Morphology of melt-crystallized poly(ethylene 2,6-naphthalate) thin films studied by transmission electron microscopy
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Morphology of melt-crystallized poly(ethylene 2,6-naphthalate) thin films studied by transmission electron microscopy Masaki Tsuji,a) Fernando A. Novillo L.,b) Masahiro Fujita, Syozo Murakami, and Shinzo Kohjiya Laboratory of Polymer Condensed States, Division of States and Structures III, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan (Received 27 February 1998; accepted 20 March 1998)
Thin films of poly(ethylene 2,6-naphthalate) (PEN) were isothermally crystallized at 190 ±C after being melted at 300 ±C. Morphological observation by transmission electron microscopy (TEM) showed the spherulitic texture in the films. Selected-area electron diffraction (SAED) indicated that the crystals in the films are the a form, as expected from our thermal condition for crystallization. The SAED pattern from the untilted specimen was characterized by the fairly intense reflection ring accompanied by other weak rings, and this intense ring was indexed as 010. A series of SAED patterns, which were obtained from the same specimen area tilted at various angles in the TEM column, suggested that the crystallites are oriented with their (001) planes being preferentially parallel to the film surface. Subsequently, a set of the dark-field images of the two-dimensional spherulite taken by using two different parts of the 010 reflection ring revealed that most of the crystallites in such a spherulite are oriented with their (010) planes being parallel in its radial direction. In addition, the spherulites in small pieces (0.05–0.08 mm thick) of PEN, which had been crystallized under the same thermal condition as above, were determined to be negatively birefringent by polarizing light microscopy.
I. INTRODUCTION
Poly(ethylene 2,6-naphthalate) or poly(ethylene naphthalene-2,6-dicarboxylate) [PEN; see its molecular formula illustrated in Fig. 1(a)] is one of the high-performance polymers for wide use. PEN has naphthalene rings in its main chain in place of all the benzene rings of poly(ethylene terephthalate) (PET), and accordingly the melting point and Young’s modulus of PEN are both higher than those of PET.1–3 Thus, PEN is now utilized, for example, for automotive parts4 and electrical and audio-visual applications such as base films for longplay videotape of high quality.5 So far, extensive studies on crystallization and/or solid-state structures/properties of PEN have been reported: crystal structures,6 – 8 structural change/formation during uniaxial drawing9 –12 or biaxial stretching,9 during injection molding,13,14 during high-speed meltspinning,15 –17 or by solid-state coextrusion,18,19 crystal modulus,3,20 liquid-induced crystallization,21 glass transition and melting behavior,22 existence of a mesophase,23 time-resolved fluorescence,24 and electroluminescence.25 Photodegradation or photochemical reaction by various a)
Author to whom correspondence should be addressed. e-mail: [email protected] b) On leave from Chemistry Sciences Faculty, Centr
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