Solubility of Polybutene in Pure Solvents . H. C. EVANS AND D. W. YOUNG Standard Oil Company of N e w Jersey, Elizabeth, N. J. URING the past few years D interest in the preparation and properties of long-
A
Staudinger assumed that solvents which do not allow the polymer molecules to be extended as long threads are poor solvents. Also, Lovell and Hibbert (4) determined the viscosities of polyoxyethylene glycol in dioxane and carbon tetrachloride. By the use of Huggins’ theoretical equation (g) of the viscosity of chain molecules in solution, Lovell and Hibbert stated t h a t t h e polyoxyethylene chain appears to be highly convoluted in solution. Reports have been written covering t h e physical a n d chemical properties of polybutene, in which solvents and nonsolvents of the polymer have been listed, but no attempt has been made to study the degree of solvation. At some solvent-polybutene concentrations we have already observed considerable instability of mixtures where viscosity determinations were erratic. It was known that the viscosities of polybutene solvent blends in higher concentrations do not obey any concentration-viscosity law which might be applied for blending purposes. Several workers have observed very large viscositytemperature effects for some blends which do not bear out for other solvents or even for the same solvent in other concentrations. I n view of the viscosity data published on polyvinyl chloride, polyoxyethylene glycols, and polybutene, an investigation was initiated to study the degree of solubility of the polymer polybutene. It was hoped that information could be obtained to indicate if the thickening power of polybutene is due to shape of molecule, solvent, or solvent capacity.
limited study has been made of the solubility of polybutene in sixty pure solvents at room temperature. By the use of the specific viscosity constant, at a concentration of I O grams of polymer per liter, the degree of polybutene solvation has been calculated for thirty-four solvents. The viscosity number of the polymer solutions over the approximate concentration range of 10 to 80 grams per liter has been measured. Log N has been found b y this method not to be a linear function of concentration in the higher concentration ranges of polybutene. It is indicated that chlorinated solvents having dielectric constants greater than about 8 will not dissolve high-molecular-weight polybutene at room temperature.
chain polymers has been intensified because of t h e i r importance in the manufacture of improved petroleum products, plastics, and chemicalresistant paints. Materials such as polybutene and rubber form solutions, the viscosities of which increase rapidly with concentration. Typical viscosity-concentration data for dilute solutions of polybutene have been published (7). A number of workers have determined the viscosities of several polymers in dilute solutions, and from these investigations equations have been proposed for expressing viscosity as a function of molecular constitution. One of the most important considerations has been the question of whether very high polymeric substances exist in solution as long macromolecules, completely dispersed, or as aggregations of much shorter molecules associated in the micellar state. Staudinger (6), one of the chief proponents of the former view, carried out a large amount of work on the viscosity of solutions of such linear polymers. His conclusions regarding chain length were based almost entirely on such measurements interpreted on the basis of the viscosity relation:
N.su/Cgm = KnM ( 1) or Neu/C = K,P (1-4 where Nap = specific viscosity = relative viscosity, N , - 1 C, concentration of recurring unit, moles/liter M = molecular weight C = concentration of polymer, grams/liter P = polymerization grade 5
Many attempts (6) were made to use the difference between the observed and calculated values of Staudinger’s K constant as a measure of the solvation of polymer in solution. The results are not always reliable, however, because in some cases the particles are proposed by Staudinger to be present in solution in a structural form other than rigid, randomly kinked rods. Staudinger (6) and a number of other workers reported deviations from Equation 1in the region of “dilute” solutions. As an example of this effect it has been demonstrated that polyvinyl chloride in dioxane does not give a straight line when the N , d C value is plotted against molecular weight. Polyvinyl chloride with a polymerization number of 1000 had about the same N,,/C value as a polyvinyl chloride with a polymerization number of about 2500. This fact has been explained on the assumption that the molecules are not extended in dioxane.
