Copolymer Retention in Thermal Field-Flow Fractionation: Dependence on Composition and Conformation

Earlier studies of copolymer thermal diffusion are extended here to include several new random and block copolymers of polystyrene (PS) and polyisoprene (PI). Thermal diffusion coefficients for these polymers in tetrahydrofuran and cyclohexane were obtained by thermal field-flow fractionation (ThFFF). The results confirm the dependence of thermal diffusion (and therefore ThFFF retention) on the radial distribution of monomers in the solvated macromolecule. For random copolymers and block copolymers that assume a random configuration in solution, the thermal diffusion coefficient DT is a linear function of monomer composition. This relationship provides a basis for obtaining compositional information on such copolymers by ThFFF. For copolymers subject to radial segregation of its monomers, thermal diffusion is dominated by monomers located in the outer (free-draining) region of the solvated polymer molecule. The dependence of retention on the radial distribution of monomers provides a basis for evaluating bonding arrangements in copolymers.