Swelling of Silicone Elastomers RAT L. HAUSER', CHARLES A. WALKER, .4ND F. L. KILBOURNE, JR. D e p a r t m e n t of Chemical Engineering, Yale University, and Connecticut Hard Rubber Co., New Haven, Conn. \
s
IVELLISG phenomena, although deleterious in physical
effects, provide one of the principal opportunities for studying the physical and thermodynamic properties of crosslinked polymers. The classical swelling methods of Scott ( 1 7 ) and Gee ( 7 )and the theoretical equations of Flory (6) and Huggins (9) are well established in the field of polymer chemistry. The solution properties of various dimethylsiloxane polymers have been reported by a number of investigators. Bueche (5)has reported a study very similar in results but different in method from the work herein described. The relations between intrinsic viscosity and molecular weight of linear polydimethylsiloxane have been reported by Flory and others (6). Reported values of solubility parameter for this polymer range from about 5.0, calculated from Wilcock's ( 2 1 ) vapor pressure data, t o 7.7 (cal./cc.)1'2, estimated by Bueche (S). Polymer-solvent interaction coefficients, p (in equations of Flory and Huggins), are given by Scott ( 1 6 ) as 0.498, from osmotic pressure of methyl ethyl ketone solutions, and by Osthoff and Grubb ( I S ) as 0.28, from the vapor pressure of octamet,hylcyclotetrasiloxane solutions; Bueche (3) gives values for several solvents which are based upon p = 0.465 for toluene as determined from light-scattering measurements. The methods of the present study depart considerably from established procedures, in that the swelling of polymer samples was measured volumetrically. Approximate values of Mc,the molecular weight between cross links, were calculated for silicone elastomer vulcanized with various concentrations of dibenzoyl 1
Present address, University of Colorado, Boulder, Colo.
peroxide. Values of interaction coefficients are given and compared Kith those of other investigators; and a new method for determining the solubility parameter of a polymer is presented, using the authors' swelling data and those of Bueche (3). PREPARATION OF TEST SAMPLES
A commercial silicone elastomer, SE-76, produced by the General Electric Co., was used for all swelling measurements; this material was chemically similar to the polydimethylsiloxane used by Bueche (5)but probably differed in average molecular weight and molecular weight distribution. The viscosity-average molecular weight) of the raw unfractionated polymer was determined ( 1 5 ) t o be 480,000 by the equation obtained from Flory and others (6) for dilute met,hyl et.hyl ketone solution a t 26" C. log [ 7 ]
=
-3.1781
+ 0.522 log M
(1)
where [v]is the intrinsic viscosity and -If is the viscosityaverage molecular weight. This material probably contained more low molecular weight polymer than that used by Bueche, which had a weight-average molecular weight of T80,OOO as determined by light-scattering measurements. The elastomer was milled with 2.0% dibenzogl peroxide (except where specified otherwise) and vulcanization took place with press cure, 15 minutes a t 250" F., followed by oven cure, 24 hours a t 300" F. From the vulcanized elastomer, test samples were cut 8/4 X X 0,070 inch and a l/ra-inch hole was punched in one end of each. Polymer density was determined by pycnometer to be 0.976. IMMERSION TUBES
Sample
j=So,"e"+ F i g u r e 1.
