Ronald Koningsveld

Two-dimensional analysis of copolymers by size-exclusion chromatography and gradient-elution reversed-phase precipitation chromatography

Abstract Poly(styrene—co-acrylnitrile) samples were fractionated by size-exclusion chromatography and subsequent high-performance precipitation liquid chromatography (HPPLC) of effluent fractions. HPPLC was performed on a reversed phase column by using a mobile-phase composition gradient with eluting power increasing from 2,2,4-trimethylpentane as a non-solvent to tetrahydrofuran as a solvent. A mixture of two model copolymers of 23 and 30 wt. % acrylonitrile, having molar masses of 825 and 190 kg/mol, respectively, and a commercial SAN copolymer were studied. The correction of retention volumes for the influence of molar mass was determined, and applied in the evaluation of the data for the commercial sample.

Thermodynamics of mixed polymer melts

Abstract The compatibility of polymer mixtures is discussed from a thermodynamic standpoint. Deviations from the simple lattice theory (Flory-Huggins) show up sensitively in phase diagrams. Possible molecular origins for such deviations are discussed. Experimental techniques that have recently been developed to deal with highly viscous mixtures are described.

Isotope effect in polymer compatibility

SummaryThe deuterium isotope effect on liquid-liquid phase behaviour in polymer blends was investigated with Gordons Pulse Induced Critical Scattering Method. Spinodals in mixtures of polystyrene and polybutadiene were found to be sensitive to replacement of H by D in the polybutadiene. The results indicate a difference in heat of mixing between PS/PBH and PS/PBD-6 as well as an influence on the entropy of mixing.

Multiple critical points in polymer solutions

Abstract Some years ago Tompa formulated the conditions under which ternary polymer solutions can separate into three liquid phases. His considerations were based on the classic thermodynamic treatments by Korteweg, Van der Waals, and others, and he found by analysis of a suitable Gibbs free energy of mixing function that a strictly ternary system (solvent + two polymer homologues differing in chain length) would need a minimum ratio of the chain lengths of the two polymeric components to separate into three phases. It is shown here that Torapas limiting condition (minimum chain-length ratio) conforms with a triple critical point which arises from the confluence of two double-plait points upon a decrease of the chain-length ratio. Tompas criterion is generalized to include polydisperse homopolymers with more than two components, as well as the effect of concentration dependence of the interaction parameter x. These conditions prove to be obeyed quantitatively by actual polymer/solvent systems such as po...