Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(vinyl pyrrolidone)-poly(ethylene glycol)s in non-polar solvent

Dielectric relaxation study of binary mixtures of poly(vinyl pyrrolidone) (PVP) (M-w = 40000 g mol(-1)) and poly(ethylene glycol)s (PEGs) (M-n = 200, 400 and 600 g mol(-1)) with concentration variation was carried out in dilute solutions of benzene at 10.1 GHz and 35degreesC. The average relaxation time tau(0), corresponding to segmental motion tau(1) and group rotations tau(2) was determined for PVP-PEGs mixtures. A comparison of these mixtures relaxation times was made with the relaxation times of PEGs in benzene solvent. The evaluated tau(0) values of PVP-PEGs mixtures in benzene solution are assigned to the reorientation of PEG molecules. It has been observed that the tau(0) value of PVP-PEG200 mixtures increases with increasing concentration of PVP but their values are small in comparison with the tau(0) value of PEG200 molecules. In the case of PVP-PEG400 and PVP-PEG600 mixtures, the evaluated values of tau(0) are greater than the corresponding tau(0) values of PEG400 and PEG600 molecules in benzene solvent. The variation in tau(0) values in these systems has been discussed by considering the stretching effect in the PEGs molecular chains in PVP-PEGs mixtures in benzene solutions. The high value of distribution parameter alpha (approximate to 0.4 to 0.7) suggests that in these mixtures there is a large contribution of segmental motion and group rotations to the relaxation processes. The nature of the formation of hydrogen-bonded PVP-PEG complex heterogeneous network due to hydrogen bonding between carbonyl groups of PVP monomer units and terminal hydroxyl groups of PEGs is discussed. Furthermore, the elongation behaviour of PVP-PEG complex networks in benzene solvent and the molecular dynamics in the mixture due to breaking and reforming of hydrogen bonds has been explored by comparing the evaluated relaxation times and the Kirkwood correlation factor of pure PEG molecules for their possible use in drug control release systems. The relaxation times of these mixtures are independent of their viscosity, but the elongation of the mixture network is influenced by the PEG chain length and the number of hydroxyl groups in comparison with the number of carbonyl groups in the mixtures. (C) 2003 Society of Chemical Industry.