Cross-sectional view of immersion t u b e
Cap and hook portion are removable from immersion chamber. Calibrated male is placed along lower portion of capillary side arm t o right. Illustration is drawn t o seale. Total height of tube is about 10 inches
-4new type of ininlersion tube was designed and constructed in order t o provide I apid and accurate measurements of swollen volume of the elastomer samples while avoiding the possibility of solvent evaporation or contamination. Although very different from the voluminometer designed by van Wijk ( 1 9 ) , the apparatus employed the same principle of liquid displacement and \vas similar in some respects t o the instruments of Rostler ( 1 4 ) . Figure 1 shows a cross-sectional view of the glass immersion tube. Volume measurement was based upon displacement of a discernible volume of solvent vihich was being used as the swelling medium. The lo\Ter portion of the tube F a s filled with solvent to a convenient level, as indicated by the meniscus position in the lower portion of the capillary (2-mm. uniform bore) side arm. At any level of liquid in the main chamber (within the limits of measurement) there existed a corresponding level of the liquid in the side arm; and, because the side arm Fits inclined approximately 5' from the horizontal, a level change in the immersion chamber caused a 12-fold greater change of the meniscus position in the side arm. Thus, placement of a small rubber sample within the main tube, or removal therefrom, resulted in a considerable change of liquid level in the side arm. Capillary rise in the side arm amounted to 1.6 t o 2 inches, depending upon the solvent, and was assumed t o remain constant throughout the range of measurement for a particular series of tests. The removable cap and hook portion of the immersion tube 1202
July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
performed a triple function: suspension of the sample in the solvent, removal of the sample for volume measurements, and sealing of the tube with a mercury well to prevent excessive vapor loss. The immersion tube was clamped onto a mounting arm (Figure 2), which held it in position by means of two pins and provided initial screw adjustment of the side-arm slope. Onto the face of the mounting arm was cemented a strip of green millimeter graph paper which was numbered for calibration. Lines on this scale were easily visible through the capillary tube and readings of liquid level were estimated to the nearest 0.1 mm. with the aid of a jeweler's lens. The upper return half of the capillary was calibrated in centimeters as a guide to the eye for making readings perpendicular to the face of the millimeter scale. Six immersion tubes mounted upon a heavy steel plate were placed radially about the central control unit of a constant temperature bath. The lower portion of each tube passed through the plate and was kept a t 25" i 1' C. The pins in each mounting arm were fitted into holes in the mounting plate and a supported, spider-shaped guide frame prevented accidental tipping of the tubes, yet permitted facile removal for cleaning. Figure 3 presents a cross section of the mounting unit, and Figure 4 illustrates the setup with the immersion tubes in operating position.
1203
Stirrer (Mounted Independently) W
- P l a y
- 1
Fe nw a 1 I T her rnoregulator Water Bath 11
Figure 3.
Schematic cross section of mounting unit for immersion tubes
CALIBRATION
Calibration of the tubes to relate volume within the immersion chamber t o liquid level in the side arm was effected by dropping uniformly sized metal pellets into methyl ethyl ketone contained in the chamber and by reading the scale according to the new meniscus position obtained upon the addition of each pellet. As initial volume of each sample was determined most accurately by weight and density measurements, the calibration curves were related to absolute volume by frequent weighings of polymer samples during the swelling tests and by volume calculations from solvent and polymer density. For these weighings, each swollen elastomer sample was held immediately above the immersion chamber (in an atmosphere saturated with solvent vapors) and permitted to drain off excess solvent; the sample was then placed in a tared weighing bottle containing the same swelling agent. This procedure helped prevent the frequent errors which arise from too much surface solvent or, a t the other extreme, excessive solvent absorption or evaporation and attendant deswelling. (The errors arising from deswelling during dry weighing are too frequently ignored. With solvents as volatile as benzene, the deswelling during l minute can be equivalent to the incremental swelling of 24 hours; hence the practice of blotting and/or dry weighing may substantially alter the slope as well as the magnitude of the incremental swelling curve.)
Some tubes are being cleaned, others are in operation with samples immersed in benzene. Liquid level in side arm of tube at left front is visible
out immersion periods of 5 minutes to a t least 140 hours. All tests were performed in duplicate and the accuracy of volume measurement was considered 170 during the slotv incremental period of swelling. Even though the mercury seal in each immersion tube served its purpose well, some evaporation of solvent occurred during the measurements, so that concurrent determination of partial volume change wa3 impractical with this apparatus. The change of partial volumes during swelling is usually neglected. After each use, immersion tubes were twice rinsed with solvent, acetone, and water and then filled with sulfuric acid-dichromate
*
VOLUME MEASU-REMENT
Initial volume of the samples was determined via weight and density. After the fresh swelling agent in the immersion chamber had reached the controlled temperature of 25' C., the sample was placed on the wire hook and immersed in the swelling agent. At selected time intervals, the meniscus position was read on the scale, the sample was lifted from the solvent and permitted to drain, and the scale reading was again noted. The swelling rate was thus followed for all polymer samples and solvents through-
Slope Adjustment S c r e w s - m
J u b e Clamo
J
Figure 4. Apparatus for measuring swell of silicone elastomers in solvents
- - -
-
Figure 2.
