NONAQUEOUS EMULS POLYME PZATION SYS E. L. Carr and P.E.Johnson T h e Fireatone Tire & Rubber Company, Akron, Ohio
A
ture polymerizations, while the high volatility of ammonia \vould enable the isolation of the polymer and recovery of the medium. Moreover, the exceptionally low viscosity of ammonia would facilitate agitation. Simila,rly, the low melting point of hydrazine hydrate would be of interest in low temperature polymerizations. The physical properties of hydrazine place it in a group with water. It is not insisted that, each of these liquids be necessarily compatible with the process of emulsion polymerimhion of hydrocarbon monomers, but it is suggested that the most satisfactory approach t'o the adaptation of a givenliquid is an empirical one. If the monomer and liquid medium are mutually immiscible in some degree the most obvious procedure, and the one t'hat forms the basis of the work described in this paper, is t o substitute the t'est liquid directly for the water of a xorkable aqueous recipe. In the case of such liquids as ammonia and hydrazine it niay be necessary to depart radically from the aqueous recipes in order t,o achieve polymerization. Thus, in the ammonia system hydrazine and its derivat'ives are the analogs of hydrogen peroxide and its derivatives in the rrater system. By pursuing this and other pertinent analogies it' may be possible to evolve interesting emulsion polymerization systems. I n the present paper exploratory esperinient,s with liquid animonia, iormic acid, a,nd formamide are described in which the ingredients other than the liquid medium are limited to materials that have been found effective in water emulsion recipes.
preliminarl in\estigation was made with the objective of adapting to emulsion polymerizations liquid mediums other than water. Formaznide with a sodium lauq 1 sulfate emulsifier was adapted to the homopolymerization of stqrene and the copolymerization of butadiene with styrene. The formamide latices were stable and similar in general characteristics to the corresponding water latices. The butadiene-styrene copolymers prepared in formamide system were similar to GR-S in physical properties. Modification with dodecyl mercaptan w-as less efficient in formamide than in water system. Heterogeneous recipes formulated in formic acid and in liquidammonia failed to yield polymerization. Formamide as the antifreeze for low temperature polymerization gave the advantage of low viscosity as contrasted with glycerol.
T
HROUGHOUT the development of emulsion polymerization only one liquid has received much consideration as the continuous niedium in emulsion recipes-namely, water-and properly so in viex of its favorable economic and technological position. I t is of interest, however! t80consider the possibility of using liquids other than water as the medium in emulsion polymerizat,ion. ' 4 number of liquids may conceivably be adapted to this purpose, or a t least adapted to tbe forniulat,ion of recipes simulating the water systems in physical characteristics. Presumably the first requirement is n low order of miscibilit,y of liquid medium and niononicr. Whet,her polvmerization would succeed aft>erest'ablishment of the required heterogeneous system would depend on whether the liquid medium were antagonistic to the polymerization mechanism. Some liquids v-hich would naturally come int,tr consideration as mediums are listed in Table I.
Table I.
Liqiiid \$-a ter
Formaniide Formic arid Ammonia Ethylene glycol Glycerol Hydrazine Hydrazine hydrate Density range d i n =
c c:
200 b 250 c -33.50 d 11.l0 C . 1'
Emdsifykng Agents in Fornramide and Formic Acid Preliminary tests indicated solubility of diene monomers and some vinyl monomers, and solubility of conventional emulsifying agents and other recipe ingredients in formarnide and formic acid. Emulsification tests were made of selected surface active agents in these liquid mediums. The emulsifying agent (0.1 gram) was dissolved in 5 ml. of forniamide or formic acid, and 2 ml. of styrene were shaken with the emulsifier solution. Rate of separation was c,ompared with that for an emulsifier-free mixture of monomer and medium. Some results are tabulated in Table 11, n-here a plus sign indicates great.cr emulsifying action than in t'he absence of emulsifying agent, and the increasing numerals indicate the order of decreasing emulsifying effectiveness.
Liquid Properties
Formiila
HzO
B.P. C. i (,(I
i92 HCOXH: HC02H io0 E -33 6 SHE C ~ H I ( O H ) T 197 290 CaHa(0H)r 113 S2H4 N J ~ HHz0 I i !b
:G.P., C.
