Computational Investigation of New Separation Schemes for Branched Polymers

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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 Changs group
showed otherwise.
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.
Computer simulation determined partition
coefficients K for linear and star polymers when
modeled as self-avoiding walks with slightly more
adsorptive ends
Prof Changs 2D-LC chromatograms of PS standards
and Star-shaped PS