Aqueous Phase Diluents in Emulsion
Polvmerization of Svnthetic Rubber J
J
L. H. HOWLAND, J. A. REYNOLDS, AND R. W. BROWN United States Rubber Co.,P.O. Box 110, Naugntuck, Conn.
T
HE emulsion polymerization of synthetic rubber of the GR-S
type in media other than water is of interest because of possible effects on polymer structure and also because of the need for an internal antifreeze in polymerizations carried out below 0" C. Although no polymers prepared a t subfreezing temperatures are currently in production, experimental work is being conducted. Methanol has become the standard internal antifreeze in these experimental subfreezing GR-S polymerizations, although glycol, glycerol, electrolytes, and other materials have been proposed (6, 7 ) . Some work has been carried out also on polymerizations in formamide and other anhydrous media ( 2 ) . However, no systematic investigation of organic diluents or replacements for
%WATER IN METHANOL
WATER METHANOL BmADIENE
WZZZ74
Figure 1. Distribution of Components in System Containing Butadiene, Water, and Methanol
the water phase in emulsion polymerizations seems to have been published. Early in the program of development of low temperature polymerization a considerable number of diluents were investigated in this laboratory (4, 8). This paper deals with the distribution of a series of water soluble compounds between water and monomer phases in polymerization systems, emulsion polymerization of butadiene-styrene mixtures with part or all of the water replaced by other materials, and vulcanizate properties of polymers prepared in the presence of diluents.
then removed through a hypodermic needle. Complete separation of the two phases was possible. Dissolved butadiene was removed from the water-organic diluent phase by refluxing over a steam bath for about 10 minutes. The remaining mixture was then analyzed by distillation, density, or refractive index depending on the organic diluent used. Suitable calculations established the distributions. SGRFACE TENSION MEASUREYENTP. A duSouy tensiometer, calibrated with distilled water, was used to measure surface tension. A t intervals, the instrument was checked with water, and if the surface tension of this measurement did not agree with the former value, the intervening samples were rechecked. Samples containing soap were measured a t 40" to 45' C. since they were gelled a t room temperature. F0.4M COLLAPSESTUDIES.The collapse time of 20-inch columns of foam was determined using a I-inch jacketed borosilicate glass tube into which the sample was introduced. Air was then blown through a '/Z-inch sintered glass disk into the liquid to produce the foam. A s soon as a 20-inch column of foam had formed, the air was shut off and timing begun. When the surface of the liquid had cleared of foam, the elapsed time was noted as the foam collapse time. A number of the samples did not produce a 20-inch column of foam and were recorded as zero minutes foam life. PoLYwmIzATIoN STUDIES. The monomer conversion was determined by one of two methods, depending on the boiling point of the diluent used. If the diluent boiled belon- 100" C., the solids content of the latex was determined after butadiene had been allowed t o vent off. However, if it had a higher boiling point, the latex was coagulated, the polymer was washed thoroughly, dried, and the conversion calculated from the dry weight. Polymerizations a t temperatures higher than 45" C. were carried out in a stainless steel bomb while those a t 45" C. and lower temperatures were conducted in bottles. DISTRIBUTION BETWEEN PHASES IN WATER-DILUENTMONOMER SYSTEMS
I n order for a compound t o serve as a replacement for part of the aqueous phase in emulsion polymerization it must be pref-
EXPERIMENTAL
DIAGRAMS O F SYSTEMS CONTAIKING BUTADIENE, L\rATER, AND VARIOUS ORGANIC DILUENTS. The follon-ing mixture was used for determination of the distribution of components for the phase diagrams: Parts by Weight Butadiene 100 Water organic diluent 180 PH.4SE
