Chemicals Used in Red-Lime Muds 0. W. VAN DYKE AND L. M. HERMES, JR. Magnet Cove Barium Corporation, Houston, Tex. Ih order to study the effect of quebracho, sodium hydroxide, and lime, which are the chemicals used in red-lime mud, dry clay was dispersed in solutionscontainingvarious amounts of these chemicals alone and in combination. On adding the dry clay to the prepared chemical media, the results should approximateconditions similar to those encountered by solids from the formation which enter a mud during drilling. The viscosity of the muds prepared in this manner was used as an index of the behavior of a clay entering the chemical environment created. The results show that no one of these chemicals is responsible for the observed behavior of clay solids entering a red-lime mud. There are strong indications that a very powerful dispersingeffect results from the combinationof the proper amounts of quebracho, sodium hydroxide, and lime, and this is thought to explain the resistance to viscosity buildup of red-lime muds during drilling.
T
chemicals in the range of concentrations used in red-lime mud. The test muds made in this manner were stirred for 10 minutes on a high s ed mixer, a d 2 hours, and stirred 5 minutes o? a Qh speed)emiuer, and t , viscosity was measured on a Garnson Mscometer a t rotor speeds of 100 and 600 r. .m. I n order to determine the effect of aging, the above procegure was repeated after 72 hours of agin . Measurements of pH, filtration properties, and filtrate anef sis were made after the muds were aged 72 hours. Because ofthe thixotropic character of mud sus nsions, the measured values of viscosity are greatly the rate of shear. A shear rate of 600 r.p.m. has influenced been adopted as a standard for mud viscosity measurements. Viscosity measurements a t low rates of shear are indicative of gel strength.
g”y
To simplify the recording of the data in the tables, the word “viscosity” has been used to indicate the viscosity of the suspension in centipoises, measured a t a rotor speed of 600 r.p.m. The word “gel” has been used to indicate the viscosity a t a rotor speed of 100 r.p.m. Table I gives the data recorded when various amounts of clay were dispersed in water. Figure 1 shows a plot of the viscosity data of this system. The viscosity increased with aging. Table I1 gives the data recorded when various amounts of clay were dispersed in water solutions containing 0.5, 1.0, 2.0, and 3.0 pounds per barrel of quebracho. (One pound per 42gallon barrel is equivalent to 1 gram in 350 mi.) These data show that quebracho acts as a mild dispersing agent. The viscosities of specific concentrations of clay are slightly lower in quebracho solutions than in distilled water. The filtration properties are also lower. Figure 2 is a plot of the viscosity of an 8% clay made up in water containing various amounts of quebracho. This shows that little reduction in viscosity is
