Polymer Sorbents Based on Polyimides K. I . Sakodynsky, N. S. Klinskaya, and L. I. Panina Karpov Insfifufe of Physical Chemistry, Moscow, Sovief Union
Thermally stable polymers based on polyimides have been examined as column packings for gas chromatography. Some structural and gas chromatographic properties of these sorbents are reported. The polymers studied have porous structure, a large total pore volume, and a large average pore radius. Polymer sorbents based on polyimides possess a specificity of molecular interaction, which is assumed to be due to the presence of imide and carbonyl functional groups on the surface of these sorbents. They are suitable for lhe'separation of high-boiling compounds, having boiling points about 200-300 " C and over.
Porous polymer sorbents on a styrene a n d divinyl benzene base are used in gas chromatography but t h e upper temperature limit of their applicability is 250 "C. The availability of thermally stable polymer sorbents would extend both the range of compounds which could be eluted and the temperature range of operation of gas chromatography on porous polymers. T h e first steps in this direction have been already made by Van Wijk who used a polymer based on 2,6-diphenyl phenylene oxide (1, 2). We have investigated the possibility of using two types of polymer on a polyimide base: (1) pyromellitic dianhydride and diamine diphenyl ether (Polysorbimide-l), and (2) dianhydride of benzophenone-tetracarboxylic acid and diaminodiphenyl ether (Polysorbimide-2). These polyimide sorbents are irregular yellow colored particles, soluble in concentrated nitric and sulfuric acids but insoluble in organic solvents. The polyimide sorbents studied were synthesized by polymerization in a n inert diluent. Some properties of polyimides and their synthesis were described by Adrova, Bessonov, Laius, and Rudakov (3).
i 1
0.2
0.4
0.6
or8
Figure 1. Isotherms of nitrogen adsorption 1 on Polysorbimide-1 2 on Polysorbimide-2
EXPERIMENTAL Apparatus. The chromatographic measurements were carried out on a L.Ch.M.-YA chromatograph of Russian origin, equipped with a thermal conductivity detector, The packed columns were stainless steel tubes, 1-m long and 4-mm i.d. All measurements were made at a column temperature of 170 "C and helium carrier gas flow rate of30 ml/min. Sitrogen adsorption isotherms were obtained using a Carlo Erba "Sorptomatic" instrument and measuring a t the boiling point of nitrogen. Surface areas were estimated using the initial portion of the isotherms in the relative pressure range up to p / P s = 0.3-0.35 and applying the B E T equation. The mercury porosimetric measurements were carried out using a Carlo Erba" Porosimeter" instrument. T h e investigations of thermal stability of the sorbents were conducted on a Paulik-Paulik-Erdeg derivatograph (Hungaria, Budapest) in inert helium gas at a rate of heat of 5 "C/min. Electron micrographs were obtained using a Jeol scanning electron microscope .JSh1-2. ( 1 ) R. Van Wijk, "Advances in Chromatography 1970," A . Zlatkis, Ed Houston, Texas 77004, 1970, p 1 2 2 . (2) R . Van Wijk. J. Chromafogr. Sci., 8, 418 (1970). (3) N. A . Adrova, M . I . Bessonov, L. A. Laius, and A . P. Rudakov, "Pol. yimides-new class of thermally stable polymers," Nauka. Lenln. grad, 1968.
Table I. Some Structural Characteristics of Polyimides Characteristic Polysorbimide-1 Polysorbimide-2 Surface area, m'/g 67.5 41.8 Pore volume, cm3/g 1.35 1.10 Average pore radius, A 1000 10000
Free fall density, g/cm3
0.38
0.30
Preparation of Columns. The polysorbimide particles were packed into columns by vibration and conditioned at 350 "C at a carrier gas flow rate of 30 ml/min for 3 hours. Then the columns were cooled to the desired starting temperature.
