Shuji Matsuzawa

Cross polarization/magic angle spinning 13C n.m.r. study of solid structure and hydrogen bonding of poly(vinyl alcohol) films with different tacticities

Abstract Cross polarization/magic angle spinning (CP/MAS) 13C n.m.r. measurements have been performed at room temperature for poly(vinyl alcohol) (PVA) films with different tacticities to obtain information about the structure and hydrogen bonding in the crystalline and non-crystalline regions. 13C spin-lattice relaxation analyses have revealed that three components exist for each sample, with different spin-lattice relaxation times T1C, which are assignable to the crystalline, less disordered non-crystalline and amorphous components. Using such differences in T1C, we separately recorded the spectra of the crystalline and non-crystalline components, and then analysed the triplets of the CH resonance lines appearing in both spectra in terms of three Gaussians which should be ascribed to CH carbons associated with two, one and no intramolecular hydrogen bond(s) in the mm, mr and rr sequences. As a result, it has been found that the relative intensities of the triplets are not in accord with the contents of the triad sequences, suggesting the formation of intramolecular and intermolecular hydrogen bonds in the meso sequences at almost equal probability. The effects of water on hydrogen bonding have also been examined for the almost atactic PVA sample.

Structural studies on ethylene-tetrafluoroethylene copolymer 1. Crystal structure

Abstract The crystal structure for an ethylene-tetrafluoroethylene (ETFE) alternating copolymer film containing highly ordered crystal regions was determined. The unit cell is orthorhombic with the dimensions: a = 8.57 A , b = 11.20 A , and c ( chain axis ) = 5.04 A . Four planar zigzag chains are packed in the unit cell. The lateral packing mode is similar to that of orthorhombic polyethylene (PE). A study on the mode of double orientation confirmed that the crystal structure of ETFE, which has been assumed to be pseudo-hexagonal, is indeed orthorhombic as described above, although it has paracrystalline disorder.

Structural studies on ethylene-tetrafluoroethylene copolymer: 2. Transition from crystal phase to mesophase

Abstract A thermo-reversible, first-order transition from an orthorhombic crystal lattice to a hexagonal lattice (mesophase) was found in ethylene-tetrafluoroethylene alternating copolymer by using X-ray diffraction. The transition was shown to be the order-disorder transition with a wide pretransitional temperature range, which was caused by rotational motion around the chain axis as often observed in planar zigzag polymers like polyethylene. A characteristic anisotropy of the thermal expansion coefficient of the crystal lattice was observed in the pretransitional range. By combining dilatometric data with the X-ray data on crystal expansion, the copolymer composition, the fraction of ordered orthorhombic region in the crystal phase and the crystallinity were obtained. Furthermore, the relaxations observed in a dynamic viscoelastic measurement were analysed by comparison with the crystal expansion.

Anomalous swelling of poly(vinyl alcohol) film in mixed solvents of dimethylsulfoxide and water

Abstract The swelling behaviour of dried and annealed poly(vinyl alcohol) (PVA) films was investigated in several mixed solvents of dimethylsulfoxide (DMSO) and water with different solvent compositions. The swelling ratio versus time curves obtained in DMSO-rich solvents were shown to be of anomalous swelling type: the swelling ratio first increased in proportion to time for a while and then catastrophically expanded on approaching the equilibrium ratio. Further, crazing of the films occurred before the catastrophic expansion. These results indicated that the swelling obeyed case II diffusion of solvent through glassy PVA. It was shown that the relaxation rate of the glassy PVA molecules was the key factor that dominated the nature of swelling. The relaxation rate was sufficiently low in the DMSO-rich solvents and too high in the water-rich solvents for the anomalous swelling to be detected. The crystallinity of PVA was also a factor by which the relaxation rate and thus the swelling rate could be controlled over a wide range.

Studies on the temperature dependence of the elastic modulus of crystalline regions of polymers: 14. Poly(vinyl alcohol) with different tacticities

Abstract The temperature dependence of the elastic modulus E 1 of crystalline regions in the direction parallel to the chain axis has been measured by X-ray diffraction for poly (vinyl alcohol) (PVA) with different tacticities. The E 1 value for PVA with 55.4% syndiotactic diads, sPVA (55.4%), decreased above 120°C, which was in accordance with that of atactic PVA. The lattice spacing for the (0 2 0) plane (the fibre axis is b ) also decreased with increasing temperature. The thermal expansion coefficient α c changed discontinuously around the temperature range where E 1 began to decrease. These phenomena could be explained using the kinked-chain model, where a small amount of a contracted portion, such as a kink, was incorporated into the chain molecule as in the case of atactic PVA. On the other hand, the El value of sPVA (63.0% ) remained unchanged till 150°C. The value of α c did not change with increasing temperature in this case. Consequently, the molecular motion that is responsible for the decrement of E 1 is considered to be restricted for sPVA (63.0%) because of strong intermolecular hydrogen bonds. Further, increasing the syndiotacticity is considered to be one of the most effective ways to introduce high heat resistance into PVA.

Melting of the blends between syndiotacticity-rich and atactic poly(vinyl alcohol)s

A highly syndiotacticity-rich (s-) poly(vinyl alcohol) (PVA) of a 66 s-dyad% [s(66)-PVA] was blended by a solution method with atactic (a-) PVA of a 55 s-dyad% and another s-PVA of a 61 s-dyad%. The s(66)-PVA was shown to be able to produce cocrystallized phases with the other PVAs by investigating the melting behavior. The melting temperature and heat of fusion changed with the average syndiotacticity that was controlled by blending two PVAs with various compositions. As a result, the maximum melting temperature and the maximum heat of fusion appeared when the average rr triad value was 0.40, indicating that the high nucleation rate due to the high syndiotacticity component decreased the morphological factors such as the crystal size or the order of molecular packing.

