Structural properties and phonon-like modes in glass-forming polymers

Blends of isotactic Polypropylene (iPP) and Oligo Cycle Pentadiene (HOCP) w ere studied both from a structural (SAXS and SANS) and dynamical (Raman sca ttering) point of view. In the solid state these blends present a lamellar morphology, crystalline iPP layers alternating to amorphous iPP+HOCP layers . The blend phase diagram is characterized by the existence of a miscibilit y gap. SAXS and SANS techniques are applied to investigate the structural. features of both in-gap and out-of-gap blends. SAXS and SANS patterns were Fourier inverted in order to extract the self-correlation fuction of the el ectronic (scattering length) density gamma(x). gamma(x)'s were analysed in terms of a pseudo two-phase model, in the case of out-of-gap blends. This m odel allows to derive structural parameters, such as crystalline, amorphous and total(long period) thicknesses. As far as the dynamical response is co ncerned, low-frequency depolarized light scattering measurements on iPP, Po lyethylene (PE) and their blends with HOCP, at melting point, were performe d. This experimental dynamical study has the goal to show the main role pla yed by the effective vibrational density of states in comparison with the r eorientational diffusion contribution, since relaxations and vibrations are the two main terms that contribute to low-frequency Raman spectra of glass formers. On the other hand, the existence of a boson peak, characteristic of glass-forming systems, whose center-frequency shifts towards higher valu es, increasing the percentage of HOCP, indicates the disorder effect connec ted to the presence of this component in the polymer ic blends, as also sho wn by the evolution of the dynamical correlation length, R-c. Furthermore i n the very low frequency range a crossover (omega(CO) similar to 0.1 THz) f rom a spectral phonon-like contribution to a fracton-like is detected. This behaviour has been interpreted accordingly with the recent theories on the excess of spectral density in such a kind of systems.