Chemistry Reference
In-Depth Information
filter paper (available from Osmonics Inc.,
Cat# Z50WP04750). The filtered fractions
are dried overnight in a vacuum oven at
60
8
C and weighed on an analytical balance
before further testing.
Figure 3 shows the analytical TREF
profile comparing an olefin block copoly-
mer (0.878 g/cc, 1.5 I
2
) to a random
copolymer (AFFINITY
TM
VP8770, 0.887
g/cc, 0.9 I
2
) and a polymer blend (0.89 g/cc,
1.0 I
2
) with components that are represen-
tative of the hard and soft segments within
the olefin block copolymer. Although not a
perfect comparison, the differences shown
in Figure 3 cannot be reconciled by the
slight differences in density and melt index
of these polymers. Table 2 summarizes the
analytical characteristics of these polymers.
Figure 3 shows that for this particular OBC,
90 wt% of the polymer eluted at a peak
temperature of 80
8
C. The nearly complete
elution of this OBC, despite being 0.878 g/cc
(19 wt% crystallinity) is unique when com-
pared to the blend and random copolymer
that have peak elution percentages of
35 wt% and 75 wt%, respectively. For the
0.889 g/cc blend, the 35 weight % of the
ATREF peak is consistent with the tar-
geted amount of high crystallinity polymer
made. The fraction eluting below 30
Results and Discussion
Figure 2 shows that olefin block copolymers
produced by chain shuttling catalysis have a
relatively constant melting-point-versus-
density relationship. Karande et al.
[3]
have
shown that OBCs exhibit elastomeric
character while still retaining a high melting
point (115-120
8
C) which is attributed to
the presence of HDPE-like hard segments.
However, the observation of a high melting
point alone is not sufficient to confirm a
polymer's blocky nature. When compared
to random copolymers, OBCs in the
solid-state have a unique crystal morphol-
ogy and show improved physical properties
such as compression set, elastic recovery,
and abrasion resistance.
[3,5]
C
8
Figure 2.
Melting point characteristic of olefin block copolymers.
