MOLECULAR-ORIENTATION IN POLYESTER FILMS USING POLARIZED LASER RAMAN AND FOURIER-TRANSFORM INFRARED SPECTROSCOPIES AND X-RAY-DIFFRACTION

Polarized laser Raman and FTIR spectroscopies, as well as wide angle X -ray diffraction (WAXD), have been employed in order to investigate th e distribution of molecular orientation in uniaxially drawn solution-c ast films of well-characterized polyesters, bearing hexyl side chains, at different draw ratios. Both the second ([P-2(cos theta)]) and four th ([P-4(cos theta)], only with Raman) moments of the segment orientat ion distribution function have been determined. Results reveal physica lly meaningful trends of both P-2 and P-4 with draw ratio. A critical comparison among the three techniques confirms the sensitivity of Rama n and FTIR to order at molecular level, when detecting the orientation of a particular segment, compared to similar WAXD results that provid e information on the larger scale liquid crystalline domain orientatio n only and thus correspond to higher values of P-2. Therefore, the cor responding dependencies of P-2 on draw ratio are also different. A sim plified approach for the analysis of the Raman spectra, based on the c ylindrical symmetry of the Raman tensors at a specific vibrational nor mal mode, demonstrates the effectiveness and usefulness of this techni que for accurately and fully determining the molecular orientation in rodlike polymers.