Chemistry Reference
In-Depth Information
non-random and is in fact blocked, because
it deviates from that of a statistically
random copolymer in a theoretically pre-
dictable manner. Since the amount of
comonomer can be predicted from a given
elution temperature for a statistically ran-
dom copolymer, the ''blockiness'' of an
olefin block copolymer can be defined on
the basis of Flory's equilibrium crystal-
lization theory.
[8]
For random copolymers,
Flory proposed a theoretical relationship
for the probability of having a minimum
crystallizable sequence length determined
primarily by the equilibrium crystallization
temperature. The conditional probability of
sequential monomer insertion (ethylene in
the case of the OBCs described here) is
defined as
. The magnitude of the condi-
tional probability, p, is compared to the
molar fraction of monomer in the whole
polymer, X
A
, (refer to Figure 6) to test
whether, based on a random probability of
the intrachain monomer distribution, the
copolymer is random. If the conditional
probability of observing a crystallizable
sequence is less than that determined by
average molar monomer content of the
whole polymer, then the polymer is des-
cribed as having an alternating distribution.
If the probability of observing a crystal-
lizable sequence was greater than that
determined by the average molar monomer
content of the whole polymer, then the
polymer is described as having a blocky
p
Figure 6.
Flory's polymer probability definitions.
