- Email: [email protected]
permeability and permselectivity relationship of polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride. II
Eur. Polym. J. Vol. 32, No. 11, pp. 1313-1317,1996 Copyright 0 1996Elswier Science Ltd
Pergamon
PIk !300143057(%)ooow-8
Printed in Great Britain.. All fights reserved
00143057/96S15.00+ 0.00
STRUCTURE/PERMEABILITY AND PERMSELECTIVITY RELATIONSHIP OF POLYETHERIMIDES FROM 1,4-BIS(3,4-DICARBOXYPHENOXY) BENZENE DIANHYDRIDE. II YUESHENG
LI,* MENGXIAN
DING and JIPING XU
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China (Received 2 August 1995; accepted in final form 27 October 1995)
Abstract-Gas permeability coefficients of a series of aromatic polyetherimides, which were prepared from 1,4_bis(3,4dicarboxyphenoxy) benzene dianhydride (HQDPA) with various aromatic diamines, to HI, O2 and Nr have been measured under 7 atm and at the temperature range 30-100°C. A significant change in the permeability and permselectivity resulting from the systematic variation in chemical structure of the polyetherimides was found. Among the polyetherimides, that were prepared from phenylenediamine and methyl substituted phenylenediamines, the increase of permeability is accompanied by a decrease of permselectivity. The polyetherimides that were prepared from 3,5-diaminobenzoic esters have lower permselectivity than the others. However, the polyetherimide from 3,5diaminobcnzoic acid possesses much higher permselectivity than the others due to cross-linking. Copyright 0 1996 Elsevier Science Ltd
INTRODUCTION Aromatic attention
polyetherimides have attracted much as membrane materials for gas separation
because of their favorable gas separation properties, high mechanical strength, excellent chemical and thermal stability, and better processability than the traditional polyimides such as those prepared from pyromellitic dianhydride (PMDA) or 3,3’,4,4’biphenyl tetracarboxylic dianhydride (BPDA) [l-3]. A large number of aromatic polyetherimides may be prepared from various double ether dianhydrides with different diamines. A good understanding is needed of the relationship between the gas permeability and permselectivity and the structure of polyetherimides to optimize polyetherimide membrane materials for gas separation. Hence, it is necessary to investigate systematically the effect of the chemical structure on the gas permeability and permselectivity of the polyetherimide. Eastmond et al. investigated the permeability of various isomeric polyetherimides to CO, and CI-L, indicating that the structure of double ether dianhydrides and diamines affects strongly on CO,/CI-L separation property [41. In the previous paper, we reported the relationship between chemical structure and the permeability and permsekctivity of the polyetherimides that were prepared from HQDPA with various bridged diamines [S]. The results showed that the structure of diamines, especially, substitutes on the benzene ring *To whom all correspondence
should be addressed.
has a strong effect on the permeability and permselectivity. In the present study, the permeability coefficients of HZ, Oz and N2 through a series of HQDPA-based polyetherimides, which were prepared from phenylenediamines with various substitutes, were measured to investigate the effects of diamine structure on the gas permeability and permselectivity of HQDPA-based polyetherimides. EXPERIMENTAL Materials
The diamines used for this study were 1,3-phenylenediamine (PDA), 2,4_toluene d&mine (TDA), mxylene diamine (XDA), 2,4,6-trimethylphenylene diamine (TMPDA), 3,5-diaminobenzoic acid (DBA), 3,5-diamino methylbenzoate (DAMB) and 3,5-diamino ethylbenzoate IDAEB). HODPA. XDA. DAMB and DABB were prepared in o;r laboratory. PDA and TDA were purchased from Shanghai Chemical Agent Factory (P.R. China). TMPDA and DBA were bought from Aldrich Chemical Co. All the monomers were finally purified by vacuum sublimation or recrystallization before use in polymerization. The solvent dimethylacetamide (DMAc) was dried at 30°C with 4 8, molecular sieve for one week, followed by distillation under nitrogen atmosphere. The purity of the permeation gases used was more than 99.95%. Apparatus and procedure The molecular structure of the polyetherimides is shown in Scheme 1. The homogenous membranes for tests were prepared by solution casting. The membranes were characterized according to the procedure described in the previous paper [S]. The permeability coetBciettts to Hz, Or and Nr were measured under 7 atm and at the temperature range from 30 to 150°C.
1313
Yuesheng Li et al.
1314
V3
HQDPA-PDA
HQDPA-TDA
HQDPA-TMPDA
V3 V3
HQDPA-DBA
V3
HQDPA-DAMB
COOH
HQDPA-DAEB
COOCH3
COOC2H5
Scheme 1. Chemical structure of the polyetherimides used in this study.
