Crystalline Morphologies of Polychloroprene Thin Films as Revealed by Transmission Electron Microscopy Observation
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Crystalline morphologies of polychloroprene thin films as revealed by transmission electron microscopy observation Toshiki Shimizu, Masaki Tsuji,a) 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 23 June 1998; accepted 8 October 1998)
Thin films of polychloroprene (CR; Neoprene-W) were made by casting its solution (2.0 wt%) in benzene onto the water surface, and some of them were stretched by a desired amount of strain (e) in their “molten” state. The specimens thus prepared were then crystallized and examined by transmission electron microscopy. Morphological observations in bright- and dark-field imaging modes and selected-area electron diffraction analysis revealed directly that filamentous entities observed in the bright-field image are the edge-on lamellar crystals. It was, therefore, confirmed that the morphological results obtained from the thin specimens of CR without any electron staining are basically in accord with those reported so far for the OsO4 -stained thin films of CR.
I. INTRODUCTION
Polychloroprene (CR), which is produced by emulsion polymerization of 2-chloro-1,3-butadiene, is substantially the first synthetic rubber.1–3 The electronwithdrawing chlorine atoms in CR deactivate the double bonds toward attack by oxygen and ozone, and also provide CR with polarity. Consequently, CR is resistant to swelling by nonpolar hydrocarbon solvents. As compared with so-called general-purpose rubbers such as natural rubber (NR) and styrene-butadiene rubber (SBR), CR has several superior properties: higher weatherability, higher heat/flame resistance, better adhesion to polar substances such as metals, and lower permeability to air and water vapor.1–5 Recently, various kinds of CR (and CR with some additives) have been developed for many applications, e.g., covering/coating material for electric wire/cable, rubber hose, and so on.1–5 The major component of CR is trans-1,4-polychloroprene,6,7 and accordingly CR crystallizes upon standing or straining. The C–Cl bond in CR is polar, and therefore the bond enhances interchain interaction and promotes crystallization.2,4 In analogy with other polymers such as polyethylene and NR, crystallization is one of the important factors that influence physical properties of CR; for example, Young’s modulus of NR increases with increasing crystallinity.8 If crystallization is controlled according to our expectations, more advanced performance and/or new properties might hopefully be added to this material. As already known, the crystallization rate of CR depends a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 4, Apr 1999
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strongly on the configuration of CR, namely on the content of trans-1,4 units in CR, which is influenced by polymerization temperature.3,9 The crystalliza
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