HE rotary drilling fluids used in the drilling of oil wells must possess specific physical and chemical properties to accomplish their purpose. Several of the common treating chemicals used in drilling mud have recently been used in combination, resulting in a type of drilling fluid called “red-lime mud.” Red-lime muds are muds which have been treated with relatively large amounts of sodium hydroxide (caustic soda), quebracho, and lime. For many years caustic soda and queIwacho have been used to treat muds when drilling cement; although not always recognized as such, this oftentimes resulted in red-lime mud. We do not know who first deliberately added lime or cement to a caustic-quebracho mud, but Cannon reported using cement in an alkaline tannate mud in April 1938, in a well in southern Louisiana ( 1 ) . Red-lime muds are being used extensively in a number of areas TABLE I. CLAYIN DISTILLEDWATER with very good results, and present practical knowledge is sufWabr ficient for satisfactory control in the field. Many theories in LOSS. ”#? 2 Houm’ Aging 72 Hours’ Asins ~1.~30 regard to the behavior of red-lime muds have been advanced, % Vis.’ Gelb Vis. Gel Min. pH but a completely satisfactory explanation has yet to be given. 1 .o 1.5 1.0 ... LI.0 1.2 1.7 1.8 1 .o This appears to be another case where field practice is ahead of 1 .o ... 8.2 2.5 1 .o 3.0 2.8 8.7 17.4 theory. This paper by no means purports to give a complete 3.7 3.8 8.7 14.2 3.0 1 .o 5.7 6.4 4.9 8.8 12.4 6.8 explanation of red-lime mud behavior, but it is hoped the data 10.6 18.2 12.0 10.8 22.0 8.8 28.3 24.6 70.4 presented will contribute to a better understanding of this sub86.0 9.2 8.8 57.5 69.9 235.0 196.0 8.1 8.8 ject. Visoosity of suspension in aentipoises, measured at rotor speed of 600 Experience in the field has shown that red-lime muds are very ram. b Viecoeity a t rotor npeed of 100 ?.p.m. resistant to viscositv and gel strength buildup during drilling i f e v e n t h e most colloidal shales. I n order to study the effect of the TABLE 11. CLAYIN WATERCONTAININQ VARIOUSAMOUNTS OF QUEBRACHO chemical environment created by the chemiuebraoho. Clay, Hooq’ Adng 72 Hours’ Aging Water L ~ ~ ~ , cals used in red-lime mud upon clay solids, %WBM. Wt. % vis. Gel Vis. Gel M1./30 Min. pH suspensions were prepared by adding dry clug 0.5 5 5.4 6.8 5.7 8.7 11.0 7.3 to solutions of the chemicals used in red-lime 7 18.8 52.8 20.0 52.8 8.5 7.1 8 52.0 178.0 56.9 180.0 7.3 7.2 mud. .The reason for adding the dry clay to 9 113.0 426.0 120.0 448.0 6.2 the chemical solutions was to observe its be1.0 7 19.8 56.7 20.8 56.7 8.5 7.0 8 44.5 146.0 46.2 143.0 7.6 7.0 havior in a chemical environment similar to 9 90.1 345.0 95.1 335.0 6.2 7.1 that encountered by formation solids entering 2.0 6 9.5 22.0 9.7 22.0 10.0 6.3 a red-lime mud during drilling. Commercial 7 18.5 60.6 19.5 56.7 8.8 6.4 8 40.6 145.0 45.1 145.0 7.6 6.5 Wyoming bentonite was used as the clay in all 9 78.3 298.0 83.6 293.0 6.9 6.7 the test muds prepared. 3.0 6 8.4 22.0 9.1 22.0 8.7 6.5 7 18.0 60.6 18.3 52.8 8.3 6.2 The procedure followed was to add the d r r 8 40.1 135.0 40.1 125.0 7.1 6.5 9 79.9 307.0 82.2 290.0 6.5 6.4 cla to water solutions of uebracho, caustic so&, lime, and various com%inations of these 1901
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1902