+
This mixture was prepared for each diluent and each different concentration of diluent and I ~ Fplaced : in a 24-ounce bottle that \vas then rotated for 30 minutes a t 45' C. in a constant temperature mater bath a t 10 r.p.m. This brought the temperature of the mixture to about 45' C. and ensured proper mixing of the components. After removal of the bottle from the bath, it was allowed to stand motionless for 5 minutes during which time the phases separated completely. The lower water phase was
'0
10
PO ? .O 40 X WATER IN ETHANOL
x)
€0
70
WATER ETIIANOL BUTADIENE
BO
90
n mzzz
Figure 2. Distribution of Components in System Containing Butadiene, Water, and Ethanol
2738
Kx,
I N D U S T R I A L A N D ENG INEERING CHEMISTRY
December 1953
erentially soluble in water in the presence of the monomers to be employed. If the compound is to be used as a total replacement for the water phase it must be esspntially immiscible with the monomers in the absence of water. In Figures 1 to 12 the distributions between phases of a number of organic compounds between butadiene and water are shown graphically. All amounts are in weight per cent. In these graphs butadiene is represented by a solid bar, the organic diluent by a crosshatched bar, and water by an open space. In some systems-e.g., water-methanol, Figure 1-no separation of phases occurred with certain water-diluent mixtures, so the interface is shown a t 100% of the distribution. Figures 1 to 3 show the changes in monomer solubility of the three lowest primary alcohols. It is evident that with up to about 6OY0 methanol or 50% ethanol in the water phase the organic diluent remains largely in the water and little butadiene is solubilized. However. l-orooanol appears predominantly ,in the monomer phase even at low concentrations. Figures 4 to 6 % show that ethyl2 ene and propylene glycoland glycerol all remain completely in the water phase even %WATER IN I-PRPANQL WAER I - m N Q L Ezzzd a t very high conW A O E N E Is centrations, and Figure 3. Distribution of Comtherefore should ponents in System Containing be considered for Butadiene, Water, and 1-Propanol use as a total replacement for the water in emulsion polymerization. Diethylene glycol and the ethanolamines are also preferentially soluble in water a t all concentrations (Figures 7 to 10). Of the other compounds investigated, only formamide (Figure l l ) , acetic acid (Figure 12), and ammonia (Figure 13) remain in the water phase a t relatively high concentrations. Dioxane, 2-propanol, acetaldehyde, methyl formate, methylal, and diethylamine are all preferentially soluble in butadiene under the conditions employed. I
- -
t
PHYSICAL PROPERTIES OF SOAP SOLUTIONS IN WATERDILUENT MIXTURES
I
Since considerable differences were found in the behavior of polymerization systems containing glycol or glycerol as compared with those containing methanol, i t appeared of interest to determine whether differences could be detected in the physical properties of solutions of soap in the water-diluent mixtures. Figure 14 shows the variation of surface SURFACE TENSION. tension with composition (weight per cent) of water-glycol and water-methanol mixtures containing 2.7% Office of Synthetic Rubber soap. The variations were rather minor, and it is apparent from a comparison of the surface tensions with polymerization rates (Figures 16 and 17) that there is no correlation. RATE OF FOAM COLLAPSE.While venting polymerization systems containing methanol, it was noted that the system containing 50% by weight of methanol in the water phase had very little tendency to foam whereas the system containing 10% of methanol in the water phase was very foamy. It was, therefore, thought advisable to determine rates of foam collapse using those organic diluents on which rates of polymerization had been obtained. From Figure 15 it may be seen that those systems containing acetone and methanol had very low foam lives when compared with systems containing ethylene glycol and glycerol,
