Theory of chromatographic separation of linear and star-shaped binary block-copolymers

Equations for the distribution coefficient of heteroarm stars are derived by using a model of an ideal chain in a slit-like pore; these equations together with those previously reported for linear block-copolymers are applied to describe chromatography of such copolymers. According to the theory, the retention generally depends on molar mass, composition, and architecture (microstructure and topology) of copolymers, on pore size and on adsorption interaction of chain units A and B. Three special modes of chromatography are studied in detail. (i) If interactions for A and B are close to the critical point of adsorption (CPA), the retention practically does not depend on architecture, and high molar mass copolymers can be separated by composition. (ii) At SEC condition for B and strong adsorption for A, copolymers in principle can be separated by architecture; better separation is expected in wide pores. Retention of linear block-copolymers decreases with increasing of the number of blocks; for heteroarm stars the theory predicts retention decreasing as: AB > StarAAB > StarABB; StarAAAB > StarABBB > StarAABB; StarAAAAB > StarABBBB > StarAAABB > StarAABBB. (iii) At the CPA for B copolymers AB, BAB and heteroarm stars regardless molar mass of B, MB, can be separated by MA. The same is true for ABA and ABAB…A in narrow pores. While the retention of AB, BAB, Star AB…B and Star AAB…B is the same, copolymers AB, ABA and linear multiblock-copolymers can be separated, as well as symmetric and very asymmetric triblock-copolymers ABA.