The unit cell expansion of branched polyethylene as detected by Raman spectroscopy: an experimental and simulation approach
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Raman spectroscopy has become a commonly used technique for the study of phase structure in semicrystalline polymers [1, 2, 3, 4, 5, 6, 7, 8]. Among them, polyethylene (PE) is one of the more deeply explored materials. However, there are still some remaining questions concerning the effect molecular and structural features in the intensity and position of characteristic Raman signals. The Raman crystallinity band appearing in linear PE at 1415 cm−1 is thought to arise from factor group splitting, where the two PE chains packed in the orthorhombic unit cell cause the CH2 bending vibrational mode to split with a second component appearing at 1440 cm−1 [4, 9, 10]. The other characteristic band appearing at 1460 cm−1 has been shown to arise from superposition of rocking combination modes, which interact with the crystal mode with symmetry B3g . Changes in the crystalline phase, i.e. in the unit cell parameters for example as a result of temperature changes or the inclusion of short...
KeywordsLocal Density Approximation Fermi Resonance Interchain Interaction Orthorhombic Unit Cell Comonomer Content
We acknowledge to M.T. Expósito for kindly supply some of the copolymers studied in this work. J. Otegui thanks the CSIC (Post-graduate I3P Program) for the tenure of a fellowship. J.F. Vega acknowledges the MEC for a Ramón y Cajal Tenure (2006). Thanks are due to the CICYT (MAT2006-0400 project) for financial support.
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