RESULTS AND DISCUSSION
Synthesis
and characterization
OfpoIyerherimides
Polyetherimides may be synthesized through the general reaction of a diamine with a dianhydride, followed by imidizing either thermally or chemically. When the method of chemical imidization was used, HQDPA-XDA, HQDPA-TMPDA, HQDPADAMB and HQDPA-DAEB are soluble in some organic solution such as dimethylacetamide, dimethylformamide, CHCh, but HQDPA-PDA. HQDPA-TDA and HQDPA-DBA are insoluble in those. It is more convenient to prepare membranes from soluble polyetherimides than from polyetheramide acid precursors. To remove the effect of non-chemical structure on the permeability and permselectivity, however, the traditional process, solution condensation of HQDPA with a stoichiometric diamine, solution casting membrane, and then thermal imidization, was adapted in this work. Some physical properties of the HQDPA-based polyimides studied are listed in Table 1. Wide angle X-ray diffraction (WAXD) curves of all polyetherim-
ides were broad and structureless, indicating that the polyetherimides were amorphous. The fractional free volume of the polyetherimides were calculated by equations (1) and (2).
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAED
(1)
FFV =
(2)
VrWlp)
where Vr is the free volume of smallest repeat unit, M is the weight of smallest repeat unit, p is the density of polyetherimide at 25°C and V, is van der Waals volume calculated by the group contribution method reported by Lee and Bondi [6,7]. Eflect of temperature polyetherimides
on
gas
permeability
of
The permeability coefficients of the representative polyetherimide membranes to Hz, 02 and N2 are illustrated in the form of Arrhenius plots in Figs 1 and 2. It is obvious that a linear relationship exists between log P and l/T in each polyetherimide. In other words, the Arrhenius equation holds:
Table 1. Some physical properties of HQDPA-based
Polyetherimide
Vr = M/p - 1.3V,
qnnh in
Glass transition tempcratun
cresol
TN (“C)
Density (‘+/8)
0.71 0.78 0.69 0.72 0.86 0.67 0.68
262 275 297 325 286 248 241
1.380 1.338 1.304 I .267 I.384 1.371 1.353
polyetherimide Special free
Fractional
volume SFV (Cm’/@
free volume FFV
0.085 0.096 0.105 0.117 0.096 0.094 0.096
0.117 0.128 0.137 0.148 0.133 0.129 0.130
Gas permeation through HQDPA-based polyetherimides Table 2. Apparent
I :
IA 2: 2
2.4
2.6
2.8
lc@w
3.0
3.2
3.4
w-9
Fig. 1. Temperature dependence of the permeability coefficients of HQDPA-PDA and HQDPA-TDA. Solid (-): HQDPA-PDA, dash (---): HQDPA-TDA.
log P = log PO- E&2.303 RT)
(3)
where R is the universal gas constant, T is the absolute temperature (K) and Ep is the apparent activation energy of gas permeation. Because all the HQDPA-based polyetherimides studied here were in the glassy state in the experimental temperature activation energy of gas range, the apparent permeation does not change with temperature. Table 2 listed the apparent activation energy of HZ, O2 and Nz permeation through polyetherimides.
1:
0.1 :
1315
activation energy of gas pemxation polyetherimidw
of the
Polvetherimide
HZ
02
NZ
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAEB
14.6 12.0 11.1 10.6 14.8 13.3 12.1
18.4 14.7 11.9 8.54 20.3 15.3 12.4
26.1 18.9 14.8 13.2 28.7 20.6 18.1
Among the polyetherimides prepared from PDA and the methyl substituted phenyldiamines, the decrease of Ep is accompanied by the increase of the permeability coefficients of polyetherimides. Additionally, there is a larger decrease in the gas permeability with large molecule, such as Nz, than in that with small molecule, such as Hz. As diamine was varied from PDA through DAMB to DAEB, EP of polyetherimide to each gas decreases, progressively. Opposed to HQDPA-DAMB and HQDPA-DAEB, although the permeability coefficient of HQDPADBA to Hr and O2 are higher than those of HQDPA-PDA, the corresponding Ep does not decrease but increases. Permeability andpermselectivity of methyl substituted polyetherimides The glass transition temperature is controlled by the chain segmental movement of polymer. The methyls substituted on C-N bond ortho-positions of polyetherimides restrict the chain segmental movement of the polymers. The more methyls on C-N bond ortho-positions, the less the chain segmental movement of polyetherimides is. Consequently, from through HQDPA-TDA and HQDPA-PDA HQDPA-XDA to HQDPA-TMPDA, the chain segmental mobility decrease, respectively, which causes the glass transition temperatures of the polyetherimide to increase, gradually. As shown in Table 1, with the increase of methyl, on the benzene ring of diamine residuals, the density of HQDPAbased polyetherimides decrease, progressively, and the fractional free volumes increase gradually. The reason is that side substituted CH, restrict the chain segmental packing of polyetherimides. Gas permeation through a homogenous polymer membrane depends on the fact that the penetrant must experience a series of diffusional jumps as it permeates across the polymer membrane. These jumps are mainly controlled by the fractional free volume and the chain segmental movement of polymer [8]. Increase of the fractional free volume or augmentation of the chain segmental mobility will all increase the permeability and decrease the permselectivity of the polymer [9]. As shown in Fig. 3, Table 3. Petmaability coefkients and penns&?ctivity coefkients of oolvetherimides at 30°C
O.Olb
2.2
*
’
2.4
.
