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SynopsisThe coupling of a high-temperature liquid chromatograph (Waters 150C) with a home-made continuous capillary viscometer is described. This detector is the only one suitable for high-speed GPC when the small volume of the mobile phase prohibits the coupling with a classical viscometer. The pressure drop of the GPC effluent through the capillary is continuously measured along with the refractive index change. This dual detection leads to the determination of the intrinsic viscosity as a function of the elution volume, thus allowing a precise use of Benoit's universal calibration. The accuracy of our system is demonstrated in the case of the characterization of linear and branched polyethylene samples. The results concerning the average molecular weights as well as the branching factors (structure parameter g' and long-chain branching frequency X) are in close agreement with those obtained by the classical way (coupling traditional GPC and discontinuous viscometry). It is well known that an estimate of the X coefficient is extremely dependent on several hypotheses. However, for a set of commercial low-density polyethylenes, we obtained X values about 0.5 X with no marked change along the molecular weight range.

A method is proposed for determining the thermodynamic characteristics of macromolecules grafted on an inert plane. Based on Flory's theory for macromolecular solutions and gels, the swelling of such a grafted phase by a solvent is calculated. Results are applied to evaluate the partition coefficient of a solute between grafted molecules and a solvent. Variations of this coefficient with the molecular sizes of the solvent, solute, and grafts and with the interactions between these molecules are studied.The behavior of a macromolecule in the vicinity of an interface is useful for understanding the adsorption of polymer~l-~ and for explaining the fractionation observed in gel permeation chromatography (GPC).4-6In the particular case of a macromolecule attached by one of its ends to a surface, numerous applications are suggested: liquid-liquid chromatography, selective absorption of pollutants, compatibilization of prosthesis with blood, stabilization of polymer emulsions, supported catalysis, etc.The thickness of the polymer layer adsorbed on a surface and its variation with molecular weight has been experimentallyThe segmental distribution of grafted macromolecules has been evaluated both theoretically and by ~i m u l a t i o n~~'~ but their thermodynamic characteristics have not been systematically studied. These characteristics should allow one to better understand the behavior of grafted materials. Hence, we investigated the problem and using Flory's theory on macromolecular solutions,13J4 we calculated the swelling by a solvent of a macromolecular phase grafted on a plane and we deduced the partition coefficient of a solute between the two phases of such a system.15 ModelAs depicted in Figure 1, we take as our model N3 nonentangling polymer chains grafted onto an inert plane. That is, chains are independent and there is no adsorption effect on the wall.According to the lattice liquid theory13J4 solvent and polymer molecules are assumed to be constituted of segments of identical volume. Thus, each molecule of solvent is composed of rl segments and each molecule of polymer is composed of r3 segments.This rough model, representative of graft phases used in practice, requires the specification of only a few parameters and the resulting expressions can be easily applied to experimental data. For example, it elucidates the behavior of chemically bonded stationary phases which have gained increasing importance in liquid chromatography. Free Energy of Mixtures solvent with the grafted phase is AF I F = A F M + A F E L The free-energy change involved in the mixing of a ( l a ) in which A F M is the free energy of mixing AFM = A H M -TASM (Ib) and A F E L is the elastic free energy due to the molecular expansion of the grafted chains in the solvent. 1. Computing E n t r o p y of A S M Mix. Consider a solution consisting of N , molecules of solvent and N3 molecules of polymer. The number of permissible patterns of the two kinds of molecules in such a system is Q.When the polymer molecules have one end attached to a surfa...

We have synthetized an optically active macromolecular chromatographic packing from cross-linked polyacrylamide grafted with an optically active ",-amino acid. This packing, in the form of small beads, slightly swells in water. Its granularity, porosityand rigidity are suitable for high pressure liquidchromatography. Such packings, complexed by a metallic ion, are efficient for the resolution of many underivatized racemic a-amino acids by elution with water. As an example,on one of these packings, containing Cu++ ions, enantiomers of valine, threonine, isoleucine, serine, phenylalanine, tyrosine, tryptophan, and asparagineare completely resolvedin less than one hour. ADVANCES IN THE CHROMATOGRAPHIC RESOLUTIONOF ENANTIOMERS