RESULTS AND DISCUSSION Figure 1 shows nitrogen adsorption isotherms on polysorbimides. Such isotherms are characteristic of macroporous sorbents. The mercury porosimetric method was used to measure t h e total pore volume and pore size distribution. Figures 2 and 3 show integral and differential curves of the distribution of pore volume according to the radii on Polysorbimides-1 and 2, and Table I presents some structural characANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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% 1.4
4.2
f.C
0.8
0.6
0.4
0.2
Figure 2. Integral and differential curves of the distribution of pore volume according to the radii on Polysorbimide-1
10.2
I
'
2.0
2.5
3.0
3.5
40
4.5
;I
5.0 4 2
Figure 3. Integral and differential curves of the distribution of pore volume according to the radii on Polysorbimide-2
Table I I . Retention of Unsalurated Compounds Relative to n-Pentane, T = 170 "C t R / t R of n-pentane
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Sorbate
bp. "C
Mol wt
Polysorbimide-1
Polysorbimide-2
Polysorb-1
n-Pentane Pentene-2 Pentadiene-l,5 Hexane Hexene-1 Cyclohexane Cyclohexene Benzene Methylcyclohexane Toluene
36.1 36.9 44.1 68.7 63.5 a i .4 83.0 80.1 100.9 11 0.6
72.1 70.1 68.1 86.2 84.2 84.2 82.1 78.1 98.2 92.1
1.o 1.3 2.1 2.4 3.0 2.5 4.3 6.8 5.3 15.5
1.o 1.5 1.8 2.0 2.5 1.0 3.0 4.5 1.3 11.3
1.o 1.04 1.2 2.3 2.2 3.0 3.3 2.9 5.6 6.8
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
Figure 4, a and b. Scanning electron micrographs of Poiysorbimide-1
I 90 80
"
50
300
a50 Eo0
250 300 3m 400 450 500 0 0 600 650 W O
-
72
Figure 5. Thermogravimetric curves for Polysorbimide-1 (1) and Polysorbimide-2 (2) teristics of these particular sorbents. They have a large total pore volume and a large average pore radius. The total pore volume of polyimides is commensurable with the total pore volume of polymer sorbents on a styrene and divinyl benzene base (polysorhs). Figure 4, a and b, illustrate the porosity of the Polysorhimide-1 surface. This result was obtained during the scanning electron microscope investigation of the sorbent. The macroporous structure of the polyimides studied seems t o be due to the method of synthesis in a n inert diluent. Figure 5 shows the thermogravimetric curves for Polysorbimides. We can see that they have a high thermal stability. and thus can he used in a eas chromatoeraoh ., . till 400 'C a t least. Tahles 11-VI11 show the retention characteristics of molecules helonging to different classes on porous Dolyimides. . . The principal retention characteristics may he summarized as follows: The retention of unsaturated compounds depends not only on the boiling point and molecular weight h u t also on
Table 111. Retention of Polar Molecules Relative to n-Pentane, T = 170 "C t d t n Of o-pentane Polysorb-
Sorbate
Water Methanol Ethanol Acetonitrile Acetone Diethyl ether n-Pentane
crlA')
1.49 3.23 5.06
...