Viscosiry, M$ipoisv
Surface Tension. Dynes Cni. 72" 38 ,2 18.20 23.4; 47.7 63.4" 01 a', 74.1"
Table TI.
Emulsification Tests in Forniamide and Formic Acid
Emulsifying A g e n t
0 6 O i ro 1.26
Formainide"
Formic Acidb
e. '' Distilled formamide. h.p. 0 1
Forniamide, ethylenc glycol. and glywroi were suggested iii patent clairne ( 2 )for the emulsion polymerieation'of the haloprene monomers, although no details were given in the case of forniamide and ethylene glycol. Formamide, formic acid, and liquid ainnionia are the basis of the present paper; a successful recipe has been developed in the case of formamide but not in t,he case of the other two mediums. The liquids 1ist)edin Table I have a wide range of properties. The ext'remely low melting and boiling points of liquid ammonia n~oulcibe advantageous in low tempera-
h 4e-i nnn-
/4 mm
i l l
Dodecylisothiouioniulr? liydrobromide; reacts with iormamide. ( j A higher alkyl sulfonic acid salt (Du Font). e Cetyldimcthylbenzylammoniiirn chloride as Triton K-60, a 2 5 % paste in xater.
I n these emulsification tests the test conipound was either soiuble to a clear solution or formed a cloudy solution similar t o an aqueous soap solution Dodecylisothiouronium hydrobromide dissolved in formamide to a clear solution from which white cry+
1588
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1949
1589
IO0
convension vs. (K,S20,
0.5,
T a b l e 111.
TIME ODM 1 . Y )
Emulsion Polymerization in F o r m a m i d e at 50"
c.
B X
C 180
......
Formamide" Formamide Sodium lauryl sulfate
ISOLATED POLYMER
..
18!)
,5
3
xlszos
0 . .s 0.7
0 .3 Dodecyl mercaptan .. Styrene 25 50 Butadiene 73 .. Conversion, %> 16 hours .. .. 1011 2 1 . 5 hours .. 67 . ;7 24 hours 63 . 0 .. 2 6 . 5 hours 72.0 .. 27 6 hours 7 7 . 5 (64.3) Gel Yo Raw polymer 64.0 10 passes 45.5 Intrinsic viscosity, 10 paysen 1.6 a Du Pant technical, B.P. 91' a t 4 nmx,, fraationated ilirougli 42-cm. column packed with glass rings.
\O
30
94 TIME ( H R .
10
i0
)
F i g u r e 1. Comparison of Conversion Values tals separated in the course of a few minutes; it was soluble without reaction in formic acid but gave negligible emulsification. I n the case of SF flakes the finely powdered material dissolved readily in formamide when the mixture was warmed to 40" or higher, but at room temperature the translucent solution set to a firm gel as in water. The solution of SF flakes exhibited poor emulsifying properties. Sodium oleate was moderately easily soluble in formamide but exhibited only slightly better emulsifying action than SF flakes. Cetyldimethylbenzylammonium chloride was a very effective emulsifier in both formamide and formic acid, part of its effectiveness being possibly attributable to the water in the Triton K-60 paste. The material MP-189-EF was easily soluble and a good emulsifier in both formamide and formic acid. Only in the case of sodium lauryl sulfate in formamide medium was polymerization obtained. In formic acid no polymerization was obtained in any of several recipes tested.