’
2.6
.
’
2.8
.
’
3.0
.
’
3.2
.
3
lOOOR( K“) Fig. 2. Temperature dependence of the permeability coefficients of HQDPA-DBA and HQDPA-DAEB. Solid (-): HQDPA-DBA, dash (---): HQDPA-DAEB.
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAEB
3.15 8.37 16.3 37.3 5.67 5.33 7.79
0.149 0.395 I .08 4.S2 0.179 0.234 O.S29
0.0158 o.oSO4 0.183 0.846 0.0147 0.0344 0.0756
237 166 89.2 44.1 386 15s 103
9.4 7.9 5.9 5.3 12 6.9 7.0
Yuesheng Li et al.
1316 Table 4. Permeability
coefficients and permselectivity polyctherimides at 100°C
Polyetherimide HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DEA HQDPA-DAMB HQDPA-DAEB
HZ
OS
NZ
11.3 20.4 31.2 81.3 17.1 14.3 19.2
0.586 1.13 2.63 6.61 0.793 0.787 I .33
0.104 0.215 0.551 2.26 0.125 0.160 0.292
coefficients of 0 HQDPA-DBA
Hz/N* 02/N> 109 94.9 61.5 36.0 137 89.5 65.8
5.6 5.3 4.7 2.9 6.4 4.9 4.6
300
c :s
250
8 a
200 HQDPA-DAMBO
“%I
‘\ ‘\
logarithms of permeability coefficients of the polyetherimides, prepared from PDA, TDA, XDA, and TMPDA, to H2, O2 and N? increase linearly with the increase of the methyl on the diamines and meanwhile, the permselectivity coefficients for HJN2 and 02/N2 decrease progressively. As shown in Fig. 4, the order of increase of permeability is also that of increase of fractional free volume of these polyetherimides. This fact indicates that the fractional free volume variation plays a dominant role in determining the permeability and permselectivity change compared with subtle differences in the chain segmental mobility of the methyl substituted polyetherimides in this case. Comparison of HQDPA-DBA
and HQDPA-PDA
Carboxylic group (-COOH) is a strong polar substituent. Polyetherimide with carboxylic group, HQDPA-DBA, has high H-bond energy and high orientation energy. This results in that HQDPADBA has much higher cohesive energy than other HQDPA-based polyetherimides. By the way, there can be intermolecular cross-link structure in HQDPA-DBA. Consequently, the glass transition temperature of HQDPA-DBA is much higher than HQDPA-PDA and the chain segmental mobility is much lower than HQDPA-PDA. Carboxylic group is also a bulky substituent that restricts the chain segmental packing. Hence, the fractional free volume of HQDPA-DBA is higher than HQDPA-PDA. The polymers with high fractional free volume and low chain segmental mobility, especially cross-link struc-
lOOr
I
b\
50
‘\ .
“;;p . .
