Butadiene Polvmers and Polyisoprene J
PREPARED BY ALFIN AND EMULSION PROCESSES J. D. D’IANNI, F. J. NAPLES,
AND
J. E. FIELD
The Goodyear Tire & Rubber Company, Akron, Ohio
*
A series of synthetic rubbers (polybutadiene, butadienestyrene copolymers 90/10, 80/20, and 70/30, and polyisoprene) was prepared by the conventional emulsion polymerization process used for GR-S. For comparison a similar series was prepared in pentane solution with an Alfin catalyst (a complex of sodium isopropoxide and allyl sodium). Use of the Alfin catalyst resulted in a n extremely rapid rate of polymerization and gave 65 to 90% yield of polymer i n 30 minutes a t 30 O C. Compared to the corresponding emulsion polymer, the Alfin polymer was of much higher average molecular weight (as measured by inherent viscosity), had a higher gel content, contained substantially more external double bonds (as determined by perbenzoic acid titration), and showed lower value? for den-
sity and refractive index. Infrared absorption studies confirmed the higher percentage of external double bonds in the Alfin polymers, and indicated a greater proportion of the trans- configuration around the internal double bonds than in the emulsion polymers. X-ray diffraction patterns showed a crystalline component, in the structure of Alfin polybutadiene, the amount of which decreased with .increasing styrene content. Alfin polyisoprene and all the emulsion polymers gave amorphous x-ray diffraction patterns under test conditions. Gum and tread stocks of all the polymers were prepared for evaluation. Alfin polybutadiene exhibited higher tensile strength and improved abrasion resistance than emulsion polybutadiene, but higher values for stiffening and freezing points.
D
isoprene consumed a portion of the catalyst by metalation and other side reactions. Complete details are given in the experimental section and Table I.
URING the past decade a tremendous amount of research and development work on emulsion polymerization processes for synthetic rubber has led to the successful production of GR-S and more recently to the improved type popularly known as “cold rubber” ($4). Research interest, however, has also been shown in other polymerization techniques, such as the use of sodium (6, 17, $3) and Alfin catalysts. The Alfin catalysts were the discovery of A. A. Morton and have been the subject of intensive research by him and his associates (19). The typical Alfin catalyst is a complex of the sodium compounds ,of an alcohol and an olefin, and one with which a great deal of work has been done is the PP type (sodium isopropoxide-allyl sodium). The discovery of these catalysts, the types of compounds that form these catalysts, the methods of testing them, the unique features of Alfin polymerizations, the variations possible with different catalysts, the formulation of the catalyst complex as a doubly coordinated cyclic ring structure, and a large amount of additional research work, on organometallic compounds and their reactions with mono- and polyolefins are completely covered in the papers of Morton and his associates. It was considered of interest to prepare polybutadiene, several butadiene-styrene copolymers, and polyisoprene with an Alfin PP catalyst supplied by Morton and to compare these unusual synthetic rubbers with polymers made from the same monomers by the conventional emulsion polymerization technique. This paper describes the preparation of these polymers and compares their physical properties as the raw polymers and in compounded and vulcanized gum and tread-type stocks.