Method of Solubility Determination At the beginning of the work it was felt that if “true solutions” were formed by polybutene-solvent blends, they should obey the well-known approximate relation given in Equation 2, and that any deviation from this equation should indicate the presence of insoluble polymer and the formation of a semistable solution. Later it was found that this is merely an empirical equation which holds approximately in a number of cases. Deviations are always observed; but lacking a better equation for the wide range of concentration studied, we have used,this relation as an arbitrary standard to observe variations in the thickening power of the polymer: log relative viscosity
concentration
461
= constant
INDUSTRIAL AND ENGINEERING CHEMISTRY
462
4.0
FIWE I
Vol. 34, No. 4
X
FIG^^ 2
VISWSITY PXATIONSHLPS OF 104,000 U.W.
P3LyWrnE
3.6
a. OLCTllS
-
3.2 -
2.8-
2.4 -
li 0.8' 10
20
30
K4ME OF S O L v h T N - P h W
HKmm H @ m
2.0 -
N-OCTANE ISO-CCTtwB
Him0 co.
1.6 -
mmm
VARSOL NO.
2
rnOsEIE
I
I
40
50
I
I
60
1
70
0.8
80
IO
20
30
10
20
30
40
50
60
70
80
90
50
GO
70
80
90
t
2.2
,.41/ii LEO!DD
x0
"&E OF SOLVE"
-CYC CYCLOLo"E
X
I .01
IO
I
I
20
30
CO?IC~~T&ATION OF 104,000 MOL, KT+ POLYWJTZNE IN O
40 W PER LITEX
Figures 1 to 4
40
CONCmWTIOh' OF 104,000 IdOL. "T. POL-
Dl O
W W LXTER
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
April, 1942
FIGURE 6
FIGURX 5
4.01
VISCOSITY RELATIONSHIPS OF 104,000 M. PI. POLyEmmF I N ETIms
VISOOSITYFZL&TIONSIIIPS OF 104,000 M.W. I N CKLORINATiD HYDROCARBOW
POL-E
”I
3.6 -
2.6
53.2-
1
8
E
463
2.8 -
8 8
“2.4-
2.0
-
1.6 -
1.2’ 10
L
1
1
I
I
20
30
40
50
60
I
I
70
80
”7 0
20
30
40
50
60
CONCXVIQATION OF 104,000 MOL. WT. POLYBUTEC3 I?? DRllb3 PER LITEB
Figures 5
It was known that electroviscous effects (B), particle shape, etc., could operate in causing the viscosity to differ from the calcubted viscosity. Therefore, viscosity measurements do not give a true picture of polybutene solubility. As a check on solvent power as indicated by the viscosity results, an alcohol precipitation prooedure was used to study the stability of solutions. A solution that requires a large amount of low-molecular-weight alcohol or nonsolvent before the polybutene is precipitated will indicate qualitatively a better solvent than a solution that requires a small volume of alcohol. Erbring (1) found it advantageous to study the interaction between solvent and substance to be dissolved, not only from a chemical structure viewpoint but also with consideration of physical data, such as dielectric constants. He found that the amount of alcohol necessary to precipitate polybutene in solution was proportional to the dielectric constant of the alcohol. Erbring (1) reported an alcohol precipitation method for the comparison of the solubility of high-molecular compounds in solvents. This procedure was used to study the stability of polybutene solutions. The method makes it possible to list solvents in order of their capability of being blended with alcohol by the use of “alcohol number”. The procedure is based upon the fact that alcohol will precipitate polybutene from solution, and the intensity of light reflected in a nephelometer is proportional to the quantity of particles in suspension. The amount of alcohol necessary varies with the temperature, dielectric constant of the alcohol and solvent, and the concentration of the solution. I n this work a blank was always titrated to determine if a cloud was produced by mixing solvent and alcohol alone. The nephelometer or cloud point method is well suited for a study of a polybutene solution of IO grams per liter, as the colloidal precipitate formed by the
and 6 action of the alcohol does not settle a t room temperature a t a fast rate when the relative turbidity is about 200 to 600 per cent. Erbring showed that, when the degree of relative turbidity (y axis) is plotted against the concentration of alcohol (x axis) an S-shaped curve is obtained. I n other words, the ascent of the curve is extreme. This may indicate that polybutene precipitation takes place throughout the solution within a narrow range of concentration of alcohol.