Syndiotacticity-rich poly(vinyl alcohol) fibers spun from N-methylmorpholine-N-oxide/water mixture

Aqueous NMMO solutions containing NMMO above 50% are good solvents for syndiotacticity-rich poly(vinyl alcohol) (s-PVA). Although water is not a good solvent and dissolves s-PVA at temperatures above 100°C, the mixtures dissolve it at temperatures below 100°C. s-PVA fibers were prepared through get-spinning of s-PVA/NMMO/water (NMMO : water = 70 : 30) mixtures in cold water and wet-spinning of the solution in methanol. The mechanical properties and fine structure of the drawn fibers were examined based on the results of measurements of tensile properties, thermal properties, birefringence, and optical and electron microscopic observations. The strength and Youngs modulus of the drawn fibers were approximately to 2.0 and 45 GPa, respectively. The reason why the fibers with theoretical mechanical properties could not be prepared was surmised to be related to the structure of the amorphous regions.

Ageing of poly(vinyl alcohol) gels prepared from dimethylsulfoxide/water solutions

Abstract In order to elucidate the structure of poly(vinyl alcohol) (PVA) gels, the gels studied were aged for as long as 500 days at 30°C. The original gel was formed from PVA solutions in a mixed solvent of dimethylsulfoxide (DMSO) and water by chilling at −34°C for one day. The aged gel was shown to have a well grown crystal phase, in that the melting endotherm from differential scanning calorimetry could be clearly separated into two or three components, which were named A, B and C, in order of melting temperature. The enhancement of the gel modulus and the solvent exclusion observed in the aged DMSO/water gels could be atrributed to phase separation, which facilitates crystallization into the B and C components. The A component was shown not to bear a strong relationship to the high modulus and the exclusion of solvent, although it may be the most common crystallite grown from PVA solutions.

Mechanical denaturation of high polymers in solutions

SummaryIn order to clarify the mechanism of crystallization under molecular orientation, the rates of precipitation of poly(vinyl alcohol) (PVA) from aqueous solutions under shearing force were measured under various conditions. The fractionation was carried out by separating the precipitates at time intervals. The shearing force was brought about in the solutions by stirring. The rate of precipitation was found to depend not only on the thermal motion of molecules, but also on the fluidity of the solution. In other words, at temperatures above 45°C, the initial rate of precipitation became smaller with increasing temperature, but at 45 °C it was higher than that at the lower temperature than 40°C. The rate of precipitation at 35°C decreased with the increase of the polymer concentration. At the constant polymer concentration, the maximum of the rate of precipitation was recognized at a certain chain length. The molecular weight of fractions decreased in the order of fractionation. As compared with the non-solvent addition method, the difference in the s-(diad) % of the initial fraction and the last fraction was large in the case of stirring fractionation. Therefore, the stirring fractionation of PVA depends not only on the molecular weight, but also on the tacticity.ZusammenfassungUm den Kristallisationsmechanismus von Polyvinylalkohol (PVA) unter Molekülorientierung aufzuklären, wurde unter verschiedenen Bedingungen die Fällungsgeschwindigkeit von PVA in wäßrigen Lösungen unter Schubspannung gemessen, die Fraktionierung mit diskontinuierlicher Abtrennung der Niederschläge durchgeführt. Die Schubkraft wurde durch Rühren der Lösung erzeugt. Es wurde gefunden, daß die Fallgeschwindigkeit nicht nur von der thermischen Molekularbewegung abhängig ist, sondern auch von der Fluidität der Lösung. Bei Temperaturen über 45°C nahm die Anfangspräzipitationsgeschwindigkeit mit steigender Temperatur ab, während sie bei 45°C höher war als diejenige bei Temperaturen unter 40°C. Die Fällgeschwindigkeit bei 35°C sank mit zunehmender Konzentration des Polymeren. Bei konstanter Konzentration des Polymeren wurde der maximale Wert der Präzipitationsgeschwindigkeit bei einer bestimmten. Kettenlänge beobachtet. Das Molekulargewicht der Fraktion nahm gemäß der Reihenfolge der Fraktionierung ab. Beim Vergleich zur Fraktionierung durch Fällen mit einem Nicht-Lösungsmittel für das Polymerisat war bei der Fraktionierung durch Rühren der Unterschied im Gehalt an syndiotaktischen Diaden zwischen der ersten und der letzten Fraktion groß. Daraus ist zu schließen, daß die Rührungsfraktionierung von PVA nicht nur vom Molekulargewicht, sondern auch von der Taktizität abhängt.

High strength and high modulus poly(vinyl alcohol) by the gel ageing method

The gel ageing method was proposed for producing high strength and high modulus poly(vinyl alcohol) (PVA) materials. The PVA gel prepared from a solution in a mixed solvent of dimethylsulfoxide water (v/v)=80∶20 at -34 °C was moulded into a gel sheet and then aged in water at 10 °C for several months. The gel sheet was dried and then drawn at 200 °C. The tensile strength and the modulus of the drawn film were 2.8 and 72 GPa, respectively. These excellent properties are discussed in relation to the structures of the aged gel, the dried gel (namely the film) and the drawn film using the results from X-ray diffraction, differential scanning calorimetry and birefringence measurements. As a result, the most important process was shown to be the ageing process. If the crystallites with relatively low melting temperatures, which were called the B and C crystallites, were grown in the aged gel, the mechanical properties of the drawn film from it were as high as those described above. The orientation of the crystallites mildly caused during drying of the gel sheet was also shown to be a key structure which facilitated the high extension of the chain in the subsequent drawing process.