1435
V O L U M E 22, NO. 11, N O V E M B E R 1 9 5 0 9 microgram-atoms per liter. A single series of data is given for the 1.5-cm. cell. Its curve is linear to 30 micro*-atoms per liter, but has a usable range to at least 60 microgram-atoms per liter. These figures indicate the wide range of concentration that may be mearmred by the instrument. The absolute accuracy decreases with decreasing length of cell, but the percentage error for y y given concentration is about the same for all three cases-for e?uunp!e, a t a scale reading of about 300 the percentage error is approximately *3%. The phosphates were run by the ceruleomolybdate method of Denigb as applied to sea water by Atkins (I), with the modifice tion that samples w e d analyzed in the colorimeter within 5 t o 10 minutes after the stannous chloride had been added. It has been found that the maximum color is developed in that time. The results of a typical calibration are presented in.Table I. The corresponding calibration curve is given in Figure 7. The curve is linear to 2.5 microgram-atpms per liter. The points are distributed within t0.05 microgram-atoms per liter of the curve with the exception of one a t concentration 1.5 microgram-atoms per liter. This figure for the margin of error is substantiated by numerous other calibration runs. The electric eye photometer, in common with other photoelectric colorimeters, has certain advantages over visual comparators. Errors due to eye fatigue and color blindness are elimi-
d.Eye fatigue becotnes especially important a3 a wurce of error when visual colorimeters, which employ an eyepiece, are used at sea. In such analyses as that for phasphate in sea water where the color is t d t o r y , it is important to determjne the optimum time after the addition of reagents to take the reading. Thie m a y be done with the present instrument, as the rate of fsding of the color may be measured. ACKNOWLEDGMENT
The author wishes to express his appreciation for the many helpful suggestions from members of the staff of the Woods Hole Oceanographic Institution and in particular for the contributions of Robert Walden, who designed and built the electronic assembly. LITERATURE U T D
(1) Atkins, W. R. G., J. Marine Eiol. Assoc. United Kingdon, 13, 119; 14,447; 15,191; 16,821 (1923-30). (2) Cooper, k,. H. N., PTOC. Rou. SOC.London, 118B,419 (1935). (3) Harvey, H. W., “Recent Advances in the Chemistry and Biology of Sea Water,” London, Cambridge University Press, 1945.
RECEIVED November
14, 1949.
Contribution 492 from the Wooda Hole
Oceanographic Institution.
Apparatus for Turbidimetric Study of Polymerization Activators T. W. SARGE, Suran Development Laboratory, The Dow Chemical Company, Midland, Mich.
T
H E principal object of the present esposition is to describe a simplified turbidimeter and to present experimental dits relating particularly to the polyinerization of monomer-insoluble polymers, as those of vinylidene chloride. Obviously, the prinviple upon which the study is founded is not new: the developnierit of haze, and eventually of opacity, produced by the formation of colloidal particles which first scatter and then eventually, :tlmost completely, obstruct the path of transmitted light The instrument first devised by Jackson for measurement of water turbidity was later converted to a turbidimeter for sulfur analysis ( 3 ) and more recently modifications of technique and apparatus permit the study of solids showing haze, such as plastic films (1, 2). Polymer chemistry presents an intermediate field for the application of turbidimetry, or viewed somewhat differently,
A simple turbidimeter for the measurement of dynamic polymerization phenomena is described. By graphical analysis of the direct data, i t is possible to obtain Pi, the induction time of polymerization, as well as dZ/dt, the slope or change of intensity which is proportional to the rate of polymerization a t the interval examined. By an extension of the data, a simple but workable equation relates the over-all rate of polymerization as determined by actual bottle or semiplant polymerizations to the turbidimetric data as follows: Rate of polymerization (observed) = k X 1/P1 X dZ/dt (T,catalyst)
polymerization processes may be studied by dynamic turbidimetry, whereas the applications previously mentioned involve static concentration (in liquid) or static form (in solid). Expressed more specifically, it appears possible to obtain in situ relative quantitative data on polymerization phenomena, such as polymerization induction time, polymerization rates, influence of inhibitors and catalysts (by effect on induction time and rate polymerization), and the effect of concentration of reagents, inhibitors, catalysts, and other additaments. DESCRIPTION OF APPARATUS
An extremely simple apparatus was designed to enable assembly from readily available parts. Figure 1 shows all the essential cooperative parts, while Figure 2’indicates the over-all size.
Data are presented for the vinylidene and vinyl-type monomer which form monomer insoluble polymers, but i t is also shown that if a precipitant is added to the original monomer, polymers that are normally soluble in monomer may likewise be examined. Direct application to problems of monomer purity, catalyst concentration, effect of inhibitors, influence of comonomers on polymerization rate, etc., are discussed, and i t is suggested that the apparatus may generally be used to study emulsion stability, and reactions where concentration, time, temperature, and cloudiness are factors.
