Eiko Ito

Miscibility of PVDF/PMMA blends examined by crystallization dynamics

Abstract The crystallization dynamics of blends of poly(vinylidene fluoride) (PVDF) with atactic-, syndiotactic- and isotactic-poly(methyl methacarylate)s (PMMA) were analysed by differential scanning calorimetry under isothermal conditions. Crystal growth rate ( G ) decreased with increasing weight fraction of PMMA (φPMMA) for PVDF/at-PMMA and PVDF/syn-PMMA blends. However, G of PVDF/iso-PMMA blends depended only on the degree of supercooling (Δ T ) and was independent of φ spPMMA . Surface free energy (σ) of PVDF crystals evaluated from G and nucleation rate depended on φ spPMMA for PVDF/at-PMMA and PVDF/syn-PMMA blends, although σ of PVDF/iso-PMMA was almost constant and independent of φ spPMMA . These results suggest that PVDF/at-PMMA and PVDF/syn-PMMA blends are miscible but PVDF/iso-PMMA blends are immiscible, a finding which was confirmed by the phase diagrams as determined from cloud point measurements.

FTIR spectroscopic study on crystallization process of poly(ethylene‐2,6‐naphthalate)

In situ Fourier transform infrared (FTIR) measurements were carried out to elucidate conformation changes occurring during the isothermal melt crystallization of poly(ethylene-2,6-naphthalate) (PEN). Based on the band assignments for the components of the amorphous, α-crystal form, and β-crystal form of PEN in film samples, the in situ data was analyzed in terms of the amorphous- and crystal-trans conformations. It was observed at a higher isothermal crystallization temperature that the formation of amorphous-trans conformations precedes the growth of crystals.

Magnetic orientation of poly(ethylene-2,6-naphthalate)

A new finding is reported of the magnetic orientation of poly(ethylene-2,6-naphthalate) (PEN) near its melting point, evidenced by X-ray analyses and magnetic birefringence measurements. Since PEN does not exhibit features characteristic of liquid-crystalline polymers under a polarization microscope, the magnetic orientation was unexpected. The orientation is probably due to some ordered structure susceptible to a magnetic field, but the detail of the structure is not fully understood at present.

In situ FTIR spectroscopic study on crystallization process of isotactic polystyrene

The melt crystallization process of isotactic polystyrene (i-PS) was studied by means of in situ Fourier transform infrared (FTIR) spectroscopy, with a focus on the conformational changes during the induction period. The spectra obtained during the induction period suggested the occurrence of some ordered structure that is characterized by higher regularity and packing of the helical moieties than observed in the melt. This ordered structure was clearly different from the amorphous structure, and close to the crystal structure. The Avrami analysis indicated that the formation process of the ordered structure at the late stage of the induction period is similar to the growth process of the crystallites after the induction period.

Change of amorphous state of poly(ethylene terephthalate) by heat treatment below the glass transition temperature

Abstract Several papers have demonstrated that structural changes in the amorphous regions of semicrystalline polymers can be produced by heat treatment below the glass transition temperature (Tg). In this paper, we report structural change in the amorphous phase of poly(ethylene terephthalate), heat-treated below and above Tg. The density, the Tg, the endothermic peak at Tg and the relative spectral intensity in the 973 cm−1 band (due to the CO stretching vibration), all increased with heat treatment below Tg, but the specific heat decreased. The stability of the amorphous state was examined by further heat treatment at temperatures above Tg and sufficiently high for crystallization, and it was verified that structural changes in the amorphous regions do not result in acceleration of the rate of crystallization. We therefore suggest that the amorphous region is one phase, rather than two phases consisting of random and regular regions.

Magnetic orientation of poly(ethylene-2,6-naphthalate) during crystallization from melt

Magnetic orientation of poly(ethylene-2,6-naphthalate) [PEN], reported in the previous paper, was studied in detail. Birefringence, X-ray and infrared analyses were carried out on the samples quenched at different periods of the crystallization time during the crystallization at 255°C in the magnet (6T). These analyses showed that the orientation observed in the birefringence measurements starts during the induction period in which little crystallinity is observed with respect to the X-ray and infrared measurements. At a later stage of crystallization, the samples exhibited the orientation of crystallites with the c-axis parallel to the magnetic field.