barrel of lime, the viscosities of all suepensions i n c r e a s e d with aninn. -.., Fighe 4 is a plot of the 2-hour and pH i2-hour viscosities of muds made by sus12.3 12.2 pending 6% clay in water containing 12.1 various amounts of lime. This plot re12.1 12 .o veals two interesting effects of lime upon 12.0 12.6 clay solids. First, it shows an abrupt 12.6 rise and fall in vimosity with the maxi12.5 12.8 mum in the range of 1 pound per barrel, 12.4 and a leveling off of the viscosity with 12.4 12.4 concentrations greater than 2 pounds 12.9 per barrel of lime. Secondly, it illus12.9 12.9 trates graphically the increase in viscos12.9 ity due to aging of all muds except the 12.8 12.8 ones made in water containing 0.5 pound 12.8 13.1 per barrel of lime. 13.1 The series of muds made up in water IS.1 13.0 containing 0.5 pound per barrel of lime 13.0 had a very high initial viscosity which 13.0 13.0 dropped decidedly upon aging. The data in Table IV show that no calcium is present in the filtrates of the muds in this series. This is evidence that the clay adsorbed the calcium during the aging period, thereby removing any excess calcium that would be present to flocculate the mud at the time of the 72-hour viscosity measurement. The solubility of lime (calcium hydroxide) in distilled water at room temperature (25" C.) given in the literature is 806 p.p.m. of calcium (2). In order to obtain a better understanding of the solubility of lime under the conditions of its use in mud, various amounts of commercial hydrated lime were added to distilled water, and the soluble calcium was determined. The effect of various amounts of caustic soda on the soluble calcium content of lime suspensions was also determined. The data in Table V, which are plotted in Figure 5, indicated that slightly more than 1 pound per barrel of lime is required for a saturated solution. I t also shows t h t caustic soda depresses the solubility of lime. Figure 6 reveals interesting information about the solubility of calcium in the muds made with lime water. The filtrate calcium content becomes constant at different values, depending on the clay concentration. None of the values approaches the solubility of lime given in the literature or indicated by the data in Table V. The filtrate calcium decreases with increasine amounts of clay in water containing a fixed amount of lime. From these data it seems that clay depresses the solubility of lime
ThBLBI 111, CLAY IN WATEB CONTAINING V.iWOUS . ~ ~ O I J N T COF $ CAUSTIC Caustic, Clay. 2 Hours' .4ging 72 Houra' Aping waqerL , , ~ ~ , Lb./Bbl. Wt. % Via. Gel Via. Gel M1./30 iMin. 0.5 1 2.4 14.4 1.8 3.0 50.0 16.3 2 14.4 117.0 36.0 3 38.9 286.0 3'7 31.5 6.6 27.0 4 78.9 542.0 14.0 68.4 18.5 5 158.0 High 26.8 135.0 14.2 6 High High 52.3 235.0 12.2 1 2.1 8.4 1.7 4.9 55.0 1.0 2 10.4 72.4 3.7 25.8 39.0 3 31.7 225.0 9.2 76.3 26.5 4 71.8 502.0 18.5 147.0 19.5 5 140.0 Hjgh 28.6 220.0 15.0 43.9 345.0 11.2 7 8 High 68.5 510.0 11.6 1 1.5 3.0 1.5 2.0 2.0 41.0 2 3.9 22.0 2.5 14.4 60.0 3 12.4 74.8 8.8 29.6 27.0 200.0 8,4 72.4 20.6 4 32.7 5 56.5 371.0 16.8 141.0 15.5 6 90.6 614.0 29.1 239.0 14.8 7 162.0 High 50.4 4434.0 11.8 1 .o 60.0 1 1.2 1.0 1.5 3.0 2 2.5 10.6 2.0 8.8 35.0 3 5.2 31.5 2.7 18.2 26.0 4 15.5 96.0 5.8 46.9 27.0 5 25.2 168.0 11.4 96.0 17.2 6 48.2 341.0 20.5 166.0 15.0 7 83.9 566.0 36.2 200.0 12.0
:$
f
I
WEIGHT X CLPY
Figure 1. Viscosity of Various Concentrations of Clay i n Distilled Water
Vol. 42, No. 9
8ODh
I
