Effect of diluents on membrane formation via thermally induced phase separation

The effect of diluents on isotactic polypropylene (iPP) membrane formation via thermally induced phase separation was investigated. The diluents were methyl salicylate (MS), diphenyl ether (DPE), and diphenylmethane (DPM). Th e cloud-point curve was shifted to a lower temperature in the order iPP-MS, iPP-DPE, and iPP-DPM, whereas the crystallization temperature was not infl uenced so much by diluent type. Droplet-growth processes were investigated under two conditions: quenching the polymer solution at the desired tempera ture and cooling at a constant rate. Although droplet sizes were in the ord er IPP-MS, iPP-DPE, and iPP-DPM in both cases, the difference was more pron ounced with the constant cooling rate condition. Scanning electron microsco py indicated that interconnected structures were obtained when the polymer solution was quenched in ice water. The effect of the diluents on these str uctures was observed. (C) 2001 John Wiley & Sons, Inc.