"'1443
Anal. Chem. 1983, 55, 1443-1445
Acid Hydrazide Characterization for Polyimide Analysis Harold G. Linde" and Stephen Meeks, Jr. IBM General Technology Division, Essex Junction, Vermont 05452 Commercial polyimides are widely used as thermally stable dielectrics and overcoats (I). Material limitations and application requirements have evolved a variety of functionally similar polymers, whose properties are modified by structural differences in diamine and/or tetraacid constituents. This variability prompted a simple, accurate, analytical method to identify polymer precursors. In an effort to resolve differences in polyimide systems, Mlejnek and Cveckova (2) and others ( 3 , 4 )have suggested alkaline hydrolytic methods to cleave polymeric units into their component monomers (Figure 1). Although successful, these methods me slow and frequently plagued by incomplete hydrolysis of the amide linkages formed after solubilization of the polyimide in the alkaline hydrolysis medium. Consequently, the reactions me inadequate for accurate analytical studies. Hydrazinolysis (5) incorporates a reactive amine species into the intermediate generated in the initial imide opening; its neighboring proximity to the newly formed amide linkage allows rapid and complete cleavage of the polymer (6, 7) as shown in1 Figure 2. The resulting hydrazide derivative, and the free amine liberated by hydrazinolysis, are easily isolated by extraction and simple filtration of the acidified reaction mixture.
EXPERIMENTAL SECTION Apparatus. Infrared spectra were recorded on a Perkin-Elmer 283B infrared spectrophotometer. Gas chromatographic analyses were run on a Hewlett-Packard 5700A GC with a 58UOA data station. A 12 ft X lJ4in. 10% SE30 phase on Chromosorb W was used for both acid ester and amine analysis. Conditions for amines were as follows: 60 mLJmin He; program 180 "C, hold 4 min; program 8 "C/min to 280 "C, hold 16 miq injection port and TCD 250 "C. Conditions for methyl esters were as follows: 85 mL/min He; 280 "C isothermal; injection port 400 "C, TCD 360 "C. Eastman 6060 silica gel thin-layer chromatographic sheets, Eastman Kodak Co., Rochester, NY, were used in thin-layer analysis; preparative TLC was accomplished by using E. Merck F254 silica plates, Brinkman Instruments Inc., Westbury, NY. Reagents. Polyimides used in this study were either solutions of commercial polyamic acids, amide-imides, or developmental samples prepared for investigational use. Cured polyimide films were employed in each hydrolysis procedure. The polyimides were prepared by oven curing a thin film of polyamic acid solution for 2 h at 200 "C; the imidization was monitored by IR anaPysis; and films appeared solvent-free after this procedure. Hydrolytic reagents were of analytical quality and were used as received. Caution: Hydrazine is a severe poison and cancer-suspect agent. A number of diamines,liberated by the hydrolytic methods described here, are also cancer-suspect agents. Aqueous Hydrazine Hydrolysis. About 35 mg of cured polyimide film was placed into a 5-mL "Reactivial" flask with stirrer. Three milliliters of 20% aqueous hydrazine solution (prepared by neutralizing hydrazine dihydrochloride with 2 equiiv of potassium hydroxide) were added and the mixture waa heated to 100 OC ,with stirring. After 4 h the solution was cooled; at this point the polymeric film had deteriorated and had been replaced by a suspended precipitate. The mixture was extracted with 1mL of ether, and the ether layer (containing the free amines) was removed and evaporated. The diamines were expeditiously chromatographed, avoiding oxidation. Concentrated hydrochloric acid (1mL) was added to the reaction mixture with stirring, and the resulting solid filtered under vacuum in a Buchner funnel. This hydrazide precipitate was washed with two 2-mL aliquots of water and dried in a desiccator 0003-2700/83/0355-1443$01.50/0
Table I. Fluorescence, Infrared Data, and Thin-Layer Retention Values of Acid Hydrazides Separated on Silica Gel with THF,Diethylamine, Water (4:4:1.5) Rf
fluorescence
PMA BTDA ODPA TMA
0.25 0.25 0.32 0.7 +
rusty red yellow blue yellow
1650; 1495; 1560 1640; 1600; 1555 1650; 1595; 1495 1650; 1595; 1530
HFPDA
0.7
blue
1250; 1585; 1210; 1640
acida
IR, cm-'
0.85 a
Abbreviations as per Table 111.
