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polyimide blends for pervaporation and gas separation studies
ELSEVIER
Synthetic h1etals 84 (1997) 801-802
Polyaniline/Polyimide
Blends for Pervaporation and Gas Separation Studies
Tim M. Sua, Ian J. Ballb, Jeanine A. Conklinc, Shu-Chuan Huangb, Rhonda K. Larsonb, Song L. Nguyenb, Belinda M. Lewb and Richard B. Kanerb a Department of Chemistry, City College of San Francisco, San Francisco, CA 94112, USA b Department of Chemistry and Biochemistry and Solid State Science Center, University of California, Los Angeles, CA 900951569, USA ’ Surface Modification
Branch, US Naval Research Lab, Washington,
DC 203755345,
USA
Abstract Free-standing fully dense films have been successfully produced from drying blends of polyaniline and a polyamic acid precursor to polyimide. These blends exhibit an improved thermal stability relative to polyaniline. In gas permeability studies, a polyaniline/polyimide blend has a greater gas selectivity and shows an increase in permeability for all gases studied relative to polyimide. Pervaporation of water and water/acetic acid mixtures has been performed using these blends. The selectivity of the blends for water/acetic acid mixtures is considerably improved from that of undoped polyaniline and is comparable to that of HCl doped polyaniline. This is consistent with some of the polyamic acid acting as a “polymeric” dopant. The polymeric dopants also lead to lower fluxes for water/acetic acid relative to undoped polyaniline. Keywords:
1.
Polyaniline
and derivatives,
Solid/gas interfaces, Solid/liquid
interfaces
Introduction
The potential advantage of polymer blends is that they can lead to a favorable combination of properties from two homopolymers. Polyaniline is an air stable conjugated polymer that shows potential as a membrane for separating gases [I] and liquids [2]. Polyimide is a thermally stable polymer that has been extensively studied as a gas separation membrane [3,4]. Previous research [1,5,6] has demonstrated that polyamic acid can be utilized as a “polymeric” dopant, forming polyaniline/polyimide blends. Experiments on these blends are reported here for gas separation and pervaporation. 2.
Experimental
The polyimide used in these experiments was synthesized condensation reactions between 3,3’,4,4’by benzophenonetetracarboxylic acid (BTDA) and 4,4’oxydianiline (ODA). The monomers (Aldrich) were purified by sublimation at 200°C under vacuum. The monomers were mixed in a 0.98 mole ratio of BTDA/ODA in Nmethylpyrrolidinone (NMP) to form the polyamic acid precursor. Polyaniline was synthesized as described in reference [7]. Blends were prepared by mixing the appropriate amount of BTDA/ODA solution with a 10% wt/v solution of polyaniline. The casting solution was spread onto a glass plate and dried at 100 “C for one hour, 200 “C! for one hour, and then 300 ‘C for 15 minutes. This imidizes the polymer and forms polyimide. Blends were then “doped” in 1.0 M HCl solution, and “undoped” in 0.1 M NHhOH to remover residual NMP. An idealized structure of the blend formed is shown in Figure 1. 0379-6779/97/$17.00 0 1997 Elsevier Science S.A. All rights reServed PU SO379-6779(96)04153-7
Figure 1. A schematic polyaniline/polyimide blend. polymers represent interactions before polyamic acid is imidized.
representation of a The dotted lines between which are most prevalent
In a pervaporation experiment, a free-standing membrane (50-150 pm thick) is placed on a porous, stainless steel support inside a pervaporation flange cell and sealed by orings. The downstream side of the apparatus is evacuated until the membrane is thoroughly degassed. The per-meant collector is cooled to -65°C in order to maintain a low pressure and to condense the permeant. The experiment is begun when 200 mL of feed solution is added to the feed reservoir. Feed solutions of 50% acetic acid/50% water were investigated. Experiments were run for 72 hours for the polyaniline/polyimide blends. of the The composition permeant were determined from ‘H-NMR. Gas separation studies were performed using a standard manometric method for membranes [l]. Gas separation studies reported here involve a 50/50 polyaniline/polyimide blend.