Laboratory Procedure PREPARATION OF SAMPLE.The technique of pre aring polymer solutions has been found t o be important, as the Righer molecular weight material appears t o undergo some degradation when shaken violently in solution (‘7). A solution of 81 500 molecular weight polybutene (1 gram of polymer per liter) in diisobutylene gave a viscosity of 0.973 centistoke at 20’ C., but after the solution had been shaken violently for 2 hours at room temperature, the viscosity was 0.940 centistoke at 20’ C. To exclude the possibility of breakdown, the present experimental solutions were made with a minimum amount of agitation. The general rocedure chosen, after some preliminary investigation, was asow ll!f:s The solution was obtained by cutting the polybutene (molecular weight 104,000) t o about 0.6 om. cube or smaller, placing the weighed sample in a 125-ml. narrow, clear glass oil bottle, and adding to this the calculated voiume of solvent from a raduated buret. The total volume of polymer solution pre are8 was about 100 ml. As soon as the solvent had been ad&d, the bottle was tightly corked and then placed on the laboratory desk for about 5 days. This operation permitted the polymer t o soften and swell in the solvent at room temperature. After the polymer appeared to be very soft, the “solution” or mixture was gently agitated by hand intermittently from 5 to 15 minutes a day over a period of 15 to 20 days. When the solution appeared t o be uniform, the bottle was allowed t o stand a t room tem erature. VISCOSITY ~ETERMINATION. The viscosity was then measured on about 30-40 ml. of the solution at 37.7g6 C. (100’ F.), usin a Ubbelohde viscometer. The viscometers were thermostate8 in a water bath, and the temperature was held t o an accuracy
Vol. 34, No. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
464
TABLEI. SOLUBILITY BEHAVIOR OF POLYBUTENES AT ROOM TEMPERATURE
Solvent
Properties of Solvent DiAv. Temp. electric Temp. Mol. Wt. of VisB. P. a t conof E of Poly- cosity 7600mm., stant E detn.. butene Detn., C. (8) O C. (7) O C.
0 g./l.
Viscositya of Solutions in Centistokes, a t Polybutene Concentration of: 10 20 30 40 50 60 70 80 90 100 g./L g,/l. g./L g./L gJ!. g./l. g./l. g./l. &/I. g./l.
PARAFFINS n-Pentane n-Hexane n-Heptane n-Octane Isooctane Hydro Co. trimer Varsol No. 2 Kerosene
35.95 68.75 98.40 125.75 116.00 150-180 152-193 190-274
1.80 20.3 1 . 8 7 20 1 . 9 7 20 1 . 9 6 20
. . . . . . . . . .
. . . . .
.
.
n-Pentene ( - 2) Dimer (diisobutylene) Trimer (triisobutylene)
36 102.6 130-170
. . . . .
Cyclohexane Methylc yclohexane
80.8 100.8
2.05
20
Benzene Toluene Xylene Tsopropylbenzene n-Prop lbenzene MesityKene Cymene Amylbenzene
79.6 110.5 137-140 153.4 157.5 164.6 176.0 194
2.28 2.33 2.57
20 20 20
2136 2.35
20 20
Trichloroethylene . Perchloroethylene Ethylene dichloride Ethylene dichloride 8-Trichloroethane pTrichloroethane %-Tetrachloroethane 8-Tetrachloroethane Pentachloroethane Isopropyl chloride n-Propyl chloride 2,2-D1ohloropropane 1 2-Dichloropropane Iiobutyl chloride n-Amyl chloride Amylene dichloride
39.8 39.8 61.2 76.7 48.4 60.3 48-60 86.7 120.8 83.7 83.7 113.5 113.5 146.3 146.3 161.9 36.5 46.5 70.5 95.9 68.0 105.7 130-175
hlethanol Ethanol n-Pentanol Tetradecanol Heptadecanol
64.5 78.3 137.9 263.2 309.0
. . . .
,.
. . . . .
. . . . .