-
Preparation of Hydrazide Standards. Hydrazides were prepared from known tetraacids following the procedure of Fieser (IO). These standards were used for TLC analysis and infrared comparisons. Thin-Layer Chromatography (TLC) of the Hydrazides. Hydrazides were chromatographed on silica gel sheets in a solvent composed of tetrahydrofuran, diethylamine, and water (4:4:1.5). After a 12-cm development, the chromatogram was dried under a stream of nitrogen and the hydrazides were visualized by long ultraviolet (UV) fluorescence (see Table I). Preparative TLC was carried out in the same solvent system with E.Merck silica gel F254 glass plateia. UV visualized bands were scraped from the plate and eluted with methanolJammonium (101). The filtered solution was dried under a nitrogen stream, one drop of concentrated HCI was added, and the mixture brought to dryness. The residual solid was rinsed with 1 mL of water (to remove chlorides) and dried. 2,2-Bis(3,4-dicarboxyphenyl)hexafluoropropane,Basic hydrolysis of Du Pont 2566 yielded a tetraacid with an unusual 1210 cm-1 (C-F) absorption in the infrared region. In melting this acid undergoes a change at about 220 "C, partially liquifying but then resolidfying and finally melting, 241-245 OC. 'Ihis melting is consistent with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane which forms the anhydride on heating (1.2). The mass spectrum of the tetramethyl acid ester reveals a molecular weight of 536 with major ions at 505 (-OCH,) and 459 (OCH,, -CH30CH3) and is consistent with the hexafluoro ester (C2,H16°6F6).
RESULTS AND DISCUSSION This study evaluated hydrolytic reagents in their ability to cleave component monomers from a series of cured palyimide resins. A dettliled list of these polyimides, by component composition, is given in Table 11. While it was found that a wide concentration range of both aqueous and methanolic potassium hydroxide or tetramethylammonium hydroxide solutions caused polyimide reaction, in no case was hydrolysis complete since acidification of the reaction mixtures invariably yielded red-brown, ether-insoluble, amide components. Infrared and chromaitographic data for free acid and amine components, isolated by hydrolysis, are included with characteristic polyimide IR absorptions in Table 111. Tetramethyl acid esters (8,9),classical derivatives prepared by tube or on column pyrolysis of TMAH acid salts, offered a useful (but crude) alternative method of acid component identification. Separation of these derivatives was accomplished on a SE30 phase GC column. Infrared and GC data, summarizing the analysis of these useful ester derivatives, is also given in Table 111. Complete degradation of polyimide systems was accomplished by hydrazinolysis in 20% aqueous hydrazine. This 0 1983 Amerlcan Chemical Society
1444
ANALYTICAL CHEMISTRY, VOL.
55, NO. 8, JULY 1983
Table 11. Polyimides Investigated in the Study simple name or designation a
isolated acid component(s) PMA ODPA TMA
BTDA
PI 5057 PI 2525: (2550b) PI 2566 Skybond 703c AI-10 BTDA-ODA BTDA-MPDA Copolymer ODPA-ODA
HFPDA
isolated amine(s) ODA MDA MPDA
X
X
X X X X X X
X X
X X
X X
X
a Abbreviations: BTDA, benzophenonetetracarboxylic acid; PMA, pyromellitic acid; ODPA, oxydiphthalic acid; TMA, trimellitic acid; HFPDA, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane;ODA, 4,4'-oxydianiline; MDA, 4,4'-methylenedianiline; MPDA, m-phenylenediamine. A product of Du Pont. A product of Monsanto. A product of Amoco.
Table 111. Infrared and Gas Chromatographic Data for Selected Polyimides and Component Monomersa polyimide type; IR
hydrolyzed acid; IR
PMA-ODA 1495; 1720; 1235; 1370 BTDA-ODA 1495; 1720; 1235 BTDA-MDA 1720; 1770; 1365 TMA-MDA 1720; 1515; 1375 BTDA-ODA-MPDA 1720; 1500; 1240; 1375 ODPA-ODA 1725; 1500; 1245 BTDA-MPDA 1720; 1355; 1490 HFPDA-ODA 1500; 1730; 1245
PMA 1700 (broad); 1270; 1410 BTDA 1700 (broad); 1600; 1280 BTDA
PMA ester 1735; 1250; 1120; 1440 (5.90) BTDA ester 1730; 1280; 1240 (37.10)
TMA 1700; 1285; 1410 BTDA
TMA ester (tri ester) 1730; 1250; 1290 (3.59)
ODPA 1710; 1680; 1280; 1230 BTDA
ODPA ester 1720; 1495; 1600 (27.73)
HFPDA 1710 (broad); 1260; 1210; 1185
HFPDA ester 1735; 1260; 1215 (13.07)
tetramethyl ester; IR (GC)
amine; IR (GC) ODA 1490; 1210; 815 (23.0) ODA MDA 1515; 1625; 1270 (23.0) MDA MPDA 1600; 1620; 1500 (6.15) ODA MPDA ODA o-tolidine (27.50) p-phenylenediamine (6.7 6)
a Abbreviations as per Table 11; IR = three strongest IR absorptions (cm-' ) in order of intensity (four, if two are of equal intensity), GC = retention time in min under conditions given in the Experimental Section.
