Influence of solvent quality on successive solution fractionation (SSF) efficiency of high-density polyethylene

BACKGROUND: Preparative successive solution fractionation (SSF) is a powerful technique for obtaining narrow‐dispersity fractions on a multi‐gram scale of high‐density polyethylene (HDPE). In a previous paper, the operative separation mechanisms during SSF of a broad HDPE in cyclohexanone were studied. Two mechanisms, and not only one as expected from the literature, contribute to the separation of HDPE molecules according to their molar mass (MM). The very low MM chains are separated by a solid–liquid (S–L) mechanism, while the longer chains are isolated by a liquid–liquid (L–L) phase separation. In the present paper, the influence of a poorer solvent, diphenyl ether, is reported. RESULTS: It is shown that the relative importance of the S–L mechanism with respect to the L–L one is altered by the use of this solvent. The L–L temperature range is increased in diphenyl ether while the S–L transition temperature remains unchanged. Consequently, the SSF efficiency is improved. Large amounts (on a gram scale) of narrow‐dispersity fractions are isolated, mainly by the L–L mechanism. Polydispersities are about 1.5 (compared to 2.0 for cyclohexanone) and a broader MM range of closer molar mass distribution fractions is available. CONCLUSION: This work demonstrates that the use of diphenyl ether, a poorer solvent than cyclohexanone (always used as SSF solvent for polyethylene in the literature), leads to an improvement of SSF efficiency for an essentially linear HDPE. The differences of behaviour during the separation with cyclohexanone or diphenyl ether are explained by the establishment of a phase diagram. Copyright © 2009 Society of Chemical Industry