6.32 9.02 9.05
&, D
1.84 1.71 1.68 3.94 2.73 1.17 0
imide-l
0.8 1.0 1.9 3.3 3.0 1.5 1.0
PolySorbimide-2 POIySOrb-1
1.3 1.7 3.0 3.7 2.5 2.0 1.0
0.12 0.19 0.40 0.60
0.69
0.87 1.0
I
the presence and nnmher of double bonds in the molecule: 2-pentene and 1,3-pentadiene appear on the chromatogram after pentane; and 1-hexene, after hexane. I t is also Characteristic that cyclohexene and benzene, the boiling point of which is lower t h a n t h a t of cyclohexane, are more strongly retained on polysorbimides t h a n the latter. ANALYTICAL CHEMISTRY, VOL. 45, NO. 8. JULY 1973
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Table I V . R e t e n t i o n s R e l a t i v e to n - P e n t a n e of S u b s t a n c e s H a v i n g S i m i l a r B o i l i n g Points, T = 170 "C tR/tR
Sorbate
bp. "C 64.7 64-65 78.4 77.1 76.8 81.6 81.4 100.0 97.8 101.0 98.4
Methanol Tetrahydrofuran Ethanol Ethyl acetate Carbon tetrachloride Acetonitrile Cyclohexane 'Water n-Propanol Nitromethane +Heptane
Mol wt
Pz D
32.0 72.1 46.1 88.1 153.8 41.05 84.16 18.0 60.1 61.0 100.2
1.71
Polysorbimide-1
of n-pentane
Polysorbimide-2
1 .o 4.9 1.9 5.3 3.6 3.3 2.6 0.8 4.2 5.8 4.5
1.68 1.81
0 3.94
0 1.84 1.64 3.54
0
1.6 4.3 3.0 4.0 2.2 3.6 1.o 1.3 5.5 8.6 3.0
Table V. R e t e n t i o n s , R e l a t i v e to n - P e n t a n e , of S u b s t a n c e s H a v i n g S i m i l a r M o l e c u l a r W e i g h t s , T
Moi wt
n-Hexane Ethyl acetate Dioxane Diethyl ether n-Pentane Tetrahydrofuran n-Butanol Acetone N itromethane Acetic acid
86.2 88.1 88.1 74.1 72.1 72.1 74.1 58.1 61 .O 60.1
Polysorbimide-1
bp. "C
k D
68.7 77.1 100.8 35.6 36.1 64-66 11 7.5 56.2 101.0 118.1
0 1.81 0 1.17
... 1.63 2.85 3.54 1.70
3.1 0.1 1 .o 1.o 4.8
of n-pentane
Polysorbimide-2
2.4 5.3 9.1 1.4 1 .o 4.9 6.8 3.0 5.9 5.8
0
0.19 2.3 0.4 2.4 3.1 0.6
= 170 " C
tR/tR
Sorbate
Polysorb-1
1.8 4.0 8.0 2.0 1 .o 4.35 10.5 2.5 8.7 8.66
Polyso rb-1 2.3 2.4 4.4 0.9 1 .o 2.3 2.8 0.7 1 .o 1 .o
T a b l e V I . R e t e n t i o n s of C h l o r i n a t e d M e t h a n e s R e l a t i v e to n - P e n t a n e , T = 170 " C
t X / t H of n-pentane Sorbate Dichloromethane C h lorofor m Carbon tetrachloride n-Pentane
~~
Mol wt
bp. "C
P,D
84.9 119.4 153.8 72.1
40.1 61.3 76.8 36.1
1.62 3.06 0 0
~~~
Polysorbimide-1 Polysorbimide-2 2.1 3.7 3.6 1 .o
Polysorb-1
2.8 4.0 2.2 1 .o
0.9 2.1 3.1 1 .o
~~
T a b l e V I I . R a t i o of C o r r e c t e d R e t e n t i o n V o l u m e s of N o r m a l A c i d s to N o r m a l A l c o h o l s H a v i n g a n E q u a l N u m b e r of C a r b o n A t o m s , T = 170 "C Components to bp 'C Moi wt Polysorbimide-1 Polysorbimide-2 Polysorb-1 CH3COOH
118.1
C~HSOH
78.4 141.1
60.05 46.1
97.2
74.08 60.1
163.5 11 7.5
74.1
88.1
3.7
4.6
2.5
4.0
4.4
3.5
3.5
3.8
2.0
Table V I I I . R e t e n t i o n s , R e l a t i v e t o n - P e n t a n e , of I s o m e r i c A l c o h o l s , 7 = 170 " C
t R / t H of n-pentane Sorbate n-Propanol Isopropanol tert-Butanol sec-Butanol lsobutanol n-Butanol
1372
Mol wt
bp. "C
Polysorbimide-1
Polysorbimide-2
Polysorb-1
60.1 60.1 74.1 74.1 74.1 74.1
97.8 82.4 82.8 99.5 108.0 11 7.5
4.5 3.0 2.6 4.2 5.1 6.8
5.5 3.5 2.3 6.0 7.7 10.5
0.9 0.7 1.2 1.8 2.2 2.8
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
4
40 !
