SYNOPSISIn order to improve the separation characteristics of membranes for pervaporation, the introduction of fluoroalkyl groups into poly ( 1-trimethylsilyl-1-propyne) (PTMSP) was achieved by two methods. First, 3,3,3-trifluoropropyldimethylsilylated PTMSP was prepared via metalation of PTMSP followed by treating with 3,3,3-trifluoropropyldimethylchlorosilane. About 6 mol % of 3,3,3-trifluoropropyldimethylsilyl group was introduced by the polymer reaction. Second, the copolymerizations of 1-trimethylsilyl-1-propyne (TMSP) with 1-(3,3,3-trifluoropropyldimethylsilyl) -1-propyne (FPDSP) or 1-( lH,lH,BH,BH-tridecafluorooctyldimethylsilyl) -1-propyne (FODSP) were carried out to afford TMSP/ FPDSP or TMSP/FODSP random copolymers. The ratio of TMSP monomer unit and the comonomer unit, x / y , was in the range of 99/1-85/15. All the chemically modified PTMSP membranes showed ethanol permselectivity for pervaporation of aqueous ethanol solution. In particular, the introduction of less than about 5 mol % of fluoroalkylsilylated units into PTMSP effectively enhanced the selectivity. However, excess introduction of FODSP comonomer unit caused a decrease of the selectivity, with the value being smaller than that of PTMSP membrane. Furthermore, tetrahydrofuran, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their dilute aqueous solutions using a TMSP/FPDSP copolymer membrane.
INTRODUCTIONRecently, we investigated the chemical modification of poly (substituted-acetylene) , in order to achieve the improved selectivity and stability at gas permeation or to attain the higher permselectivity of alcohol for the separation of aqueous alcohol solution by the pervaporation te~hnique.'-~ In particular, the introduction of short polydimethylsiloxane (PDMS) chain' or trialkylsilyl group5 into poly( 1-trimethylsilyl-1-propyne ) ( PTMSP ) caused excellent alcohol permselectivity at pervaporation, which was higher than that of a PTMSP membrane. The high selectivity for alcohol with our modified * To whom correspondence should be addressed. PTMSP membrane was considered to be induced by a delicate alteration of membrane structure, which was brought about by an increase of hydrophobicity and the maintenance of high permeability coefficient of the original PTMSP membrane with the introduction of short PDMS chain or trialkyl group. PTMSP membrane has been known to contain excess free volume.6 The greatest gas permeability and the ethanol permselectivity of this membrane is thought to be due to the existence of free volume.6~~ Fusaoka et al. has prepared poly ( l-alkyldimethylsilyl-1 -propyne ) and evaluated the separation property of aqueous ethanol solution as compared with PTMSP membrane.s He also suggested that if the alkyl group was changed to ethyl, hexyl, or octyl group, the separation factor was below 1. Thus, the membranes showed water permselectivity at pervaporation. This interesting result suggests that the 1227 1228 NAGASE E T AL. specific membrane structure of PTMSP is very important to achieve eth...