Comprehensive Two-Dimensional Liquid Chromatography Analysis of a Block Copolymer

Abstract

A two-dimensional liquid chromatography (2D-LC) method, normal phase liquid chromatography (NPLC) for one dimension and reversed phase liquid chromatography (RPLC) for the other dimension, was employed to map the molecular weight distribution (MWD) of the individual blocks of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer. The first-dimension (1st-D) NPLC separates PS-b-PI according to the PS block length while the second-dimension (2nd-D) RPLC separates PS-b-PI according to the PI block length. For the first-dimension NPLC separation, the column temperature was controlled to improve the resolution while the 2nd-D RPLC was run isothermally to reduce the separation time. The MWD information of individual blocks provides equivalent information to MWD and chemical composition distribution of a block copolymer. In this analysis, the effluent from the 1st-D LC separation is concentrated before the injection to the 2nd-D LC by use of a trap column, which allows an efficient interface between the two LC separations. Over 200 different block copolymer species could be identified from the 2D-LC chromatogram.