Scale
Immersion tube mounting a r m
Bolts at right adjust inclination of side arm
b
INDUSTRIAL AND ENGINEERING CHEMISTRY
1204
cleaning solution for a day. Preparation for the next test involved thorough rinsing with distilled water, acetone, and then the next sxelling agent. SW ELLIXG AGENTS
811 the common solvents were of reagent purity and most weie redistilled before use as sm-elling agents. The perfluoro (methyl)cyclohexane was D u Pont FCS 326 and of unknown, but satisfactory, purity for this study. RATE OF POLYMER EXTRACTIOh
Early in the course of this study it became apparent that a measurable amount of polymer was inevitably extracted by the solvent from the swollen elastomer. Because this removal of material affected the exact determination of v2, the volume fraction of polymer within the sn-ollen network, the extraction phenomenon was considered in conjunction with each swelling test. This extraction process could arise from the presence of nonvulcanized molecules entrapped among the cross-linked systems, from breakdoxn of the polymer network during smelling, or from both causes The former cause would permit extraction of a limited amount of unattached polymer; the latter would lead t o continued extraction throughout the total period of saturation with swelling agent. Several weighed samples of silicone elastomer Rere immersed in benzene a t 25" C. and after specific time intervals they mere removed and dried t o constant n-eight. The loss of weight during immersion was, of course, the amount of polymer extracted from the swollen network. Extraction rates in benzene a t 25' C. for three silicone elastomers are shown in Figure 5 . As expected, the extraction was greatest for the least tightly cured elastomer (sample A, 0.5Y0 benzoyl peroxide vulcanizate), Yhich lost 197, of its weight after 180 hours' immersion. The rates of extraction were approximately exponential. Of greatest significance here is the continued extraction of sample B (2.077, benzoyl peroxide) throughout the total 1250 hours of immersion in benzene. Similar samples, which were given an accelerated extraction by benzene using Soxhlet apparatus a t higher temperature, failed to attain constant weight after 350 hours. The authors conclude from these results that polymer extiac-
Figure 5 .
Vof. 48, No. 1
tion during swelling is probably due t o both of the causes mentioned above. The amount or rate of p o i p i e r extraction was ascertained for all swelling tests and the svielling data were corrected for this effect as explained below. Correction involved the use of a fraction based upon extraction data:
V,
-
V,
=
volume of polynier after immersion volume of polymer prior to immersion
Effect of Dibenzyl Peroxide Concentration on Swelling. Silicone elastomers are normally vulcanized with about 2 parts of benzoyl peroxide per 100 parts of polymer; higher concentrations do not produce a significantly tighter cure, and smaller amounts may lead t o incomplete cross linking. Extreme concentrations of 0.5, 2.0, and 8.0 parts per 100 weie chosen for this study and elastomer samples were swollen in benzene. Swelling curves n-ere plotted in logarithmic coordinate. Figure 6 illustrates the method by which swelling and extraction data were combined t o obtain z 2 as a function of immci sion time. The swelling data were eypressed by a fraction:
-VVib_,
volume of sample prior to immersion volume of sir-ollen sample
Sample A, vulcanized with 0.5% benzoyl peroxide II Sample B. vulcanized with 2.0% benzoyl peroxide Sample C, vulcanized a-ith 8.0Vo benzoyl peroxide
4)
(3)
whose product n-ith F p / V Ofrom extraction data satisfied the proper definition of V Z , volume fraction of polymer within the swollen network, as given by Flory ( 5 ) . (For routine tests these data were plotted on three-cycle logarithmic graph paper and the multiplication step involved mere addition of logarithms with the aid of dividers.) The exponential nature of the initial and incremental portions of this swelling curve was repeated throughout practically all ininvestjigations of this study. Log-log linearit'y was found over swelling periods of 5 minutes t o about 4 hours and again from about 8 hours t o duration of immersion, which v a s generally about 145 hours; for one sample ( 2 7 , benzoyl peroxide) this was continued throughout 1250 hours in benzene. The continuance of sn-elling after the polymer sample has reached an "equilibrium" ~ o l u m eis usually attribut,ed to oxidative breakdon-n of the cross-linked network (17, 1 8 ) . For a silicone elastomer that is highly resisrant to ozone attack, the likelihood of oxidative breakdowi j s small; however, hecause the tensile strength of the elastomer lyitliout reinforcing pigment is very
Rates of extraction of polymer f r o m swollen samples diiring irrlnlersion in benzene
A
(2)
