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SynopsisAn application of the high temperature coupling of a gel permeation chromatograph with a home-made continuous viscometric detector is described. It concerns the comprehensive characterization of ethylene-vinyl acetate copolymers. Suitable chromatographic conditions are chosen to enable a correct use of the universal calibration concept. Through analysis of poly(viny1 acetate) fractions and commercial polyethylene samples, a comparison is made with the results of classical measurements. Average molecular weights as well as intrinsic viscosity appear to be in good agreement within experimental error, which proves the system for the characterization of random ethylene-vinyl acetate copolymers. In attempting to obtain a reliable estimate of long chain branching frequency A, a series of commercial samples has been selected, with the vinyl acetate weight fraction within the range 045%. As a rule, experimental viscosity law exhibits two parts, a straight line with a Mark-Houwink exponent 0.7 in the low molecular weight region and a curvature, well smoothed by a third-degree polynomial regression. Consequently, long chain branching does not appear before a limiting molecular weight of about 50,000. Beyond this limit, X is 0.5 X with no dependence on molecular weight, which resembles low density polyethylene.

SYNOPSISIn this paper, the shape of chromatograms obtained by elution of copolymers with a mixture of solvent-nonsolvent of variable composition has been studied from a theoretical point of view. It is assumed that the thermodynamic quality of the mixture a t which the copolymer is eluted depends only on its composition and not on its mass and structure. If one characterizes the polydispersity in composition, assuming that each constituent obeys a molar mass distribution of the Zimm-Schulz type, one can draw the following curves: concentration of the copolymer versus eluant composition. They depend on three parameters, including composition of the copolymer and the polydispersity of each constituent. The most striking result is that the shape of the chromatogram changes dramatically when one increases the polydispersity of either constituents. For low polydispersities, one obtains a classical peak. For large polydispersities, the chromatogram has a minimum for the intermediate values of composition and presents peaks in the vicinity of the pure homopolymers. This can be explained easily by a qualitative argument.

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