The corresponding emulsion polymers were prep’ared by the usual procedure, and pertinent data are given in the experimental section and Table 11. RAW POLYMER PROPERTIES
It was considered desirable to make a complete study of the properties of these unique polymers and compare them with emulsion polymers prepared with the same monomers. One of the most striking features of Alfin polymers is their extremely high molecular weight. Inherent viscosities, as listed in Table I, range from 10.1 to 14.5-values never obtained on similar polymers made by emulsion or other polymerization processes. Values as high as 29 have been obtained with polybutadiene prepared in this laboratory with other Alfin catalysts. Gel content for polybutadiene was high and decreased regularly for the butadiene-styrene copolymers as the percentage of styrene was increased. The butadiene-styrene 70/30 copolymer and polyisoprene were both free of gel. It has been the authors’ experience over a period of several years that polyisoprene prepared with Alfin catalysts is invariably gel-free. When the polymers were homogenized by a moderate amount (10 to 15 passes) of cold milling, the inherent viscosity values were substantially reduced. Simultaneously the gel content of polybutadiene was slightly increased, whereas the gel contents of the butadienestyrene copolymers were substantially reduced. The molecular weight distribution of an Alfin polybutadiene has been studied by osmotic pressure methods (7‘). The molecular weight of the lowest fraction was calculated to be 1,400,000,or higher than of the highest fraction of GR-S (about 750,000). Because it was not feasible to assign numerical values to the extremely high molecular weights, it was not possible to determine a precise relationship between inherent viscosity and osmotic molecular weight, as originally planned. The extremely high molecular weights of Alfin polymers are
POLYMER PREPARATION
Alfin polymers were prepared by dissolving the monomers in y t a n e and adding the appropriate amount of PP catalyst. olymerizations were carried out a t 30” C. in a thermostatically controlled water bath. Butadiene and butadiene-styrene 90/10, 80/20, and 70/30 mixtures polymerized t o conversions of 65 to 90% in 30 minutes. Isoprene polymerized to a 78.5% conversion in 1 hour. The butadiene-styrene mixtures and isoprene required more catalyst than butadiene, inasmuch as styrene and
95
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
96
TABLE I. RAWPOLYMER Charge B/S 100/0 90/10
80/20 70/30 Isoprene
Catalyst, AIL
Conversion,
22.5 26.0 30.0 34.0 36.0
65 66 90 86 78.5
PROPERTIES O F
Inherent viscosity Uninilled LIilled [XI % gel [:TI % gel
%
12.6 14.6 12.5 10.1 11.9
39.3 17.3 14.8 0 0
9.7 10.5 10.1 5.4 7.4
reflected in the difficulty in obtaining a true Mooney viscosity value. Although many determinations were made with both the large and small rotors, reliable figures were not obtained because of internal shearing and slippage of the rotor, particularly in the case of polybutadiene. The butadiene-styrene copolvmers behaved more normally and the values obtained were probably more accurate. nilooney viscosity values obtained on Alfin polymers were in the range 30 to 90 (small rotor). One test on the Olsen flow tester gave a flow of 0.005 inch per second at 212"F. and 1000 pounds per square inch, which would indicate a true small rotor Mooney viscosity of over 150.
Vol. 42, No. 1
ALFINPOLYMERS Acid Perbenzoic Oxidation,
Refractive Index a t
Iodine No.
Unsat.
% Ext. Bonds
25O C.
dZ5
463 407 362 325 360
98.9 86.9 77.1 69.2 96.4
27.5 25 5 23.0 24.0 20.0
1.5184 1,5232 1.5300 1.5371 1.5180
0.887 0.899 0,919 0.922 0.905
43.8 1.9 7.0 0 0
%
Density,
centages (40 to 60%) of external double bonds than either of the two types under discussion (4, 2.3). The differences would indicate that each type of polymer is formed by a different polymerization mechanism, particularly in the propagation step. Refractive index and density measurements were also made on these polymers to obtain information relative to molecular structure. The results agreed reasonably well with those previously reported ( 4 , 10, 16, 21, 28) except that the Alfin polybutadiene prepared for this study showed a lower density value
(-4). In Figure 1 are plotted the refractive indexes of the two types
TABLE 11. RAWPOLYMER PROPERTIES OF EMULSION POLYMERS Charge B/S 100/0 90/10 80/20 70/30
Isoprene
DDM, % 0.625 0 GO 0.55 0.55 0.30
Hours a t
c.
Conversion,
ML/
64.5 62.8 64.5 63.6 66.1
212 89 74 62 53 58
%
43O 27.5 23 5 19.3 1G 29
Inherent Viscosity Unmilled Milled [iVl % g e l [.VI % g e l 2.94 3.18 2.60 2.33 2.61
0.7 0 2.8 1.5 1.9
Table I1 summarizes inherent viscosity data for the emulsion polymers prepared for this study. The values were in the normal range of 2 to 3 and the gel contents were less than 2.8%. Iodine number determinations for both polybutadiene rubbers gave values very close to the calculated figure. From similar data on the butadiene-styrene copolymers, the styrene contents were calculated, on the basis that the iodine number for polybutadiene represented zero styrene content: % Styrene Found %
Perbenaoic
.
