Characterization of Ethylene Copolymers with Liquid Chromatography and Melt Rheology Methods

Abstract

Melt rheology and polymer chromatography methods were applied to characterize molecular heterogeneities in products of free radical copolymerization of ethylene with methyl acrylate and vinyl acetate comonomers performed in continuously stirred tank and tubular reactors. We found that the ethylene-vinyl acetate copolymers made in both reactors had similar linear viscoelastic properties typical to branched products of the high pressure process. But the ethylene-methyl acrylate copolymers obtained in the tubular reactor had unusually high melt viscosity at low shear rate and much lower onset of shear thinning despite the narrower molecular weight distribution and the lower overall amount of long-chain branches compare to their autoclave counterparts with similar average molecular weight and chemical composition. Using interaction polymer chromatography method called gradient elution at critical point of adsorption we found that ethylene-acrylate copolymers from the tubular reactor had very broad chemical composition distribution, which was consistent with a significant difference in reactivity ratios between ethylene and acrylate comonomers. Such chemical composition heterogeneity can be a reason for the observed unusual rheological properties of these copolymers.

Characterization of synthetic copolymers by interaction polymer chromatography: Separation by microstructure

“…Thus, similar to polymer blends, all fractions with the same chemical composition will elute with the solvent band corresponding to the CPA for this composition. Besides the aforementioned chlorinated polyethylene, we recently demonstrated gradient separations at CPA (including gradient elution on zirconia‐based columns at high temperature) of ethylene‐acrylate and ethylene–vinyl acetate copolymers obtained in tubular and autoclave reactors 12. We believe that the majority of successful separations of statistical copolymers by chemical composition reported in literature starting with the pioneer works of Tanaka et al .…”

Separation of amorphous and semicrystalline parts of LLDPE with high‐temperature interactive liquid chromatography

“…The first successful separations of random copolymers (although not polyolefins) with solvent gradient chromatography were described by Teremachi, 14 Tanaka et al, 15 Mori et al, 16 and Mourey. 17 Brun et al [18][19][20][21][22][23][24] elaborated theoretical simulations and added experimental measurements (with chlorinated PE and other random copolymers), which enable to explain the retention behavior of random copolymers in mixed mobile phases. Additional experiments, which confirmed the hypothesis of Brun et al, were realized by Bashir and Radke.…”