LOCAL-STRUCTURE OF POLYETHYLENE MELT STUDIED BY PULSED NEUTRON TOTAL SCATTERING

Structure factors S(Q) of deuterated polyethylene (PE) in the solid and liquid states have been measured at 20, 130, and 170-degrees-C in a wide range of Q from 0.55 to 25 A-1 by means of pulsed neutron total scattering technique. Very local intrachain structure of the PE melt, such as C-D and C-C bond lengths and angle CCC, angle DCD, and angle CCD bond angles, is determined from a high Q part of S(Q), and is compared with that of solid PE. Interchain structure of the melt is also discussed, assuming that the PE chains are built of small segments of five-CD2-units like pearl necklaces and furthermore, that orientations between the segments are completely uncorrelated and chain connectivity is entirely ignored. The experimental S(Q) is reproduced reasonably well by this simple model with an effective diameter sigma of the segments of 4.34 A and a packing fraction eta of the segments of 0.28, which are consistent with the experimental number density of the PE melt. The different size of the segments like four or six-CD2-units, however, gives poor results with the values of sigma and eta being inconsistent with the experimental number density.