Conformational distribution of poly(ethylene oxide) in molten phase and in aqueous solution by quasi-elastic and inelastic light scattering

We report on measurements performed by Raman scattering, PCS and ultrasonic velocity measurements on poly(ethylene oxide) both in the molten phase and in aqueous solution. Increasing the polymerization degree, m, the Raman analysis of the D-LAM (disordered longitudinal acoustic mode) spectral contribution to the pure polymers reveals a behaviour of the centre frequency and linewidth which has been connected with an oligomer-polymer transition occurring at m congruent to 13. In aqueous solutions the frequency increase towards values corresponding to the crystal ones and the sharpening of the D-LAM spectral contribution indicate that the addition of water,destroys the intermolecular interactions and stiffens the coil structure. In addition evidence of a more ordered conformation with respect to the melt phase is presented. The temperature analysis of the D-LAM band and of the hydrodynamic radius, evaluated by PCS, reveals that the solvent power of water increases up to T = 45 degrees C, decreasing at higher temperature. Interpreted in conjunction with ultrasonic data these apparently differing findings provide a coherent interpretative key capable of encompassing the structural properties of our systems. Finally the role played by inter- and intra-molecular interactions is discussed within the framework of current theories.