acwmplished by the u8e of concentrations of quebracho greater than 1.0 pound per barrel. Table I11 gives the data recorded on muds made by dispersing various amounts of clay in water solutions containing 0.5, 1.0, 2.0, and 3.0 pounds per barrel of caustic soda. Within the range of concentrations investigated, caustic soda had a flocculating effect upon the clay. The flocculating effect of the caustic soda environment was more pronounced a t 2 hours than after aging 72 hours. This point is illustrated by Figure 3, which is a plot of the 2-hour and 72-hour viscosity of a 4% clay mud made up in water containing various amounts of caustic soda. This plot also shows that the viscosity rises to a maximum at approximately 1 pound per barrel, after which there is a sharp drop and leveling off of the viscosity in the range of 2 pounds per barrel. Muds were also made by suspending various amounts of clay in water containing 0.5, 1.0, 2.0, 4.0, and 6.0 pounds per barrel of lime. The lime used in these teets was an ordinary commercial hydrated lime, such as is commonly used in oil well drilling muds. Table IV shows the data recorded on these muds. The water containing lime produced an environment that flocculated the oUEnR*CHo'8BL w A ~ R Figure 3. Viscosity of 4% clay. The viscosity of these suspensions was higher per given Figure 2. Viscosity of 8% Clay Clay i n Water Containing concentration of clay than those muds made in distilled water. i n Water Containing Various Various Amounts of Sodium Except for the muds made in water containing 0.5 pound per Amounts of Quebracho Hydroxide
5
September 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
1803
chemicals must produce an effect that is entirely different from either of them Calcium, alone. Lime 72 Hours' Aging wakr Lb./' clay, 2 Hours' .4rring G ~ I ~ 1 . 1 3 0Min. p~ P &it. m. The combination of quebracho and Bbl. Wt. % Vis. Gel Vis. caustic soda has long been known to be 4.0 31.5 3.0 16.3 68.0 11.5 0 0.5 3 4 11.6 84.0 3.1 20.1 31 .O 11.5 0 an effcctive diepersing agent for clay b 61.2 411.0 9.5 70.4 20.8 11.4 0 solids. Table VI is a record of the data 6 143.0 High 26.6 227.0 15.4 11.4 0 1.0 3 8.1 70.4 11.6 102.0 Over 100 12.2' 104 obtained when various amounte of clay Over 100 112.0 18.5 161.0 4 13.2 12.1 3s were dispersed in water containing 1 Over 100 12.1 18 34.5 250.0 5 22.8 176.0 Over 100 319.0 74.1 502.0 12.0 15 pound per barrel of quebracho and cauetio 6 45.7 2.0 3 7.6 64.5 11.6 110.0 Over 100 12.3 3SO soda in amounts of 0.5, 1.0, and 2.0 4 14.4 123.0 19.3 168.0 Over 100 12.3 230 pounds per barrel. Inspection of the Over 100 12.2 191 5 20.8 188.0 26.8 226.0 6 29.4 250.0 36.4 208.0 Over 100 12.2 145 data in Table VI shows that the vis4.0 34 6.3 50.8 8.9 82.0 Over 12.6 517 cosities of muds made in water contain11.2 108.0 16.3 149.0 Over 100 100 12.5 433 5 19.0 161.0 24.9 223.0 Over 100 12.5 330 ing both caustic soda and quebracho 6 28.6 239.0 35.0 208.0 Over 100 12.3 224 were decidedly lower for a given per 0.0 4 10.8 94.0 15.9 147.0 Over 100 12.6 475 cent of clay than the viscoeity of muds 5 17.3 155.0 24.1 217.0 Over 100 12.6 402 6 26.3 226.0 33.0 292.0 Over 100 12.5 330 made in distilled water. It is evident 7 37.3 311.0 44.8 376.0 Over 100 12.5 263 that a combination of causti&soda and auebracho is a more Dowerful disDersing TABLE V. SOLUBILITY OF LIME agent than either of them indivi&alli 4 Lh./Bbl. of Lime in Figure 7 graphically illustrates the dispersing effect of a comCaustic Soda Solution In Distilled Water bination of a fixed amount of quebracho and varying amounts Cauetic Calcium, Calcium, Calcium. soda Lime, p. .m. tbeor. of caustic soda. The sharp drop in viscosity brought about by IhJbhl. "&t? lb./bbl, %lt. p.p.m." pH increasing amounts of caustic soda up to 1 pound per barrel 0.5 450 0.5 530 772 12.9 1.0 260 1,544 13.2 1.0 792 further emphasizes the part that caustic soda plays in intensifying 2.0 112 3,088 13.2 2.0 880 the dispersing action of quebracho. 