3.4
Two-Dimensional Liquid Chromatography
The most relevant structural parameters of a complex polyolefin are MMD and
CCD. Other structural features such as branching (SCB and LCB distributions) as
well as the distribution of functional groups are not less important but are more
difficult to analyse.
For the last three decades, the analysis of the bivariate CCD-MMD distribution
was limited to the combination of TREF and SEC. As early as 1981, the first
automatic TREF-SEC instrument was introduced by Nakano and Goto [103]. They
were able to present the molecular heterogeneity of complex polyolefins in 3D
diagrams where the TREF elution temperature (as a measure of CCD), the molar
mass and the detector output (as a measure of concentration) were plotted against
each other; see e.g., Fig. 2.8. A fully automated cross-fractionation instrument was
introduced by Polymer Char in 2005, see schematic diagram in Fig. 2.7 [104].
In one of the latest developments, HT-TGIC was coupled to SEC for the analysis
of the molecular heterogeneity of EPDM [105]. In this case, the EPDM was not
fractionated by crystallizability but by adsorptive interaction with a graphitic
stationary phase. The contour diagram of a typical EPDM sample, together with
the reconstructed CCD and MMD plots, is shown in Fig. 3.37. The quantitative
copolymer composition was determined using a dual wavelength IR detector
revealing the numberr of CH 3 groups per 1,000 carbons.
Over the last 20 years, comprehensive 2D-LC has developed into a powerful
analytical technique for the analysis of the molecular heterogeneity of complex
polymers [4, 5]. Coupling of different liquid chromatographic separation methods
enables the high resolution of multiple distinctive molecular distributions. Until
recently, however, the application of 2D-LC was limited to ambient temperature; it
was only in 2009 that the introduction of a commercial instrument based on HT-2DLC was announced. In this instrument, isocratic and solvent gradient separations
can be conducted in the first dimension to provide information on the chemical
composition (functionality, branching) of olefin copolymers and polyolefin blends.
A photograph of the instrument is shown in Fig. 3.38. It comprises a separate
sample dissolution and injection module, a solvent delivery module and a chromatographic unit containing two separate column ovens for the HPLC and the SEC
columns. The instrument is equipped with RI, IR and ELSD detectors, with options
to add a MALLS or viscometer detector.
Ginzburg et al. [106, 107] and Roy et al. [108] published the first results on
2D-LC for polyolefins. The system used by Roy et al. [108] was the same as
described by Macko et al. [84, 85, 87]. The separation of EO copolymers with
regard to chemical composition and molar mass was achieved on this system.
Online coupling of gradient HPLC and SEC for the separation of blends of PP
stereoisomers, ethylene-propylene rubbers (EPRs), ethylene-norbornene
copolymers and ethylene-1-hexene copolymers was employed by Ginzburg
et al. [106]. Hypercarb as the stationary phase and 1-decanol-TCB as the mobile
phase were used for all separations at an operating temperature of 160
C. As an
example, the 2D contour diagram (composition vs. molar mass) of one of the
3.4 Two-Dimensional Liquid Chromatography
119
Two-Dimensional Liquid Chromatography
The most relevant structural parameters of a complex polyolefin are MMD and
CCD. Other structural features such as branching (SCB and LCB distributions) as
well as the distribution of functional groups are not less important but are more
difficult to analyse.
For the last three decades, the analysis of the bivariate CCD-MMD distribution
was limited to the combination of TREF and SEC. As early as 1981, the first
automatic TREF-SEC instrument was introduced by Nakano and Goto [103]. They
were able to present the molecular heterogeneity of complex polyolefins in 3D
diagrams where the TREF elution temperature (as a measure of CCD), the molar
mass and the detector output (as a measure of concentration) were plotted against
each other; see e.g., Fig. 2.8. A fully automated cross-fractionation instrument was
introduced by Polymer Char in 2005, see schematic diagram in Fig. 2.7 [104].
In one of the latest developments, HT-TGIC was coupled to SEC for the analysis
of the molecular heterogeneity of EPDM [105]. In this case, the EPDM was not
fractionated by crystallizability but by adsorptive interaction with a graphitic
stationary phase. The contour diagram of a typical EPDM sample, together with
the reconstructed CCD and MMD plots, is shown in Fig. 3.37. The quantitative
copolymer composition was determined using a dual wavelength IR detector
revealing the numberr of CH 3 groups per 1,000 carbons.
Over the last 20 years, comprehensive 2D-LC has developed into a powerful
analytical technique for the analysis of the molecular heterogeneity of complex
polymers [4, 5]. Coupling of different liquid chromatographic separation methods
enables the high resolution of multiple distinctive molecular distributions. Until
recently, however, the application of 2D-LC was limited to ambient temperature; it
was only in 2009 that the introduction of a commercial instrument based on HT-2DLC was announced. In this instrument, isocratic and solvent gradient separations
can be conducted in the first dimension to provide information on the chemical
composition (functionality, branching) of olefin copolymers and polyolefin blends.
A photograph of the instrument is shown in Fig. 3.38. It comprises a separate
sample dissolution and injection module, a solvent delivery module and a chromatographic unit containing two separate column ovens for the HPLC and the SEC
columns. The instrument is equipped with RI, IR and ELSD detectors, with options
to add a MALLS or viscometer detector.
Ginzburg et al. [106, 107] and Roy et al. [108] published the first results on
2D-LC for polyolefins. The system used by Roy et al. [108] was the same as
described by Macko et al. [84, 85, 87]. The separation of EO copolymers with
regard to chemical composition and molar mass was achieved on this system.
Online coupling of gradient HPLC and SEC for the separation of blends of PP
stereoisomers, ethylene-propylene rubbers (EPRs), ethylene-norbornene
copolymers and ethylene-1-hexene copolymers was employed by Ginzburg
et al. [106]. Hypercarb as the stationary phase and 1-decanol-TCB as the mobile
phase were used for all separations at an operating temperature of 160
C. As an
example, the 2D contour diagram (composition vs. molar mass) of one of the
3.4 Two-Dimensional Liquid Chromatography
119