%WATER
H
2739
--
WATW ETHYLENE GLYCOL ezzZm BUTAOIENE
ETHYLENE GLYtOL
Figure 4. Distribution of Components in System Containing Butadiene, Water, and Ethylene Glycol
which have good foam lives a t concentrations as high as 60% diluent by weight. These data seem to correlate well with the rate of reaction data presented in the next section. It is evident t h a t acetone and methanol, which cause low foam lives above about 30% concentration, do not permit good polymerization rates above 35 to 40% concentration, while the systems containing ethylene glycol and glycerol, which do not decrease the foam life as much, permit good polymerization rates with as high as 90% organic diluent. It appears, therefore, that there is a correlation between foaminess or foam stability and rate of polymerization when varying amounts of organic diluents are present in a polymerization system. In the methanol system, it seemed likely that the soap had become too soluble t o micellize and, t h e r e fore, various amounts of salt were added to a water-soap-methanol solution, in an effort to decrease the solubility, OIL PHASE and the foam break rate of these solutions '0 10 20 30 40 was tested. Table I JO %WATER IN PROPYLENE WYWL WATER a summarizes the data
- - __ PROPYLENE GLYCOL BUTAOIENE
eTLpil
Obtained*
Figure 5. Distribution of Components in System Containing Butadiene, Water, and Propylene Glycol
The results presented in this table indicate that while the foam stability increases with i n c r e a s i n g salt concentration, the gel temperature also increases. The temperature of the soap solution before foaming was 4 5 O C. Higher molecular weight and consequently less soluble soaps than Office of Synthetic Rubber soap were tested in an attempt to speed up polymerizations in methanol-water systems. However, the improvement in rate was not significant. POLYMERIZATION RESULTS
WATER-DILUENT MIXTURESAT 45' c. Methanol, ethylene glycol, and glycerol were selected for study as diluents for the
TABLE I. EFFECTOF ELECTROLYTE O N FOAM STABILITYI N A
WATER-METHANOL MIXTURE
Sodium Chloride, % 0 1 5
Break of 20-Inch Foam Column, Time Impossible t o get 20-inch column 0.05 minute Foamed freely but gelled as foam
INDUSTRIAL AND ENGINEERING CHEMISTRY
2740
Vol. 45, No. 12
water phase in polymerizations with the Mutual formula at 45" C. The recipe is shown in Table 11. Figures 16 to 18 show a fundamental difference between methanol and the polyhydroxy compounds in that Kith increasing concentration of methanol a point is reached at which polymerization dies out abruptly after a few hours. At still greater methanol concentrations no polymerization takes place a t all. With ethylene glycol and glycerol, on the other hand, the rate of polymerization decreases rather steadily as the concentration of diluent is increased, but there appears to be no tendency for the reaction to die out a t low conversions. 0 WATER-AMMONIA M I x T u R E s AT ' 5 C. Ammonia is, in many X WAFS IN GLYCEROL WTER avcERoL respects, an excellent antifreeze for aqueous systems. Its low WADLENE molecular m-eight, high solubility in water, and easy volatility Figure 6. Distribution of Components in System make it highly efficient and easily recoverable. Although amContaining Butadiene, Water, and Glycerol monia even in small amounts inhibits some polymerization recipes (3)it was found ( 1 , 8) that others, particularly hydroperoxide catalyzed systems activated by polyethylene polyamines (9) and the diazothioether-ferricyanide systems (6),are quite insensitive even w to large amounts of ammonia. Table I11 3 shows the effect of increasing amounts of ammonia in a 5" C. polyethylene polyamine activated polymerization recipe. c In general it has been found that with ammonium soaps in this formula a small amount of excess ammonia is necessary for good rates XWATER IN D i n w e a y c o L WATER = % WATER