. . . . . 9.2 9.2 4.8 2.2 2.4 9.4
...
20 20 20 20 20 20
..
3.4 2.4 10.4 10.4 10.0 10.0 8.0 8.0 3.7
20 20 20 20 20 20 20 20 20
7.7 10.2
20 18.8
...
...
.. ..
7.1 6.6
20 11
30.2 24.1 13.7
25 25 25
...
..
. . . . . . . . . .
104,000 20 104,000 37.78 104,000 37.78 104,000 37.78 104,000 37.78 104,000 37.78 104,000 3 7 . 7 8 104,000 37.78
0.425 0,438 0.549 0.653 0.647 0.842 1.05 1.62
2.81 15.6 2.61 12.4 3.82 20.2 5.51 29.2 5 . 4 0 27.6 6.37 27.5 9 . 6 4 43.0 13.50 58.9
57.0 43.4 70.9 80.4 56.8 90.5 131.2 189.2
OLEFINS 104,000 20 0 , 4 0 3 2.59 11.65 5 4 . 0 104,000 37.78 0.665 5.68 25.05 105.7 104.000 37.78 1 . 2 0 10.38 44.74 177.5 NAPRTHENES 104,000 37.78 0.971 13.20 64.64 122 104,000 37.78 0.808 9 . 5 4 45.60 115 AROMATICS 104,000 37.78 0.623 2.47 13.2 53.2 0.606 3 . 1 7 11.6 56.6 104,000 37.78 104,000 37.78 0.665 5.24 18.1 6 3 . 2 104,000 37.78 0.771 5 . 5 8 2 7 . 4 79.3 104,000 37.78 0.844 6.66 2 7 . 9 78.4 104,000 37.78 0.703 5.55 2 2 . 7 73.5 104,000 37.78 1.00 7.89 33.2 80.0 104,000 37.78 1 . 2 3 10.33 4 0 . 0 99.1 CHLORINATED HYDROCARBONS 104,000 37.78 0.361 0 . 3 7 . . . .... 12,000 37.78 0.361 0 . 5 3 .... 104,000 37.78 0.405 2 . 8 7 l 3 : 3 44.1 104,000 37.78 0.533 4 . 4 0 1 7 . 7 59.0 0.358 2 . 8 4 1 3 . 1 104,000 37.78 .... 104,000 37.78 0.400 0.40 ... .... 104 000 37.78 0.380 1 . 2 7 6.43 2 9 . 8 104:OOO 37.78 0.421 3.45 1 5 . 6 48.6 104,000 37.78 0.498 5 . 4 6 2 4 . 9 79.3 104,000 37.78 0.573 0.57 0.57 . . . . 12,000 37.78 0.573 0 . 5 7 0.57 . . , 104,000 37.78 0.686 0.66 0.69 . . , . 12,000 37.78 0.686 . . . ./ . . . .,. 104,000 37.78 0.862 1.53 1 . 7 7 . . . . 12,000 37.78 0.862 1 . 1 5 1.57 . . . . 104,000 37.78 1.14 8.72 41.7 135 104,000 20 0.442 15.9 .... 0.452 . . . . i i : 3 104,000 37.78 .... .... 104,000 37.78 0.623 0.623 . . . 104,000 37.78 0.634 0.642 . . . .... 104,000 37.78 0.507 3.62 1 2 . 7 58.8 104,000 37.78 0.587 4.21 1 8 . 3 52.2 0.949 5.44 15.1 66.8 104,000 37.78 ALCOHOLS 12.000Not detd. . . . . . . . . . . . . . . 12.000 Notdetd. . . . . . . . . . . . . . . 12:OOO Not detd. . , . . io4,ooo 37.78 12.75 i i : 4 ' 13.6 104,000 37.78 21.59 28.5 31.2 44.5
ii:i
170 172 280 276 278 274
... 779
162 312 533
1100 2245 3167 2992 1996 2898
...
975 1052 1382 1498 1244 1578 1970 4934
544 441 1494
951 2118 2260
1050 3581 5422
... 124: 1 162 136
...
. . I
175 28 2
... ,.. ...