%
-
Monomer Ratio Charged, B/S
Alfin
Conversion
Emulsion
Conversion
100/0 90/10 80 /20 70/30
0 12.1 21.8 29.7
65 66 QO 86
0 7.8 14.7 24.9
65 63 65 64
Although the data were not conclusive because of variations in the percentage conversion, it seemed likely that styrene was entering the Alfin copolymers at a more rapid rate than butadiene, whereas butadiene entered the emulsion copolymers more rapidly. Perbenzoic acid titrations were carried out to obtain information on the relative amounts of internal and external double bonds corresponding, respectively, to 1,4- and 1,2- addition of the butadiene units during polymerization. The Alfin butadiene polymers were calculated to contain 24 to 27.5% of their double bonds as external double bonds. Polyisoprene exhibited a slightly lower value, 20%. These results were somewhat lower than previously reported (4) for polymers prepared with a similar organometallic catalyst, exrept in the case of polyisoprene. The emulsion butadiene polymers, on the other hand, were calculated to contain 17 to 22.5% of their double bonds as external double bonds, and polyisoprene l6%, values which were in excellent agreement with those reported previously (4, 14, 22). Thus the Alfin polymers were found to contain only a moderately greater percentage of external double bonds than emulsion polymers. Sodium-catalyzed polymers, however, contain much larger per-
2.92 2.81 2.50 2.16 2.63
%
Iodine No.
0 0.9 0.5 2.2 1.0
Acid Oxidation, Unsat. % Ext. Bonds
460 424 392 345 369
98.0 90.4 83.6 73.6 98.9
22.5 21.5 22.0 17.0 16.0
Refractive Index a t 2 5 O C.
Density~
dZ5
1.5159 1.5243 1.5299 1.5378 1.5212
0.893 0.902 0.916 0,933 0.897
of polymers as a function of styrene content (as calculated from the iodine number). Although the difference in value was small for the two polybutadienes, the curves showed that for a given styrene content the Alfin polymer had a lower refractive index, Schulze and Crouch (IS) recently studied the refractive index of sodium-catalyzed butadiene polymers as a function of styrene content and found lower values than for the corresponding ernulsion polymer; they attributed the difference to the higher vinyl side-chain content of the sodium polymers. This explanation is probably not applicable here because of the relatively small difference in this characteristic. In Figure 2 are plotted the density values of the two types of polymers as a function of styrene content. The *4lfin polymers consistently showed lower density values than the emulsion polymers. These two features-lower density and lower refractive index values-were interpreted to mean that the rllfin polymers contained a higher percentage of the trans- configuration ,540
d 0
v)
N
,535
+ a X W
,530
n
f w
.525
1 I1.520 (r
LI W
a
-
I515 .
0
5
10
%
15 20 STYRFNE
25
30
Figure 1. Comparison of Alfin and Emulsion Polymers
35
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950 .940
I
/
Ci .930 0
v)
N
l-
.920
a
> k
2!w
.910
.goo
n .890 .880 0
I
I
I
I
I
I
5
IO
15
20
25
30
%
35
STYRENE
Figure 2. Comparison of AIfin and Emulsion Polymers
around the internal double bonds than did the emulsion polymers. In the case of simple olefins (bo), the trans- isomer almost invariably exhibited lower refractive index and density than the cisisomer. Hart and Meyer (10) recently reported that the refractive index of butadiene polymers decreased as the trans- isomer content increased. Measurements (3,18,18, 97) on rubber and balata indicated higher density and refractive index for balata, but fiozen or crystalline rubber gave considerably higher values than rubber in its normal state, so that in this case it was difficult to separate the effects of geometric isomerism and crystallinity on the properties under discussion.
