Monte Carlo study of supramolecular polymer fractionation: selective removal of chain stoppers by phase separation

Supramolecular polymers consist of bifunctional monomers that join and break reversibly. Supramolecular polymer solutions are often polluted by monofunctional contaminants, which drastically reduce the chain-forming capabilities of the system. Unfortunately, the monofunctional contaminants are difficult to remove due to the physical and chemical resemblance with the bifunctional counterparts. In this paper, we present a method to specifically remove the monofunctional contaminants from a supramolecular polymer solution. The general idea is to induce phase separation by decreasing the solvent quality and to remove the most dilute phase. This concept is explored by means of a recently developed Monte Carlo scheme to calculate the compositions of the coexisting liquid phases. The simulations provide a proof of principle that the proposed purification method is suitable to remove the monofunctional contaminants efficiently. The calculations indicate that, at the right experimental conditions, the vast majority of the monofunctional contaminants can be removed in this way while retaining most of the bifunctional monomers. Because of the general nature of the arguments presented here, it is to be expected that the results are applicable to a large variety of supramolecular systems. Moreover, the method is very suitable for large-scale applications because only solvent is added and no tedious chromatographic steps are required.