induced spinodal decomposition of poly(ethylene-co-vinyl acetate)methyl methacrylate mixture and the influence of incorporating poly(vinyl acetate) macromonomer☆

Abstract The structural development during radical polymerization of a mixture of methyl methacrylate (MMA) and poly(ethylene-co-vinyl acetate) (EVA) was investigated by light scattering and optical microscopy. In the early stage of polymerization, the mixture of MMA/EVA was a single phase. As the polymerization of MMA proceeded, phase separation took place via spinodal decomposition (SD). This was supported by the characteristic change in light-scattering profile with reaction time. Analysis by the linearized and scaling theories showed that the reaction-induced phase separation behaviour was different from the familiar thermally induced SD during isothermal annealing after temperature jump. The scaling analysis showed that the final phase-separated structure may be formed by the interruption of a co-continuous percolation structure. Moreover, to investigate the effect of graft copolymer on SD, a poly(vinyl acetate) (PVAc) macromonomer with a methacrylate end-group was added to the MMA/EVA mixture to yield PMMA-PVAc graft copolymer during the polymerization. The incorporation of PVAc macromonomer increased the dominant wavenumber of the final frozen phase-separated structure (smaller periodic distance). The reasons seem to be that the concentration fluctuation growth is suppressed until the system reaches a deep quench depth at which the fluctuation should have a large wavenumber, and that the coarsening is retarded at the late stage by the graft copolymer formed in situ.

Effect of the shear flow on the phase behaviour of polystyrene/poly(vinyl methyl ether) blend

Abstract The effects of simple shear flow on the phase behaviour of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend, which shows a lower critical temperature (LCST)-type phase diagram, have been studied by cloud point measurements, by using a special shear apparatus. The shear-induced demixing and mixing have been observed for all of the compositions at low and high shear rate, respectively. However, at higher shear rate, the cloud points were independent of the shear rate and almost constant. In addition, the shear effect was found to be composition dependent and the largest change took place near the critical composition. The effects of rotation speed and sample thickness were also studied for the sample of PS/PVME=30/70. The values of the cloud point were strongly affected by the rotation speed and the minimum of the cloud point systematically shifted to higher shear rate values with increasing rotation speed under the constant sample thickness. The sample thickness was also found to have a pronounced effect on the cloud point under constant rotation speed, where the immiscibility region in the cloud point–shear rate diagram seemed broader with increasing sample thickness. However, the samples of PS/PVME=30/70 completely phase separated at 17°C above the quiescent cloud point at high shear rate, regardless of the applied rotation speed and sample thickness.

LCST-type phase behaviour and extremely slow demixing phenomenon in polymer blends of poly(acrylonitrile-co-styrene) and poly(maleic anhydride-co-styrene)

Abstract Phase behaviour of the binary blends of poly(acrylonitrile-co-styrene) and poly(maleic anhydride-co-styrene) was investigated by the cloud point method, using very long isothermal annealing (up to 97 h). A lower critical solution temperature (LCST) type phase diagram was found. Kinetic studies on demixing at the two-phase region above the LCST were carried out by light scattering. The demixing rate was very slow. This extremely slow demixing was interpreted in terms of the overlap of two effects: first, the interaction parameter χ 12 is a slowly increasing function of temperature, i.e. the thermodynamic driving force for the demixing is not as large as expected from the quench depth in the phase diagram; and, secondly, the chain mobility is small, due to the small deviation of the LCST from the glass transition temperature of the mixture.

Upper and lower critical solution temperature behaviour in polymer blends and its thermodynamic interpretation

Abstract The simultaneous occurrence of upper (UCST) as well as lower critical solution temperatures (LCST) in polymer blends can be explained in terms of a refined version of the Prigogine-Flory-Patterson theory. A generalized interaction parameter is introduced which is ruled by three contributions: (i) the segmental interaction, (ii) the free-volume effect, and (iii) the size effect represented by a parameter ϱ. The gap between LCST and UCST depends highly on the parameter ϱ. With increasing size effect, the UCST and LCST approach and, finally, merge into an hourglass-shaped binodal.

Binary miscible blends of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile): I. Rheological behavior

Viscoelastic properties of poly(α-methylstyrene-co-acrylonitrile) and poly(methyl methacrylate) blends have been systematically investigated below and above the lower critical solution phase-separation temperatures. In the one-phase regime, the viscoelastic characteristic parameters of the blends, such as zero shear viscosity, η 0, and entanglement plateau modulus, G N 0, were found to be composition dependent. A negative deviation of the composition dependence of G N 0 from the linear-mixing rule was detected indicating that the total number of entanglement points per unit volume in the blends is smaller than the sum of those in the two constituent pure components. Similar behavior was also seen in the composition dependence of η 0. The linear-viscoelastic properties of the blends were found to be greatly changed by phase separation in the two-phase regime. The change in the viscoelastic properties was clearly observed in the failing of the Williams-Landel-Ferry (WLF) superposition principle and sudden changes in the slopes of the temperature ramps of some of viscoelastic material functions as well as an appearance of a second plateau at a small value of frequency in the classical frequency dependence of the complex dynamic viscosity (η *). This large change in the linear-viscoelastic properties might be attributed to an additional contribution of concentration fluctuations to the material functions at the phase-separation temperatures. The phase diagram of the blends was also estimated rheologically and the result was in good agreement with the cloud point measurements obtained visually under quiescent condition at a heating rate of 1°C/min.