Polymer Structure Determination Using Simultaneous Small- and Wide-Angle X-ray Scattering and Differential Scanning Calorimetry

Abstract

Experimental technique for the characterisation of the thermal--morphological properties of materials by X-ray scattering have been developed at Daresbury. Many thermal events, for example melting endotherms, are signals of phase transitions and thus changes in morphology. Collection of DSC and X-ray patterns simultaneously aids interpretation of the thermal behaviour. In many systems that morphology covers size-scales from the atomic to the microscopic, i.e. Å to μm. There are obvious advantages in collecting both the wide angle (sizes from 1 to 20 Å) and small angle (sizes from 20 to 1000 Å) X-ray patterns simultaneously to unambiguously characterise such thermal events. The new SAXS/WAXS technique makes this possible with a time resolution of 0.1 second which allows heating rates up to 120 °C min -1 . Simultaneous SAXS/DSC and SAXS/WAXS techniques are shown to provide an unambiguous method to follow the structural changes taking place during the programmed heating of a range of multiphase polymeric materials. The principles of the experiments are illustrated with specific examples of polyethylene terepthalate, high density polyethylene and block copolyurethanes.The experimental technique of DSC or DTA is often used in the thermal characterisation of structure-property-relations in polymers [1]. The phenomena investigated, such as melting and glass transitions in semi-crystalline polymers or the glass transitions of blends, are associated with strong morphological features. Much of the knowledge concerning the crystallisation of polymers comes from the application of programmed heating and cooling, and isothermal crystallisation studies by DSC combined with postmortem assessment of morphology by either X-ray diffraction or microscopy. Similarly, the existence of phase separation in polymer blends [2] or microphase separation in block copolymers [3] is often assessed by DSC with confirmation sought by scattering, microscopy and dynamic mechanical thermal analysis. The kinetics of

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