structural features like long chain branching and stereoregularity can also be
obtained by these method combinations.
A fascinating new development in column-based chromatographic techniques
for polyolefin analysis is high-temperature interaction chromatography. In contrast
to crystallization-based techniques, interaction chromatography can address the
complete sample irrespective of whether it is crystalline or amorphous. The use
of gradient HT high performance liquid chromatography (HPLC), liquid chromatography at critical conditions at high temperatures above 120
C, HT-HPLC based
on precipitation–redissolution or adsorption–desorption for chemical composition
analysis of polyolefins have been reported in recent years. These methods are a
major breakthrough in the field of chemical composition analysis of polyolefins.
They overcome the drawbacks of other techniques used previously for chemical
composition analysis as they address both the amorphous and the crystalline part of
the sample. The ultimate recent development in polyolefin analysis is coupling of
HT-HPLC with online size exclusion chromatography. This fascinating development leads to the molar mass distribution of the sample as a function of its chemical
composition. Two-dimensional (2D) HT-HPLC is a major advancement in polyolefin analysis and promises to be the future for research-oriented polyolefin
laboratories. The most recent step regarding hyphenation of 2D-HT-HPLC is the
coupling with infrared and light scattering detectors.
High-temperature field-flow fractionation (HT-AF4) overcomes the columnrelated problems of previous separation techniques like sample degradation or
sample loss due to interactions with the stationary phase or the column frits.
HT-AF4 is particularly useful for ultrahigh molar mass samples and can emerge
as the first choice for very high molar mass polyolefins in future. It remains to be
seen if HT-AF4 (similar to column-based fractionation methods) will be
hyphenated with spectroscopic detectors or will be used as one dimension in
two-dimensional experimental set-ups in the future.
To summarize, all techniques used for polyolefin characterization have
advantages and disadvantages. Some information can be obtained more reliably
from one technique and some other from other techniques. One has to decide on the
problems to be addressed using a given technique. Nevertheless, 2D-HT-HPLC
seems to be one major technique to be used for polyolefin analysis in the future due
to its ability to provide molar mass distribution as a function of chemical composition distribution of the sample which is not possible by other approaches.
The fact that there is constant progress in developing new separation methods for
polyolefins has been demonstrated very recently by introducing high-temperature
thermal gradient interaction chromatography. In addition to using an interacting
stationary phase, temperature gradients are used to enhance separation of complex
olefin copolymers.
174
5 Conclusions and Future Trends
obtained by these method combinations.
A fascinating new development in column-based chromatographic techniques
for polyolefin analysis is high-temperature interaction chromatography. In contrast
to crystallization-based techniques, interaction chromatography can address the
complete sample irrespective of whether it is crystalline or amorphous. The use
of gradient HT high performance liquid chromatography (HPLC), liquid chromatography at critical conditions at high temperatures above 120
C, HT-HPLC based
on precipitation–redissolution or adsorption–desorption for chemical composition
analysis of polyolefins have been reported in recent years. These methods are a
major breakthrough in the field of chemical composition analysis of polyolefins.
They overcome the drawbacks of other techniques used previously for chemical
composition analysis as they address both the amorphous and the crystalline part of
the sample. The ultimate recent development in polyolefin analysis is coupling of
HT-HPLC with online size exclusion chromatography. This fascinating development leads to the molar mass distribution of the sample as a function of its chemical
composition. Two-dimensional (2D) HT-HPLC is a major advancement in polyolefin analysis and promises to be the future for research-oriented polyolefin
laboratories. The most recent step regarding hyphenation of 2D-HT-HPLC is the
coupling with infrared and light scattering detectors.
High-temperature field-flow fractionation (HT-AF4) overcomes the columnrelated problems of previous separation techniques like sample degradation or
sample loss due to interactions with the stationary phase or the column frits.
HT-AF4 is particularly useful for ultrahigh molar mass samples and can emerge
as the first choice for very high molar mass polyolefins in future. It remains to be
seen if HT-AF4 (similar to column-based fractionation methods) will be
hyphenated with spectroscopic detectors or will be used as one dimension in
two-dimensional experimental set-ups in the future.
To summarize, all techniques used for polyolefin characterization have
advantages and disadvantages. Some information can be obtained more reliably
from one technique and some other from other techniques. One has to decide on the
problems to be addressed using a given technique. Nevertheless, 2D-HT-HPLC
seems to be one major technique to be used for polyolefin analysis in the future due
to its ability to provide molar mass distribution as a function of chemical composition distribution of the sample which is not possible by other approaches.
The fact that there is constant progress in developing new separation methods for
polyolefins has been demonstrated very recently by introducing high-temperature
thermal gradient interaction chromatography. In addition to using an interacting
stationary phase, temperature gradients are used to enhance separation of complex
olefin copolymers.
174
5 Conclusions and Future Trends