Small‐angle X‐ray scattering study on concentration dependence of polymer chain dimension

The concentration dependence of polymer chain dimensions was studied by a new type of “tagged polymer method” in small‐angle X‐ray scattering. A small fraction of partially iodinated polystyrene, the tagged polymer, was mixed with polystyrene in toluene. From the excess scattering originated from the iodine, the radius of gyration of the polystyrene chain (M v = 110000) was estimated at various concentrations. It was found that the chain dimension decreases first rapidly and then decreases gradually with increasing polymer concentration, and that, in the bulk, it coincides with the unperturbed chain dimension. The result was compared with theoretical predictions. The theories applicable to low concentrations could predict well the chain dimension upto mass concentrations of ca.0,1 g/cm 3 , while the theories applicable to higher concentrations could not predict well the chain dimension at high concentrations. The conformation of the polymer chain was also discussed. More compact conformations than a random coil as well as the bundle model were not supported by the results.