10
1 H2
100
Permeability coefficients ( barrier)
Fig. 4. Plot of Hz permeability coefficients vs Hz/N2 selectivity of the polyetherimides.
ture, possess high permeability and high permselectivity. Hence the permeability coefficients of HQDPA-DBA to HZ and O2 are higher than those of HQDPA-PDA, and the permselectivity coefficients of HQDPA-DBA for HI/N* and 02/N2 are much higher than those of HQDPA-PDA. For example, the permeability coefficients of the polyetherimide to H2 and O2 increase by 51 and 17%, respectively, while the permselectivity coefficients of the polyetherimide for HZ/N2 and 02/Nz increase by 41 and 27%, respectively. Permeability andpermselectivity of HQDPA-diaminobenzoates
Carboxylic ether groups (-COOR) differ from the carboxylic group in many respects. First, the volume of carboxylic ether groups is much greater than that of the carboxylic group. Second, carboxylic ether groups are flexible substituents and have strong plasticization effect, but the carboxylic group does not. Third, carboxylic ether groups are inert substituents and do not react with amine, in the process of imidization of polyamide acid precursor. Therefore, the polyetherimides which were prepared from 3,Sdiaminobenzoate possess lower glass transition temperature, namely, higher chain segmental
8-l
d
HQDPA-DAEB 0
100
_ 10
I
12 -
0 HQDPA-DBA
r .P 2
IO-
8 x .F
s-
‘n
+
P’
6-
5
4-
HQDPA-DAMB HQDPA-DAEB :
I 0
.
I 1
.
1 2
.
1 3
Methyl number Fig. 3. Effect of methyl number on diamine on the permeability of HQDPA-based polyetherimides.
21 .‘.‘I
0.1
1
0, Permeability coefficient Fig. 5. Plot of 0~ permeability coefficients vs OZ/NZ selectivity of the polyetherimides.
Gas permeation through HQDPA-based polyetherimides
mobility, than HQDPA-PDA and lower segmental package density, e.g. higher fractional free volume, than HQDPA-PDA, but lower fractional free volume than HQDPA-DBA. These facts result in the polyetherimides prepared from 3,5-diaminobenzoate having higher permeability than HQDPA-PDA. The strong plasticization of -COOR causes a larger increase of N2 (with large molecular kinetic diameter, 0.364 nm) permeability coefficients than of H1 and OI (with small molecular kinetic diameter, 0.289 and 0.346 nm, respectively). Consequently, the permseiectivities of the polyetherimides prepared from 3,5-diaminobenzoate for H2/N2 and 02/N2 are much lower than those of HQDPA-PDA. -COOC2HJ is larger than -COOCHp, and the former has a stronger plasticization than the latter. HQDPA-DAEB has higher fractional free volume and higher chain segmental mobility than HQDPA-DAMB. This means that the permeability coefficients of HQDPADAEB to each gas are larger than those of HQDPA-DAMB, but the permselectivity coefficients of HQDPA-DAEB for Hz/N2 and 02/N2 are smaller than HQDPA-DAMB, shown in Figs 4 and 5. As shown in Table 1, the fractional free volumes of HQDPA-DAMB and HQDPA-DAEB are lower than that of HQDPA-DBA. Therefore, the permselectivity coefficients of HQDPA-DAMB and HQDPA-DAEB for Hz/N2 and 02/N2 are much lower than those of HQDPA-DBA. CONCLUSION
For HQDPA-based polyetherimides, the effect of temperature upon gas permeability coefficients can be
1317
described well by the Arrhenius equation. The structure of the diamine monomers has a very strong effect on the permeability and permselectivity of HQDPA-based potyetherimides. Among methyl substituted polyetherimides, the permeability increases, but the permselectivity decreases, and can be explained by the increase of the fractional free volume of the polymers. The polyetherimides, which are prepared from 3,5-diaminobenzoic esters, with higher chain segmental mobility due to strong plasticization by carboxylic ether groups, possess lower permselectivity than the others. However, HQDPA-DBA exhibits much higher permselectivity than the others due to cross-linking. authors are grateful for the financial support granted by the National Natural Science Foundation of China. Acknowledgement-The
REFERENCES
Barbari, W. J. Koros and D. R. Paul. J. Membr. Sci. 42, 69 (1989). 2. K. V. Peinemann, K. Fink K. and P. Witt. J. Membr. I. T. A.
Sci. 127, 215 (1986). 3. K. Kneifel and K. V. Peinemann. J. Membr. Sci. 65, 295 (1992). 4. G. C. Eastmond, J. Paprotny and I. Webster. Polymer 34, 2865 (1993). 5. Y. Li, X. Wang, M. Ding and J. Xu. Polym. Inr. 37,52 (1996). 6. &‘. h;l. Lee. Pofym. Eng. Sci. 20, 65 (1980). 7. A. Bondi. J. Phvs. Chem. 68,441 (1964). 8. K. C. C’brien, \;5;.J. Koros anh G. d. Husk. J. Membr. Sci. 35, 217 (1988). 9. K. Tanaka, H. Tits, M. Okamo and K. Okamoto. Polymer 33, 585 (1992).
