Table 1. Blend 1
Analysis of 2,6-Di-ferf-butylp-cresol Blends Added Found (p.p.m.) (p.p.m.) 20
current, the diffusion current is taken as the difference between the current of the sample and the blank at 0.60 volt, an approximate voltage value for a normal diffusion current plateau.
19.0
RESULTS
20.7 2
100
3
200
4
300
104 101 191 208 196 214 309 295
*/*inch off the end of the rod with a fine-tooth saw (6). Ten milliliters of pentane are processed as a blank along with the sample. Since 4M26B does not give a normal diffusion plateau but a drawn-out wave with a slowly rising
The analysis of blends of 4M26B in transformer oil is shown in Table I. Table I shows t h a t the relative error of the method is 5%. It is necessary to pass the sample through the 10% water-alumina gel prior to the adsorption of 4M26B on dry alumina gel, since interfering, naturally occurring polar compounds would cause high results. By use of this technique, phenols, aromatic amines, quinones, disulfides, thiols, carbazoles, and pyrroles do not interfere if present in concentrations of less than 0.5%. The analysis time is approximately 2.5 hours for one sample and 3 hours for three samples. The method can be applied to other hydro-
carbon samples, and the lower limit can be extended by using larger sample sizes. The method has not been applied to used transformer oils. Any oxidation product of 4M26B which contains the hydroxyl group would be oxidized and calculated as 4M26B, giving high results. LITERATURE CITED
(1) Braithwaite, B., Penketh, G., ANAL. CHEM.36, 185 (1964). (2) Gaylor, 17. F., Conrad, A. L., Landed, J. H., Zbid., 29, 224 (1957). (3) Gaylor, V. F., Elving, P. J., Zbid., 25, 1078 (1953). (4) Morris, J. B., Schempf, J. M., Zbid., 31. 286 (1959). (5) Phillips, -M.’ A., Hinkel, R. D., J. Ag. Food Chem. 5,379 (1957). (6) Suatoni, J. C., Snyder, R. E., Clark, R. O., ANAL.CHEM.33, 1894 (1961).
JOSEPH C. SUATONI Physical Sciences Division Gulf Research & Development Co. Pittsburgh, Pa.
Kinetics of Polymerization by Infrared Spectrometry SIR: Many methods have been developed to measure rates of polymerization (2). Some of these are capable of determining individual rate constants, while others measure the overall rate of polymerization. Most of these methods require lengthy preparation and sensitive equipment. The use of spectrometry is not new in kinetic studies of chemical reactions. Visible and ultraviolet spectrometry are used frequently since the absorption in one part of the spectrum will often increase or decrease in intensity as the reaction proceeds. Thus, periodic spectral analysis of the reaction mixture may indicate the course of the reaction (6). Most of the previous work involving infrared measurements in polymerization kinetics entailed periodic sampling of the reaction, followed by absorption measurements of one or more reactant(s) (1). I n the present study, a continuous sampling of the reacting solution is accomplished by incorporating a small monitoring pump in a closed cyclic system. Hence, a complete picture of the reaction is obtained while it proceeds.
coupled to a Texas Instruments Servo Riter Recorder Type PWS. The pump was a Beckman Solution Monitoring Pump No. 74601, having Teflon (or Viton) connections and valves. A maximum output of 5 ml./minute was available. Figure 1 represents schematically the general arrangement of
EXPERIMENTAL
Reagents. Toluene, the solvent used in all the experiments, was the Baker Analyzed Reagent. T h e monomers were obtained from Rohm and Haas and kept in a deep freeze until required. An oxygen-free grade of nitrogen was used. The infrared spectrometer was a Perkin-Elmer Model 337, equipped with an expanded scale read out, which waa 1272
ANALYTICAL CHEMISTRY
Figure 1 . apparatus
Schematic diagram of
the apparatus. A is the reaction vessel, B a 0.1-mm. KBr cell, C the pump,
D a constant temperature bath, and E a magnetic stirrer.
