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 bran ched, low density (LD) polyethylenes indicate that these systems form a one -phase mixture in the melt. However, the maximum spatial resolution of pinh ole cameras is approximate to 10(3) Angstrom and it has therefore been sugg ested 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 scatter ing from the different phases would not be resolved. We have addressed this hypothesis by means of USANS experiments, which confirm that HDPE/LDPE ble nds are homogenous in the melt on length scales up to 20 mm. We have also s tudied blends of HDPE and short-chain branched linear low density polyethyl enes (LLDPEs), which phase separate when the branch content is sufficiently high. LLDPEs prepared with Ziegler-Natta catalysts exhibit a wide distribu tion of compositions, and may therefore be thought of as a "blend" of diffe rent species. When the composition distribution is broad enough, a fraction of highly branched chains may phase separate on mu m-length scales, and US ANS has also been used to quantify this phenomenon.