Pergamon
PIk !300143057(%)ooow-8
Printed in Great Britain.. All fights reserved
00143057/96S15.00+ 0.00
STRUCTURE/PERMEABILITY AND PERMSELECTIVITY RELATIONSHIP OF POLYETHERIMIDES FROM 1,4-BIS(3,4-DICARBOXYPHENOXY) BENZENE DIANHYDRIDE. II YUESHENG
LI,* MENGXIAN
DING and JIPING XU
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China (Received 2 August 1995; accepted in final form 27 October 1995)
Abstract-Gas permeability coefficients of a series of aromatic polyetherimides, which were prepared from 1,4_bis(3,4dicarboxyphenoxy) benzene dianhydride (HQDPA) with various aromatic diamines, to HI, O2 and Nr have been measured under 7 atm and at the temperature range 30-100°C. A significant change in the permeability and permselectivity resulting from the systematic variation in chemical structure of the polyetherimides was found. Among the polyetherimides, that were prepared from phenylenediamine and methyl substituted phenylenediamines, the increase of permeability is accompanied by a decrease of permselectivity. The polyetherimides that were prepared from 3,5-diaminobenzoic esters have lower permselectivity than the others. However, the polyetherimide from 3,5diaminobcnzoic acid possesses much higher permselectivity than the others due to cross-linking. Copyright 0 1996 Elsevier Science Ltd
INTRODUCTION Aromatic attention
polyetherimides have attracted much as membrane materials for gas separation
because of their favorable gas separation properties, high mechanical strength, excellent chemical and thermal stability, and better processability than the traditional polyimides such as those prepared from pyromellitic dianhydride (PMDA) or 3,3’,4,4’biphenyl tetracarboxylic dianhydride (BPDA) [l-3]. A large number of aromatic polyetherimides may be prepared from various double ether dianhydrides with different diamines. A good understanding is needed of the relationship between the gas permeability and permselectivity and the structure of polyetherimides to optimize polyetherimide membrane materials for gas separation. Hence, it is necessary to investigate systematically the effect of the chemical structure on the gas permeability and permselectivity of the polyetherimide. Eastmond et al. investigated the permeability of various isomeric polyetherimides to CO, and CI-L, indicating that the structure of double ether dianhydrides and diamines affects strongly on CO,/CI-L separation property [41. In the previous paper, we reported the relationship between chemical structure and the permeability and permsekctivity of the polyetherimides that were prepared from HQDPA with various bridged diamines [S]. The results showed that the structure of diamines, especially, substitutes on the benzene ring *To whom all correspondence
should be addressed.
has a strong effect on the permeability and permselectivity. In the present study, the permeability coefficients of HZ, Oz and N2 through a series of HQDPA-based polyetherimides, which were prepared from phenylenediamines with various substitutes, were measured to investigate the effects of diamine structure on the gas permeability and permselectivity of HQDPA-based polyetherimides. EXPERIMENTAL Materials
The diamines used for this study were 1,3-phenylenediamine (PDA), 2,4_toluene d&mine (TDA), mxylene diamine (XDA), 2,4,6-trimethylphenylene diamine (TMPDA), 3,5-diaminobenzoic acid (DBA), 3,5-diamino methylbenzoate (DAMB) and 3,5-diamino ethylbenzoate IDAEB). HODPA. XDA. DAMB and DABB were prepared in o;r laboratory. PDA and TDA were purchased from Shanghai Chemical Agent Factory (P.R. China). TMPDA and DBA were bought from Aldrich Chemical Co. All the monomers were finally purified by vacuum sublimation or recrystallization before use in polymerization. The solvent dimethylacetamide (DMAc) was dried at 30°C with 4 8, molecular sieve for one week, followed by distillation under nitrogen atmosphere. The purity of the permeation gases used was more than 99.95%. Apparatus and procedure The molecular structure of the polyetherimides is shown in Scheme 1. The homogenous membranes for tests were prepared by solution casting. The membranes were characterized according to the procedure described in the previous paper [S]. The permeability coetBciettts to Hz, Or and Nr were measured under 7 atm and at the temperature range from 30 to 150°C.
1313
Yuesheng Li et al.
1314
V3
HQDPA-PDA
HQDPA-TDA
HQDPA-TMPDA
V3 V3
HQDPA-DBA
V3
HQDPA-DAMB
COOH
HQDPA-DAEB
COOCH3
COOC2H5
Scheme 1. Chemical structure of the polyetherimides used in this study.