Emulsion Polymerization in Formamide Systems
-
Recipes in formamide using sodium lauryl sulfate as the eniulsifier and potassium persulfate as the peroxidic initiator, with styrene and a butadiene-styrene (75/25) mixture as the monomers, were charged in bottles and agitated a t 50" C. The sodium lauryl sulfate and potassium persulfate dissolved readily t o a clear solution. As polymerization set in the free monomer was largely taken up a t a low conversion level t o form a bluish translucent latex with a high degree of transparency. As the conversion increased beyond 50% the transparency was gradually replaced by t h e milkiness typical of water latices. In Table I11 are given three typical recipes. The conversion figure given in parenthesis is the isolated-polymer conversion estimated on the basis of early comparisons between vented sample conversion figures and isolated-polymer conversion figures. A more recent comparison of the two methods of determining conversion is described below. The conversion values without parenthesis except for Recipe C are calculated from the loss of weight by venting a sample of latex and assuming all free butadiene vented and the unvented portion to correspond t o 75/25 polymer. This determination of conversion was only a rough approximation used to follow the conversion quickly during a run. It gave increasingly high values as conversion increased. Neither the vented sample method nor the total solids method based on a dried sample was completely satisfactory for estiniating conversion; only isolation of the polymer gave the true value
of conversion. The dry sample method was likely to give much
too high values unless conducted very carefully, with attention to frequent renewal of drying surface during the 20 minutes required for thorough drying. For this reason the vented sample method (although giving high values) served well to indicate the course of conversion, the final conversion in most runs being determined by isolation of the polymer. The polystyrene conversion was determined by isolation of polymer from a measured portion of the latex. A comparison of conversion values obtained by different methods is shown graphically in Figure 1. I n a carefully conducted experiment the vented sample method and dry solids method of estimating conversion were compared. A recipe similar t o B of Table I11 but with dodecyl mercaptan (dodecanethiol, DDM) a t 1.4 parts was run a t 50" C. A syringe sample was vented 10 minutes and weighed, and the vented sample was then dried under an infrared bulb. At low conversions there is little difference between the two values. As conversion increases the difference between the two methods increases. The vented sample method gives a value considerably higher than the isolated polymer value, presumably because of the retention of butadiene in the polymer particles. The h a 1 dried sample value is somewhat below the isolated polymer value, possibly as a result of some splattering and charring. Potassium persulfate and dodecyl mercaptan, the catalyst and modifier, respectively, were varied in a series of runs in Recipe €3 of Table 111,results of which are recorded in Table IV.
T a b l e IF-. Catalyst and Modifier in F o r m a m i d e Recipe a t 50" C. Run SO. I 1 2 3
4
3 I1 6
KaSnOr 0.3 0.6 0 6 0.5 0 6.1
0.5
DDM 0 0 1 1
7 7 4 4
Cqnveraon. 70"
$,o
Gel, Hours 14 24
41
24
66 5
48 3
P sa
0.0
33.5 0 ,0 42.0h 0.oc
14 0 7
4~ 0 64
28 28
59
64
4.5c
Intrinsic 7-iscosity 1.58 1 37 1.49
2.08 1.58
..
l'i
polymrr conversion. * Isolated Raw polymer. 10 passes through hand-tightened mill.
d 5%
water on formamide added to recipe.
In Table IV it is seen that the polymer of 40% conversion with persulfate at 0.3 and dodecyl mercaptan a t 0.7 is gel-free and has a relatively low intrinsic viscosity (run 1). When the persulfate concentration was doubled, the rate was increased and considerable gel was produced (run 2). -1large increase of modifier to 1.4
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1590
Vol. 41, No. 8
MODULUS AND T E N S I L E
Table VI.
Diazothio Ether Recipes at 40" C. 1
Formamidea lauryl sulfate
S030:9n
2
36 1 0.04
.. .. ..
72500
2000
4
3
36 1 0.2 0.2
36 1 0.2
36
1 0.2 0.2 0.4
..
..
..
..
1Q.38
Styrene 5 5 3 5 15 Butadiene 1: 15 15 None None 16-hour conversion Kone Xone a B p 9 l 0 a t 4 mm. Tblsl diazothio 0-naphthyl ether. pH as read x i t h Beckman p H meter adjusted with aqueous reference buffer. pH of forinamide 6.94.
concent,ration of the negat.ive ion of the medium and thereby decreased the concentration of hydrogen ion.
I
I 80
40
Figure 2.