The reaction vessel was an ordinary three-necked flask, with provision for a nitrogen inlet. Method of ODeration. All uuantitative spectral heasurements -are dependent on Beer’s Law (7’). This law holds for all wavelengths and, hence, includes radiation in the infrared portion of the spectrum. There are, of course, deviations from the law, the most common of which is caused by solvent-solute interaction. The need, therefore, arises for a check on the linearity of the selected peak in relation to concentration. The criteria for the selection of a peak require that it must be distinguishable from solvent bands, decrease or increase with the speed of the reaction, and obey Beer’s Law. Under these conditions, the sequence of operation is calibration of the spectrometer and polymerization. A suitable frequency is chosen for the monomer, a t which absorption decreases as the polymerization proceeds. The instrument is locked a t this frequency and standard solutions are run in the spectrometer, at set slit openings, cell path lengths (0.1 mm.) and intensity of sample beam. These settings are maintained for the rest of the experiment. Thus, various absorptions are obtained (at the select frequency) which can be reproduced on the strip chart recorder coupled to the spectrometer. This recorder measures time on one axis and the degree of absorption on the other. Calibration graphs can then be drawn relating the amount of absorption to the concentration of monomer. The recorder also serves as an amplifier and, hence, increases the
added and the progress of the polymerization measured. The results are displayed on the recorder. See Figure 2.
1000 p.p.m.
RESULTS
..2 0 0 p.p.m,
Y
3
I
CONCENT R A T I O N
Figure 2. General form of graphs obtained from the recorder The figures refer to the parts per million of the methyl ether of hydroquinone used as inhibitor
sensitivity of the apparatus to changes in concentration. The reaction vessel is charged with the monomer solution, the pump started, and the initial concentration measured at equilibrium temperature; the initiator (azobisisobutyronitrile) is then
We have used this apparatus to study three different types of reaction, vie., addition, decomposition ( 5 ) , and polymerization which is discussed here. The system chosen for study was the polymerization of ethylacrylate in toluene; since the rate of polymerization is of a reasonable order a t 60’ C. (the thermostatic bath temperature), a peak occurs a t 805 cm.-I in the monomer which decreases in intensity, according to Beer’s Law on polymerization (this is an outdeformation which is of-plane C-H eliminated in the polymer), and the polymer, as well as monomer, is soluble in the same solvent, toluene. Order of t h e Reaction. Monom e r Concentration. Keeping the initiator concentration constant (1.5% based on the monomer), solutions of varying monomer concentration were polymerized (20, 12, 10, and 8%). Since,
where .TI is the monomer concentration,
aoo
600
Figure 4. Infrared spectrum showing the frequencies used (marked with X ) in the system ethylacrylate-maleic anhydride
- Maleic Anhydride; ---
2.6
2.1
1 is the initiator concentration, x is the order with respect to the monomer concentration, y is the order with respect to initiator concentration,
a graph of log
-
n
I-
x 2.2 h
4 a m
Y
0
2.0
4
Figure 3. Order of reaction with respect to monomer concentration M is the concentration of ethylacrylate in moles/liter. T is time in minutes The flgures refer t o 1 = 8%; 2 = 10% and 3 = 12% starting concentrations of monomer
Ethylacrylate
;F;
- - us. log [MI
will give a straight line with a slope equal to y. See Figure 3. Experimentally a value for y of 1.6 was found. Initiator Concentration. Similarly, by keeping the monomer concentration constant and varying the initiator concentration, the value of x can be obtained. The rate constant K can be evaluated from the slope of the plot
Induction Period-of Polymerization. The induction period of a polymerization reaction can be easily studied in this apparatus since the onset of the reaction is readily distinguished in the auxiliary recorder (Figure 2). Standard 20% solutions of ethylacrylate were polymerized with 15, 200, and 1000 p.p.m. of the methylether of hydroquinone as inhibitor. No major differences in the rate of VOL. 38, NO. 9, AUGUST 1 9 6 6
1273
20
40 .Time
Figure 5.
