Chemistry Reference
In-Depth Information
unknown film sample. We were pleasantly
surprised to see the very good fit between
the predicted and the experimental data for
the film sample. With the success of this
study, it is possible to say that under
favorable conditions, the 3D-TREF can
be quite useful for quantitative studies of
polymer blends and can be used as a tool for
the compositional reverse-engineering of
fabricated products.
determined by the 3D-TREF method. This
can be explained with the help of the
sketches shown in Figure 15 and 16.
Figure 15 depicts a GPC experiment
where a ZN-LLDPE sample is separated
across the MWD in the x-direction. The
downward pointed wide-arrow in the mid-
dle of the Figure is an illustration for this
ZN-type MW-SCB dependency, i.e., the
SCB (or co-monomer content) decreases
with increasing molecular weight. What
researchers wish to achieve is the reversed
MW-SCB dependency in the product, i.e.,
the MW-SCB trend depicted by the upward
pointed wide-arrow in the Figure. The
nature of the MW-SCB analyses is obvio-
usly a two-dimensional problem. We need
comonomer detection (e.g. FTIR) in the
y-direction to complement the GPC-MWD
information in the x-direction. This is how
the GPC-FTIR method works. Alterna-
tively, one can also get the SCBD information
by a cross-fraction of GPC fractions by a
second TREF analysis, as depicted on the left
y-axis of the sketch. This would be called a
GPC-TREF cross-fractionation.
To explain how 3D-TREF works to
determine MW-SCB dependency, we turn
the GPC-based sketch in Figure 15 into the
TREF-based sketch in Figure 16 by a 90
Characterization of Reverse
MW-SCB Dependency
Comonomer incorporation is a very impor-
tant practice for optimizing the properties
of LLDPE and HDPE products. It is highly
desirable to have the comonomers distrib-
uted more in the higher molecular weight
fractions of the sample to achieve a greater
effect of the comonomer presence to the
polymer property. For catalysis research
and product development, there is a strong
need for analytical techniques that can
determine the molecular weight depen-
dency of comonomer and SCB distribution
in polymer products. One approach has
been reported with the use of an online
Fourier transform IR detector (FTIR) in a
GPC experiment.
[9]
However, in a rather
roundabout way, some aspect of the poly-
mer MW-SCB dependency can also be
8
rotation of the plot. In this case, we now
Figure 15.
A sketch to explain the determination of polymer MW-SCB dependency by GPC-FTIR analysis.
