Choose sephadex with molecular weight cutoff smaller than the  polymer or protein. This selection ensures that the small molecule can enter the pores and the large protein/polymer does not enter the pores. The larger polymer will elute out in the void volume. (Note: If the void volume is not known then one can determine it.) The small molecules will elute out later. Thus they can be separated.

For polymers mixtures, you can try GPC. The elution is based on the size of the macromolecules (more exactly, it is function of their hydrodinamic radius).