SMALL-ANGLE NEUTRON-SCATTERING STUDIES OF PARTIALLY LABELED CRYSTALLINE POLYETHYLENE

Partially deuterated (DPE) and conventional (PE) polyethylene are used to study chain conformations in melt-crystallized blends. The deuteri um fraction y ranged from 0. 19 to 0.59, resulting in melting temperat ure differences DELTAT(m) = 1-2-degrees-C between PE and DPE. Small-an gle neutron scattering (SANS) from molten or quench-crystallized blend s yields single-chain radii of gyration R(g) which apparently depend o n y and are as much as 15% larger than values reported from experiment s with fully labelled (y = 1) polyethylene. Quenched PE/DPE blends giv e Gaussian-like scattering patterns out to q = 0.1 angstrom-1, the lim it of these studies. This implies considerably more intramolecular cor relations at distances of 10-50 angstrom than derived from a similar e xperiment employing fully deuterated chains. The present result is tho ught to be more representative of semicrystalline polyethylene since D PE and PE are nearly perfectly matched. Crystallization by slow coolin g creates non-statistical concentration fluctuations which result in e xcess forward SANS, so a melting point difference of 1-degrees-C is st ill sufficient to trigger 'clustering' or 'segregation' of PE and DPE. Intensity decays at q > 0.05 angstrom-1 to the same value as in quenc hed samples, regardless of crystallinity changing from 0.52 to 0.74. T hese results are shown to be consistent with dominant 'near-adjacent r e-entry' during crystallization of polyethylene from the melt.