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Structural characteristics of an amorphous polymer melt, poly(propylene oxide) (PPO), have been studied by combining neutron and x-ray diffraction experiments and computer modeling using the reverse Monte Carlo (RMC) technique. The neutron diffraction experiments were performed on hydrogenous as well as deuterated samples. The experimentally determined nearest-neighbor distances were found to be in good agreement with literature data. The RMC modeling was applied for interpretation of the diffraction data to obtain more detailed structural information on bond angles, intermediate and long range correlations. For the intermediate range structure, the experimental structure factors demonstrate a first diffraction peak at about 1.45 Å−1, which from the RMC produced model can be related to the interchain distance of an almost random packing of the polymer chains. To investigate the chain conformation, partial atomic pair correlation functions have been calculated for atoms belonging to monomers close in sequence. The results show that the most probable conformation is a “stretched” trans conformation, where two consecutive methyl groups are pointing in almost opposite directions. Calculated bond and dihedral angle distributions support this finding and demonstrate the ability of the RMC method to produce polymer structures in good agreement with experimental results.

The structural dynamics of a polymer electrolyte model material, poly͑prolyene oxide͒ (PPO)-LiClO 4 ͑and PPO for reference͒, has for the first time been studied using coherent quasielastic neutron scattering. By a combination of neutron spin echo and inverse time-of-flight techniques we investigate the relaxation function in an experimental time window 10 Ϫ12 Շt Շ10 Ϫ8 s at a momentum transfer corresponding to the distance between neighboring interchain segments. We find that the relaxation of the correlation between neighboring chains is slower and more stretched in the polymer salt complex compared to the pure polymer. The data can, for both PPO and PPO-LiClO 4 , be described by a stretched exponential function with temperature independent stretching parameters. While the relaxation times follow the macroscopic viscosity for the former, they do not for the latter. The slower relaxation in PPO-LiClO 4 compared to PPO and the failure of the viscosity scaling in PPO-LiClO 4 may be explained in terms of a temperature dependent effective molecular weight induced by cations acting as cross links between chains. We discuss the origin of the extra stretching of the relaxation in the polymer salt complex under the aspect of heterogeneity, comparing it with data in the literature. We find that the stretching to the major part is intrinsic or at most due to heterogeneities on an atomic length scale. The molecular length scale of the experiment allows for the first time a direct connection to the renewal time in the dynamic disordered hopping model for ion transport in polymer electrolytes.

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