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RESEARCH PRODUCT

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The countercurrent extraction method recently developed for the continuous polymer fractionation (CPF) was applied to linear polyethylene (Mw = 55 kg/mol; Mn = 16,7 kg/mol). At temperatures higher than 130°C, moderately concentrated solution of polyethylene were extracted to remove the low-molecular-weight components. Discontinuous fractionation experiments served to detect the best suited solvents. Diphenyl ether was chosen to demonstrate that the present extraction can be performed even with the same single solvent used to prepare the feed. For very high-molecular-weight polymers, mixed solvents are, however, normally better than single ones, since they allow an easier tailoring of thermodynamic conditions, and yield much less viscous solutions. Mixtures of tetralin and triethylene glycol turned out to be best suited for polyethylene. By means of four successive CPF runs with the single solvent, polyethylene fractions with non-uniformities U = (Mw/Mn) − 1 of approx. 0,3 to 0,4 were obtained on a 100 g scale. The rule of thumb that U can be halved in each CPF step without extensive optimization of the method was corroborated.