IN E T H W M I N E E T ~ $ ~ ~ I N E E of polymerization, but that further increases DIETWLENEGLYCOL BUTADIENE BuTADlENE have little effect. The largest amount of amFigure 7. Distribution of ComFigure 8. Distribution of Cornmonia in the above series gives a freezingpoint Ponents in System Containing ponents in System Containing of about -20" C. to the aqueous phase, Butadiene, Water, and EthanolButadiene, Water, and Diethylene A M M O N I 4 ANTIFREEZE AT -18' c. Although amine Glycol the rates obtained a t 5" C. indicated that polymerizations a t -18' C. should proceed at a reasonable rate with ammonia as antifreeze res d t s were quite erratic until it was discovered that it was necessary to emulsify the charges before cooling to -18" C. When preliminary emulsification was carried out either by shaking the capped bottles containing all ingredients except hydroperoxide at room temperature or rotating in a 5" C. bath for a few minutes before cooling to -18' C., polymerization took place readily. Table IV shows the results '0 10 20 30 40 50 of a series of polymerizations Kith varying %wiTERIN TR'ETWNCLPMINETRIET~-~lN~ E amounts of potawium hydroxide added to the BUTAOIENE charge. I t appears that slightly better results Figure 9. Distribution of ComFigure 10. Distribution of Cornare obtained mith reduced amounts of potassium ponents in System Containing ponents in System Containing Butadiene, Water, and Diethanolsoap' Butadiene, Water, and Triethanolamine amine
-
B
-
-
-
I
3 B
i5
%WATER IN FORhUMIDE
WATER FORMWIDE BUTAOIENE
PI
Figure 11. Distribution of Components in System Containing Butadiene, Water, and Formamide
% WATER IN M C I A L ACETIC ACID
AG:zRm,, E BUTADIENE
0
Figure 12. Distribution of Componcnts in System Containing Butadiene, Water, and Acetic Acid
BUTADIENE
-
Figure 13. Distribution of Components in System Containing Butadiene, Water, and Ammonia
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1953
2741
5
4
1 $2
I
00 a
I
I
I
2b
Figure 14.
I
d
SI
,
I
4L x) % WATER IN SOLUTION
83
70
60
90
0
Surface Tension of Ethylene Glycol and Methanol Solutions in Water
X WATER
IN
MIFREUE
SOLUTON
Figure 15.
Foam Break Rate of Soap-Antifreeze-Water Solutions
Figure 17.
x WATER IN E ~ E M am Effect of Ethylene Glycol o n Polymerization Rate of Type 1 Recipe at 45" C.
TABLE 11. MUTUALGR-S FORMULA Parts by Weight Butadiene Styrene
75 25
KzSzOa Office of Synthetic Rubber soap
0.3 5.0 0.45 180
Dodecyl mercaptan Water
TABLE111. EFFECTOF AMMONIAON POLYETHYLENE POLYAMINE ACTIVATED 5" C. POLYMERIZATION RECIPE Parts by Weight
Polymerization recipe Butadiene Styrene Diisopropylbenzene monohydroperoxide Tetraethylenepentamine Ammonium laurate Potassium chloride Mixed tertiary mercaptans ammonia Water
71 29 0.15 0.15 5.0 0.20 0.30 180
+
Ammonia ("8) parts by w e i g h Conversion.0'3'
0 40
0.6 100
1.4 100
5.6 92
17 97
22 92
I % WATER IN UYCEROL
Figure 18.
I
20
/
I
%
60 7'0 80 WATER IN METHANOL
50-'
~-
90
KO
TABLE IV. POLYMERIZATION AT - 18' C. WITH AMMONIA
Figure 16. Effect of Methanol on Polymerization Rate of Type 1 Recipe at 45' C. c
Effect of Glycerol on Polymerization Rate of Type 1 Recipe a t 45" C.
Addition of small amounts of ferric chloride and ethylenediamine-tetraacetic acid gave some improvement in rate, conversions as high as 75% being obtained in 20 hours a t -18" C. in some runs. NONAQUEOUS SYSTEMS. The results with the Mutual recipe in which water was almost wholly replaced by glycerol and ethylene glycol led t o polymerizations carried out in the complek absence of water. Glycerol has given the best results of the compounds tested. Table V shows polymerization data obtained in a number of different experiments. Polymers were prepared at varying Mooney viscosities with the Mutual formula at 45' C. in anhydrous glycerol for evaluation in tread stock vulcanizates. The latices were stripped of residual monomers with steam, flocculated with sodium chloride and sulfuric acid, washed thoroughly, and dried.
