Separation of Poly(styrene-block-t-butyl methacrylate) Copolymers by Various Liquid Chromatography Techniques

The separation of a mixture of three poly(styrene- block-t -butyl methacrylate) copolymers (PS- b -P t BMA), consisting of polystyrene (PS) blocks of similar length and t -butyl methacrylate (P t BMA) blocks of different lengths, was performed using various chromatographic techniques, that is, a gradient liquid chromatography on reversed-phase (C18 and C8) and normal-phase columns, a liquid chromatography under critical conditions for polystyrene as well as a fully automated two-dimensional liquid chromatography that separates block copolymers by chemical composition in the first dimension and by molar mass in the second dimension. The results show that a partial separation of the mixture of PS- b -P t BMA copolymers can be achieved only by gradient liquid chromatography on reversed-phase columns. The coelution of the two block copolymers is ascribed to a much shorter P t BMA block length, compared to the PS block, as well as a small difference in the length of the P t BMA block in two of these copolymers, which was confirmed by SEC-MALS and NMR spectroscopy.