STRUCTURAL-PROPERTIES OF POLY(PROPYLENE OXIDE) FROM DIFFRACTION EXPERIMENTS AND REVERSE MONTE-CARLO SIMULATION

Structural characteristics of an amorphous polymer melt, poly(propylen e oxide) (PPO), have been studied by combining neutron and x-ray diffr action experiments and computer modeling using the reverse Monte Carlo (RMC) technique. The neutron diffraction experiments were performed o n hydrogenous as well as deuterated samples. The experimentally determ ined nearest-neighbor distances were found to be in good agreement wit h 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 interm ediate range structure, the experimental structure factors demonstrate a first diffraction peak at about 1.45 Angstrom(-1), which from the R MC produced model can be related to the interchain distance of an almo st random packing of the polymer chains. To investigate the chain conf ormation, partial atomic pair correlation functions have been calculat ed for atoms belonging to monomers close in sequence. The results show that the most probable conformation is a ''stretched'' trans conforma tion, where two consecutive methyl groups are pointing in almost oppos ite directions. Calculated bond and dihedral angle distributions suppo rt this finding and demonstrate the ability of the RMC method to produ ce polymer structures in good agreement with experimental results. (C) 1998 American Institute of Physics. [S0021-9606(98)52441-5].