SHORT-RANGE ORDER IN SOME POLYMER MELTS FROM X-RAY-DIFFRACTION

Wide-angle X-ray diffraction measurements were performed on polymer me lts of isotactic and syndiotactic polypropylene (IPP and SPP), poly(et hylenepropylene) (PEP), polystyrene (PS), polyisobutylene (PIE), and p olyethylene (PE), to study the dependence of the short-range structure of polymer liquids on chain architecture. Total structure functions, which comprise intra- and intermolecular contributions, were derived f rom the scattering data. The trivial Fourier components of the intramo lecular structure (C-C similar or equal to 1.54 Angstrom and C-C-C sim ilar or equal to 2.55 Angstrom) were subtracted from the total structu re functions. The remaining functions contain only those intramolecula r contributions dependent on the chain's conformational degrees of fre edom, plus the intramolecular contributions. The structural difference s between the polymers in momentum space are discerned only when the t rivial components are subtracted. This subtraction also reduces the ef fects of truncation errors on Fourier transformation to real space. Th e short-range structure of PIE appears very different compared to all the others, which correlates with anomalies in a number of physical pr operties for this polymer. (C) 1996 John Wiley & Sons, Inc.