The liquid chromatography of macromolecules under limiting conditions of desorption (LC LCD) is based on a combination of exclusion and adsorption separation mechanisms. Eluent promotes desorption of macromolecules that are dissolved in an adsorption-promoting liquid and injected into a liquid chromatographic (LC) column packed with porous adsorptive packing. The zone of sample solvent forms an “adsorption promoting barrier”. Under properly chosen, “limiting”, conditions the transport of adsorbing polymer species along the column is slowed since they cannot pass the above adsorption-promoting barrier. As result, macromolecules of various sizes and molar masses leave LC column in the form of a rather narrow band immediately behind the zone of their initial solvent. At the same time, other kinds of polymer chains which exhibit lower affinity toward column packing and less adsorption surmount the zone of their original solvent. They are eluted in the size exclusion chromatographic mode. In this way macromolecules with different chemical structures can be discriminated. The LC LCD idea has been tested with a model system comprising poly(methyl methacrylate) probes, silica gel column packing, toluene (adsorbing liquid), and tetrahydrofuran (desorbing liquid). Some applications of this novel LC procedure have been proposed. They include separation of two-component and multicomponent blends, various kinds of copolymers, and oligomers.

As a rule, critical conditions in liquid chromatography of synthetic macromolecules are adjusted by both mixed mobile phase composition and temperature. The application of single component eluents is attempted in the present study. The enthalpic interactions in the column are controlled exclusively by temperature. Poly(methyl methacrylate)s (PMMA), poly(n-butyl methacrylate)s (PnBMA), and polystyrenes (PS) in various solvents are investigated with bare silica gel and silica C18 bonded phases. Using a series of single eluents based on various esters, PMMA probes, and bare silica gel, it is shown that minute variations in eluent nature strongly affect polymer retention, and temperature represents a too weak parameter to adjust critical conditions in thermodynamically good solvents. The idea is proposed and tested that the sensitivity of polymer retention toward temperature variations increases in the vicinity of Θ conditions, where the structure of macromolecules in solution strongly depends on temperature. The critical conditions have been identified in some single eluents which are thermodynamicaly poor solvents for polymers investigated, namely, acetonitrile for PMMA at 66 °C and dimethylformamide for PnBMA at 154 °C and for PS at 95 °Csall with C18 bonded silica gel. A "criticallike" elution was also observed in cyclohexane for PS at 9 °C with silica gel C18 packing, which is well below the Θ temperature. It is demonstrated that poly(methyl methacrylate)s can be separated according to stereoregularity in the area of critical conditions using acetonitrile eluent and silica C18 column packing. The excessive polymer peak broadening and decreased recovery which were observed in some mixed mobile phases are diminished in the single component critical eluents studied, but they are not fully eliminated.