3.0 82 888 6 176 13.2 4.0 13.2 880 9:264 6.0 A aeries of muds was prepared by adding various amounte of Assuming 100% Ca(OH)z and infinite aolubility. clay to water containing 1 pound per barrel of quebracho and lime in amounts of 0.5, 1.0, 2.0, 4.0, m d 6.0 pounds per barrel. The data obtained from this work are recorded in Table VII. In order to obtain viscosities in the desired range, much larger in water. It has bren shown that the presence of sodium hyamounts of clay had to be used in the muds of this series than in droxide in water suppreacles the solubility of lime. It is reaaonany of the others prepared. This was the first indication of the able to assume that calcium has replaced sodium in the clay in powerful dispersing effect of combinations of lime and quebracho. these mude, which has resulted in the formation of eodium Figure 8 illustrates this point clearly. A mud containing 9% hydroxide, and explains the decrease in soluble calcium with clay made in water cohtaining 1 pound per barrel of quebracho increasing amounts of clay. Unfortunately, none of the chemicals used in red-lime mud had a viscosity of 95.1 ~ p .A mud prepared in the same way and alone seems to create an environment in which clay solids behave containing the same amounts of materials except for the addias in red-lime muds. It is evident that combinations of thesc tion of 2 pounds per barrel of lime had a viscosity of only 3.9 cp. The dispersing action of the quebracho-lime combinations observed in this test cannot be explained by the behavior observed in the tests with quebracho and lime individually. The data in Table VI show that caustic soda increased the dispersing
TABLE IV.
CLAYIN WATERCONTNNING VARIOUS AMOUNTS OF
LIME
c
Figure 5. Solubility of Lime Figure 4. Viscosity of 6% Clay in Water Containing Various Amounts of Lime
A.
Soluble calcium us. l i m e concentration
8. Soluble calcium of solution oontaining 4 lb. per bbl. of l i m e u.. s o d i u m hydroxide
concentration
M M D S LIME I BBL WATER
Figure 6 . Soluble Calcium in Clay Suspensions In water containing various a m o u n t s of l i m e
INDUSTRIAL AND ENGINEERING CHEMISTRY
1904
Vol. 42, No. 9
1 POUND PER BARREL OF QUEBRACHO AND TABLE VI. CLAYIN WATERCONTAINXNG VARIOUSAMOUNTSOF CAUSTIC Caustic
Lb./Bbl: 0.5
Clay, Wt. % 7 8 9 10
1 .o
6 7 8 9
2.0
2 Hours' Aging Vis. Gel 13.2 20.1 29.1 45.0 71.0 125.0 167.0 376.0 3 .O 6.8 18.2 41.1 123.0 288.0 5.4 6.8 9.5 16.3 20.3 46.9 46.7 117.0
72 Hours' Aging Vio. Gel 15.2 25.8 36.1 64.5 83.0 178.0 188.0 503.0 4.9
water L ~ M1./30 Min. 9.5 8.3 7.0 6.1
~
~ pH 10.2 10.2 10.1 10.1
,
6.8
. ? .I2 8.7 15.9 37.3
6.8 14.4 27.7 64.5
10.9 9.5 8.5 7.2
12.0 12.0 12.0 11.7
1 POUND PER BARREL OF QUEBRACHO AND TABLE VIJ. CLAYIN WATERCONTAINING VARIOUS AMOUNTS O F LIME Lime,
Lb./Bhl. 0.5
Clay, Wt. % 7 8 9 10
1 .o
0
4.0
7
8
9 10 11 9 10 11 12 13 14 9 10 11 12
6.0
13 14 15 9 10 11 12 13 14 15
2 Hourr' Aging Gel 6.9 10.0 14.0 23.9 34.7 62.5 83.0 208.0 1 .o 3.0 4.9 4.4 7.3 12.5 24.9 66.4 80.8 270.0 4.1 10.0 5.4 14.4 7.5 23.9 13.8 52.8 33.0 127.0 61.2 226.0 3.6 12.5 4.9 22.0 6.6 25.8 9.1 52.8 18.0 92.0 27.4 194.0 33.3 198.0 3.6 16.3
Vis.
... 7.3
9.1 13.0 23.1 37.7
,..
