The effect of short chain branching on local chain organisation in isotopically labelled blends of polyethylene

The complementary techniques of small angle neutron scattering (SANS) and infra-red spectroscopy have been used to determine features of molecular trajectory for isotopic blends incorporating linear polyethylene and copolymers containing butyl or hexyl branches. SANS data show both a more compact conformation for a copolymer guest molecule than for a linear guest and also a smaller molecular expansion with increasing molecular weight when both guest and host are copolymers. These blends also show the smallest proportion of {110} isolated guest stems, while wholly linear blends show the largest proportion, on the evidence of the infra-red CD2 bending band profiles. Estimates are made of the sizes of ‘groups’ of adjacent stems, and these also show a corresponding dependence on the sample type, indicating a higher proportion of adjacent re-entry for copolymer blends than for linear blends.