investigate the calibration behaviour of different polyolefins in detail. An even
more complex situation is encountered when the calibration standards are injected
into the first dimension and undergo the entire 2D-LC separation. In this case, very
scattered data have been obtained, as is seen in Fig. 3.42c, which cannot be
explained at present.
3.4.2 Analysis of Ethylene-Vinyl Acetate Copolymers [106]
3.4.2.1 Aim
EVAs are copolymers of ethylene and vinyl acetate and are commercially important
products. These products can be used for a variety of applications including the
production of films, foams or hot melt adhesives, depending upon their comonomer
content. As is true for all copolymers, these materials can exhibit distributions with
respect to molar mass, chemical composition and branching. Therefore, it is
essential to develop comprehensive characterization methods for these copolymers.
The detailed characterization helps to optimize their synthesis and to develop
structure–property correlations.
EVA with low vinyl acetate contents are semi-crystalline materials that can be
separated according to composition by TREF. EVA copolymers containing 9–42 wt
% VA were analysed. It was found that copolymers with VA contents higher than
20 wt% are fully amorphous and thus cannot be separated by TREF or CRYSTAF.
It is, therefore, the aim of the present application to separate EVA copolymers over
the entire comonomer concentration range by HT-HPLC. The molar mass information shall be obtained by online coupled SEC.
3.4.2.2 Materials
• Calibration standards. Linear PE standards (Polymer Standards Service, Mainz,
Germany).
• Polymers. EVA copolymers were obtained from Exxon-Mobil Chemical
(Meerhout, Belgium) and Bayer (Leverkusen, Germany). Their characteristics
were as follows: M w (kg/mol)/PDI/VA (mol%): Escorene 0019 (Exxon Mobil)
197.5/3.1/6.5; Levapren 450 (Bayer) 377.9/8.1/20; Levapren 800HV (Bayer)
224.6/4.1/57.
3.4.2.3 Equipment
• Chromatographic system. A prototype chromatographic system for HT-2D-LC
(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 instruments, Houston,
Texas, USA) equipped with two 200 μL loops was employed for hyphenation of
HT-HPLC and HT-SEC. The 8-port valve was switched every 2 min in order to
126
3 Column-Based Chromatographic Techniques
more complex situation is encountered when the calibration standards are injected
into the first dimension and undergo the entire 2D-LC separation. In this case, very
scattered data have been obtained, as is seen in Fig. 3.42c, which cannot be
explained at present.
3.4.2 Analysis of Ethylene-Vinyl Acetate Copolymers [106]
3.4.2.1 Aim
EVAs are copolymers of ethylene and vinyl acetate and are commercially important
products. These products can be used for a variety of applications including the
production of films, foams or hot melt adhesives, depending upon their comonomer
content. As is true for all copolymers, these materials can exhibit distributions with
respect to molar mass, chemical composition and branching. Therefore, it is
essential to develop comprehensive characterization methods for these copolymers.
The detailed characterization helps to optimize their synthesis and to develop
structure–property correlations.
EVA with low vinyl acetate contents are semi-crystalline materials that can be
separated according to composition by TREF. EVA copolymers containing 9–42 wt
% VA were analysed. It was found that copolymers with VA contents higher than
20 wt% are fully amorphous and thus cannot be separated by TREF or CRYSTAF.
It is, therefore, the aim of the present application to separate EVA copolymers over
the entire comonomer concentration range by HT-HPLC. The molar mass information shall be obtained by online coupled SEC.
3.4.2.2 Materials
• Calibration standards. Linear PE standards (Polymer Standards Service, Mainz,
Germany).
• Polymers. EVA copolymers were obtained from Exxon-Mobil Chemical
(Meerhout, Belgium) and Bayer (Leverkusen, Germany). Their characteristics
were as follows: M w (kg/mol)/PDI/VA (mol%): Escorene 0019 (Exxon Mobil)
197.5/3.1/6.5; Levapren 450 (Bayer) 377.9/8.1/20; Levapren 800HV (Bayer)
224.6/4.1/57.
3.4.2.3 Equipment
• Chromatographic system. A prototype chromatographic system for HT-2D-LC
(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 instruments, Houston,
Texas, USA) equipped with two 200 μL loops was employed for hyphenation of
HT-HPLC and HT-SEC. The 8-port valve was switched every 2 min in order to
126
3 Column-Based Chromatographic Techniques