43.0 54.7 78.2 147.0 255.0
72 H o l d Aging Vis. 21.3 43.9 06.7 3.4 5.7 8.4 16.3 42.9 3.9 4.9 6.0 10.6 20.8 42.0 4.7 5,7 7.6 11.8 21.3 31.4 40.1 5.1
Gel 16.3 50.8 114.0 290.0 1.0 9.0 14.4 37.7 68.4 6.8 6.8 14.4 24.0 37.0 102.0 14.4 22.0 31.5 50.8 84.0 121.0 170.0 22.0
8.2 10.8 15.9 29.4 48.7
41.1 50.8 80.2 137.0 268.0
8.5
...
...
Water L ~ M1./30iMin. 9.4 7.8 6.8 5.6 19.0 13.0 11.0 8.5 8.0 24.0 18.0 16.5 12.6 9.9
~
~
pH 8.9 8.9 8.8 8.5 11.2 11.1 11.0 10.8 10.7 11.9 11.8 11.8 11.8 11.8 11.7 12.1 12.1 12.1 12.0 12.0 12.0 12.0 12.0
,
WUNW LIME I B E L WATER
Figure 8. Viscosity of Clay Suspensions i n Water Water containing 1 lb. per bbl. of quebracho and various amounts of lime
power of quebracho, but this increase in effectiveness is much less pronouncctl 8.6 than that obtained with lime. Thew 41.0 data strongly indicate the possibility of 33.0 29.0 a calciumquebracho compound possess21 .o ing powerful dispersing properties. 22.0 19.4 It was pointed out above that prac20.0 tice used in the field for preparing and 47.5 controlling red-lime muds is ahead of ... ... 37.5 12.0 theory. In other words, the concentra34.5 12.0 30.5 12.0 tions of quebracho, caustic soda, and lime 28.0 12.0 required to give stable muds with the de26.0 12.0 sired properties have been found by tri:11 in the field. This practical knowledge is used in establishing the chemical environment for the next series of tests. A typical red-lime mud, as used in the field, contains approximately 2 pounds per barrel of qucbracho, 3 pounds per barrel of caustic soda, and 4 pounds per barrel of lime. In order to investigate the effect of such a chemical environment on clay solids, a series of muds was prepared by adding dry clay to water containing the above-mentioned concentrations of quebracho, caustic soda, and lime.
1I z
8 POUNDS CAUSTIC SOOA I BBL WATER
Figore 7.
Viscosity of Clay Suspensions in Water
Water containing 1 Ib. per bbl. of quebracho and various amounts of sodium hydroxide
WEIGHT % CLAY
Figure 9. Viscosity us. Per Cent Clay i n Various Chemical Environments
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
September 19%
TABLEVIII. CLAYIN WATER CONTAINING 2 POUNDS PER BARREL OF QUEBRACHO, 3 POUNDS PER BARREL OF CAUSTIC, AND 4 POUNDS PER BARREL OF LIME Water
clay. Wt. % 6
10 16 20
2 Hours, Acing Via. Gel 2.3 1.1 3.7 2.8 16.0 23.9 32.2 60.6 190.0 106.0
72 Hoiim, Arrha Via.
2.3 3.7 16.1
16.1
131.0
Gel 1.1 4.9
275.8 64.6 231.0
&l)& Min.
f2.Q
PH
..*
8.8
12.9 12.9 12.9
6.6
12.9
8.0
The data of this scries were recorded in Table VILI. The viscosity of the resulting muds for a given concentration of clay was lower than any of the other muds studied. The filtration properties were also relatively low, indicating the clay solids were in a dippersed state.