802
TM. Src et al. /S~wtheticMetals
Table 1 Permeability (BTDA/ODA),
of gases polyaniline
Gas
(in Barrers) through and a 50/50 blend.
Polyimide
50/50 Blend
3.33 0.174 0.028 0.979 0.017
H2 02 N2 co2 CH4
7.40 0.282 0.027 1.281 0.015
polyimide
Polyaniline (base) 4.59 0.174 0.019 0.828 0.004
84 (1997) 801-802
Pervaporation experiments involving 50% acetic acid/50% water mixtures indicate that the 25/75 polyaniline/polyimide blends have the highest permeant fluxes of all of the samples. The 50/50 blends have a permeance only slightly higher than pure polyimide. The 75/25 blends have a permeance of roughly the same magnitude as pure polyaniline. In most cases, water was virtually the only component in the permeant, indicating that the selectivity of the blends was comparable to, or perhaps even slightly better than, doped polyaniline [2]. 4.
Table 2 Separation polyaniline
factors for selected and a 50/50 blend.
Gas
Polvimide
C02/CH4
59 120 6.2
H2&
02/Ni
3. Results
and
gases through
50150 Blend 85 270 10
polyimide,
Polyaniline 180 240 9.1
Discussion
Gas permeability measurements performed on the films are summarized in Table 1. For all gases tested, the permeability of the blend was higher relative to the permeability of the base form of polyaniline, and higher than or similar to that of the polyimide. Ordinarily, an increase in the permeabilities of two gases leads to a decrease in selectivity between those gases [8]. Contrary to this axiom, the separation factors for the blend are comparable to polyaniline with the exception of CO2/CH4 which is closer to polyimide. An improvement of properties as compared to the parent polymers appears to have been achieved by this blend.
Q 1.5 9 % 23 8 1.0 9 g b a 0.5
Conclusions
Free-standing thin films of polyaniline/polyimide blends were successfully prepared from solution. Gas permeability studies show that 50/50 polyaniline/poIyimide blends in general provide permeabilities higher than those of either homopolymer. The separation factors of the blends was higher than those for the polyimide homopolymer, but lower than or equivalent to those for base polyaniline. In pervaporation experiments, only the 25175 polyaniline/polyimide blends show higher permeances than membranes of pure polyaniline. The other blends show permeant fluxes on the same order of magnitude as the homopolymers. In all cases, the selectivity of the blend membranes was higher than for undoped polyaniline, and was on the order of the selectivity for doped polyaniline. Experiments involving unimidized polyaniline/polyimide blends are in progress.
Acknowledgments This work was supported by the Office of Naval Research, Grant # N00014-93-1307, the CULAR Program and the American Society for Engineering Education (JAC). The authors thank Dr. B.R. Mattes for useful discussions.
References
[II PI [31 [41 [51
0.0
[61 O/100
25175
50150
75125
100/O
Blend Composition Figure 2. The permeant fluxes of 50% acetic acid/50% through polyaniline/polyimide blends.
171 water
PI
B.R. Mattes, M.R. Anderson, J.A. Conklin and R.B. Kaner, Synth. Met., 55-57 (1993) 3655. I.J. Ball, S.-C. Huang, T.M. Su, A.P. Berger and R.B. Kaner, Polytn. Preprints, 37 (1996) 672. Y.D. Moon, B.K. Oh and Y.M. Lee, Polym. Bulletin, 29 (1992) 431. W.J. Koros, M.R. Coleman and D.R.B. Walker, Annu. Rev. Mater. Sci., 22 (1992) 47 M. Angelopoulos, N. Patel, and R. Saraf, Synth. Met, 55-57, (1993) 1552. S.-C. Huang, J.A. Conklin, T.M. Su, I.J. Ball, S.L. Nguyen, B.M Lew and R.B. Kaner, Polytn. Mat. Sci. Eng., 72 (1995) 323. W.S. Huang, B.D. Humphrey and A.J. MacDiarmid, J. Chetn. SOL, Faraday Trans., 82 (1986) 2385. T.H. Kim, W.J. Koros and G.R. Husk, Separ. Sci. Tech., 23 (1988) 1611.
