LIQUID-CHROMATOGRAPHY OF POLYISOPRENES - DETERMINATION OF CRITICAL COMPOSITION USING NON PROTIC BINARY AND ACIDIC TERNARY SOLVENT MIXTURES

Mixed solvent systems for the critical liquid chromatography of polyis oprenes are investigated. Under critical solvent conditions, the energ etic and entropic interactions between the polymer and the stationary phase cancel each other, the free energy of interaction approaches zer o and the retention time is independent of the polymer chain length. C ritical conditions for polyisoprene-silica gel have been established f or a non-protic binary solvent mixture [i-octane-tetrahydrofuran (THF) ; critical composition at 0.88% (v/v) of THF] and a ternary system con taining an acidic component [i-octane-[0.5% (v/v) acetic acid in methy l-tert.butylether (MTBE)]; critical composition at 0.65% (v/v) of the acetic acid-MTBE mixture]; (C) 1997 Elsevier Science B.V.