CRITICAL CONDITIONS IN THE LIQUID-CHROMATOGRAPHY OF POLYMERS

The liquid chromatography of polystyrene and polymethylmethacrylate have been investigated using porous silica gel packings. It has been found that the size exclusion and interactive modes of chromatography can be combined in a single column, operating isocratically, provided the thermodynamic quality of a mixed eluent is precisely controlled. In our experiments the ratio of a nonpolar thermodynamically good-solvent (toluene) and a polar nonsolvent (methanol) were systematically varied. The calibration curves were observed to shift rapidly towards the vertical, particularly for mixtures thermodynamically much poorer than the theta-composition. Furthermore, binary mobile phase compositions were identified where the retention volume was independent of the molar mass of the polymer probe. These ''limiting conditions'' have been measured on polymers up to two million daltons and have been found to be largely pressure insensitive. They potentially can be applied for the molecular weight analysis of block and graft copolymers, and for polymer blends, since the separation according to size is deconvoluted from the separation by chemical composition.