Synthetic h1etals 84 (1997) 801-802
Polyaniline/Polyimide
Blends for Pervaporation and Gas Separation Studies
Tim M. Sua, Ian J. Ballb, Jeanine A. Conklinc, Shu-Chuan Huangb, Rhonda K. Larsonb, Song L. Nguyenb, Belinda M. Lewb and Richard B. Kanerb a Department of Chemistry, City College of San Francisco, San Francisco, CA 94112, USA b Department of Chemistry and Biochemistry and Solid State Science Center, University of California, Los Angeles, CA 900951569, USA ’ Surface Modification
Branch, US Naval Research Lab, Washington,
DC 203755345,
USA
Abstract Free-standing fully dense films have been successfully produced from drying blends of polyaniline and a polyamic acid precursor to polyimide. These blends exhibit an improved thermal stability relative to polyaniline. In gas permeability studies, a polyaniline/polyimide blend has a greater gas selectivity and shows an increase in permeability for all gases studied relative to polyimide. Pervaporation of water and water/acetic acid mixtures has been performed using these blends. The selectivity of the blends for water/acetic acid mixtures is considerably improved from that of undoped polyaniline and is comparable to that of HCl doped polyaniline. This is consistent with some of the polyamic acid acting as a “polymeric” dopant. The polymeric dopants also lead to lower fluxes for water/acetic acid relative to undoped polyaniline. Keywords:
1.
Polyaniline
and derivatives,
Solid/gas interfaces, Solid/liquid
interfaces
Introduction
The potential advantage of polymer blends is that they can lead to a favorable combination of properties from two homopolymers. Polyaniline is an air stable conjugated polymer that shows potential as a membrane for separating gases [I] and liquids [2]. Polyimide is a thermally stable polymer that has been extensively studied as a gas separation membrane [3,4]. Previous research [1,5,6] has demonstrated that polyamic acid can be utilized as a “polymeric” dopant, forming polyaniline/polyimide blends. Experiments on these blends are reported here for gas separation and pervaporation. 2.
Experimental
The polyimide used in these experiments was synthesized condensation reactions between 3,3’,4,4’by benzophenonetetracarboxylic acid (BTDA) and 4,4’oxydianiline (ODA). The monomers (Aldrich) were purified by sublimation at 200°C under vacuum. The monomers were mixed in a 0.98 mole ratio of BTDA/ODA in Nmethylpyrrolidinone (NMP) to form the polyamic acid precursor. Polyaniline was synthesized as described in reference [7]. Blends were prepared by mixing the appropriate amount of BTDA/ODA solution with a 10% wt/v solution of polyaniline. The casting solution was spread onto a glass plate and dried at 100 “C for one hour, 200 “C! for one hour, and then 300 ‘C for 15 minutes. This imidizes the polymer and forms polyimide. Blends were then “doped” in 1.0 M HCl solution, and “undoped” in 0.1 M NHhOH to remover residual NMP. An idealized structure of the blend formed is shown in Figure 1. 0379-6779/97/$17.00 0 1997 Elsevier Science S.A. All rights reServed PU SO379-6779(96)04153-7
Figure 1. A schematic polyaniline/polyimide blend. polymers represent interactions before polyamic acid is imidized.
representation of a The dotted lines between which are most prevalent
In a pervaporation experiment, a free-standing membrane (50-150 pm thick) is placed on a porous, stainless steel support inside a pervaporation flange cell and sealed by orings. The downstream side of the apparatus is evacuated until the membrane is thoroughly degassed. The per-meant collector is cooled to -65°C in order to maintain a low pressure and to condense the permeant. The experiment is begun when 200 mL of feed solution is added to the feed reservoir. Feed solutions of 50% acetic acid/50% water were investigated. Experiments were run for 72 hours for the polyaniline/polyimide blends. of the The composition permeant were determined from ‘H-NMR. Gas separation studies were performed using a standard manometric method for membranes [l]. Gas separation studies reported here involve a 50/50 polyaniline/polyimide blend.