... ...
... 473 177
,..
... ...
154 279 152
&p-Dichloroethyl ether
34.6 139-141 187-190 56-58 (14 mm.) 175-179
3:3b
.....
12,000 Not detd. . . . . io4,ooo 37.78 0.766 104,000 37.78 1.13 104,000 37.78 1.04
7.02 6.83
ii:i2 25.85 24.90
.
104,000 37.78
1.40
1.40
4.3
20
3.1
16
..
.....
1.40
ESTERS Isoamyl formate Butyl acetate Isoamyl butyrate Isoamyl caproate Methyl oleate
122-123 118-127 159-179 85-109 (15 mm.) 189-191 (10 mm.)
. . . . . . . . . .
. . . . . . . . . .
128.7 15.4 20 Mesityl oxide 190-212 . . . . . Solvenol No. 1 91.6 7.2 20 Ethyl sulfide a Viscosity determined b y A. S. T. M. method at 35O C. f Hard precipitate a t 2 5 O C. ~7 Soft precipitate a t 25" C. I Solid, clear gel.
104,000 37.78 104,000 37.78 io4,ooo 37.78 104.000 37.78
0.736 0.876 0.969 1.42
0.736 0.736 0.950 . . . 1.12 1.11 4 . 0 0 15.49
454 478 484 490 514 440 627 800
1213 1543 1752 1771 1933 1628 2280 2700
104,000 37.78
7.84
8.27
9.63
. . . . . . . . . . . .
1780 2337 2500 2900
. . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..I.
.I
779.0
I749
l9i7
48.9
....
..
.. .. ..
5665
1.16 495 16.1
..
.. .. ..
i.'is i:ia
..
..
i.'i6
16.7
16.8
16.9
2044
I
.
13,778
.... .,.. .... .... ..
..I ....a
7,461 18,555
... .J . . ..f ., . . I . . . .k .. ..I . . . .* .... . . , .i ....
.. ..I
. . ,.I .... ....
....
. . . . . ...I . . . . . . . .J
.. .. .. ..
....
. . . . . . . . . . . . 15.3
. . .d
I .
. . . . . . . . . .
.......
3,5256
........
I
. . . . . . . . . . . . 1.13
3,150
........
. . . . . . . . . . . . . . . . 17i9 .. .. .. ... .. . . . 1868 .. .. .... ... .... .. . . . .. .. .. .... ... .. .. .. . . . 1247 . , .... .. . . . 1171 .. .... ... .. .... . . ... .. .. .. .... ... .. .... ... .. .... ... .. . . ... .. .. .... .. .. .. i i 3 7 . . . . . . , . .. .. .... ... .. .. .. .... ... . . .... ... .. .. .... .. .... .. 38i: o 3220 ....
124' .':: . . . . . . . . . . . . . . 262 ...
12.18
2660 5040 5510
. . . . . . . .
i3:x
::::
:::I
. . . . . . . . . . . .
...
. . . . . . . . . 46.2
1 : :: 1::: ........
. . . . . . . . . . . .
...
:I::
1.12
. . . . . . . . . . 3092 3251
. . . . . . . . . . .
ETHERS
Ethyl ether n-Butyl ether n-Amyl ether Isoamyl ether
. . . . . . . . . .
. . . . . . . . . . . .
501 372 145 152 185 292 300 259 370 625
. . . . . . . .. . h
577 433 627 641 546 671 761
.. I
.
.. 1 .