Magnetic Orientation of Crystalline Polymers in View of Liquid Crystallinity during Induction Period of Crystallization

Abstract Magnetic orientation of poly(ethylene-2,6-naphthalate) (PEN) and isotactic polystyrene (iPS) has been reported. The orientation starts to occur during the induction period of isothermal melt crystallization process, i.e. during the initial stage of crystallization process where no crystal growth is yet observed with respect to the wide angle X-ray diffraction. In the case of PEN, the crystallites obtained at later stages of crystallization were aligned with its c-axis parallel to the magnetic field, while in the case of iPS, the crystallites obtained were aligned with its c-axis perpendicular to the magnetic field. X-ray, infrared, and magnetic birefringence measurements indicated that mesophases appearing during the induction period could be responsible for the magnetic orientation of these polymers.

Effects of drawing on molecular motions in polycarbonate

SummaryThe effect of drawing on the molecular motions in amorphous polycarbonate is studied by the dielectric relaxation with following conclusions.(1)A structural model for the drawn polycarbonate is obtained from the data of the density, the birefringence and the height of the endothermic peak atTg. The molecular chains of polycarbonate are supposed to be oriented to the draw direction and packed closely by drawing. No process similar to that in polyethylene terephthalate occurs in polycarbonate.(2)The rate of the torsional oscillation of the frozen chains in the glassy polycarbonate varies with the draw ratio. It decreases at first and then increases near the severance. This behavior can be explained by the local mode relaxation theory and the structural model proposed here.(3)The behavior of polycarbonate by drawing was compared with that of polyethylene terephtalate and discussed.ZusammenfassungDer Effekt der Verstreckung auf die molekularen Bewegungen im amorphen Polycarbonat wurde mit dielektrischen Messungen studiert. Folgende Schlüsse lassen sich ziehen:1.Ein Strukturmodell für das verstreckte Polycarbonat läßt sich aus den Daten für die Dichte, die Doppelbrechung und die Höhe des endothermen Piks naheTg erzwielen. Die molekuraren Ketten des Polycarbonate werden durch die Streckung dicht gepakt. Kein Prozeß ählich demjenigen in Polyänthylenterephthalat tritt in Polycarbonat auf.2.Die Maximallage für ihre Absorption Polycarbonat verändert sich mit dem Streckenverhältnis. Sie sinkt zuerst und steigt dann in der Nähe der Streckgrenze an. Dieses Verhalten kann mittrels der Relaxations-theorie der lokalen Moden und des hier vorgeschlagenen Strukturmodells erkäkt werden.3.Das Verhalten des Polycarbonats beim Verstrecken wird mit demjenigen des Polyänthylenterephthalats verglichen und diskutiert.

Change of the amorphous state by heat treatment below the glass transition temperature

Abstract This study was undertaken to elucidate the state of a polymer in the amorphous state through a change of motion of the molecular chain caused by heat treatment below the glass transition temperature. From dielectric measurements of amorphous poly(ethylene terephthalate) heat-treated below T g , it was found that the average relaxation time, the distribution of relaxation time and the dielectric strength increase with increase of heat treatment. From these results, it was concluded that the amorphous state becomes more random by heat treatment.

Effects of drawing on molecular motions in poly(ethylene terephthalate)

SummaryEffects of drawing on molecular motions in amorphous poly(ethylene terephthalate) (PET) were studied by the dielectric relaxation measurements. The rate of the segmental motion increases by small drawing and turns to decrease with draw ratio in large draw ratios. The local mode relaxation time in glassy PET was found to vary with draw ratio in a more complex manner than the segmental mobility does. These variations of molecular motions are explained in terms of the free volume in PET. A structural model for the drawn PET is postulated from the evidences on the variations of the density, the birefringence and the dielectric properties with the draw ratio. That is, the small drawing promotes the molecular orientation more or less but produces unstable chain conformations accompanied with a local volume increase, while the high drawing enhances the molecular aligment.ZusammenfassungEinfluß von Verstreckung auf die molekulare Bewegung in amorphem Polyäthylenterephthalat (PET) wurde mittels der dielektrischen Relaxationsmethode untersucht. Die Geschwindigkeit der segmentförmigen Bewegung nimmt mit schwacher Verstreckung zu, jedoch mit starker Verstreckung ab. Für die Relaxationszeit der lokalen Mode in glasigem PET wurde gefunden, daß sie sich mit dem Verstreckverhältnis komplizierter ändert als die segmentförmige Mobilität. Diese Variationen der molekularen Bewegungen werden durch den Begriff des freien Volumens erklärt. Ein Modell des verstreckten PET wird aus den Nachweisen der mit dem Verstreckverhältnis geänderten Dichte, der Doppelbrechung und der dielektrischen Eigenschaften erschlossen. Nämlich: eine geringe Verstreckung fördert mehr oder weniger die molekulare Orientierung, ruft jedoch eine von der lokalen Volumenvergrößerung begleitete unbeständige Kettenanordnung hervor, während eine starke Verstreckung die molekulare Ordnung erhöht.