Critical retention behaviour of polymers : a study on the influence of some practical parameters

Liq. chromatog. under crit. conditions is an important tool for the microstructural characterization of telechelic polymers and block copolymers. Until now, only little information on the practical aspects of this technique is available. The influence of some important practical parameters was investigated, using polystyrene. Crit. conditions depend strongly on the type of column packing. The soly. of polymers under crit. conditions for different solvent-non-solvent combinations differs to a great extent. For different solvent-non-solvent pairs on reversed-phase systems, a roughly const. eluent strength in terms of the Hildebrand soly. parameter, under crit. conditions is found. Temp. can be a useful tool for fine-tuning crit. conditions. On normal-phase systems, however, the retention of polystyrene changes non-monotonously with temp., which limits the use of temp. variations. It is not possible to obtain exact mol. mass independence on any of the investigated systems, which can not be ascribed to chem. differences. This makes the validity of the current theories on crit. conditions questionable. Esp. for the higher-mol.-mass polystyrenes, peak broadening increases significantly when going from size exclusion conditions to crit. conditions. This phenomenon can limit the application of liq. chromatog. under crit. conditions to a certain mol. mass range. The compn. of the solvent in which polystyrenes are dissolved prior to injection, has to be exactly the crit. solvent compn., in order to suppress zone splitting as much as possible. For higher-mol.-mass polystyrenes this effect cannot be completely prevented. [on SciFinder (R)]