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1956
1205
I .o
0.6
1.0 0.6
0.4 0.2 0.1 0.06
I .o
IO DURATION OF SWELL-HOURS
0.1 Figure 6.
100
Swelling rate of sample A (Table I) in benzene
---
Extraction data, Vp/Vo, of upper curve were eombined with swelling data, 0 Vo/Va, center, t o obtain UPi n lower curve as function of time
low (about 25 pounds per square inch), a mechanical breaking of stretched polymer chains or cross links is quite probable. The extreme case illustrated in Figure 6 pointedly emphasizes the need for correlation of extraction data for accurate swelling results, as the volume of this sample decreased after the first 40 hours of immersion. Extrapolation of the raw swelling data, V,/V,, to zero time on linear coordinates could lead to rather embarrassing results if extraction corrections were ignored. To determine the equilibrium volume fraction of polymer within the swollen network, UZ, for use in the Flory ( 5 ) M c equation, the incremental portion of the V,/Vs = uz curve was plotted on rectangular coordinates and then extrapolated linearly to zero time in accordance with the usual procedures. An alternative possibility for defining an equilibrium value of v2 may be obtained by extrapolating toward each other the two linear portions of the swelling curve of Figure 6 . The value thus obtained differs only slightly from that resulting from the standard practice, but such a procedure is not yet to be recommended unless theoretical justification is possible. The equilibrium values of v 2 are listed in Table I and the values of M,, the molecular weight between cross links, are expressed as functions of the polymer-solvent interaction coefficient, p , according to the Flory ( 5 ) equation for a n assumed tetrafunctional network
M, =
-dLVl(L.II 3
In (1 - u d where dz = polymer density and VI = molal volume of solvent. Using Bueche's (31value of p = 0.52 for benzene and polydimethylsiloxane, M , for sample A would appear to be 533,000, or slightly larger than the viscosity-average m o l e c u l a r . weight (480,000) of the linear polymer prior to cross linking. This apparent discrepancy is not serious because, especially for sample A, a small error in
-
2)
+ + pvzZ
either v z or p causes a manyfold larger error in the value of M,.. Moreover, the fact that 19% of the polymer of this sample was extracted by the swelling agent, indicates that many of the smaller molecules were not vulcanized into the system and hence average molecular weight is higher after swelling than before vulcanization. Nevertheless, this test gives some evidence that p should be less than 0.52 for benzene and polydimethylsiloxane. Interaction with Swelling Agents. Samples of silicone elastomer vulcanized with 2% of benzoyl peroxide were swelled in the ten organic solvents listed in Table 11. Eight of these swelling agents were hydrocarbons. The ultimate extraction of polymer a t 145 hours varied according to solvent from 0 to s'%, and swelling measurements were again corrected for the extraction influence. Log-log linearity of
(4) a
LZ
Table 11.
Table I.
Effect of Benzoyl Peroxide Concentration
Sample
Parts Benzoyl Peroxide
~a
A
0.5
0.080
B
2.0
o'206
C
8.0
0.229
Me 5330 0.532
533,000
O T'Oo0 8 c p 838 O T
14,700
~
-p
12,000
Based on p = 0.52 given b y Bueche (3).
Swelling of Polydimethylsiloxane by Solvents VlO,
M ,a
61a
Swelling Agent Cc./iitole (Cal./C6.)1/2 90.16 9.22 (t) Methyl ethyl ketone 89.40 9.16 Benzene 106.85 8.91 Toluene 123.46 8.82 Xylene 162.2 (11) 8 . 5 (18) d-Limonene 108.74 8.20 Cyclohexane 128.33 7.83 AIethyloyclohexane 163.52 7.55 n-Octane 131.60 7.27 ?&-Hexane 195 (8) 6 . 0( 8 ) Perfluoromethylcyclohexane o Physical properties calculated from (IO,18) unless otheruh 5 Based upon fi = 0.465 from Bueche (3) for toluene.
v1
0.285 0.206 0.170 0.182 0.183 0.148 0.137 0.141 0.138 0.98
va ( 3 )
0 : ik9 0.170
...