RESULTS AND DISCUSSION
Synthesis
and characterization
OfpoIyerherimides
Polyetherimides may be synthesized through the general reaction of a diamine with a dianhydride, followed by imidizing either thermally or chemically. When the method of chemical imidization was used, HQDPA-XDA, HQDPA-TMPDA, HQDPADAMB and HQDPA-DAEB are soluble in some organic solution such as dimethylacetamide, dimethylformamide, CHCh, but HQDPA-PDA. HQDPA-TDA and HQDPA-DBA are insoluble in those. It is more convenient to prepare membranes from soluble polyetherimides than from polyetheramide acid precursors. To remove the effect of non-chemical structure on the permeability and permselectivity, however, the traditional process, solution condensation of HQDPA with a stoichiometric diamine, solution casting membrane, and then thermal imidization, was adapted in this work. Some physical properties of the HQDPA-based polyimides studied are listed in Table 1. Wide angle X-ray diffraction (WAXD) curves of all polyetherim-
ides were broad and structureless, indicating that the polyetherimides were amorphous. The fractional free volume of the polyetherimides were calculated by equations (1) and (2).
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAED
(1)
FFV =
(2)
VrWlp)
where Vr is the free volume of smallest repeat unit, M is the weight of smallest repeat unit, p is the density of polyetherimide at 25°C and V, is van der Waals volume calculated by the group contribution method reported by Lee and Bondi [6,7]. Eflect of temperature polyetherimides
on
gas
permeability
of
The permeability coefficients of the representative polyetherimide membranes to Hz, 02 and N2 are illustrated in the form of Arrhenius plots in Figs 1 and 2. It is obvious that a linear relationship exists between log P and l/T in each polyetherimide. In other words, the Arrhenius equation holds:
Table 1. Some physical properties of HQDPA-based
Polyetherimide
Vr = M/p - 1.3V,
qnnh in
Glass transition tempcratun
cresol
TN (“C)
Density (‘+/8)
0.71 0.78 0.69 0.72 0.86 0.67 0.68
262 275 297 325 286 248 241
1.380 1.338 1.304 I .267 I.384 1.371 1.353
polyetherimide Special free
Fractional
volume SFV (Cm’/@
free volume FFV
0.085 0.096 0.105 0.117 0.096 0.094 0.096
0.117 0.128 0.137 0.148 0.133 0.129 0.130
Gas permeation through HQDPA-based polyetherimides Table 2. Apparent
I :
IA 2: 2
2.4
2.6
2.8
lc@w
3.0
3.2
3.4
w-9
Fig. 1. Temperature dependence of the permeability coefficients of HQDPA-PDA and HQDPA-TDA. Solid (-): HQDPA-PDA, dash (---): HQDPA-TDA.
log P = log PO- E&2.303 RT)
(3)
where R is the universal gas constant, T is the absolute temperature (K) and Ep is the apparent activation energy of gas permeation. Because all the HQDPA-based polyetherimides studied here were in the glassy state in the experimental temperature activation energy of gas range, the apparent permeation does not change with temperature. Table 2 listed the apparent activation energy of HZ, O2 and Nz permeation through polyetherimides.
1:
0.1 :
1315
activation energy of gas pemxation polyetherimidw
of the
Polvetherimide
HZ
02
NZ
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAEB
14.6 12.0 11.1 10.6 14.8 13.3 12.1
18.4 14.7 11.9 8.54 20.3 15.3 12.4
26.1 18.9 14.8 13.2 28.7 20.6 18.1
Among the polyetherimides prepared from PDA and the methyl substituted phenyldiamines, the decrease of Ep is accompanied by the increase of the permeability coefficients of polyetherimides. Additionally, there is a larger decrease in the gas permeability with large molecule, such as Nz, than in that with small molecule, such as Hz. As diamine was varied from PDA through DAMB to DAEB, EP of polyetherimide to each gas decreases, progressively. Opposed to HQDPA-DAMB and HQDPA-DAEB, although the permeability coefficient of HQDPADBA to Hr and O2 are higher than those of HQDPA-PDA, the corresponding Ep does not decrease but increases. Permeability andpermselectivity of methyl substituted polyetherimides The glass transition temperature is controlled by the chain segmental movement of polymer. The methyls substituted on C-N bond ortho-positions of polyetherimides restrict the chain segmental movement of the polymers. The more methyls on C-N bond ortho-positions, the less the chain segmental movement of polyetherimides is. Consequently, from through HQDPA-TDA and HQDPA-PDA HQDPA-XDA to HQDPA-TMPDA, the chain segmental mobility decrease, respectively, which causes the glass transition temperatures of the polyetherimide to increase, gradually. As shown in Table 1, with the increase of methyl, on the benzene ring of diamine residuals, the density of HQDPAbased polyetherimides decrease, progressively, and the fractional free volumes increase gradually. The reason is that side substituted CH, restrict the chain segmental packing of polyetherimides. Gas permeation through a homogenous polymer membrane depends on the fact that the penetrant must experience a series of diffusional jumps as it permeates across the polymer membrane. These jumps are mainly controlled by the fractional free volume and the chain segmental movement of polymer [8]. Increase of the fractional free volume or augmentation of the chain segmental mobility will all increase the permeability and decrease the permselectivity of the polymer [9]. As shown in Fig. 3, Table 3. Petmaability coefkients and penns&?ctivity coefkients of oolvetherimides at 30°C
O.Olb
2.2
*
’
2.4
.
