Online comprehensive two-dimensional liquid chromatography (LC × LC) is a technique of great importance, because it offers much higher peak capacities than separations in a single dimension. When analyzing polymer samples, LC × LC can provide detailed information on two mutually dependent polymer distributions. Because both molecular-weight distributions and chemical-composition distributions are typically present in synthetic copolymers, combinations of interactive LC with size-exclusion chromatography (SEC) are especially useful for (co)polymer analyses. Commonly applied SEC separations in the second dimension take several minutes, so that a total LC × LC experiment typically requires several hours. This renders LC × LC unsuitable for routine analysis. In the present study we have explored possibilities to perform fast and efficient online comprehensive two-dimensional analysis of polymers using contemporary ultrahigh-pressure liquid chromatography in both dimensions (UHPLC × UHPLC). Gradient-elution UHPLC in the first dimension allowed efficient separations of polymers based on their chemical composition. SEC at ultrahigh-pressure conditions in the second dimension offered very fast, yet efficient separations based on molecular size. The demonstrated UHPLC × UHPLC separations of industrial polymers could be performed within 1 h and provided comprehensive information on two-dimensional distributions.

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In order to determine the chemical composition distribution (CCD) of styrene-butadiene copolymers, gradient polymer elution chromatography has been performed. The separation is mainly based on differences in solubility among the copolymer molecules with different chemical composition. The solubility of a copolymer is dependent on the following parameters: temperature, type of solvent/non-solvent mixture, molecular mass of the polymer and the chemical composition of the polymer. The resolution of the gradient polymer elution chromatographic separation and the molecular mass dependency are influenced by the solvent/non-solvent combination. In order to obtain a reliable separation according to chemical composition, the differences in solubility must be sufficiently high and the molecular mass dependence must be negligible. In order to separate styrene-butadiene copolymers, synthesized by emulsion polymerization, a tetrahydrofuranacetonitrile gradient was used. After calibration of the chromatographic system with styrene-butadiene copolymer standards, the CCD of styrene-butadiene copolymers could be calculated.

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