1905
environments studied, typical viscosity curves have been plotted in Figure 9. It is evident from this chart that a very wide range of viscosity-solids relationships is possible for a single clay, depending upon the chemical environment in which it is dispersed. Figure 9 vividly shows the increase in dispersing power obtained from combinations of the chemicals used in redlime mud as compared to these chemicals used separately. For example, more than twice the amount of solids can be tolerated in water containing quebracho, caustic soda, and lime than in distilled water for any given viscosity. This behavior has been observed in solids entering red-lime muds under conditions of use in the field. This offers a probable explanation of the resistance to viscosity build-up of red-lime muds during drilling. These studies suggest the probability that a very powerful dispersing agent is formed when quebracho, oaustic soda, and lime are combined in the right proportions. It is probable that the dispersing action of such a compound on clay solids plays a major role in the behavior of red-lime m n h
SUMMARY
ACKNOWLEDGMEYT
Viscosity measurements of clay suspensions prepared by adding dry clay to water containing the individual chemicals used in redlime mud and various combinations of these chemicals have been used to indicate the effect of theae chemicals upon the behavior of clay solids. During the process of drilling, formation solids enter a mud in much the same way as the clay was added to the various chemical solutions in preparing the muds for this series of tests. The observation of the behavior of the clay solids in the various chemical environments prepared in these testa should lead to a better understanding of the behavior of formation solids entering a similar chemical environment. In order to summarize the data showing the relative effect upon clay solids of the various ehemical
The authors are indebted to the Magnet Cove Barium Corporation for permission to publish this paper. Acknowledgment is also made to L. E. Heinze, Jr., for his assistance in the Iaboratory. LITERATURE CITED
(1) (2)
Cannon, G . E., O i l & GasJ., 45, No. 52,101 (May3, 1917). Seidell, Atherton, “Solubilities of Inorganio and Organio Compounds ’ Vol. I, New York, D. Van Nostrand Co., 1928.
RECEIVEDJanuary 18. 1960. Presented at the Fifth Southwest Renional Meeting, AMEBICANCwsmcar, SOCIETY. Oklahoma City, Okla.. Deoimber 10, 1949.
Diazothiolic Esters (Diazo Thio Ethers) INITIATORS AND MODIFIERS OF POLYMERIZATION REACTIONS W. B. REYNOLDS’ AND E. W. COTTEN Applied Science Research Laboratory, University of Cincinnati, Cincinnati, Ohio Diazothiolic esters (diazo thio ethers) are useful initiators for polymerization reactions. In addition to functioning as chain initiators, these materials exert a powerful “modifying” or “regulating” action leading to the production of soft benzene-soluble polymers. They are of particular utility in the emulsion polymerization and copolymerization of diene monomers such as butadiene. Polymerizationrates obtained depend upon the structure of the diazo thio ether and the amount used. Both oilsoluble and water-soluble diazo thio ethers function as initiators and modifiers in emulsion polymerizations.
I
T IS generally recognized that emulsion palymerization reactions are initiated by free radicals, which are generated in the reaction mixture either by thermal or catalytic decomposition of a free-radical-forming substance or by a single-electron oxidation or reduction. The decomposition of organic peroxides and diazoamino compounds are well known examples of the former, while Present addreaa, Phillips Petroleum Company, Bartla%ville,Okla.
the oxidation of aliphatic mercaptans by persulfate is the best known example of the latter. Regardless of the manner in which the radical Re i j generated, it may, presumably, initiate polymer chains either by adding to a monomer unit or by oxidizing a monomer unit to a free radical by extracting a hydrogen atom therefrom. The very active radicals obtained from the decomposition of a peroxide such aa benzoyl peroxide possibly initiate chains by extracting hydrogen atoms from monomer units as well as by addition to monomer units. Furthermore, they are probably too active to exhibit pronounced chain-terminating proclivities when generated only at moderate rates. On the other hand, the aliphatic mercapto radicals obtained from the oxidation of mercap tans are relatively unreactive and probably initiate chains only through addition to monomer units. These unreactive radicals might also be expected to exist in appreciable concentrations in polymerization systems and thus be important chain-terminating factors. This latter capacity of mercapto radicals is difficult to assay, because it cannot be readily distinguished from the chaintransfer of the mercaptan molecule.
