Liquid Chromatography at the Critical Condition (LCCC), is often used for analysis of block copolymers where solvent conditions are chosen to minimize the molecular weight dependence of one of the blocks upon retention ("the critical condition").1 In this work, Gibbs ensemble Monte Carlo simulations are used to examine the effect of monomer sequence on retention in LCCC. The freely-jointed copolymer chains consist of two monomer types: athermal (A) and critical condition (B). Partitioning between a mobile phase and a spherical or cylindrical pore is examined for linear polymers in five sequences: alternating, diblock, both triblocks, and tetrablock. Furthermore, the partitioning of copolymers with 3, 4, or 5-arm star or H architectures is studied, and the limitations of using LCCC to characterize the molecular weight of copolymers assembled from polydisperse hompolymers are explored. It is shown that a small molecular weight dependence remains at the critical condition which implies that there is no true critical condition where the dependence of retention on molecular weight is zero for any architecture. This suggests that polymer separations can be optimized by finding a near-critical condition, but likely not adhered to over a large molecular weight range found in some polymer samples. The retention order of the copolymers depends on the monomer sequence in both linear and H architectures and multiple B blocks exhibit cooperative adsorption in the nonlinear architectures; hence, the copolymer partition constants all deviate from values determined assuming additive free energies of transfer calculated from the partition constants of the homopolymer chains. The elution order does not differ between spherical and cylindrical pores, but a spherical pore of the same diameter yields greater separation. 1Strigel, A. M.; Yau, W. W.; Kirkland, J. J.; Bly, D. D. Modern Size-Exclusion Liquid Chromatography, Second Edition; Wiley 2009.

Monte Carlo simulations of copolymers in liquid chromatography at the critical condition utilizing different pore shapes

251st National Meeting (2016)

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