9-
a7-
5
6-
5-
43Figure 7. Separation of esters
ai-
1 80
go
400
I40
420
T 'C
Figure 6. Dependence of t h e relative retention time of C 4 isomeric alcohols on their boiling points ( t r of n-pentane taken as
a standard) 1, on Polysorb-1, 2. on Poiysorbimide-1; 3. on Polysorbimide-2
1. hexyl phenyl acetate, 2. heptyl phenyl acetate, 3. octyl phenyi acetate, 4 . nonyl phenyl acetate, 5 . decyl phenyl acetate. Column: Poiysorbimide2, 1.5 m X 4 mm i.d. Column temperature: 330 "C. He flow rate 30 mi: min, Detector T.C.
The retention of alcohols and acids on polysorbimides is considerably greater than on Polysorb-1 ( a n analog of Chromosorb 102). It should be noted t h a t on the polymers
3
A Figure 8. Chromatogram of aromatic compounds 1 Benzene 2 naphthalene 3 a-methylnaphthalene, 4 acenaphthene. 5 phenanthrene Conditions as for Figure 7
The retention of polar molecules depends on the value of the dipole moment and on the ability of the compounds to form hydrogen bonds with the sorbent surface. This is illustrated by the increase in retention time when passing from pentane to acetonitrile (Table 111) as well as by the resolution of compounds with closely similar boiling points (Table IV) and those with similar molecular weights (Table V). T h u s , nitromethane on polyimides is retained more strongly than heptane in spite of t h e significantly lower molecular weights, acetonitrile is retained more strongly than cyclohexane, ethyl acetate, more strongly than n-hexane. Similarly with the chloromethanes, chloroform leaves the column later t h a n t h e heavier and higher boiling carbon tetrachloride, while dichloromethane is retained two or three times as strong as n-pentane; on Polysorbimide-2 it is even more strongly retained than carbon tetrachloride (Table t?).
investigated, a greater retention of fatty acids capable of forming stronger hydrogen bonds is observed as compared to alcohols with the same number of carbon atoms (Table VII). The retention of isomeric alcohols is determined mainly by the difference in the boiling points and volatilities of the components to be resolved. A stronger retention of molecules of normal structure is observed as compared to t h a t of branched alcohols, although the values themselves of the relative retention time of alcohols on polyimides exceed the respective values on Polysorb-1 (Table VIII). More than t h a t , as can be seen in Figure 6, the angle of slope of the dependence of the relative retention time of isomeric Cq alcohols on their boiling points increases when passing from Polysorb-1 to Polysorbimide-1, and to Polysorbimide-2. An examination of the results obtained shows t h a t polymer sorbents on a polyimide base possess a specificity of ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
1373
A
2
3
I
1
i 2 3 4 5 Figure 10. Separation of alcohols
0
6
7
8
9nt1,'L
1. 1-octanol, 2. I-undecanol, 3. 1-hexadecanol. Column: Polysorbimide1 , 1-m X 4-mm i.d. Column temperature: 320 "C. H e flow rate 30 ml/ min. Detector T.C.
6
i
2
j
imin
Figure 9. Separation of pyrrolidones 1 , water, 2. butyric lactone, 3. N-methylpyrrolidone, 4 . N-vinylpyrrolldone. Column. Polysorbimide-1, 1-m X 4-mm 1.d. Column temperature: 250 "C.He flow rate 30 ml/min. Detector T.C.
molecular interaction which is assumed to be due to the presence of imide and carbonyl functional groups on the surface of the sorbents.
,' ,
1374
.,
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8 , JULY 1973
Polysorbimides are suitable for the separation of highboiling polar compounds such as alcohols, esters, aromatic hydrocarbons, pyrrolidones, aldehydes, and ketones. Figures 7 to 10 show chromatograms of the resolution of compounds belonging to several classes. These separations were effected a t 330 "C. High maximum operating temperature (