0
L o
0
0
/
I
Jn H2N-@O@NH2
Figure 1. Hydrolytic cleavage of a typical polyimide into parent tetraacid and diamine components. reaction proceeded rapidly at 100 "C and was complete within 4 h. Free amines were extracted with ether from the crude mixture and were identified by GC and IR; acidification yielded the hydrazide which was collected by filtration. Thin-layer analysis in tetrahydrofuran, diethylamine, and water (4:4:1.5) on silica gel revealed these hydrazides as fluorescent zones of characteristic color and Rf values (Table 111). These derivatives were collected by preparative thin-layer chromatography and compared, by infrared analysis, to hydrazides prepared from the pure acids by another route (IO). Hydrazinolysis proved to be the most rapid, reliable, and complete method of polymer cleavage and the resulting hydrazides are convenient acid derivatives for accurate identifications. This method has proven suitable in identifying monomeric polyimide components in mixed acid and mixed amine copolymers and blends.
+
Figure 2. Hydrazide formation through hydrazinoiysis.
ACKNOWLEDGMENT Grateful appreciation is given to R. Gleason for his helpful discussions during this study. Registry No. PI 5057 (repeating unit), 25036-53-7;PI 5057 (copolymer),28501-43-1;PI 2525 (repeating unit), 79121-87-2;PI 2566 (repeating unit), 39940-16-4;PI 2566 (copolymer),69639-26-5; SKYBOND 703 (repeating unit), 26913-87-1; SKYBOND 703
Anal. Chern. 1983, 5 5 , 7445-1448
(coDolvmer). 26875-02-5: AI-10 (reDeatineunit), 29087-9!5-4:ALlO (cipoiymerj, 25895-32-3; BTDA-ODA ccopolymer),26875-71-8; BTDA-ODA (repeating unit), 24991-11-5; BTDA-MPDA (copolymer), 25300-72-5; BTDA-MPDA (repeating unit), 25868-65-9; BTDA-PMA-ODA (copolymer), 85629-22-7; ODPA-ODA (copolymer), 85629-23-8; ODPA-ODA (repeating unit), 52325-20-9.
LITERATURE CITED (1) Sroog, C.E. "Encyclopedia of Polymer Science and Technology"; Wiley: New York, 1969;Vol. l l , pp 247-272. (2) Mlejnek, 0.; Cveckova, L. J . Chromatogr. 1974, 94, 135.142.
r445
(3) Schlueter, D.; Singia, S. Anal. Chem. 1977, 49. 2349-2353.
(4) Haslam, J.; Will& H.; Squirrell, D. "Identification and Analysls of Plastics", 2nd ed ; ILIFFE Books: London, 1972;pp 311-312. (5) Ing, H.; Manske, R. J. Chem. Soc. 1926, 2348. (6) Jones, J. J . folym. Sei., Part C IB69, 22, 773-784. (7) Dine-Hart, R.; Parker, D.; Wright, W. Br. folym. J . 1971, 3 , 226-234. (8) Robb, E.; Westbrook J. Anal. Chem. 1963, 35, 1644. (9) Bailv. J. Anal. Chem. 1967. 39. 1485.
(io)
Fleser, L. "Experiiments In Organic Chemistry"; D. C. Heath and Co.: Boston, MA, 1957;pp 199-200. (11) Rogers, F. E. Chnm. Absfr. 1968, 68, 304199.
RECEJYED for review October 13,1982. Accepted April 4,1983.