a t -70" C. The Alfin polyisoprene in similar dilatometric measurements gave a negligible volume decrease, 1 X lo-' cc. per gram, after 120 hours' equilibration a t -20' C. The emulsion polymers also exhibited negligible crystallization under these conditions. Because Alfin polybutadiene was thus shown to be crystalline and the butadiene-styrene copolymers probably retain varying amounts of this characteristic, one might question the statement that the lower density and refractive index values, as compared with values for the completely amorphous emulsion polymers, were indicative of a higher content of trans- isomer. However, the corresponding amorphous Alfin polybutadiene would be expected to have lower density and refractive index than the crystalline form, by analogy with natural rubber and its crystalline or frozen form, so that the disparity in these values would be increased rather than diminished. Fortunately, there were independent data available from infrared absorption studies, as discussed below, which confirmed the statement that the Alfin polymers had a larger proportion of the trans- isomer than the emulsion polymers. RESULTS OF X-RAY DIFFRACTION STUDIES
The x-ray diffraction pattern of an uncompounded unstretched sample of Alfin polybutadiene, shown in Figure 3, indicates a randomly oriented crystalline component to be a part of the polymer structure. The outermost diffraction ring in this pattern does not result from the polymer structure but is due to an impurity retained in the polymer which can be removed. I n order to obtain a diffraction pattern for a stretched sample of this polymer, it was compounded and cured. The diffraction pattern for a vulcanized sample stretched about 100% is shown in Figure 4. The sharp ring shown in Figure 3 now forms the equatorial arcs which indicate that the crystallites of this crystalline component have a preferred orientation approximately parallel to the direotion of stretching. This is further evidence that this crystalline component is a structural constituent of the polymer. The structural regularity exhibited by the crystalline component present in the Alfin polybutadienes is not evident in any of the Alfin polymers of isoprene, stretched or unstretched a t room temperature, A representative diffraction pattern is shown in Figure 5 for an uncompounded and unstretched sample. As
Figure 3. Alfin Polybutadiene Unstretched c
The crystallization of Alfin polybutadiene has been studied by dilatometric measurements in this laboratory and by others (7). The crystallizability, as measured by total observed volume decrease, was 3.9 X lo-' cc. per gram after 24 hours' equilibration at -20' C. This value represented only a moderate change and indicated that, the polymer was crystalline a t room temperature, Confirmation of this fact was substantiated by the x-ray diffraction pattern of the unstretched polymer (Figure 3) as discussed below. A volume decrease of 12.6 X 10-8 cc. per gram after 126 hours' equilibration at - 10 O C. was reported (7) for another sample of Alfin polybutadiene. The frozen sample was not completely melted until a temperature of 50" C. was reached. A sample heated for 1 hour at, 70" C. and then immersed in a dr$ ice-alcohol mixture a t -70" C. was still crystalline. This technique had previously produced amorphous balata
97
Figure 4. Alfin Polybutadiene Stretched
98
INDUSTRIAL AND ENGINEERING CHEMISTRY
before, the outermost diffraction ring does not arise from the polymer structure. The appearance of the crystalline structure in the Alfin polybutadienes has been observed by other investigators ( 7 ) . Although a similar structure has been observed for emulsion polybutadienes which were polymerized and exposed for diffraction data at lower temperatures (b), the structure of mutual recipe polymers has not been orderly enough to show crystalline characteristics, except when stretched and exposed for x-ray diffraction data a t low temperatures (9). Because the crystalline portion of the polybutadiene structure has been deduced t,o arise from the trans- form ( d ) , it can be concluded that this configuration is responsible for the crystalline characteristics of the Alfin polymer. I t can be further concluded that the structural component of the Alfin polymer resulting from 1,4- addition has a relatively greater proportion of the trans- configuration than the emulsion polymers. There are two immediate reasons for arriving a t this conclusion : (1) the crystalline component appears a t room temperature, whereas crystallinity is not evident in the emulsion polymers until the polymerization temperatures are lomered; ( 2 ) the infrared studies show that there is a consistently higher proportion of 1,2- addition in the Alfin structure than in the emulsion polymer. One significant observation t,hat can be made from these diffraction studies is the absence of any crystalline characteristics in the structure of Alfin polyisoprene. The characteristics of the infrared absorption spectrum indicate that the composite structure of this polymer includes more of the trans- configuration and a higher proportion of the structure resulting from polymerization by 3,4- addition than appears in the emulsion polymer structures. An appreciable