’
2.6
.
’
2.8
.
’
3.0
.
’
3.2
.
3
lOOOR( K“) Fig. 2. Temperature dependence of the permeability coefficients of HQDPA-DBA and HQDPA-DAEB. Solid (-): HQDPA-DBA, dash (---): HQDPA-DAEB.
HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DBA HQDPA-DAMB HQDPA-DAEB
3.15 8.37 16.3 37.3 5.67 5.33 7.79
0.149 0.395 I .08 4.S2 0.179 0.234 O.S29
0.0158 o.oSO4 0.183 0.846 0.0147 0.0344 0.0756
237 166 89.2 44.1 386 15s 103
9.4 7.9 5.9 5.3 12 6.9 7.0
Yuesheng Li et al.
1316 Table 4. Permeability
coefficients and permselectivity polyctherimides at 100°C
Polyetherimide HQDPA-PDA HQDPA-TDA HQDPA-XDA HQDPA-3MPDA HQDPA-DEA HQDPA-DAMB HQDPA-DAEB
HZ
OS
NZ
11.3 20.4 31.2 81.3 17.1 14.3 19.2
0.586 1.13 2.63 6.61 0.793 0.787 I .33
0.104 0.215 0.551 2.26 0.125 0.160 0.292
coefficients of 0 HQDPA-DBA
Hz/N* 02/N> 109 94.9 61.5 36.0 137 89.5 65.8
5.6 5.3 4.7 2.9 6.4 4.9 4.6
300
c :s
250
8 a
200 HQDPA-DAMBO
“%I
‘\ ‘\
logarithms of permeability coefficients of the polyetherimides, prepared from PDA, TDA, XDA, and TMPDA, to H2, O2 and N? increase linearly with the increase of the methyl on the diamines and meanwhile, the permselectivity coefficients for HJN2 and 02/N2 decrease progressively. As shown in Fig. 4, the order of increase of permeability is also that of increase of fractional free volume of these polyetherimides. This fact indicates that the fractional free volume variation plays a dominant role in determining the permeability and permselectivity change compared with subtle differences in the chain segmental mobility of the methyl substituted polyetherimides in this case. Comparison of HQDPA-DBA
and HQDPA-PDA
Carboxylic group (-COOH) is a strong polar substituent. Polyetherimide with carboxylic group, HQDPA-DBA, has high H-bond energy and high orientation energy. This results in that HQDPADBA has much higher cohesive energy than other HQDPA-based polyetherimides. By the way, there can be intermolecular cross-link structure in HQDPA-DBA. Consequently, the glass transition temperature of HQDPA-DBA is much higher than HQDPA-PDA and the chain segmental mobility is much lower than HQDPA-PDA. Carboxylic group is also a bulky substituent that restricts the chain segmental packing. Hence, the fractional free volume of HQDPA-DBA is higher than HQDPA-PDA. The polymers with high fractional free volume and low chain segmental mobility, especially cross-link struc-
lOOr
I
b\
50
‘\ .
“;;p . .
