Akiyoshi Kawaguchi

Epitaxial act of sodium 2,2′-methylene-bis-(4,6-di-t-butylphenylene)phosphate on isotactic polypropylene

Abstract Sodium 2,2′-methylene-bis-(4,6-di-t-butylphenylene)phosphate(NA-11) is widely used as a nucleating agent in the processing of isotactic polypropylene(iPP). To reveal its act as the nucleating agent on iPP, the crystallization behavior of NA-11 on isotactic polypropylene was investigated. NA-11 was crystallized on the oriented, thin iPP film from the solution in dimethyformamide at various temperatures. iPP was also crystallized from the melt on NA-11 crystals grown from ethanol. The samples thus prepared were examined by electron microscopy. NA-11 epitaxially crystallized on the iPP substrate at high temperatures, performing the crystallographical relationship, [010]NA-11//[001]iPP and (001)NA-11//(010)iPP, and iPP on the NA-11 crystals with the same orientational relationship.

Crystallization Behavior of Amorphous Poly(l-Lactide)

Amorphous poly(l-lactide) (PLLA) was annealed in two different ways: amorphous samples were heated at a given temperature to induce crystallization (one-step annealing); and amorphous samples were first crystallized at a low temperature and subsequently annealed at a higher temperature than the crystallization temperature. Samples thus prepared were measured by DSC. The original amorphous sample exhibited an exothermic peak at about 100°C (exothermic peak I), an exothermic peak just below the melting point (exothermic peak II), and an endothermic peak when it was melted. Exothermic peak I was caused by cold crystallization. When the melting points of PLLA samples, heat-treated in various ways, were plotted as a function of annealing temperature, there was discontinuity at about 120°C. From analyses of wide-angle X-ray diffraction patterns, it was found that when amorphous PLLA was crystallized at a temperature below 120°C, crystallites of the β-form formed, and when annealed at a temperature above 120°C, crystallites of the α-form grew. Thus, exothermic peak I was attributed to cold crystallization of the β-form, and peak II was caused by the phase transition of the β-form to a more stable form.

Diffusion-Limited Aggregates of Poly(Ethylene Oxide) on Alkali Halides

Poly(ethylene oxide) (PEO) was crystallized on alkali halides, such as NaCl, KCl, and KBr, from solution in isopentyl acetate. PEO dendrites first formed on alkali halide surfaces and grew to sheet the whole surface. Individual fibrils consisting of dendrites were arranged with the preferred orientation in the <110> direction on KBr and KCl, and mainly in the <100> direction on NaCl. Tetragonal lamellae grew not on the substrate directly but on the sheet platelet only, establishing a homoepitaxial relationship to the dendrites. Because the dendritic sheet that intervened between them controlled the orientation of the lamellae, tetragonal lamellae formed with a preferred orientation on alkali halide surfaces. The dendrites had morphological features of fractals, i.e., diffusion-limited aggregates (DLA). Their morphology was controlled by the diffusion process of polymer molecules on the substrate surface, as well as by epitaxial interaction. The fractal dimension (D) was obtained by analyzing the dendrites by taking the autocorrelation function of density: D ranges from 1.6 to 1.8, depending on the crystallization conditions, such as the kinds of substrate and crystallization temperature.

Dynamical observation of structural transition of polymers using an X‐ray diffraction system with imaging plates. II. Crystalline transition of poly(butylene terephthalate)

Poly(butylene terephthalate) has two crystalline forms of α and β. The α form is more stable and is transformed into the β form by stretching. The α↔β transition stress was measured at various temperatures with the use of an X-ray diffraction system with imaging plates, and the relationship between the transition stress and temperature was obtained. Further, using the X-ray diffraction system, the drawing behavior of the nearly amorphous, undrawn polymer film was observed by taking up dynamically a series of X-ray diffraction patterns while a film was being drawn. The α form never occurred during drawing at any temperature because the stress to draw the film exceeded the α→β transition stress.

Shear‐Enhanced Nucleation of Isotactic Polypropylene in Limited Space

The nucleation rate was measured by directly counting the number of nuclei, which were developed while an isotactic polypropylene melt was flowing under shear in a thin film. The nucleation rate was enhanced with an increased rate of shear, e.g., by a factor of 10 larger at the rate of shear of 14 s−1 compared with the quiescent state, at 134°C. The ratio of the shear‐enhanced nucleation rate to the nucleation rate in the quiescent state was larger at a higher temperature of crystallization, i.e., about 10 times at 134°C to 590 times at 140°C. The increase of the nucleation rate under shear flow was explained by a reduction of the lateral and end (fold) surface free energies; the product σ s 2 σ e decreased to 3.2×10−7 for the sheared melt, from 6.0×10−7 (J m−2)3 for the isotropic state. The free energy reduction was caused by transition of the nucleus formation mode from three‐dimensional folded chain nuclei to two‐dimensional bundle nuclei, in which chains lie down on the glass substrate, aligning parallel to the flow direction.