amount of the cis- configuration is also indicated by infrared data. These contributing factors, which tend to increase the disorder in the molecular chains, are probably sufficient to explain why Alfin polyisoprene does not show the similar crystalline characteristics of the Alfin butadiene polymers. The structure of Alfin butadiene-styrene copolymers has been investigated by x-ray diffraction methods. The monomer ratios used for the copolymerizations were butadiene-styrene 90/10, 80/20, and i0/30. The diffraction patterns for these are shown in Figures 6 to 8. I n comparing the diffraction characteristics of these patterns, it is evident that the 90/10 copolymer possesses an appreciable amount of crystalline material, which will shorn a preferred orientation when the sample is stretched. However, as the styrene ratio increases, the crystalline structural component becomes less prominent, and a t the i0/30 ratio the structure appears to be amorphous. Evidently, the increase in styrene con-
Vol. 42, No. 1
Figure 6. Alfin Copolymer B/S 90/10 Unstretched
tent has sufficiently disordered the molecular chains in the polymer t o prevent a crystalline component from forming. The above results indicate more crystallinity for the Alfin copolymers than was observed for the emulsion butadiene-styrene copolymers prepared a t -20" C. (92). Although it was reported that the 90/10 copolymer, prepared according to this latter method, showed crystalline characteristics at -30' C., the 80/20 and 70/30 copolymers showed no evidence of this characteristic property. Likewise, the diffraction patterns for the corresponding emulsion polymers prepared according to the mutual recipe give no indication of crystalline structure a t room temperature. RESULTS O F INFRARED STUDIES
The infrared spectra of the Alfin polybutadiene and butadienestyrene copolymers consistently show a higher proportion of its structure resulting from 1,2- addition than is shown in the emulsion polymers. This can be concluded by comparing the absorption intensities of the 996 and 914 cm.-l bands for comparable sample thicknesses of the two polymer systems. This comparison is shown in Table 111.
TABLE111. ABSORPTION IKTEVSITIES OF
PoLYnim
SYSTEMS
% Transmission Polymer Alfin polybutadiene Emulsion polybutadiene $Ifin B / S 9 O / l O Emulsion B/S 90/10 Alfin B/S 80/20 Emulsion B/S 80/20 Alfin B/S 70 30 Emulsion B/3 70/30
Figure 3. Alfin Polyisoprene Unstretched
996 cni.-1
32 58 20 50 15 50 32 65
914 cm.-l 41 58 36 50 32 50 41
65
967 cm.-1 21 23 11 16 14 17 18 25
Hart and Meyer (IO)have observed a relatively large increase in the trans- Configuration of emulsion polymers prepared a t lower temperatures, with only a slight decrease in the amount of 1,2- addition. Because the amount of 1,2- addition is considerably greater in the Alfin polymers and crystallinity is evident a t room temperatures, it can be reasoned that a larger proportion of the amount of 1,4- addition has the trans- configuration than any of the emulsion polymers. Using the transmission of the 967 em.-] band as a measure of the amount of trans-1,4- addition, the infrared data do show this to be true, at least, for the comparison between the Alfin and emulsion polymers. The comparison is shown in Table 111.
January 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
99
cosity was markedly decreased. then rose rapidly:
The gel content dropped and
The absorption spectra of the Alfin and emulsion polyisoprenes were investigated. The absence of the 802 cm.-l band and the relatively strong absorption a t 845 cm.-l in the emulsion polymer spectrum indicate that the cis- configuration predominates in the structure resulting from 1,4- addition. However, both the 802 cm.-’ and 845 cm.-l bands do appear in the absorption spectrum of the Alfin polyisoprene. As these bands have been used to distinguish the cis- and trans- forms of natural rubber polymers (II), it can be concluded that an appreciably greater amount of the trans- configuration is present in the Alfin polymer in comparison with the emulsion polymer.
Heating Period, Hours
[Nl
% Gd
01
11.0 6.8 5.4 3.2 2.9 1.5 1.2
12.6 8.3 8.4 7.4 7.6 42.5 61.4
2 3 4 20 72
A similar experiment was conducted, but 2% of a rubber peptizer, RPA No. 2, was milled into the rubber before the heat treatment. The initial milling caused a marked decrease in the inherent viscosity and gel content. The subsequent heating caused a further decrease in inherent viscosity and eventually a large increase in the gel content. The following data are plotted in Figure 9: Heating Period, Hours Before RPA No. 2 addition After RPA No. 2 addition 1 2 3 4 5 6 7 8 24 49
[Nl
% Gel
11.0 7.8 4.95 4.13 3.73 3.18 2.57 2.18 2.05 1.99 1.00 0.70
12.6 2 1 5 2
3 4 5 13 14 59 68
Alfin polybutadiene was Also plasticized by addition on the mill of 10, 20, and 40 parts (per 100 of polymer) of a liquid plasticizer, tributyl phosphate, and of a low molecular weight polyisoprene (inherent viscosity 0.43) obtained as a solution from the Union Bay State Chemical Company. The milling behavior was greatly improved by the addition of these plasticizers, particularly the latter. A good “bank” between the rolls was formed and smoothed sheets of considerably less “nerve” were obtained. Figure 7.