0: i44 0.136 0 : i4o
e specific?d.
...
p h,
Approx.
0.588 0.536 0.466 0.484 0.450 0.433 0.378 0.361 0.369 3.0
-
Me('/z p) Approx. 55s 1000
1695 1728 2250 2210 2960 3626 3000 85
Vol. 48, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
1206
EXTRACTION DATA i .o
Vp VO
--
e
VOLUME OF POLYMER ORIGINALVOLUME I..
0.9 I .o 0.6 0.4
V,
SWQLLEN VOLUME
-
vp
VOLUME OF POLYMER
-
0.2
0.8
SWOLLENVOLUME -
0.4
0.2 0.12
0.1
1.Q
10
100
200
DURATION OF SWELL-HOURS Figure 7 .
Extraction and swelling curves for silicone elastomer in four solvents listed in Table I1 A V
Methyl ethyl ketone Benzene Xylene
@
n-Hexane
Results from other swelling agents presented curves of similar nature
swelling rate was again observed during initial and incremental swelling periods for all solvents. Figure 5 is repiesentative of data obtained with four of the swelling agents. After 24 hours’ immersion in methyl ethyl ketone, measurable deswell of the elastomer sample was observed; however, the corrected value of v2 was constant or showed a slight decrease during the incremental period. Reversal of the TJa/Vs slope for the samples in methyl ethyl ketone is more evident fiom the swelling data presented in Table 111. These are the original data from two different immersion tubes and they illustrate the good precision of measurement obtainable with the immersion tubes, particularly during the period of incremental swell
Table 111. Time, Min. 5
10 20 30 40 50
60
:6
105 120 Hours 2.5 3.0 3.5 4.0
Swelling of Silicone Elastomer i n Ifethyl Ethyl Ketone I ’ d V8 Tube I1 0,764 0.745 0.658 0.660 0.555 0.555 0.501 0.501 0.460 0,466 0.434 0.439 0.420 0.419 0.396 0.399 0.385 0.380 0.374 0.365 0,359 0.353
Time, Hours 4.5
0,349 0.340 0.328 0.322
Tuber
0.338 0.327 0,319 0.313
rO/T-6
48.0 49.2 72.0 73.3 120.0
Tube I 0.322 0.312 0.307 0.298 0.802 0.298 0.308 0,298 0,298 0.300 0.303
Tube I1 0 309 0 304 0.302 0 294 0 294 0 293 0.297 0 297 0 298 0 298 0.302
121.0 143.0 144.0
0.301 0.304 0,304
0.300
5.0
5,5 23.0 24.0 25.0
0.300 0.300
The polymer-solvent interaction coefficient, p, defined by Flory’s equation, was calculated for each swelling agent using the value given by Bueche ( 3 ) (obtained from light-scattering measurements) for polydimethylsiloxane and toluene, p = 0.465. The authors consider that this value is a little too high and prefer to state only “approximate” to the other values of ,u listed in Table 11. As Bueche (3)has pointed out, however, even though the exact magnitude of these values may be in question, their relative values are proper. Despite the use of polymer batches with dissimilar molecular weights and vulcanization with different concentrations of benzoyl peroxide, Bueche and the authors obtained networks with This is apparent from virtually identical effective values of ~11~. the close similarity of values of 212 obtained by the independent investigations and by very different procedures. The average difference of results obtained with the five common swelling agents was 1.6%. DETERMINATION OF SOLUBILITY PARAMETER
I n Table I1 the solvents are listed in order of decreasing solubility parameter, 61. Inspection of this table and of the Gee ( 7 ) curve of Figure 8 reveals a ragged correlation of smell, UZ, with 61, from which estimation of polymer solubility parameter, 82, is difficult and subject to considerable error. The plotting of zi2 opposite or an assumed T71 ( & - 6 2 ) 2 , as recommended by Gee as a secondary refinement, is only partly commensurate with the Hildebrand (8) concept that
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1956
(5)
-
350(
A more revealing and theoretically accurate procedure for graphical determination of of the Flory equation:
82
‘?