I
CURE, HlH. Comparative Tests
a t the 0.6 persulfate level decreased the rate and gave a gel-free polymer of 41% conversion (run 3). The extremely high modifier level of 1.4 still yielded a high gel polymer at, GG.5'% conversion (run 6). This gel, hoxever, was dispersed by 10 passes through a cold, tight mill, and because of the easy breakdown the raw polymer was considered to be near enough like GK-Sfor comparisons described below (Table V and Figure 2 ) . I n run 5, 5% water on the formamide was included in the recipe. S o significant change was observed in the rate, but, the gel content increased markedly, indicating diminished modifier effectiveness. I n a different distillation lot of formamide (TI, of boiling point 91' a t 4 mm.) a high gel polymer of 64% conversion obtained in considerable quantity was subject,ed to a number of physical tests. It is clear from the catalyst and modifier data of Table IV that the polymerization rate is considerably lower than in an aqueous system (70% conversion in 12 to 15 hours at 50" C . ) . lloreover, modifier efficiency is much less in the formamide system. The latices result,ing from polymerization and copolymerization in the formamidc system were mobile and stable, and possessed the faintly bluish cast typical of aqueous latices. The stability was such that no tendency tovard separation or flocculation was detectable in periods as long as 1.5 years. Hyclroquinone, vdiich is readily soluble in formamide, n-as used as stopping agent. Substitution of acrylonitrile for a port,ion of the styrene in Recipe B increased t,ho rate of polymerization in a forninmide system as in a water system (Table V).
Table T7. Butadiene/Styrenei .Acrylonitrile 73/25/0 75/20/5
HCOSH, HCOn'HNa
500
120
Acceleration by Acrylonitrile Conversion,
16 hr. 29.5 53.0
%
++HT+ La
+
Potassium ferricyanide was included in one of the tolyl diazothio p-naphthyl ether recipes, but the activating effect observed in water system was not realized. A reduction-activa.tion recipe based on work of Bacon ( 1 Tvas inactive: formamide 180, sodium lauryl sulfate 5, benzoyl peroxide 0.5, sodium bisulfite 1.0, styrene 25, and butadiene 75. Recipes incorporating ingredients commonly employed in t,he formulation of aqueous redox systems likewise were without act'ivity. One such recipe was the following: I'ormamide Sodium oleate
200
5 0 2 0.75 0.25 O., 3.0
Ciimene hydroperoxide FeSOi. 7Hz0 Sa;P20, anhydroiia DDAI Dextrose Styrene Butadiene
12 13
which a.t 10" C. w-as completely inactivc in so far as polynierization was concerned. 1high monomer charge was polynierized to completion t o yield a concentrat,edlatex of 50% solids, the recipe being of the persulfate-lert-mercaptan (Sulfole €3-8) type with sodium lauryl sulfate as emulsifier. At 50" C. a conversion of 100% was reached in 48 hours, The latex was so viscous as to be barely pourable, no thinning agent having been employed.
Butadiene-Styrene Copolymer Butadiene-styrene copolymers of a 7 5 / 2 5 initial loading ratio were preparcd for comparison r i t h GR-S in certain physical tests (Table VII, Figures 2 and 3).
r
0O:
-
MODULUS AND TENSILE
24 lir. 29.7 67.0
OR-S
n Y
BD/St
c w
Various other recipes were forniula,ted in formamide with the objective of accelerating polymerization, using ingredients effective in water systems. Some recipes involving tolyl diazot,hiop-naphthyl ether are given in Table TI. I n the formulation of the diazothio ether recipes trisodium phosphate was included in two of them to produce a more allraline environment which has proved beneficial for this type of initiator in aqueous systems, For the same reason sodium metal was dissolved in the formamide (initial pH 6.94) of one recipe to give a p q of 10.38 as determined v i t h a Beckman p H met,er adjusted with an aqueous buffer. It is assumed that the sodium formed the salt of the formula HCONHSa, Tvhich by ionization increased the
HCONH-
+HCOKH-
1000
I-
(DDM 1.4)
%
A
12500 ca
0
as 0 I
O
e 0 ~
BD/3t
CURE ( M l N . )
Figure 3.