60 in
#I
minutes
Graph showing copolymer relationships
2. A mixture of 20% ethylacrylate and 20% maleic anhydride with the ethylacrylate being recorded. 3. Same mixture as 2, but with the maleic anhydride being recorded 1.
20% ethylacrylate.
polymerization were observed once the inhibitor had been destroyed. Copolymerization. The idea of following both monomers simultaneously in a copolymerization is a useful concept, giving a continuous picture of the take-up of the respective monomers into the growing polymer. Our present apparatus allows for consecutive recording only, but simultaneous recording would be possible if the spectrometer were modified to have an automatic switching of wavelengths and a two-pen recorder. Ethylacrylate and Maleic Anhydride. The infrared spectrum allows for the measurement of both monomers (Figure 4). The peaks
selected were 805 cm.-l for ethylacrylate and 555 cm.-l for maleic anhydride. For the copolymerization run, the apparatus was first calibrated for one component, the polymerization completed, and the results were plotted; then a duplicate reaction was performed, but this time the progress of the other monomer was followed. By incorporating both sets of results in one graph, the relationship between the two monomers can be seen. Figure 5 depicts such an experiment. Graph 1 represents the rate of polymerization of a 20% ethylacrylate solution. Graph 2 shows the rate a t which ethylacrylate enters the copolymer formed from a solution containing 20% ethylacrylate and 20%
X
X
J
600
Figure 6. Infrared spectrum showing the frequencies used ( X ) in the system
ethylacrylate-vinylacetate
- Vinyl acetate; --- Ethylocrylate
20
40
60
80
Time i n minuter
Figure 7.
Graph showing copolymer relationships
1. 10% ethylacrylate. 2. A mixture of 10% ethylacrylate and 10% vinylacetate with the ethylacrylate being recorded. 3. Same mixture as 2, but with the vinylacetate being recorded
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ANALYTICAL CHEMISTRY
maleic anhydride. Graph 3 repeats this last experiment observing the rate of maleic anhydride polymerization. Ethylacrylate and Vinylacetate. I n the copolymerization of ethylacrylate-vinylacetate, two separate frequencies can be identified which are capable of yielding quantitative results. According t o Figure 6, the frequencies selected were : ethylacrylate at 805 cm.-' and vinylacetate at 635 cm.-1 Figure 7 depicts the rate of polymerization of (1) a 10% ethylacrylate solution (2) a 10% ethylacrylate plus 10% vinylacetate solution, recording the ethylacrylate, and (3) recording the reaction of vinylacetate in the solution specified under ( 2 ) .
DISCUSSION
Solution polymerization of ethylacrylate was studied. Values for 2 = 1.6, y = 0.5, and k = 1.6 X 10+ mole/liters minute-’ were determined. These compare with values of 5 = 1.5, y = 0.5, and k = 8.9 X mole/liters minute-’ obtained by M. Devalerola, using benzoyl peroxide in benzene a t 60’ C. (S), but disagrees with previous workers at Osaka University who found first-order dependence (4). The above experiments indicate that this method is satisfactory for polymerization studies. In particular it eliminates the need for intensive purification of copolymers necessary in classical chemical analysis. However, it has its limitations: Fast
reactions cannot be handled; at least 30 minutes are needed for completion of 75% of the reaction. There are spectral difficulties-Le. , the need for a unique frequency to be measured. The reactants and products must be soluble although filters could be incorporated in the apparatus. It is a macroscale apparatus-Le., at least 150 ml. of solution is required. Due to the nature of the optics of the spectrometer, only nonaqueous systems can be studied. LITERATURE CITED
( 1 ) Ang, T. L., Harwood, J. H., Polymer Preprints 5 , ( l ) , 306 (1964). (2) Burret, G. M., “Mechanism of Polymer Reactions,” p. 14, Interscience, New York, 1954.
