measurements on uniaxially oriented films, three infrared absorbance peaks (at 1379, 1154 and 841 cm(-1)) prevailingly associated with the amorphous phase have been located for syndiotactic polystyrene (s-PS) samples with helical crystalline phases. A detailed study relative to the infrared peaks in the wavenumber range 870-820 cm(-1), corresponding to phenyl C-H out-of-plane bending, has shown that the 841 cm(-1) peak is fully associated with conformationally disordered sequences only for samples including trans-planar crystalline phases (alpha and beta) but not for samples including helical crystalline phases (gamma, delta and clathrates). This result has been rationalized on the basis of different intermolecular interactions between phenyl rings, occurring for trans-planar and helical s-PS crystalline phases. Moreover, a preparation procedure leading to fully unoriented films has been described for helical semicrystalline films, which generally present different kinds of uniplanar orientation. FTIR spectra of these fully unoriented semicrystalline films, by subtracting out the amorphous phase contribution with a procedure based on the 1379 cm(-1) peak, have allowed a straightforward isolation of the spectra of the helical s-PS crystalline phases and the quantitative determination of the amorphous content. (c) 2005 Elsevier Ltd. All rights reserved.