Comparative Tests
A
. I -
c
Yu,
August 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
1591
agents and many other compounds, it is possible t o prepare recipes simulating aqueous emulsion recipes. A number of such recipes were charged in bottles and agitated a t temperatures from 10' GR-S BD/St" t o 50' C. None of these charges yielded polymerization. A Conversion, % 72 64.5 66.5 number of variations are tabulated in Table IX. DDM 0.7 1.4 64 82 .5 Failure to polymerize in the presence of formic acid may indi. -10 passes cate either (1)lack of formation of initiating free radicals due to a 45 ,60 0 ..58 0 Ixrtrinsie viscosity, 1 0 passes different course of breakdown of the peroxide, or (2) preferential G u m stock Rebound %, 72O F. 57.5 59 capture of free radicals by the medium, thus precluding initiation 212O F. 72 74 of monomer radical formation. T h e high reactivity of formic Max. tensile, lb./sq. inch 175 175 T w d... rtnrk acid with oxidizing agents has been reported by numerous .. ..s.. .. Max. tensile, lb./sq. inch 2975 2350 workers (8,4, 6, 7'). 400% modulus corresponding to 1625 1400 Elongation % corresponding t o 560 520 I n the case of liquid ammonia the establishing of mechanical Crack growth, inch/hr. Unaged 0.95 1.36 systems simulating aqueous emulsion recipes was more difficult 7.95 5.60 Aged 4 days, 2 1 2 O F. because of the high degree of miscibility of monomers with the Young's modulus, lb./sq. inch -40° C. 5775 6833 liquid medium. At 0" C. isoprene, butadiene, and butadiene-50' C. 31,637 16,467 styrene (75/25) mixtures are miscible with ammonia. At -24" Bell brittle point, C. - 58 - 63 C. the butadiene-styrene combination is still miscible with ammoa Butadiene-styrene ratio 75/25. nia. Isoprene and butadiene have limited solubilities in ammonia at -24' C. while isoprene (but Table VZII. Dynamic Properties of Formarnide Butadienenot butadiene) has limited solubility at -18" C. Styrene Tread Stock These miscibility relationships are tabulated in (BD/St 75/25, DDlM 0.7, cured 80 min. a t 280° F.) nvnimir Rtnt1c Table X, based on 40 grams of anhydrous am_.I.__ ModuModumonia and 20 grams of monomer. Relative Energy lus, Internal Bl?ck lus Absorption Temp., Lb./Sq. Friction, Lb./&. Other ingredients of typical aqueous recipesSize, Stocks Inch Inch F. Inch Kpoises H2: Hf e.g., sodium lauryl sulfate and other emulsifiersStandard GR-S 212 189 5.75 99.1 277 150.2 Rebound Rebound and potassium persulfate had very low solubility 11.9 205 170.5 122 347 217 77 14.7 254 220 340 193.5 :f: in liquid ammonia. Recipes utilizing isoprene were 242 32 24.7 427 163 512 1000 1120 165.5 14 65.0 399 '18 X mixed, however, as in Table XI to form a hetero2110 -4 206.0 452 3550 79.5 geneous mixture containing undissolved emulsifyFormamide 212 224 6.37 110 217 195.5 ~~~u~ 12.75 220 178.5 326 BD/St = 376.5 122 Rebound ing agent and persulfate, and free monomer. 337 75/25 77 16.7 288 254 226 :f: Recipes involving the butadiene-styrene blend gave 32 670 36.3 626 139 357 14 1045 68.6 1185 108.5 484 'I8 a/4 a single liquid phase, The emulsification of iso-4 .. .. .. 846 7/s X a/a urene was of a low order. No Dolvmerization resulted in up t o 41 hours a t -28" C. in any of the recipes. I n Figure 2 the hard gel butadiene-styrene copolymer ( D D M 0 . 7 ) is seen to depart appreciably from the GR-S control. I n Figure 3 although the control is gbnormally low, the soft gel coTable x. Miscibility of Monomers in Anhydrous polymer ( D D M 1.4) does not differ appreciably from tmheGR-S Ammonia control. -24O C. -180 c. 00 c. Dynamic test results obtained on the forced vibrator machine BD/St = 75/25 Miscible Miscible Miscible are given in Table VI11 for the butadiene-styrene copolymer of Isoprene 2-phase 2-phase Miscible high gel (DDM * 0.7). Differences between the control and Butadiene 2-phase Miscible Miscible test polymer are slight. Table VIIS Properties of Butadiene-Styrene Copolymer Prepared in Formamide
GeKz"
__
~
-I
O
2 :$:
:$:E
-
Dynamic Tests. The test,s were made first a t 122' F., then a t 212 F. The rebound blocks were then used to cut 7 / ~ X 3 / 4 inch blocks for low temperature tests. Apparently the higher temperature had produced some permanent set and this affected the calculation of values at lower temperature.