ANTIFREEZE
Polymerization recipe Butadiene Styrene Diisopropylbenzene monohydroperoxide Dodecyl mercaptan Tetraethylene pentamine Ammonia Water Polymerized 20 hours Potassium oleate 4.7 Oleic acid .. 4:a Potassium hydroxide .. 0.3 Conversion, Yo 52 58
Parts by Weight
70 30 0.25 0.15 0.30 28 172
4:3
0.5 57
4:3
0.7 55
4:3
0.9 49
TABLE.V. GR-S POLYMERIZATION IN ANHYDROUS GLYCEROL
(1
Formula Mutual Mutual MDNa MDN p-Methoxybenzene
Time, Hours
Temperature,
6.3 45 24 24
64 45 45 - 18
c.
diazo thio-b-naphthol.
Conversion,
% 87 88 69.5 49
INDUSTRIAL AND ENGINEERING CHEMISTRY
2742
TABLEVI.
GR-S
Compound Ethylene glycol Ethylene glycol Formarnide Acetic acid" Pyridine= Anhydrous ammoniaa
OTHER
~ O L Y M E R I Z A T I O h ' IS
MEDIA
Time, Hours 432 44 168 25 112
15
Temperature,
hHYDROLTS
Monomer Conversion Xone 10 25 None h-one None
c.
45 64 45 45 45 - 18
Catalyst K&Os h1.IDh-b AIBNC AIBNC AIBNO hlDNb
TABLE VII. VCLCA~IZATE PROPERTIES OF GR-S PREPARED IN TYATER-DILUEST MIXTURES
Diluent Reaction time, hours Hydrocarbon conversion, %
h-one 15 76
Ultimate tensile, lb./sq. i n 25 min. 50 min. 90 min. Average Elongation, 70 25 min. 50 min. 90 min. Resilience, % Room temp. 2120 F.
Ethylene Glycol 20 78
Glycerol Methanol 18 30 74 76
59 74
io 72
60 67
68 79
370 820 1110
480 960 1300
400 850 1170
400 870 1270
1870 3140 3150 2720
1720 2660 2850 2410
1870 2760 3210 2570
1660 3040 3260 2660
805
650 580 500
765 645 585
715 645
43 48
43 46
44 47
700 573 43 47
555
A number of other organic compounds which were found to be insoluble in butadiene were tried in nonaqueous systems. Results are summarized in Table VI. POLYMER PROPERTIES POLYJIERS BREP4RED 4T 45' c. I n order to determine whether the presence of diluents in the aqueous phase affects the physical properties of the polymer, GR-S was prepared a t 45' C. to 75% conversion and 50 Mooney viscosity using 54 parts of methanol, ethylene glycol, or glycerol in the water phase. These polymers mere then compounded in a tread stock recipe and cured. Physical test data on these vulcanizates showed no unusual propertief (Table VII). A number of polymers prepared in 100% glycerol to varying Mooney viecosities mere also compounded and cured in a tread stock recipe. Table 1'111 shows that the stocks prepared in glycerol exhibited abnormally high qtiffening in compounding and also cured coneideralilv more rapidly than the standard GR-S
Vol. 45, No. 12
TABLEIX. VULCAXIZATE PROPERTIES OF GR-S PREPARED AT - 18' C. WITH hnr\ro;vra ASTIFREEZE Antifreeze MBTSa Mooney viscosity Uncompounded Compounded Modulus, 300%. Ib./ sq. in cured a t 2920 F. 30 min. 60 min. 90 min. Ultimate tensile, lb./sq. in. 30 min. 60 min. 90 min. Average Elongation, % ' 30 min. 60 min. rnin. 90 min. Aged tensile, aged 72 hours; 212O F. 30 min. 60 min. 90 min. Averaxe Elongation, % 30 min. 60 min. 90 min.