10
1 H2
100
Permeability coefficients ( barrier)
Fig. 4. Plot of Hz permeability coefficients vs Hz/N2 selectivity of the polyetherimides.
ture, possess high permeability and high permselectivity. Hence the permeability coefficients of HQDPA-DBA to HZ and O2 are higher than those of HQDPA-PDA, and the permselectivity coefficients of HQDPA-DBA for HI/N* and 02/N2 are much higher than those of HQDPA-PDA. For example, the permeability coefficients of the polyetherimide to H2 and O2 increase by 51 and 17%, respectively, while the permselectivity coefficients of the polyetherimide for HZ/N2 and 02/Nz increase by 41 and 27%, respectively. Permeability andpermselectivity of HQDPA-diaminobenzoates
Carboxylic ether groups (-COOR) differ from the carboxylic group in many respects. First, the volume of carboxylic ether groups is much greater than that of the carboxylic group. Second, carboxylic ether groups are flexible substituents and have strong plasticization effect, but the carboxylic group does not. Third, carboxylic ether groups are inert substituents and do not react with amine, in the process of imidization of polyamide acid precursor. Therefore, the polyetherimides which were prepared from 3,Sdiaminobenzoate possess lower glass transition temperature, namely, higher chain segmental
8-l
d
HQDPA-DAEB 0
100
_ 10
I
12 -
0 HQDPA-DBA
r .P 2
IO-
8 x .F
s-
‘n
+
P’
6-
5
4-
HQDPA-DAMB HQDPA-DAEB :
I 0
.
I 1
.
1 2
.
1 3
Methyl number Fig. 3. Effect of methyl number on diamine on the permeability of HQDPA-based polyetherimides.
21 .‘.‘I
0.1
1
0, Permeability coefficient Fig. 5. Plot of 0~ permeability coefficients vs OZ/NZ selectivity of the polyetherimides.
Gas permeation through HQDPA-based polyetherimides
mobility, than HQDPA-PDA and lower segmental package density, e.g. higher fractional free volume, than HQDPA-PDA, but lower fractional free volume than HQDPA-DBA. These facts result in the polyetherimides prepared from 3,5-diaminobenzoate having higher permeability than HQDPA-PDA. The strong plasticization of -COOR causes a larger increase of N2 (with large molecular kinetic diameter, 0.364 nm) permeability coefficients than of H1 and OI (with small molecular kinetic diameter, 0.289 and 0.346 nm, respectively). Consequently, the permseiectivities of the polyetherimides prepared from 3,5-diaminobenzoate for H2/N2 and 02/N2 are much lower than those of HQDPA-PDA. -COOC2HJ is larger than -COOCHp, and the former has a stronger plasticization than the latter. HQDPA-DAEB has higher fractional free volume and higher chain segmental mobility than HQDPA-DAMB. This means that the permeability coefficients of HQDPADAEB to each gas are larger than those of HQDPA-DAMB, but the permselectivity coefficients of HQDPA-DAEB for Hz/N2 and 02/N2 are smaller than HQDPA-DAMB, shown in Figs 4 and 5. As shown in Table 1, the fractional free volumes of HQDPA-DAMB and HQDPA-DAEB are lower than that of HQDPA-DBA. Therefore, the permselectivity coefficients of HQDPA-DAMB and HQDPA-DAEB for Hz/N2 and 02/N2 are much lower than those of HQDPA-DBA. CONCLUSION
For HQDPA-based polyetherimides, the effect of temperature upon gas permeability coefficients can be
1317
described well by the Arrhenius equation. The structure of the diamine monomers has a very strong effect on the permeability and permselectivity of HQDPA-based potyetherimides. Among methyl substituted polyetherimides, the permeability increases, but the permselectivity decreases, and can be explained by the increase of the fractional free volume of the polymers. The polyetherimides, which are prepared from 3,5-diaminobenzoic esters, with higher chain segmental mobility due to strong plasticization by carboxylic ether groups, possess lower permselectivity than the others. However, HQDPA-DBA exhibits much higher permselectivity than the others due to cross-linking. authors are grateful for the financial support granted by the National Natural Science Foundation of China. Acknowledgement-The
REFERENCES
Barbari, W. J. Koros and D. R. Paul. J. Membr. Sci. 42, 69 (1989). 2. K. V. Peinemann, K. Fink K. and P. Witt. J. Membr. I. T. A.
Sci. 127, 215 (1986). 3. K. Kneifel and K. V. Peinemann. J. Membr. Sci. 65, 295 (1992). 4. G. C. Eastmond, J. Paprotny and I. Webster. Polymer 34, 2865 (1993). 5. Y. Li, X. Wang, M. Ding and J. Xu. Polym. Inr. 37,52 (1996). 6. &‘. h;l. Lee. Pofym. Eng. Sci. 20, 65 (1980). 7. A. Bondi. J. Phvs. Chem. 68,441 (1964). 8. K. C. C’brien, \;5;.J. Koros anh G. d. Husk. J. Membr. Sci. 35, 217 (1988). 9. K. Tanaka, H. Tits, M. Okamo and K. Okamoto. Polymer 33, 585 (1992).