Table XI.
g$$y$;;~lsulfate Sodium oleate
KzSzOa
Formic Aoid and Liquid Ammonia Recipes By virtue of the jmmiscibility of many monomers with formic acid and t,he solubility in this medium of certain emulsifying
Table IX.
Benzoyl peroxide DDM Styrene
45 0.89
.... ....
0.067
....
0.1 5.5 16.5
.... Temp., C. Time, hours Polymerization
- 24
41 >lone
2
45
....
0.89
....
0.067
....
0.1 5.5 16.5
.... - 24
41 Sone
3 40
... ,..
1.1
...
0.22 0.11
.. .. ..
22.2
-28 24 None
Recipes in Formic Acid (98 to 100%)
Temp., Peroxide C. Monomer 1 KzS20a 50 BD/St 2 Benzoyl 60 BD/St 3 Benzgyl 10 BD/St 4 CHP 10 BD/St 5 KzSzOe 50 BD/St 6 CHP 10 BD/St 7 Benzoyl 60 Styrene CHP 10 BD/St a Dodecylamine hydrochloride. Cumene hydroperoxide. Dodeoylisothiouronium hyarobromide. d Cetyldimethylbenzylammonium ohloride as Triton K-60.
NO.
Recipes in Liquid Ammonia 1
Ammonia
I
Emulsifier D DB . HCla D D A , HCla DDA.HCla D D A . HCIa MP-189-EF D I T U . HBr CDMBd
Aotivation
Fe Fe Fe Fe Fe
Pormamide in Aqueous Recipes Inasmuch as the antifreeze properties of formamide-lvater mixtures are known (6), the successful polymerization in 100% formamide system led to the investigation of its value as a n antifreeze in subzero aqueous recipes. Preliminary experiments were made in an MP-189-S emulsified, benzoyl peroxide-sugar redox recipe at - 10' C. using a 75/25 butadiene-styrene charge. No adjustment of the recipe was made beyond the use of sufficient formamide t o insure sgainst freezing at the temperature em-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1592
ployed. A low polymerization rate resulted but the unmodified polymer of 32% conversion (8 days) showed good breakdown characteristics when given 10 passes through a cold tight mill (Table X I I ) . Table XII.
Breakdown Characteristics of Low Temperature Polj-mer 70
Raw 10 passes
32.2 1.45
swelling Williams' Plasticity Index Y3 Rec. 103 L30 2.30 121
3.08
0.44
intrinsic Viscosity 4.68
POLYM
equivalent solution utilizing forniarnide as antifreeze had a viscosity of only 26 centipoises. hIoreover, formamide would have an advantage over methanol, the commonly used antifreeze; at extremely low temperatures, where high concentrations are required, formamide is largely immiscible with monomers, whereas methanol t,ends t o blend monomers with the continuous medium. It is expected that improvement, in the rat,e of polymerization 111 low temperature aqueous-formamide recipes can 'ne accomplished by further changes in the recipe.
Literature Cited
2.49
A great viscosity advantage in ion. temperature recipes is given by the use of formamide as antifreeze as compared with glycerol. For example, a n aqueous solution containing' sufficient glycerol t o prevent freezing a t -40" C. had a high viscosity of 1600 centipoises a t -35" c. (Brookfield viscometer), whereas an
VOl, 41, NQ. 8
(1) Bacon, Trans. Faraday Soc.. 12, 140 (1946). ( 2 ) Carothera. U. S.Patent, 2,080,558 (1937). (3) Frye and Peyne, 6.Am. Chem. Soc., 53, 1973-90 I 19:31) (4) Hatcher and Holden, Trans. Rog. SOC.Can,, 20, 395-8