Alfin Copolymer B/S 80/20 Unstretched
A considerable increase in the absorption intensity of the 880 cm.-l band is shown in the Alfin isoprene polymer as compared to the emulsion polymer. Because this band is thought to arise from structures of the type R,R2C=CH2, it is believed that an appreciable amount of 3,4- addition is included in the structure ( 6 ) . This seems to be consistent with the increased tendency of the Alfin butadiene polymers and copolymers to polymerize by 1,2- addition. HEAT-SOFTENING AND PLASTICIZATION STUDIES
Alfin polybutadiene was found difficult to mill and compound by the conventional procedures adequate for GR-S or natural rubber. This difficulty undoubtedly was associated with the extremely high molecular weight of this polymer and with the fact that the polymer did not “break down” readily on the mill, as did natural rubber which initially was also of very high molecular weight. Instead, the Alfin polymer tended to form increased amounts of gel as milling time was increased. This phenomenon was not surprising, because a very few cross links would have a tremendous effect on a polymer of very high molecular weight. A similar phenomenon was observed in the highest molecular weight fractions of GR-S in a careful study by Yanko (29). The Alfin butadiene-styrene copolymers showed better milling properties, the improvement increasing with higher styrene content. This behavior was similar to that already observed for corresponding emulsion polymers. It is well known that emulsion polybutadiene prepared under the same conditions as GR-S has much poorer properties on the mill than GR-S. Various experiments in heat-softening Alfin polybutadiene were conducted in an attempt to improve its processibility. Heating the polymer in an air oven at 120” C. up to 72 hours did not greatly improve milling properties, although the inherent vis-
Figure 8.
Alfin Copolymer B/S 70/40 Unstretched
Results obtained with these treatments indicated that use of plasticizers was more feasible than heat-softening or mill breakdown in the practical utilization of Alfin polybutadiene. Unfortunately, the plasticized polymers showed physical properties (tensile strength, rebound) considerably inferior to those of the unplasticized polymers, PROPERTIES O F VULCANIZED POLYMERS
Gum stocks and tire tread stocks of the experimental polymers were compounded and cured for a study of physical properties, as summarized in Tables IV and V. I n the course of this work,
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
100
TABLE Iv. Charge
B/S
Tensile lb./sq. inbh
Elong.,
620 260 320 350 220
230 265 340 470
100/0 90/10 80/20
70/30 Isoprene
GUM
Gum Stocks Abrasion index
gr,
STOCK A S D E P C TREAD STOCK DATAON ALFINPOLYMERS Gehman F.P.,'C.
Test S.P., 'C.
Tensile, lb./sq. inch
Elong.,
- 69 - 62 - 53
-52.5 54 45 24 - 45
1900 1550 2000 2600 1550
80 220 300 378 210
181 29 33 28 15
280
Vol. 42, No. 1
--
-38 -50
%
E P C Tread Stocks Abrasion Gehman Index F.P., C.
Test S.P.,"C.
... 1
278 145 172 162 87
-41
- 40
- 19
-51
TABLE 1'. Gvhr STOCK AND EPC TREAD STOCKDATA O N EbfCLsIoN POLYMERS Charge
B/S
Tensile lb./sq. inch
Elong.,
200 150 150 200 200
270 400 340 390 270
100/0 90/10 80/20 70/30
Isoprene
G u m Stocks Abrasion index
5%
Gehlnan F.P., C.
Test S.P., " C .
