Retention behaviors of block copolymers in liquid chromatography at the critical condition


The partitioning of a diblock copolymer (AB) and a triblock copolymer (ABA and BAB) into a pore, at a condition similar to that employed in the experimental liquid chromatography at the critical condition (LCCC), was investigated by lattice Monte Carlo simulations with self-avoiding-walk chains. The B block is set at the predetermined critical condition where the partition coefficient of a homopolymer B has a least dependence on its chain length, and hence becomes chromatographically "invisible". The A block is set at the size-exclusion mode and is chromatographically "visible". The partition coefficients of these copolymers were compared with that of a homopolymer A with the same (total) length of the visible A block(s). The partition coefficient of a diblock, K AB, was found to be larger than K A, especially when the A block was short and the B block was long. The difference tends to vanish with an increase in the A block length or a decrease in the B block length. A smaller pore also tends to decrease the difference between the two. For the triblock copolymers, the partition coefficient for BAB, K BAB, was found to be larger than K A and was almost equal to K AB, but the partition coefficient of ABA, K ABA, was found be smaller than K A. These simulation results are in remarkable agreement with experimental observations. As a result, the length of the visible block in diblock copolymer AB and triblock copolymer BAB would be underestimated, and that in triblock copolymer ABA would be overestimated in LCCC. The origins of these observed differences in partition coefficients are explained. © 2005 American Chemical Society.

Publication Title