ANALYTICAL CHEMISTRY
1436
Not ohvious from the sketch or photograph me the following facts: The 1-ounce (3@ml.) square specimen bottles receive heat by radiation from two sides and the bottom only of the eirculeting liquid bath, the two sides in the light p&h being open. Regulation of the voltsge is a necessity, because of constant fluctuat,ions during increased and decreased loads; however, the light intensity itself may have an arbitrary value, provided i t remains const,mt. The total l i h t path is 12 inches (30 cm.), with the specimen located a t the.center. The Worner light source is also provided with a slot for receiving filters, as is the cross-shaped attachment. Water with corrosion inhibitor, such &s radiator rust inhibitor, glycol, or glycerol, provides suitable
Table I.
Polymerization of Inhibited Vinylidene Chloride (25 MI.) at 50' C. Turbidity Rate volume,
Reagent
MI.
(-dI/dC
Foot-Candlks/ Mill.
Induotion Tillle, Min.
contcnusl c i r c u l a t b , due to convection curreits arising kern the hot and cold wslls of the square bottle. TEST PROCEDURE
The composition of the test sample is the only determining fac-
25 to 28 grams) should be used, &d the volume or wvei ht should thereafter be maintained constant. Bakelite caps, with
tried
,IS".
12011119
l l O Y , SOCYCLE
Figure 3.
Turhklity Effect d u r i n g Mass Quies-
cent Polymerization of Vinylidene Chloride at
46" C.
plastic film or aluminum-faced paper or cork, form satisfactory seals, even for highly volatile monomeric compositions. In the present work, 1-mil (0.001-inch) saran film was also found satisfactory as a s e d on glass threads. It is advisable to rub off fingerprints and dust particles with lens paper from the faces of the square bottle which are to he exposed to t,he light path. The cleaned, sealed, and st,oppered bottle is now ready for insertion into the specimen slat. DATA ANDDISCUSSION
The only dstn which need be taken are time, in minutes or seconds, and fooecandle readings under constant tempersture conditions. G r a p h i c a l zridysis of the data permits one to arrive a t quantitative or semiquantitative results regarding the,progresr of polymerization. In 8. typical application, it was desired to compare the p o l y m e r i a a t ion behavior of vinylidene chloride monomer uninhibited uncatalyzed, uninhibited catalyzed with benaoyl peroxide, inhibited uncatalyzed, and inhibited catalyzed with benzoyl peroxide. The comparisons are shown in Figure 3. Disregarding the initial light intensity value (as representing only the initial clarity), it can be seen from the curves that the induction of polymerization, Pi, m d the slope, dZ/dt, which is Photograph of Turbidimeter
Figure 1. Turbidimeter
Figure 2.
V O L U M E 22, N O . 11, N O V E M B E R 1 9 5 0
2
1437 agents for initiating polymerization of inhibited vinylidene chloride monomer, the data represented in Figures 6 and 7 were obtained. The effect of increased concentration of acetyl chloride on the induction time and rate of turbidity development is easily seen in Figure 6, while Figure 7 shows the limiting effect of increased acetyl chloride concentration per se. Similarly, Figures 8 and 9 show these relationships for acetic anhydride. A summary of the.observed data is given in Table I. It is clear from the table that the turbidity rates (which should be proportional to the rate of polymerization in the early stages) are substantially equal to 1.0, and that the increase in concentration of the reagents affects, measurably, only the induction time of polymerization. This is, of course, obvious also on inspection of the curves of Figures 6 and 8. Data for adipyl chloride, not shown in the figures, give essentially the same results, with the exception of induction time which is even longer
1
n
60
I20
TIME IN MINUTES
Figure 4.
0
c
::
Figure 3 Idealized
UNINHIBITED, UNCATALYZEO. lNHl8lTOR REMOVED 8 1 N i O H
\
"
.A
I
-+ 2
-1-
I
I
0
2
0
cc
cn3coci
4
PER
ZICC
6
V I N Y L I D E N E CHLORIDE
0 0
Figure 5 .
60 I20 INDUCTION TIME, MINUTES,
Figure 7 .
P,
Effect of Increased Acetyl Chloride Concentration
Intensity Change us. Induction Time of Vinylidene Chloride at 46" C.
proportional to the rate of polymerization, are easily ol)tainetl--i.e., for curves A and R of Figure 3, Pi values are 38 and ti.5 minutes, respectively, and dZ/dt are -2 and -10, respectively. The negative values for the slope of I us. t merely indicate the decrease in transmitted light intensity as polymerization progresses. An idealized or corlbl 5 c c CH3COCI rected graph of the (s) 3 c c CHjCOCl I C 1 I C C CH3COCI curves in Figure 3 would perhaps be more suitable and. is easily drawn by starting from a common value of Z (initial) as in Figure 3 . A series of Pi and d Z / d f values, plotted in Figure 5 , shorn for different methods of activation the inverse \ 4 relationship dZ/dt a 1/P, or d I / d t = 2 k,'P,. A l s o e v i d e n t from this graph is the effect of various wash0 0 IO '20 33 40 50 ing or p u r i f i c a t i o n TIME IN MINUTES treatments on monoFigure 6. Turbidity Effect durmer reactivity. ing Mass Quiescent PolymerizaI n an effort to detion of Vinylidene Chloride at t e r n) in e satisfactory 46" C.
