Characterization of thermal diffusion of copolymers in solution by thermal field‐flow fractionation

Extending our earlier measurements of homopolymer thermal diffusion, we characterize here the thermal diffusion of nine copolymers in toluene by thermal field‐flow fractionation (thermal FFF). The copolymers are organized into groups whose members differ in one major aspect only. These differences include monomer ratios in random copolymers, block arrangements in block copolymer pairs having both linear and star‐shaped configurations, and arm numbers and arm molecular weights in star‐shaped copolymers. By examining the influence (or lack thereof) of these distinctive features on the thermal diffusion coefficient D_T, the general phenomenon of thermal diffusion in polymer solutions is further characterized. Specifically, two principal observations are made. First, for copolymers subject to the radial segregation of its monomers, thermal diffusion appears to be dominated by the monomers preferentially located in the outer (free‐draining) region of the solvated polymer molecule. Second, for copolymers lacking monomer segregation, D_T can be described by a weighted average of the D_T values of the corresponding homopolymers, where the weighting factors are the mole‐fractions of each monomer type in the copolymer.