* I
is obtained through approximation
1201
300C
Q I -IN
E50C
r”
which is mathematically valid only for small 02. This approximation is nevertheless of value for any value of v2, because it permits direct calculation from swelling data of the function:
11 2000
-ia“
(7)
F
For any series of swelling testa for which the polymer’s M , is constant, this relation provides a function whose relative value is dependent only upon the solvent and its interaction coefficient,
c5
NI‘
1500
I
-P
iiN
P.
Y
Values of this function are presented in Table I1 and plotted in Figure 8 for comparison with the Gee curve. D a t a calculated from the swelling study of Bueche ( 3 ) are included with the authors’ in this graph. The swelling results from the siloxane fluids used by Bueche ( 3 )deviate considerably from the pattern presented here, as they did from Bueche’s analysis. Mathematical treatment assuming
2
and the above Flory approximation indicates that the slope of the 2Mc KV1 (” . This would be a pure paracurve should be -
RT
bolic form (if VI were constant for a series of solvents) and zero slope would be found a t the maximum where 62 = 61. Furthermore, this parabola would be symmetrical about 82. However, the nature of mathematical error involved in Flory’s approximation and the well-known anomalies in the above relation for p combine t o yield from experimental results two nearly straight lines which intersect a t a very definite maximum of M c ( ’ / 2 - p ) a t the solubility parameter of the polymer, (s2. The solubility parameter of polydimethylsiloxane obtained in this manner is 7.5 (cal./cc.)1’2. An alternative determination, based upon results from n-hexane and methylcyclohexane which p ) , yields 82 = 7.6 by the gave comparable values of M , ( I / z principle of symmetry. (The close similarity of Vi for these two solvents permits assumption of a parabolic form.) These values may be compared with others from swelling measurements, by Boyer (20)7.35, and by Bueche ( 3 )7.7, whose estimate was based upon the same data recalculated by the authors for Figure 8.
0.20 1000
U
\
\
\
0.15
‘a
50c
0.10
0
Relation of swell of silicone elastomer to solubility parameter of solvent
Figure 8.
-- - Method right ordinate, according to basic procedure of Gee (7) proposed by authors based on approximation of vz,
F0
Flow (5) equation Swelling data of authors Swelling data of Bueche (3)
THERMODYNAMIC EFFECTS OF DISSOLVED POLYMER
The authors have made no attempt to alter the Flory equation to consider the thermodynamic effects of dissolved polymer on the swelling of an immersed sample. The free energy of swelling in a pure solvent differs from that in a dilute solution containing a
-
RELATION OF
p
TO
81
The values of polymer-solvent interaction coefficients as listed (81 - 7.55)2 in Table I1 are plotted against 0.25 in Figure 9.
+ v,
RT
Huggins (9) and Gee (7) have expressed p as a function of both heat of mixing and entropy of mixing. For the swelling data obtained in this study, their definitions of p for the assumed tetrafunctional network are virtually equivalent to the abscissa used in this graph. Whereas these theories propose a straight-line relationship with slope equal t o unity, the data of Figure 9 present a smoothly continuous but distinctly nonlinear relation. The values of p given by Bueche ( 3 )fit the authors’ curve of Figure 9 fairly well, except for those of the siloxane fluids and for that of ethyl ether, which was a relatively polar solvent included among the more docile hydrocarbons.
0.6
0.5
=t
0.4
0.3
-.-
~~
0.2
0.3
0.25 +
0.4 VI(&,
0.5
0.6
0.7
- 7.5512
Figure 9. Experimental relation of interaction coefficients to Hildebrand ( 8 ) heat of mixing term As approximated from equations of Gee (7) and Huggins (9)
1208
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
7.0
8.0
9.0
Vol. 48, No. 7
10.0
&-SOLUBILITY PARAMETER OF SOLVENT Figure 10.
Determination of polybutadiene solubility parameter
--
From data of Scott and Magat (IS) by basic method of Gee (7) procedure
---
and authors’
ACKSOWLEDGBI ENT
small amount of extracted polymer. I n this series of tests, the solution phase generally contained less than 0.1% of dissolved elastomer and less than 0.2y0in the estrenie case. Correction for these measurable effects may permit further refinement of swelling studies.
The authors wish to express their gratitude to the Quartermast,er Corps of the United States -4rmy which sponsored this research a t the Connecticut Hard Rubber Co. under E. 8.Government Contract DA-44-109-&;\I-64.
