The normal modes and their dispersions for isotactic poly(4-methyl-1-pentene) have been obtained in the reduced zone scheme using Wilson’s GF matrix method as modified by Higgs. The zone centre frequencies and Urey-Bradley potential field have been obtained by fitting the observed Fourier transform infra-red absorption bands. Some of the characteristic features of the dispersion curves are repulsion, exchange of character and Von Hove type singularities. The heat capacity obtained from the density-of-states agrees with the experimental data up to 305 K, at which glass transition sets in and the experimental curve exhibits a marked change in slope.