TREF is governed by the crystallization-dissolution behaviour of the samples in
contrast to interactive HPLC, which is based on selective adsorption and desorption
of the macromolecules. It is one of the major advantages of 2D-LC over TREF-SEC
that it enables one to address all sample components irrespective of their
crystallinity.
The following two applications of HT-2D-LC have been published previously in
[5]. They are reproduced here because they serve as excellent examples for the
power of this technique.
3.4.1 Analysis of Polypropylenes by Tacticity and Molar Mass [107]
3.4.1.1 Aim
Polyolefins are similar to other synthetic polymers in that they are complex with
regard to different parameters of molecular heterogeneity. PPs exhibit a MMD and
a distribution regarding tacticity. Due to the chiral centre of propylene, different
catalysts and polymerization conditions may result in the formation of iPP and sPP
polymer chains or subunits. When different tactic units are distributed along the
polymer chain, the material is atactic (aPP). The average tacticity of PP can be
analysed by FTIR or NMR spectroscopy. In FTIR spectroscopy, the information
relates to a global % tacticity while NMR provides the types and concentrations of
tactic triads or pentads depending on the technical parameters of the spectrometer.
Quantitative information on the composition of a single polymer chain cannot be
provided nor can a blend (of, e.g., iPP, sPP and aPP) be differentiated from a PP
containing different tactic units. It has been shown in a number of applications that
the Hypercarb stationary phase exhibits a remarkable selectivity towards different
polyolefin structures; see Sects. 3.2.2 and 3.2.3. This stationary phase shall now be
used for the separation of PP according to tactivity. The molar mass of the different
tactic polymers shall be analysed by online coupled SEC.
3.4.1.2 Materials
• Calibration standards. Linear PE and PP standards (PSS GmbH, Mainz,
Germany).
• Polymers. sPP with M w 196 kg/mol (Sigma-Aldrich, Munich, Germany), aPP
with M w 211 kg/mol (LyondellBasell, Ferrara, Italy), iPP with M w 45 kg/mol
(University of Stellenbosch, South Africa).
3.4.1.3 Equipment
• Chromatographic system. A prototype chromatographic system for HT-2D-LC
analysis constructed by Polymer Char (Valencia, Spain) was used for all
experiments. The system has an autosampler, two separate ovens, valves and
two pumps equipped with vacuum degassers (Agilent, Waldbronn, Germany).
The first oven is for thermostating the SEC column while the other one is used to
thermostat the HPLC column. The injector and a switching valve are housed in
the latter. An electronically controlled 8-port valve EC8W (VICI Valco
122
3 Column-Based Chromatographic Techniques
contrast to interactive HPLC, which is based on selective adsorption and desorption
of the macromolecules. It is one of the major advantages of 2D-LC over TREF-SEC
that it enables one to address all sample components irrespective of their
crystallinity.
The following two applications of HT-2D-LC have been published previously in
[5]. They are reproduced here because they serve as excellent examples for the
power of this technique.
3.4.1 Analysis of Polypropylenes by Tacticity and Molar Mass [107]
3.4.1.1 Aim
Polyolefins are similar to other synthetic polymers in that they are complex with
regard to different parameters of molecular heterogeneity. PPs exhibit a MMD and
a distribution regarding tacticity. Due to the chiral centre of propylene, different
catalysts and polymerization conditions may result in the formation of iPP and sPP
polymer chains or subunits. When different tactic units are distributed along the
polymer chain, the material is atactic (aPP). The average tacticity of PP can be
analysed by FTIR or NMR spectroscopy. In FTIR spectroscopy, the information
relates to a global % tacticity while NMR provides the types and concentrations of
tactic triads or pentads depending on the technical parameters of the spectrometer.
Quantitative information on the composition of a single polymer chain cannot be
provided nor can a blend (of, e.g., iPP, sPP and aPP) be differentiated from a PP
containing different tactic units. It has been shown in a number of applications that
the Hypercarb stationary phase exhibits a remarkable selectivity towards different
polyolefin structures; see Sects. 3.2.2 and 3.2.3. This stationary phase shall now be
used for the separation of PP according to tactivity. The molar mass of the different
tactic polymers shall be analysed by online coupled SEC.
3.4.1.2 Materials
• Calibration standards. Linear PE and PP standards (PSS GmbH, Mainz,
Germany).
• Polymers. sPP with M w 196 kg/mol (Sigma-Aldrich, Munich, Germany), aPP
with M w 211 kg/mol (LyondellBasell, Ferrara, Italy), iPP with M w 45 kg/mol
(University of Stellenbosch, South Africa).
3.4.1.3 Equipment
• Chromatographic system. A prototype chromatographic system for HT-2D-LC
analysis constructed by Polymer Char (Valencia, Spain) was used for all
experiments. The system has an autosampler, two separate ovens, valves and
two pumps equipped with vacuum degassers (Agilent, Waldbronn, Germany).
The first oven is for thermostating the SEC column while the other one is used to
thermostat the HPLC column. The injector and a switching valve are housed in
the latter. An electronically controlled 8-port valve EC8W (VICI Valco
122
3 Column-Based Chromatographic Techniques