Preparing poly(tetra:methylene ether) glycol with a narrow molecular weight distribution

摘要

A process for fractionating polyl(tetramethylene ether) glycols involves (a) providing a cross-flow membrane fractionation means characterised by a permeable or semipermeable membrane surface having a feed/retentate side and a permeated/ultrafiltrate side for separating relatively lower molecular wt poly(tetramethylene ether) glycol species from relatively higher molecular wt. poly(tetramethylene ether)glycol species (PTMEG); b) passing a feed stream of molten PTMEGs consisting of a distribution of PTMEG species substantially free of solvent across the feed 1 retentate side of the membrane surface of the membrane fractionation means at a temp. above the melt temp. of the PTMEG and below the decompsn. temps. of the membrane surface and PTMEG such that at least a portion of relatively lower molecular wt. PTMEG pass preferentially through the permeable or semi permeable membrane surface and c) recovering from the membrane fractionation means a permeate/ultrafiltrate fraction rich in lower molecular wt. PTMEG species characterised in a numerically smaller polydispersity than the original feed stream of molten PTMEG and a retentate fraction rich in higher molecular wt. PTMEG species also characterised by a numerically smaller polydispersity than the original feed of PTMEG. The process involves reducing the molecular wt. polydispersity of poly(tetramethylene) ether glycol.