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within the polymer is not random and that
the blocks or segments within the polymer
are blocked. Block indices can have a range
of values between zero and unity, with unity
being the largest possible deviation from
random based on the hard block composi-
tion.
temperature. When interpreted properly,
this index indicates the degree to which the
intra-chain comonomer distribution is seg-
mented or blocked. The unique crystal-
lization behavior of block copolymers
determine the magnitude of the block
index values because the highly crystalline
segments along an otherwise non-crystalline
chain tend to dominate the ATREF (and
DSC) temperature distributions.
Conclusions
A unique structural feature of olefin based
block copolymers is that the intra-chain
distribution of comonomer is segmented
(statistically non-random). Fractionating
an olefin block copolymer by preparative
temperature rising elution fractionation,
TREF, results in fractions that have much
higher comonomer content than compar-
able fractions of a random copolymer
collected at an equivalent TREF elution
temperature.
We have developed a ''block index''
methodology which quantifies the deviation
from the expected monomer composition
versus the analytical temperature rising
elution fractionation, ATREF, elution
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