. . . . . ...I . . . . . ...k . . . . . . . .L
... ... ... ............ ...I ........ . . . . . . ..I .... .._..I . . . . . ., . I 1.17f . . . . . . . .I
1.17
17.2
17.4b
MISCELLANEOUS 104,000 37.78 0.642 0.643 0.643 0.643 . . . . . .. 104,000 37.78 1.04 9.47 .. I io4,ooo 3 7 . 7 s 0.502 3.49 i4:d i.i.'i 1 9 s ' .. .. ........ D445-38T (1938). b Blue haze a t 25' C. C Blue haze a t 2OO.C; d Precipitate at 25O C. e Clear and soft precipitate. h Soluble at 66- C. 6 Soluble a t 25' C. 3 Precipitate a t 10' C., blue haze a t 25O C. k Soft
of =+=0.02'C. Timing was by a split-second precision electric timer read to *0.05 second. ALCOHOLPRECIPITATION. As a check or comparison on the viscosity determination, a modification of the alcohol precipitation method of Erbring (1) was used to study the stability of each polymer solution at 25' C. The general object of this test was to study the r c e d u r e of Precipitation of Polybutene In
several solvents w en alcohol was added. The precipitation was observed optically by measuring the intensity of turbidity with increasing concentrations of alcohol. All measurements
,
~80
.. .. .. .. .. .. .. ..
were carried out with the Kober nephelometer ( 3 ) . The end points obtained were sharp and could be reproduced within an accuracy of about 2 per cent.
Viscosity-Concentration Relationship Table 1summarizes the viscosity concentration determinations on a number of Solvents Using, in the main, a polybutene of 104,000 molecular weight. The viscosity was deter-
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1942
SOLD C L W GEL FORAE
OF CHANGES IN VISCOSITY OF POLYMER TABLE 11. COMPARISON SOLUTIONS" WITH ALCOHOL NUXBER
N d C at 25O C.
Solvent
465
FIGURE
MI. 2-Ethyl Butyl Alqohol to Form 400V0 Relative Turbidity in 25 M1. Polymer Soln. at Room Temp.
7
,/
'JISCOSITf 01 POL'fEUTlWENORMAL 6TWL E M BLENDS
2-
IO( 50
B
C o n c e r k i o n of pplymer (104,000 mol. wt.), 10 grams per liter.
b Turbid solution agitated before viscosity determination.
3
B mined a t 37.78' C. for the solvents with high boiling points and a t 20' C. for the solvents with relatively low boiling points. Table I and Figures 1 to 6 illustrate the difficulty of any solubility determination from these data alone. Poor solvents, such as the alcohols, esters, low-molecular-weight ethers, and some chlorinated hydrocarbons, identify themselves by precipitation; the poorest of these are identified by their inertness to the polybutene itself. The. slopes of the viscosity-concentrationcurves of some of the solve& following a general deviation from the Arrhenius equation (log N = K C ) tend to drop rather suddenly in the higher concentrations and thereby form plateaus on the curve a t concentrations greater than about 50 gramwper liter. We had thought it might be possible to determine the plateau for each solvent and in this way classify them in order of solubility by the concentrations which could be attained before this phenomenon took place. This idea had to be revised when it was discovered that the determination of viscosities in this range was difficult with the available equipment, and the results themselves were not always reproducible. OF POLYBUTENE SOLUBILITY AS DETERTABLE111. DEGREE MINED BY N,,/C VALUES" AT 100' F. (37.78' C.)
Parsffins
n-Hexane n-Heptane Hydro Co. trimer Isooctane Kerosene *Octane Varsol No. 2 Olefins Dimer (diisobutylene) Trimer (triisobutylene) Naphthenes Math lcyclohexane cvoloiexane Aromatics Benzene Toluene 180 ropylbenaene xyfene Cymene Mesitylene n-Pro ylbenzene Amylgenzene
Nsp/C
0.495 0.595 0.656 0.734 0.734 0.744 0.816 0.764 0.764 1.08 1.26
0.296 0.423 0.624 0.688 0'689 0'6g0
8:;:
NadC Chlorinated hydrocarbons Amylene diohloride 0.474 Chloroform 0.608 0.614 Isobutyl chloride n-Amyl chloride 0.618 0.666 Pentachloroethane s-Dichloroeth lene (48) 0.694 0,720 Trichloroethyrene 0,726 Carbon tetrachloride Perchloroethylene 0.995 Ethers n-Butyl ether 0.342 0.520 %-Amylether Isoamvl ether 0.556 Ester Isoamyl caproate 0.182 Miscellaneous Ethyl sulfide 0.596 Solvenol No. 1 0.811 0 Viscosities determined on polymer (104,000~mol.wt.) solutions at a concentration of IO grams per liter.