802
TM. Src et al. /S~wtheticMetals
Table 1 Permeability (BTDA/ODA),
of gases polyaniline
Gas
(in Barrers) through and a 50/50 blend.
Polyimide
50/50 Blend
3.33 0.174 0.028 0.979 0.017
H2 02 N2 co2 CH4
7.40 0.282 0.027 1.281 0.015
polyimide
Polyaniline (base) 4.59 0.174 0.019 0.828 0.004
84 (1997) 801-802
Pervaporation experiments involving 50% acetic acid/50% water mixtures indicate that the 25/75 polyaniline/polyimide blends have the highest permeant fluxes of all of the samples. The 50/50 blends have a permeance only slightly higher than pure polyimide. The 75/25 blends have a permeance of roughly the same magnitude as pure polyaniline. In most cases, water was virtually the only component in the permeant, indicating that the selectivity of the blends was comparable to, or perhaps even slightly better than, doped polyaniline [2]. 4.
Table 2 Separation polyaniline
factors for selected and a 50/50 blend.
Gas
Polvimide
C02/CH4
59 120 6.2
H2&
02/Ni
3. Results
and
gases through
50150 Blend 85 270 10
polyimide,
Polyaniline 180 240 9.1
Discussion
Gas permeability measurements performed on the films are summarized in Table 1. For all gases tested, the permeability of the blend was higher relative to the permeability of the base form of polyaniline, and higher than or similar to that of the polyimide. Ordinarily, an increase in the permeabilities of two gases leads to a decrease in selectivity between those gases [8]. Contrary to this axiom, the separation factors for the blend are comparable to polyaniline with the exception of CO2/CH4 which is closer to polyimide. An improvement of properties as compared to the parent polymers appears to have been achieved by this blend.
Q 1.5 9 % 23 8 1.0 9 g b a 0.5
Conclusions
Free-standing thin films of polyaniline/polyimide blends were successfully prepared from solution. Gas permeability studies show that 50/50 polyaniline/poIyimide blends in general provide permeabilities higher than those of either homopolymer. The separation factors of the blends was higher than those for the polyimide homopolymer, but lower than or equivalent to those for base polyaniline. In pervaporation experiments, only the 25175 polyaniline/polyimide blends show higher permeances than membranes of pure polyaniline. The other blends show permeant fluxes on the same order of magnitude as the homopolymers. In all cases, the selectivity of the blend membranes was higher than for undoped polyaniline, and was on the order of the selectivity for doped polyaniline. Experiments involving unimidized polyaniline/polyimide blends are in progress.
Acknowledgments This work was supported by the Office of Naval Research, Grant # N00014-93-1307, the CULAR Program and the American Society for Engineering Education (JAC). The authors thank Dr. B.R. Mattes for useful discussions.
References
[II PI [31 [41 [51
0.0
[61 O/100
25175
50150
75125
100/O
Blend Composition Figure 2. The permeant fluxes of 50% acetic acid/50% through polyaniline/polyimide blends.
171 water
PI
B.R. Mattes, M.R. Anderson, J.A. Conklin and R.B. Kaner, Synth. Met., 55-57 (1993) 3655. I.J. Ball, S.-C. Huang, T.M. Su, A.P. Berger and R.B. Kaner, Polytn. Preprints, 37 (1996) 672. Y.D. Moon, B.K. Oh and Y.M. Lee, Polym. Bulletin, 29 (1992) 431. W.J. Koros, M.R. Coleman and D.R.B. Walker, Annu. Rev. Mater. Sci., 22 (1992) 47 M. Angelopoulos, N. Patel, and R. Saraf, Synth. Met, 55-57, (1993) 1552. S.-C. Huang, J.A. Conklin, T.M. Su, I.J. Ball, S.L. Nguyen, B.M Lew and R.B. Kaner, Polytn. Mat. Sci. Eng., 72 (1995) 323. W.S. Huang, B.D. Humphrey and A.J. MacDiarmid, J. Chetn. SOL, Faraday Trans., 82 (1986) 2385. T.H. Kim, W.J. Koros and G.R. Husk, Separ. Sci. Tech., 23 (1988) 1611.