on a atomic-level flat surface like carbon or molybdenum sulfide. The desorption
volumes at increasing isothermal steps are injected into the GPC column, to obtain
the composition–molar mass interdependence in a 3D plot or the 2D projections on
the molar mass or composition curves of Fig. 41.
6 Summary, Conclusions, and Outlook
Polyolefins account for more than 50% of all synthetic polymers being produced
today. The volume and applications of polyolefins have been substantially growing
since the time of the Ziegler and Natta discoveries. With the introduction of
metallocene and other single-site catalysts, polyolefins, with the simple chemistry
of carbon and hydrogen, have evolved into complex microstructures that can be
designed through multiple reactor–catalyst processes to achieve a desired performance for specific applications.
The characterization of the new polyolefins necessarily demands a separation
step of the polymer by certain parameters and, in most cases, a cross-fractionation
is required to obtain the full bivariate distribution. Other features like long
chain branching and stereoregularity need to be characterized as well and
eventually as a function of molar mass.
Molar mass distribution is a dominant microstructure parameter that, in
copolymers, needs to be measured with additional information to account for long
chain branching, comonomer incorporation, or ethylene propylene combinations
(in the case of EP copolymers). The combination of GPC and IR spectroscopy
has been shown to be of great value in the characterization of copolymers. The
importance of automation and sample care, especially in the case of polypropylene,
has been discussed as well as the significant improvement in sensitivity by the
use of IR MCT detectors. There are big expectations for the analysis of ultrahigh
molar mass polyolefins by the new AF4 technology.
Chemical composition distribution has become the most significant microstructure parameter in the new complex polyolefins, where different polymer
families are often part of the same resin. Crystallization techniques are the most
used for measurement of the CCD and a new technique, CEF, has been shown
to be of value for high-throughput applications, with CCD measurements in less
than 1 h. Crystallization techniques can be combined with viscosity and light
scattering detectors to obtain the composition–molar mass interdependence.
The most recent development in separation is the development of high temperature interaction chromatography, which extends the composition distribution analysis
to polyolefin copolymers of very low crystallinity, which is not possible to analyze
by crystallization techniques. The analysis of complex polymers with different
composition can be analyzed in a short time by solvent gradient interaction chromatography, SGIC, on an atomically flat surface like carbon or molybdenum
sulfide packing. The addition of a second separation step by GPC (SGIC2D)
provides the capability to obtain full composition–molar mass dependence.
246
B. Monrabal
volumes at increasing isothermal steps are injected into the GPC column, to obtain
the composition–molar mass interdependence in a 3D plot or the 2D projections on
the molar mass or composition curves of Fig. 41.
6 Summary, Conclusions, and Outlook
Polyolefins account for more than 50% of all synthetic polymers being produced
today. The volume and applications of polyolefins have been substantially growing
since the time of the Ziegler and Natta discoveries. With the introduction of
metallocene and other single-site catalysts, polyolefins, with the simple chemistry
of carbon and hydrogen, have evolved into complex microstructures that can be
designed through multiple reactor–catalyst processes to achieve a desired performance for specific applications.
The characterization of the new polyolefins necessarily demands a separation
step of the polymer by certain parameters and, in most cases, a cross-fractionation
is required to obtain the full bivariate distribution. Other features like long
chain branching and stereoregularity need to be characterized as well and
eventually as a function of molar mass.
Molar mass distribution is a dominant microstructure parameter that, in
copolymers, needs to be measured with additional information to account for long
chain branching, comonomer incorporation, or ethylene propylene combinations
(in the case of EP copolymers). The combination of GPC and IR spectroscopy
has been shown to be of great value in the characterization of copolymers. The
importance of automation and sample care, especially in the case of polypropylene,
has been discussed as well as the significant improvement in sensitivity by the
use of IR MCT detectors. There are big expectations for the analysis of ultrahigh
molar mass polyolefins by the new AF4 technology.
Chemical composition distribution has become the most significant microstructure parameter in the new complex polyolefins, where different polymer
families are often part of the same resin. Crystallization techniques are the most
used for measurement of the CCD and a new technique, CEF, has been shown
to be of value for high-throughput applications, with CCD measurements in less
than 1 h. Crystallization techniques can be combined with viscosity and light
scattering detectors to obtain the composition–molar mass interdependence.
The most recent development in separation is the development of high temperature interaction chromatography, which extends the composition distribution analysis
to polyolefin copolymers of very low crystallinity, which is not possible to analyze
by crystallization techniques. The analysis of complex polymers with different
composition can be analyzed in a short time by solvent gradient interaction chromatography, SGIC, on an atomically flat surface like carbon or molybdenum
sulfide packing. The addition of a second separation step by GPC (SGIC2D)
provides the capability to obtain full composition–molar mass dependence.
246
B. Monrabal