Phase behavior of blends of linear and branched polyethylenes on micron length scales via ultra-small angle neutron scattering (USANS)

SANS experiments on blends of linear, high density (HD) and long chain branched, low density (LD) polyethylenes indicate that these systems form a one-phase mixture in the melt. However, the maximum spatial resolution of pinhole cameras is approximate to 10(3) Angstrom and it has therefore been suggested that data might also be interpreted as arising from a bi-phasic melt with large a particle size (similar to 1 mu m), because most of the scattering from the different phases would not be resolved. We have addressed this hypothesis by means of USANS experiments, which confirm that HDPE/LDPE blends are homogenous in the melt on length scales up to 20 mm. We have also studied blends of HDPE and short-chain branched linear low density polyethylenes (LLDPEs), which phase separate when the branch content is sufficiently high. LLDPEs prepared with Ziegler-Natta catalysts exhibit a wide distribution of compositions, and may therefore be thought of as a "blend" of different species. When the composition distribution is broad enough, a fraction of highly branched chains may phase separate on mu m-length scales, and USANS has also been used to quantify this phenomenon.