In the present paper, we report the Fourier transform infra-red (FTIR) spectra and an analysis of the normal modes and their dispersion, based on the calculations for an infinite chain and Urey Bradley force field with nonbonded interactions. The results thus obtained agree well with the FTIR spectra. The heat capacity obtained from the dispersion curves via density-of-states is in very good agreement with the experimental measurements between 50 and 500 K. We observed that the main contribution to heat capacity comes from the modes involving the coupling of the backbone skeletal and side-chain motions. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1406-1414, 2009