The gradual reduction of the slope of the curves as the concentration is increased can be explained by any of the discussed theories which seek to explain the reduction of the thickening power of the polymer. As the slope of the curve approaches zero (Figures 1 to 6), the system is unstable, viscosities are susceptible to mechanical treatment (for example, it was possible to increase a 11.75 gram per liter blend of polybutene in benzene from 2.17 to 4.60 centistokes a t 25' C. by violenbagitation), .and'precipitationis observed in(the-lower viscosity blends.
I
f
1
f
2-
IO5-
2**vIs60SITy OF hORhL4L KTYL ETBR 0 37.78°01'
I --
10
0.766 CZSTIS.
I
I
I
20
30
40
I
50
60
G. 104,000 MOL. ' X . POLE3WIS/LITER OF N O W U 2U1?z
Figure 7 To observe the effect of solution concentration above this plateau, Figure 7 pictures the viscosities of various concentrations of polybutene in n-butyl ether. Above the unstable range a third system about as stable as the first is formed. It is thought that this third system may follow some plasticity law up to the viscosity of the solid polymer. Also, for this solvent a solution with about 40 grams of polymer per liter shows a slight change in viscosity over the temperature range 20" to 37.78' C. A possible explanation for this phenomenon is that the polymer is present in poor solvents in two phases-a molecularly dispersed polymer-in-solvent phase and a mechanically dispersed solvent-in-polymer phase within the first phase. Accordingly, an increase in temperature will reduce the second phase and, by increasing the first phase, will increase the overall thickening effect of the polymer. As the concentration-viscosity curves could not in themselves be used to classify the solubility of the various solvents, alcohol precipitation experiments were run on several of the 10 gram per liter solutions; these results checked with the calculated N,,/C values (Table 11). I n a general way the results give excellent correlation with observed solubilities in higher concentrations of these several solvents. For example, the data in Table I1 indicate that a small amount of alcohol will precipitate the polymer from benzene, and the data p r e sented graphically in Figure 4 show that the benzene-polymer solution deviates at an approximate concentration of 70 grams per liter from the Arrhenius equation. The change in slope of the lines a t a concentration of 70 grams per liter is more apparent for benzene than the other aromatic solvents tested. Therefore, the calculated Ns,/C value was used for solubility comparison, which gives an easily determinable re-
I N D U S T R I A L A N D E N G I N.E E R I N G C H E M I S T R Y
466
TABLEIV.
SOLUBILITY BEHAVIOR OF POLYBUTENE IN CHLORIHYDROCARBONS AT ROOM TEMPERATURE
NATED
Methylene chloride Chloroform Carbon tetrachloride s-Dichloroethylene (48) s-Dichloroethylene (60) Trichloroethylene Perchloroethylene Ethylene dichloride 8-Trichloroethane s-Tetrachloroethane Pentachloroethane Isopropyl chloride n-Propyl chloride 2,2-Dichloropropane 1,2-Dichloropropane Isobutyl chloride *Amyl chloride Amylene dichloride
Polymer not sol. Polymer sol. Polymer sol. Polymer sol. Polymer not sol. Polymer sol. Polymer sol. Polymer not ,901. Polymer not sol. Polymer not sol. Polymer sol. Blue haze at 25’ C. Polymer sol. Polymer not sol. Polymer not sol. Polymer sol. Polymer sol. Polymer sol.
