Dynamical properties in glass forming polymers

Raman low-frequency depolarized light scattering measurements were performed on polymers, namely isotactic polypropylene (iPP), polyethylene (PE) and their blends with hydrogenated oligo cyclo pentadiene (HOCP) at the melting point. In the solid state these blends have a lamellar morphology, crystalline iPP layers alternating to amorphous iPP + HOCP layers. Detailed study of the experimental data showed the main role played by the effective vibrational density of states in comparison with the reorientational diffusion contribution. On the other hand the existence of a boson peak, characteristic of glass forming systems, whose centre-frequency shifts towards higher values, increasing the percentage of HOCP, denotes the disorder effect connected with the presence of this component in the polymeric blends, the occurrence of which is also shown by the evolution of the dynamical correlation length, R~. Furthermore, in the very low-frequency range a crossover (Wco about -0.1 THz) from a spectral phonon-like contribution to a fracton-like contribution is detected.