- 80 -70 - 68 -51 - 59
--63.5 74
95
55
49 30 11
% Solubility in Benzene Before cure After cure 88.6 88.6
40/275 15/300
3.4 4.8
These molded Alfin polybutadiene polymers have also exhibited abrasion resistance and gum tensile strengths which compare very favorably with values obtained with the conventionally compounded gum stock vulcanizates. The tensile strength data are compared below for several Alfin polybutadiene samples. Molded Stock
No. 4 5 9
10B
% .
Curing Conditions &fin. F.
Ib./sq. inch
40/260 40/260 40/260 40/260
600 400 650 680
Elong. 600 540 650 670
Gum Stock Tensi1e strength % lb./sq. indh Elong. 550 350 550 550
Elong.,
800 1400 2350 2750 1650
195 300 395 450 275
-58.5 - 44 - 53
it was discovered that Alfin polybutadiene could be "vulcanized" or cross-linked by heating the raw polymer in a rubber press in the same manner as the compounded stocks. The product had excellent dimensional stability and showed very little solubility in benzene. Curing Conditions Min. O F.
Tensile, lb./sq. inch
600 390 610 520
In Table IV, the gum stock tensile strength of Alfin polybutadiene is listed as 620 pounds per square inch , with lower values (220 to 350 pounds per square inch) for the butadiene-styrene copolymers and polyisoprene. In other preparations, however, polybutadiene exhibited tensile strength values of 1000 to 1100 pounds per square inch for five separate samples. In contrad, the highest tensile strength for the emulsion polymers was 200 pounds per square inch (Table V). The higher values for the Alfin polymers undoubtedly reflected the more regular molecular structure of these polymers as compared to the emulsion polymers. Because it was thought that the very high molecular weight of the Alfin polymers might have contributed to the higher tensile strengths observed, gum tensile strengths were also obtained on GR-S samples of higher Mooney viscosity (100 to 200) and thus of higher average molecular weight, prepared in polymerization recipes containing less modifier. They showed no advantage in gum tensile strength over regular GR-S. Stress-strain data were also obtained in a tread stock formulation containing 50 parts of E P C carbon black. The Alfin polybutadiene gave an ultimate tensile strength of 1900 pounds per square inch compared to 800 pounds per square inch for the emulsion polybutadiene whereas the other polymers in the two series gave equivalent results irrespective of the method of polymerization used. Not too great reliance should be placed on these data, inasmuch as (1) in most cases the per cent elongation showed the
%
E P C Tread Stocks Abrasion Gehman index F.P., C .
-
- 80 - 70 - 69 - 57
116 197 279 247 168
Test S.P.,'C. 73 -63.6
- 61 -44.5 - 58
-68.5
samples were overcured and (2) it was very doubtful that the carbon black had been properly dispersed by milling in the case of the Alfin polymers because of their extreme toughness. I n test on other Alfin polymers, tensile strength values as high as 2500 pounds per square inch for polybutadiene, 3000 to 3100 for butadiene-styrene 80/20 and 75/25 copolymers, and 2500 for polyisoprene have been obtained. As high as 4000 pounds per square inch tensile strength has been reported ( d 5 ) for an Alfin polybutadiene tread stock in which the black was dispersed in the solvent-swollen polymer immediately after polymerization Abrasion resistance of the gum and tread stocks was also determined. In both cases the Alfin polybutadiene showed remarlrably high values of 181 and 278, respectively, using the National Bureau of Standards testing machine (natural rubber stock control = 100). However, in butadiene-styrene copolymers and polyisoprene. the emulsion polymers gave ratings which were usually superior to those of the Alfin polymers. Moreover, although polybutadiene was by far the best of the Alfin polymers, the 80/20 butadiene-styrene emulsion copolymer showed comparable superiority over the rest of the emulsion polymers. The only polyisopropene stock to show good abrasion resistance was the tread stock of the emulsion polymer, Low-temperature stiffening and freezing tests were made on the gum and tread stocks by the Gehman method (8). The data are summarized in Tables IV and V, and the gum stock data on the freezing points are plotted in Figure 10. Practically identical results were obtained with the gum and tread stocks of the same polymer. The Alfin polymers showed ronsistently higher stiffening and freezing points than the corresponding emulsion polymers. These data support the hypothesis that the Alfin 75 I 70 65 60
I
I5
55 50 45 -1
g
40
35 30 25 20 15 10
5 0
0
5
IO
15
20 HOURS
Figure 9.
