Studies in the Thermal Diffusion of Copolymers Using Field-Flow Fractionation

Earlier studies of copolymer thermal diffusion are extended here to include several new random and block copolymers of polystyrene and polyisoprene. 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 monomeric units in the solvated macromolecules. For random copolymers and block copolymers that assume a random configuration, the thermal diffusion coefficient, D_T is a linear function of copolymer composition. This relationship provides a basis for obtaining compositional information on such copolymers by ThFFF. For copolymers subject to radial segregation of their monomeric units, the significance of a given unit's role in thermal diffusion increases with the radial distance of the unit from the core of the solvated molecule. The dependence of retention on the radial distribution of monomeric units provides a basis for evaluating bonding arrangements in copolymers.