In order to calculate the absorption coefficient and the refractive index of the sample a modified method for extracting the optical constants from terahertz measurements based on the concept introduced by Duvillaret et al. was used. The changes in dynamics of the polymer sample were analysed by investigating the change in the absorption coefficient at a frequency of 1 THz as a function of temperature. We have previously demonstrated that discontinuities in the temperature dependent absorption data in disordered materials can be observed that reflect changes in the molecular dynamics of the system. In many cases, including the copolymers studied here, the change in absorption with temperature is linear.