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Computational Investigation of Retention of Star Shaped
Polymers at the Chromatographic Critical Condition
Yongmei Wang, Department of Chemistry, University of Memphis
The physical properties of synthetic polymers depend strongly on their microstructures. Branching is one
such microstructure that can dramatically impact properties of synthetic polymers. Detailed molecular
characterization of branched polymers requires a full knowledge of characteristics such as the frequency of
branching, length of branch and architecture of branches (whether star-like or comb-like), and, in many
cases, separation according to these molecular characteristics is desired. Size exclusion chromatography
(SEC), widely used for obtaining molecular weight distribution, is not very effective for providing knowledge
for some of these molecular characteristics because separation in SEC is based on size. In recent years,
liquid chromatography at the critical condition (LCCC) has become popular to characterize polymer systems
with multiple distributions in addition to size distribution. While LCCC has been successfully applied to a
variety complex polymer systems, retention behavior of star shaped polymers (a specialized branch) at the
chromatographic critical condition is not known. Will the stars co-elute with linear chains if the chemical
repeat unit in the two are exactly same? Theory based on Gaussian chain model has predicted co-elution, but
experimental results provided by Prof. Taihyun Chang’s group showed otherwise.
Long arm stars
BS 10-1.48
Short arm stars
BS 2.6-8.6
Long arm stars
BS 26-1.78
We used computer simulations
to explore the origin of complex
retention behavior exhibited by
stars. We found that two
factors, excluded volume
interaction and adsorptive
ends, contribute to the
observed retention behavior as
seen in experiments.
1.4
Linear polymer
Na=9
1.2
Na=24
1.0
Rg/D
Linear PS
Na=14
0.8
0.6
0.4
0.2
0.0
0.5
1.0
1.5
2.0
2.5
K
Prof Chang’s 2D-LC chromatograms
of PS standards and Star-shaped PS
Computer simulation determined partition
coefficients K for linear and star polymers
when modeled as self-avoiding walks with
slightly more adsorptive ends
3.0