Polymers of 2-methyl-1,3-pentadiene are capable of existing in both isotactic, as well as syndiotactic, configuration. The isotactic 1,4-cispolymer also exists in two stable forms that have different melting points. A complete study of normal modes and their dispersion was carried out using Higgs modification of Wilson's dynamical GF matrix method and the Urey Bradley force field. The force constants have been best fitted to the Fourier transform infrared (FTIR) frequencies. Characteristic features of dispersion curves, like bunching, repulsion, and exchange of character between various pairs of modes, were observed and are discussed here. In addition, the frequency distribution function derived from dispersion curves was used to calculate the heat capacity in the temperature range 50–450 K.