Determination of Fluoride at Low Concentrations with the Ion-Selective Electrode Erik Kissa Jackson Laboratory-Chemicals Wilmington, Delaware 19898
and Pigments Department, E. i! du Pont de Nemours and Company,
The fluoride ion selective electrode (ISE) developed by Frant and Ross (1) is a sensitive and selective tool for the determination of fluoride ion activity (1-9). The response of the electrode has been reported to be Nernstian above M F- (10) or 1.5 X lo-" M F- in NaF and 5 X lo4 MF- in buffered IVaF solutions (11).The Nernstian response has been extended to lou0 M fluoride (9, 12) with cations strongly complexed by fluoride. However, the electrode response has been slow and sluggish at low fluoride ion concentrations (6, 13-15). The drift of electrode potential has necessitated frequent calibration (3, 10). The kinetics of the fluoride ISE response have been investigated (16-26) and its dynamic response has been shown to result from four processes: ion diffusion, reaction, L a 3 dissolution, and calibration drift (15). The procedures used for the determination of fluoride ion activities and concentrations have differed in several important aspects. The fluoride ISE has been conditioned and stored in a buffer solution (14) or in a buffered fluoride solution (2, 3,10).Barnard and Nordstrom (27) obtained a stable electrode potential in 12 to 18 min by soaking the electrode in a standard solution of a concentration similar to that of the analyte. Between immersion in analytes, the electrode is customarily rinsed with water (3), is rinsed with a buffer solution, or is not rinsed (15). The reported precision of fluoride determination, expressed as the standard deviation, decreases with the decreasing fluoride Concentration: 0.4% relative in the lov3M range (IO), 0.8% relative in the 10-1 to lo4 M range (8),about 2% relative to 3 X M range, 4% relative a t IO-' M, in the 5 X and 10% relative a t 5 X M fluoride (28, 29). We had to determine lo4 or M P in solutions produced by combustion of organic compounds in an oxyhydrogen torch. The excessive electrode drift, long response times, and inadequate prcxision necessitated development of the methods described in this report. Problems associated with the instability and drift of the fluoride ion selective electrode have been resolved by (a) limiting th,e fluoride concentration to which the electrode is exposed to a 0.01 to 0.1 mg of F-/L or 0.05 to 1.0 mg of F-/L concentration range, (b) measuring the electrode potential in the analyte by approaching equilibrium in the same direction from a higher potential to a lower potential, and (c) keeping the temperature of the solutions constant within f0.2 OC or closer. The fluoride concentration in the analyte is adjusted to the concentration range of the ion-selective electrode by
dilution or fluoride (addition, or fluoride is determined by (;he analyte addition method.
EXPERIMENTAL SECTION Apparatus. The Iluoride ion selective electrode, Orion Model 94-09A, was used in combinationwith a double junction electrode, Orion Model 90-01. 'The cell potentials were measured with the Orion Ionalyzer, Model 901. The Orion electrode holder (Catalog No. 13-641-814)was provided with a stop to keep the immersion depth of the electrodes constant. Two sets of electrodes were u s e d one set was expcxsed only to solutions containing 10-100 pg of F / L , and the other to solutiions containing 50-1000 pg of F / L (0.05-1.0 mg of F-/L). All volumetric flasks and beakers (50 mL) used were made of "Nalgene". Agitation was provided by a thermally insulated magnetic stirrer operating at a constant speed. Reagents. The standardizing solutions were prepared by successive dilutions of a stock solution containing 11.10 g of reagent-gradeNaF (dried to a constant weight at 125 OC) per liter. The standardizing solutions and analytes contained an acetic acid-sodium acetate buffer (2% by volume) prepared as follovvs: Add to 2800 mL of water 480 mL of acetic acid, reagent grade, and 500 mL of 30% sodium hydroxide solution, made of ACS certified, electrolyticNaOH pellets. Dilute to 3800 mL with water and adjust to pH 5.0 to 5.2 with sodium hydroxide. TISAB I1 (without, CDTA) or TISAB I11 (3) were used for electrolyte-containing analytes.
RESULTS AND DISCUSSION Electrode Potentiometry. The equilibration time needed
to attain a stable electrode potential decreases with increasing fluoride concentration and stirring rate, and increases wilh the increasing concentration change resulting from successive immersions (Figure 1). If the concentration difference is small, the equilibriuim time can be reasonably short even a t low fluoride concentrations. We have restricted, therefore, the exposure of the fluoride ion selective electrode to solutions differing less than 10 or 20 times in fluoride concentration. By limiting the fluoride concentration range and using a programmed immersion sequence, the equilibration time in the analyte has been reduced to 3 to 7 min even at fluoridle concentrations as low as 20 wg of F-/L. This is the lowc?r practical limit for determining fluoride conveniently, becaupe the electrode response is no longer linear below 20 fig of F-/L (lo4 M F-) (Figure 2). If the millivolt reading indicates that the fluoride concentration in the analyte exceeds the concentration range of the fluoride ion selective electrode (20-100 kg of F / L or 100-1000
0003-2700/63/0355-1445$0 1.50/0 0 1983 American Chemical Society
