Santoro, G.; Schmidt, M.; Schade, U.; Marco, C.; Ellis, G.: Polarization-modulated synchrotron infrared microspectroscopy for the study of crystalline morphology in some semicrystalline polyolefins. Journal of Physics : Conference Series 359 (2012), p. 012005/1-7

The singular nature of the synchrotron IR radiation (coherence, high brightness, etc.) has provided important advantages over thermal sources for the study of a diverse range of problems in polymeric materials, including polymer blends and composites [1,2], multi-layered polymers [3,4], micro-structured biopolymers [5] and the crystalline morphology of semicrystalline polymers [2,6,7], amongst others. Further, the high intrinsic quasi-linear polarization bending magnet radiation can provide an additional advantage when very high spatial contrast is required in the study of anisotropic materials, allowing measurements to be made without the need for polarizing elements to be inserted in the beam path [8]. By careful alignment of a defined sample axis with the polarization vector of the synchrotron beam we have employed this approach very successfully to study the nature of polymorphic interphases in model fibre-reinforced polymer composites [6,7]. The possibility of mapping the dichroic behaviour of polymer systems is of great interest, since the degree and distribution of molecular chain orientation can provide important insight into the structure-property relations of the materials. However, one of the disadvantages for high spatial resolution SIRMS measurements is the need to carefully rotate and position the sample in order to obtain viable dichroic images. Polarization modulation provides an interesting solution since it employs a photoelastic modulator to vary the electric vector from parallel to perpendicular polarization at high frequency. This technique has been combined with a synchrotron source at the IRIS beamline at BESSY II Synchrotron, Berlin [9], and used effectively to measure anisotropy in inorganic crystals [10] and hydrogen bonding and orientation in wood fibres [11]. The high brightness of the synchrotron source compensates sufficiently for the loss through the additional optical elements. In this work we describe the application of PM-SIRMS to the study of a series of carefully crystallized samples of isotactic polybutene-1 and isotactic polypropylene with different morphologies.