Fractionation of polyethylene

Abstract

Abstract The relatively rapid Desreux technique for polymer fractionation has been modified and applied to both linear and highly branched polyethylenes. The polymer is precipitated from p ‐xylene solution onto a sand column by cooling from 127° to room temperature. After removal of solvent, the column temperature is again raised to 127° and fractions are eluted, using p ‐xylene‐ethylene glycol monoethyl ether mixtures of increasing solvent power. Approximately 15 fractions are obtained and polymer recovery is essentially quantitative. The reproducibility of the integral distribution curves is within ±2% for a cumulative weight‐% of 85 or higher. In certain cases difficulty has been encountered in resolving the less soluble portion of the sample. The selective nature of the system is indicated by the fact that the reduced specific viscosities of the highest and lowest molecular weight fractions are generally in the ratio of 50 or higher.