sult for each solvent. These data are listed in Table 111. The solvency of polybutene in the chlorinated hydrocarbons is not too well understood. Because of the high density of these solvents, our usual method of solution could not be used, and some mechanical agitation had to be resorted to. This may be the cause of some of our viscosity inconsistency. No tests were made for possible breakdown. Data in Tables I and IV show that the chlorinated paraffins with dielectric constants above about 8.0 are generally nonsolvents. This dividing line is rather sharp. As no other group of solvents had members above and below this figure, we were unable to check the over-all effect of dielectric constant. Following
Vol. 34, No. 4
Erbring’s reasoning, it should be possible to forecast optimum solvent-nonsolvent ratios for low-viscosity solvent blends when the minimum dielectric constant has been determined, An illustration of the importance of dielectric constant in solubility work is the data on the isomers of dichloroethylene which show that the isomer having a dielectric constant of 2.4 was a polybutene solvent, whereas the isomer having a constant of 9.4 was not effective. Polybutene is insoluble in the low-molecular-weight alcohols; however, as might be expected, the solubility increases as the molecular weight of the alcohol is increased. Polybutene of 12,000 molecular weight is soluble in heptadecanol as high as 100 grams per liter. Polybutene (104,000 molecular weight) increased the viscosity of heptadecanol while in contact with it, but even as low as 10 grams per liter would not completely dissolve. The latter sample, after being held in contact with heptadecanol for about 12 weeks and then separated, was analyzed to have a molecular weight of 174,000; this illustrates the fractional solvation of the medium,
Literature Cited Erbring, H., Kolloid-Z., 90, 257-68 (1940). Huggins, M. L., J. Applied Phys., 10, 700 (1939). Kober, P. A., J. IND. ENG.CHEM.,10,556 (1918). Lovell, E. L., and Hibbert, Harold, J. Am. Chem. Soc., 62,2140, 2144 (1940). Staudinger, H., and Schneiders, J., Ann., 541 (a), 151-195 (1939). Taylor, H. S., “Treatise on Physical Chemistry”, 2nd ed., Vol. 11, p. 1616, New York, D. Van Nostrand Go., 1931. Thomas, R. M., Zimmer, J. C., Turner, L. B. Rosen, R., and Frolich, P. K., IND.ENG.CHIM.,32, 299-304 (1940). Turkevich, h t h o n y , and Smyth, C. P., J. Am. Chem. Soc., 62, 2468 (1940) : Schwarzenbek, E. C., personal communication; International Critical Tables, Vol. 6, p. 82 (1926).
Solvents and Plasticizers for Chlorinated Rubber
Critical D a t a
J. W. RAYNOLDS’
M. R. RADCLIFFE AND M. R. VOGEL
M e l l o n Institute, Pittsburgh, Penna.
Binney and Smith Company, Easton, Penna.
ALOGENATED rubbers have long been known, but H only the chlorine derivatives have become of commercial significance. There are three fundamental modifications in which chlorine is combined with the rubber hydrocarbon to form useful synthetic resins. 1. Rubber hydrochloride (3) is the reaction product of rubber and dry hydrogen chloride. The chemical reaction is one of addition where hydrogen chloride combines a t the double bonds of the rubber hydrocarbon. Theoretically the chlorine content may reach a total of 34.8 per cent. Commercial products usually contain from 28.5 to 30.0 per cent combined chlorine. Rubber hydrochloride is characterized by extreme flexibility, thermoplasticity, and low solubility in a limited group of solvents such as benzene and chloroform. The principal commercial use of this product has been in the manufacture of transparent wrapping film and sheeting. 2. Chlorinated rubber hydrochloride (2) is made by chlorination of rubber hydrochloride. By this reaction the final 1
Present address, T h e Raolin Corporation, Easton, Penna.
chlorine content may be raised to a total of about 40 per cent. Products of higher chlorine content have been reported but are not manufactured. As the chlorine content increases, the usual processes become uneconomic for commercial production. 3. Chlorinated rubber, sometimes called “rubber chloride”, is the product prepared by the treatment of rubber with chlorine gas. The chemical reaction, which takes place both by addition and substitution, may continue until the final chlorine content is as much as 72 per cent. Commercial products (1) now on the market usually contain between 65 and 68 per cent chlorine, for it is within this range that the economic production of a stable product is obtained. Chlorinated rubber of 65 to 68 per cent chlorine content is soluble in a wide variety of organic solvents. It is a hard and brittle film-forming resin and with proper treatment may be plasticized to yield highly useful coatings for a wide variety of industrial applications. The chemical resistance of chlorinated rubber is outstanding; clear, unplasticized films have unusual
