Time-Resolved Saxs and Waxs Studies on Ordering Process in Oriented Crystallization of Polymers
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TIME-RESOLVED SAXS AND WAXS STUDIES ON ORDERING PROCESS IN ORIENTED CRYSTALLIZATION OF POLYMERS KENJI SAIJO AND TAKEJI HASHIMOTO Department of Polymer Chemistry, Faculty of Engineering, Kyoto 606, Japan
Kyoto University,
ABSTRACT Mechanism and dynamics of the ordering process in oriented crystallization of polymers were investigated by time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXS). As a model system for the oriented crystallization, a cross-linked polybutadiene rubber with a high cis-1,4-linkage was chosen, and the structure evolution during the isothermal crystallization was investigated under constant elongations by real time and in situ analyses of the microscopic observables such as long spacing, crystallite size, SAXS integrated intensity, WAXS crystallinity and WAXS line width as well as a macroscopic observable such as stress. The isothermal ordering processes were explored in three different crystallization regimes: crystallization from (i) unoriented melts, (ii) weakly-to-moderately oriented melts and (iii) highly oriented melts. I.
INTRODUCTION
Oriented crystallization of polymers has been a subject of many theoretical and experimental investigations for a long period of time. The studies involve a fundamental physical problem concerning the effect of molecular orientation (i.e., a reduction of conformational entropy of the long-chain molecules) on liquid-solid phase transition, i.e., a problem inherent and unique to the long-chain molecular systems. Objectives of our studies are to pursue real-time and in-situ analyses of the microscopic observables which are directly related to structure rather than the macroscopic observables such as volume, heat content and etc. during the isothermal crystallization in order to clarify mechanism and dynamics of the ordering processes of the systems. As for the microscopic observables the following quantities were investigated; the long spacing L, crystallite size D, integrated scattering intensity Q, as measured by time-resolved small-angle X-ray scattering (SAXS) and crystallinity Xc as measured by time-resolved wide-angle X-ray scattering (WAXS), and as for one of the macroscopic observables the stress relaxation was observed. Similar time-resolved X-ray studies on crosslinked rubbers were carried out by Koch et al. [1] and by Schultz [2]. Cross-linked polybutadiene (PB) with a high cis-l,4-linkage was chosen as a test specimen. The rubber network was first stretched uniaxially to a given draw ratio A (A = 1 to 4.5) and then crystallized isothermally at Tc (Tc = -50 to 100 C) under the constant external draw ratio. The isothermal crystallization processes may be divided into three different regimes for the sake of convenience : Regime I for crystallization under no orientation, Regime II for crystallization under weak-to-moderate orientation, and Regime III for crystallization under relatively high orientation. A 's and Tc's covered in each regime are as follows; A= I and Tc - -50 to -20'C (Regime I), A= 2 to 3.5 and T
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