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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.

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Continuous viscometric, detection is based on the measurement of ressure drop in an on-line small capillary tube in which cErornatogra hic eluents flow at constant flow rate. This detector is ayways coupled with a concentration detector (usually refractometer) and located before it t o avoid back presrura in the refractometer. In order to obtain reliable information f o r polymer samples, it is general1 necessary to connect these two detectors to a computer whicx performs data acquisition and treatment.First we discuss the rroblem of shape, g?ometry and dimensions of the viscometer. Tge typical charactsristlcs are the result of a comproaise between contradictory hrgets, mainly small internal vblume !ow shear rate,and low prassure drop. It is shown that $oiseullle's lammar flow is only obtained when coiling radius of the measurement tube ? s greater than 6 cm which is not the cass inside tne refractometer. Accbrdingly, tiro pressura transducers are necessary t o eliminate pressure drop data comlng from refractorneter. LESEC, LECACHEUX, AND MAROTIn a second ,part, we show how to extract information from pressure variation data. By using conc?ntration data, pure solvent pressure and sample pressure it 1s possibl? to calculate intrinsic viscosity extrapolated to zsro concentration at,each,point of the chromato ram. By comparison rith intrinsic viscosity cf the pol mar use! for calibration, a correction of hydro& narcic v01une according : ? Benoit's universal calibration leads t o absolute aolecuiar welghts.In addition, for a linear polymor the knowled3~ of log [ q J versus log H leads to the determination of .'arkHouwin$ relationship coafficients. For branched polyaers. viscosity laws are curved aild the comparison betweer. the linear lar,corresponding to the linear equiyalent pol iiisr an$ the experimental law allows the daterminat:on ofl'the $ branching pirameter distribution.