Chemistry Reference
In-Depth Information
Figure 10.
Block Index results for TREF fractions of an OBC.
fraction. This provides a weighted average
of the block index and can be used as a
value to quantify the overall deviation of
the whole polymer from the expected ran-
dom behavior, as shown in Equation (4).
Additionally, by calculating the second
moment about the mean, a breadth index
can be developed that relates to the
uniformity of the block indices observed,
see Equation (5).
Average BI
¼ BI ¼
X
ðw
i
Table 8 shows the complete calculation for
the OBC example. The average block index
(ABI) for this OBC is estimated to be 0.531
and the block index breadth is 0.136.
Table 9 shows the block index results for
the in-reactor blend (produced with no
CSA) and the Ziegler-Natta LLDPE and
single-site LLDPE. As expected, the block
index average is reported to be zero for
these polymers.
BI
i
Þ
(4)
Further Applications of the Block Index
As demonstrated above, the method can be
used to quantify the deviation of olefin
block copolymers with a crystallizable hard
t
P
w
i
ð
2
BI
i
BI
Þ
Þ
P
w
i
N
BI Breadth
¼
(5)
ð
N
1
Table 7.
Preliminary values needed for block index calculations.
Variable Name
Value
Explanation
tSlope
237.8341
Slope of regression line for Log
e
of the mole fraction of
ethylene versus reciprocal of analytical TREF elution temperature (
8
K)
tIntc
0.6390
Intercept of regression line for Log
e
of the mole fraction of
ethylene versus reciprocal of analytical TREF elution temperature (
8
K)
T
A
372.15
Analytical TREF elution temperature (
8
K) of hard segment
P
A
1.000
Mole fraction of ethylene of hard segment
P
AB
0.892
Mole fraction of ethylene in whole polymer
T
AB
315.722
Equivalent analytical TREF elution temperature (
8
K) of
whole polymer calculated from whole polymer ethylene content