S0LL:BILITY PARAMETER OF OTHER POLY!MERS
LITERATURE CITED
The authors’ procedure for determining the solubility parameter of a polymer should be applicable to any swelling stud? with reliable data. Figure 10 illustrates this method for the swelling data of Scott and Magat ( 1 8 ) from polybutadiene and 12 solvents. Their values of 61 and i’, n-ere used for the authors’ calculations. Whereas Scott and Magat obtained 6? = 8.45 by an analytical procedure (based upon the same assumptions as the authors’ graphical method), the basic Gee plot, gives a value somewhere between 8.6 and 9.1, and the authors obtain 8.i (cal./cc.)1’2. Perhaps a number of inaccurately estimated values of polymer solubility parameters may be partly responsible for the little regard given to svrelling studies as a method for t,heir determination ( 1 , 3,4 ) .
(1) Boyer, R. F., Spencer, R. S., “High-Polymer Physics.” Chemical
IXIPROVED I&lMERSlO3- TUBES
Subsequent to the swelling study reported here, the aut’horsdesigned and constructed immersion tubes x i t h improved features. Because uniform bore throughout the immeision chamber should lead to straight-line calibration curves, the juncture of capillary side arm was placed near the bott’om of the immersion chamber. The small capillary (2 mm.) mas bent sharply upward parallel to the main tube for about 2 inches, then away from the immersion chamber a t an angle of approximately 85”. The upper half of the side arm was constructed of ordinary glass tubing about 5 mm. in inside diameter for economy and in order to avoid plugging due to condensation of vapors when the room temperature drops. Unfortunately, the convenience and accuracy of these immersion tubes have not yet been proved, principally because of the interrupting military obligation of one of the authors.
Publishing Co., New York, 1948. (2) Boyer, R. F., Spencer, R. S., J . Polymer Sci. 3 , 9 7 (1948). (3) Bueche, A . M., J . Polumer Sei. 15, 97-103 (1955).
(4) Doty, P., Zable, H.. Ibid., 1 , 90-101 (1946). Flory, P. J., J . Chem. Phys. 18, 108-111 (1950). Flory, P. J., Nandelkern, L., Kinsinger, J. B., Shultz, W. B., J . Am. Chem. SOC.74, 3364-7 (1952).
(5) (6)
, Gee, G.,
from Mark, H., Whitby, G. W.,eds., “Advances in Colloid Science,” vol. 11, pp. 145-95, Interscience, i i e w York, 1R46
Hildebrand, J. H., Scott, R. L., “Solubility of Konelectrolytes,” Reinhold, h-ew York, 1950. Huggins, A I . L., Ann. S. Y . Acad. Sei. 43, 1 (1942); IND.ESG. CHEM.35,980-5 (1943). International Critical Tables, 7701. 11, McGraw-Hill, New York, 1928.
Mitchell, A . D., Smith, Clarence, J . Chem. SOC. 103, 489 (1913).
Natl. Bur. Standards, Circ. C461 (1947). Osthoff, R. C., Grubb, W. T., J . Am. Chem. SOC.7 6 , 399-401 (1994).
Rostler, K. S., White, R. LI.,Rubber Age 5 8 , 985-9 (1946). Scala, L. C., Spencer, W. B ., Connecticut Hard Rubber Co., Kew Haven, Conn., unpublished data. Scott, D. TV., J . Am. Chem. SOC.6 8 , 1877-9 (1946). Scott, J. R., Trans. Inst. Rubber Ind. 5, 9 5 (1929). Scott, R. L., Nagat, &I., J . Polgmer Sei. 4 , 555-71 (1949). van VVijk, D. J., Rubber Chem. and Technol. 6 , 406-11 (1933). Warrick, E. L., Hunter, M . J., Barry, A . J., IND.EXG.C H E J I . 44, 2198-202 (1952), ref. 6.
Wilcock, D. F., J . Am. Chem. Soc. 6 8 , 691-6 (1948). RECEIVED for review November 9, 1955. ACCEPTED April 20, 1956. Division of Polymer Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955. Based on a thesis submitted by R . L. Hauser in May 1052 to the Department of Chemical Engineering, Yale University, in candidacy for the degree of master of engineering.