(3) Devalerola, M., Bull. SOC.Roy. Sci. Likge 30, 367 (1961). (4) Hachihama, Y., Sumitomo, H., Technology Rept. of Osaka Univ., 5 , No. 185, 491. (5) Hirsch, A., Bridgland, B. E., A p p l . Spectry. (in press). (6) Ingold, C. K., Nyholm, R. S., Tobe, M. L., J . Chem. SOC.1956, p. 1691. (7) Swinehart, D. F., J . Chem. Educ. 3 9 , 333 (1962).
ARTHURHIRSCH B. E. BRIDGLAND Canadian Technical Tape Ltd. Montreal, Canada
Presented in part a t the 13th Canadian High Polymer Forum, Ottawa, September 1965.
The authors are indebted to the Canadian Defence Research Board for financial support of this study.
Calibration Heater for Thermometric Titrations Marvin J. Stern,’ R. Withnell? and Richard J. Raffa,3 College of Pharmacy, Columbia University, New York, N.Y. 10023 and Chemistry Department, Brookhaven National Laboratory, Upton, L. I., N. Y. 1 1973
for thermotitrations (3, 6, 7 ) should possess the properties of small size, low inherent heat capacity, short lag time, chemical inertness, and geometry conducive to facile cleaning between titrations. This report describes the construction and evaluation of such a calibration heater. Figure 1 shows a cross-sectional diagram of a heater tip. The heater was constructed as follows: The insulation from a 15-ohmJ 1/4-watt, carbon-element resistor was removed by careful grinding. After grinding, the resistor element had a resistance of Bpproximately 20 ohms and measured approximately 1.8 mm. in diameter and 6.4 mm. in length. The resistor element was then coated with epoxy paint (equal parts of Nupon Converter RL12928 and Nupon Clear RL12272, Glidden Company, Reading, Pa.). One of the wire leads of the resistor was then snipped off t o a stub and an insulating sleeve about 6 mm. long and 2 mm. 0.d. was slipped CALIBRATION HEATER
A metric
Present address, Belfer Graduate School of Science, Yeshiva University, New York, N. Y. 10033. Address, Brookhaven National Laboratory, Upton, L. I., N. Y. 11973. Present address, Analytical Research Section, Quality Control Department, Chas. Pfizer and Co., Inc., Brooklyn, N. Y. 11206.
over the second lead. The resistor element and sleeve were wrapped with a layer of silver foil which was then soldered to the stub end of the resistor. The remaining end of the silver wrapping and the long (insulated) resistor lead
ii
-7
iNSULATED WIRE LEADS
EPOXY COATING 2 0 - O H M RESISTOR
EPOXY PAINT
SOLDER \RESISTOR
LEAD
H -Imm.
Figure 1. Cross-sectional diagram of heater tip
were soldered to ’. d a t e d wire leads. The heating element was inserted into a 22-cm. length of 4-mm. 0.d. glass tubing so that only the silver-foil-wrapped resistor element was exposed. This exposed tip was then coated and sealed into the glass tube with epoxy paint. The heater was powered with the simple Zener diode circuit shown in Figure 2. The voltage supplied to the heating element was adjusted with the coarse and fine settings. Each successive coarse setting (1 to 6) decreases the resistance in series with the heater by 25 ohms. The fine setting (0.000 to 1.000) controls an additional variable %ohm series resistor. A heater setting of 4.400, which corresponds t o a total series resistance of 65 ohms, implies a coarse setting of 4 and a fine setting of 0.400. A double-pole single-throw toggle switch served to activate the heater (via external control) and a precision stop clock simultaneously. For rough heating, the heater was activated with switch S2. Provision was made for measuring the current through the heater (indirectly by measuring the voltage at 51) and the d.c. voltage across the heater (at 52). The voltage stability of the power supply was evaluated by measuring the d.c. voltage across a heater while varying the a.c. input voltage. For input voltages from 100 to 135 v.a.c., the change in the VOL 36, NO. 9, AUGUST 1966
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