-:
t
-i.e., 80 minutes for 5 ml. I t would seem, therefore, 12 that short-chain reagents are more e f f e c t i v e t h a n long-chain o r a r o m a t i c IO GI c o m p o u n d s of the same 0 class. This is further substantiated by the' fact that $ 8 c 5 ml. of benzoyl chloride e show no reactivity a t 168 C 5 i hours under the same polyY 4 merization conditions. b I A Because it appears that f u r t h e r additions (or an increase in concentration) of t h e r e a g e n t s merely m o d i f y induction time, TIME IN M I N U T E S it is interesting to examine Figure 8. Turbidity Effect the question as to whether during RIass Quiescent Polymere thermal polymerizamerization of Vinylidene tion follows the induction Chloride at SO" C. period or whether the rate of polymerization is also altwed. Table I1 shows the values as compared with Table I The trend of the data in Tables I and I1 was confirmed by actual bottle polymerizations, which gave the results shown in Table 111. It can therefore be concluded that the polymerization which takes place in the presence of acetic anhydride is not merely thermally catalyzed, but appears also to be slightly activated. One manner of utilizing the turbidimetric data, P, and d l l d l ,
\\ \\ \,
ANALYTICAL CHEMISTRY
1438 Table 11. Polymerization of Uninhibited Vinylidene Chloride at 50" C. Reagent None
Volume None
Turbidity Rate ( -d l / d t ) , Foot-Candles/ Min. 2.00
Induction Time, Min. 38
~~
Table 111. Polymerization % Monomer Vinylidenr chloride, uninhibited Vinylidene chloride, inhibited
(CHaC0)zO None 1
*50° C. Av. Pol merization Rate, per Hour 0.28 0.53
d
I
3 2
I
I
is to attempt a correlation with observed rates of polymerization, as those given in Table 111. For example, Rate of polymerization (observed) = k X
1 X Pi
dI -
I
I
I
I l l
I
I
I
A
(1)
dt
0.53 = k X 1/10.5 X 0.94 k = 5.23
d
(2)
If now we wish t o estimate the probable polymerization rate of uninhibited vinylidene chloride monomer at the same temperature, we substitute in Equation 1 the values from Table I1 and Equation 2, giving Rate, = (5.23) (1/38) (2) = 0.275
(:3)
which approximates the observed 0.28. In another example, it was desirrd to examine the "dampening" effect of vinyl chloride monomer on the polymerization rate 0 1 vinylidene chloride monomer. Figure 10 shows the data graphically. Although there is little difference in the induction time of polymerization, there is a large difference in apparent rate of polymerization. The graphical data show, therefore, that such a turbidity test could be used advantageously to detect monomer ratios after calibration against known mixtures. The previous examples relate to systems wherein the polymer formed is insoluble in its own monomer. I n order to examine the possible utility of this turbidimetric method in monomrrsoluble systems, the polymerization of inhibited styrene was e+ amined after choosing a diluent in which polystyrene is insolul)l(~.
2E.
I
0
In order t o evaluate k , the data from Tables I and I11 for inhibited vinylidene chloride monomer are employed, giving or
I
IC
0
B
I !
< 60
120
,110
210
JSO
T i Y L IN MINUTES
Figure 11.
Turbidimetric Analysis of Styrene Polymerization at 50' C.
using parallel and crossed polaroids, in the presence of acetyl chloride but no peroxide catalyst showed no results. It is likely that higher temperatures would be more satisfactory for this study. OTHER APPLICATIONS
although no significant results have as yet been obtained, the apparatus and technique described appear to suggest possible utility in studying the following phenomena: Rapid control test for monomer purity (or monomeric compositions after calibration against knowns). Evaluation of polymerization catalyst efficiency. Evaluation of polymerization inhibitor efficiency. Evaluation of various pre- or posttreatments to monomer, catalysts, etc. Emulsion stability in the presence of possible precipitants. General precipitation or cloud occurrence or disappearance where concentration, time, temperature, and light intensity are variables.
0
0 0 C C I C H $ O l ~ 0 PER 2 5 c c
VINYLIDENE
CHLORIDE
Figure 9. Effect of Increased Acetic Anhydride Concentration
Obviously, the apparatus described would be even more usefu when rendered automatic so as to record light intensities photomc$rically and t o record the data graphically against time. LITERATURE ClTED
The turbidimetric data ale given in Figure 11. I t can be seen in general that styrene polymerizes much more sluggishly than vinylidene chloride a t 50" C. On the other hand, the activity of benzoyl chloride is now noticeable and is perhaps due to the compatibility of styrene and benzoyl chloride. An attempt to study the mass polymerization of styrene,
( 1 ) Am. SOC. Testing Materials, "A.S.T.M. Standards on Plastics," Committee D-20, p. 307 (1948). (2) Barnes, R. B., a n d Stock, C. P., ANAL.CAEM.,21, 181 (1949). (3) Muer, H. F., J.Ind.Eng. Chen., 3,553 (1911). RECEIVED September 15, 1949. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 116th Meeting of the AMERICAN CHEXICAL SOCIETY, Atlantic City, N.J.
