We have performed a series of small angle neutron scattering
(SANS) experiments on blends
of linear and branched polyethylenes to investigate the level of
branching that is required to phase separate
the system. These results confirm that the mixtures are homogenous
for all compositions when the branch
content is low (i.e., <4 branches/100 backbone carbon atoms for
molecular weight M
w ∼ 105).
However,
when the branch content is higher (typically ≥8 branches/100 backbone
carbons), the blends phase
separate. Segregation can also be driven by isotope effects, when
the molecular weight is sufficiently
high so that the product of the polymerization index and the
H/D interaction parameter
(NχHD) > 2. In
each case, the resolution of conventional SANS pinhole cameras
(Q
min ∼ 10-3 Å-1)
is adequate to determine
the state of mixing, even for systems with large domains.
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