Methanol 1 75
Ammonia L75
Ammonia 1.0
A.mmonia 1.0
57
..
60
63 94
94 114
430 1120 1590
1260 1720 2050
400 1150 1400
830 1300 1600
3230 3970 3630 3610
3220 3610 3210 3050
2840 4060 3880 3590
3970
550 500 420
930
700 590
720 5.50 520
2430 2310 2500 2410
2450 2280 2790 2510
3200 2750 2960
2790 2830 3000
2910
2870
310 280 300
180 210 290
.
a
900 R ln _.. 610 510
3fi80
3730 3760
3 00 310 330
Rleroaptobenzothiazoledisulfide.
control. Tensile strengths were somewhat lower than the control a t all levels of viscosity. POLYMERS PREPARED AT -18' c. Polymer was prepared at -18' C. for physical testing with both methanol and ammonia as antifreeze. Preliminary tests of the material prepared in the presence of ammonia gave overcured stocks, but by adiusting the accelerator level cure rates equivalent to the polymer prepared in methanol were obtained. Table I X summarizes the phvsical test data. -4s would be expected. the tensile strength of the low temperature polymers are considerably higher than those prppared a t 45' C. There appears to be no essential difference between the polymers prepared with methanol and with ammonia when allowance is made for the differences in cure rate. ACKNOWLEDGMENT
The work discussed herein was performed as a part of t h r research project sponsored by the Reconstruction Finanre Corp., Office of Synthetic Rubber, in connection with the Government Synthetic Rubber Program. LITERATURE CITED
(1) B r o w n , R. W., p r i v a t e communication (Oct. 3, 1950). (2) C a r r , E. L., a n d J o h n s o n , P. H., IND.EXG. CHEY.. 41, 1588 (1949).
(3) General T i r e & R u b b e r Po., p r i v a t e communication t o Office of S y n t h e t i c R u b b e r , Reconstruction Finance Corp.
(4) I l o w l a n d , L. H.. a n d Reynolds, J. d.,pi,ivate communication
TABLE VIII.
vVLC.4SIZATE
PROPERTIES O F GR-S PREPARED IX
100% GLYCEROL hfooney viscosity Uncompounded Compounded Modulus, 300%. lb./sq. in.: cured at 292O F. 4 5 min. 90 min. Ultimate tensile, lh./sq. in. 45 min. 90 min. Averaee
a
Standard GR-S.
Control&
Polymers Prepared in Glycerol
49 65
43 86
690 1170
1790 2030
2450 2400 2425
2040 2150
690 513
340
41 43
37
2090 320 45
62 100
..
..
79 120
..
..
1930 2130 1990 2150 1960 zjzo
86 127 2310
..
( M a y 20, 1948). Kolthoff, I. AI., a n d D a l e , W.J.,J . Polymer SCL., 3 , 400 (1948) St. J o h n , W.AI.. e t a l . , Ibid., 7 , 159 (1951). T r o y a n , J. E., Rubbei A g e , 63, 585 (1948). United S t a t e s R u b b e r Co., p r i v a t e communication to Office of S y n t h e t i c R u b b e r , Reconstruction F i n a n c e Corp. (9) W h i t b y , G. S.,Wellman, N., F l o u t s , V. W., a n d S t e p h e n s , H. I,., IND. EXG.CHEM.,42, 448 (1950).
(5) (6) (7) (8)
RECRIvED for review March 2 5 , 19.53.
-iCc~r"rED,Jiily 6 , 1953.
2310 1900 2100
290 285
290 275
300 260
41 52
40 51
41 50
Diazo-Initiated Polymers-Correction I n the article on '.Diazo-Initiated Polymers" [Willis, J. If., Alliger, Glen, Johnson, B. I,, and Otto, TV. M., 1x11 ENG.CHCV, 45, 1316 (195311 the patent cited in referenre (4)should h a w been 2,376,963.
