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. 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 Chang’s 2D-LC chromatograms of PS standards and Star-shaped PS