25 AT
30 120'
35
40
45
50
C.
Effect of Heat Softening on Plasticized Alfin Polybutadiene
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950 -30 0; 8
I-
-40
t -50 w N -60 w
w
LT LL
-70
2
2“I - 8 0 w
” -90 0
5
IO
%
Figure 10.
15 20 STYRENE
25
30
35
Comparison of Alfin and Emulsion Polymers
polymers contain a larger percentage of the trans- configuration around the internal double bonds, as deduced above from x-ray diffraction and infrared absorption studies. T I R E TESTS
Passenger car size tires containing two-way treads of GR-S and a n Alfin butadiene-styrene 80/20 copolymer were built and tested on the Government Tire Test Fleet at San Antonio, Tex. The Alfin rubber tread showed considerably less tread wear (rating, 117) than the GR-S control (rating, 100) after 11,000 miles’ testing. At the optimum cure the Alfin stock had a 300% modulus of 750 pounds per square inch, per cent elongation of 670, and tensile strength of 3120 pounds per square inch, compared to 830 pounds per square inch, 6550/$, and 3010 pounds per square inch, respectively, for the GR-S control. EXPERIMENTAL
ALFIN POLYMERIZATION PROCEDURE. The materials and general procedure recommended by Morton (19) were employed in this work. Phillips “pure grade” pentane (99 mole yo minimum urity) was dried overnight over fine sodium wire before use. $hillips “pure grade” butadiene was distilled into a flask containing anhydrous magnesium sulfate cooled in a dry ice-acetone bath, and transferred to a Dewar flask, from which it was weighed directly into the reaction bottle. Phillips pure grade isoprene was distilled just before use. Styrene meeting the specifications of the Office of Rubber Reserve (L.M. 2.2.0.1 of the O.R.R. laboratory manual) was vacuum distilled at 20 to 30 mm. of mercury pressure and used within 24 hours. The particular Alfin catalyst used in this work was prepared by A. A. Morton and his associates at the Massachusetts Institute of Technology and was of the P P type with a 7 to 1molar ratio of sodium isopropoxide to allyl sodium. I t was used within one month of the time of its preparation. Polymerizations were carried out in 16-ounce round-form narrow-mouthed screw-cap bottles which were dry and flushed with nitrogen before use. The pentane (240 ml.) was charged and warmed to 30” C. to drive air out of the bottle, the monomers (25 grams) were added and then the catalyst (amount given in Table I). A clean cork was inserted into the neck, the excess cut off, and the cap screwed on tightly. The bottle was shaken y i c k l y by hand for 5 to 10 seconds to disperse the catalyst and t en rotated to 60 r.p.m. in a water bath maintained at 30’ C. for 30 minutes (60 minutes for isoprene). All precautions were taken to eliminate moisture and oxygen from the polymerization system and catalyst. T o transfer catalyst from the original container to the polymerization bottle the following procedure was used. I n the neck of the catalyst container was placed a glass adapter with a side arm attached, through a mercury safety valve and bubbler containing sulfuric acid, to a cylinder of oxygen-free nitrogen. After the vapor space over the catalyst suspension had been flushed with nitrogen, a graduated pipet was placed in t h e open end of the adapter,
101
so that the tip was well below t h e surface of the catalyst. The catalyst was thus forced into the pipet, which was then loosened to allow the level of catalyst to fall to the desired mark. The pipet was quickly removed and its contents were discharged into the polymerization bottle. It was found desirable t o enlarge the tip of the pipet to allow the catalyst suspension to drain rapidly and to prevent clogging. At the end of the reaction period, the bottle was opened and the contents were allowed to discharge. I n the case of butadiene systems with free monomer left, there was sufficient pressure to force practically the entire contents out of the bottle. Otherwise the viscous gel was removed with air pressure or scraped out with a stiff wire. The polymer-solvent mixture was immediately cut into small pieces and added to a battery jar containing the following per 25-gram charge of monomers: 300 ml. of petroleum ether (boiling point 30 to 60” C.), 20 ml. of methanol (to destroy the catalyst), and an ether solution of phenyl 2-naphthylamine (2% calculated on weight of polymer). The mixture was covered and allowed to stand overnight; then it was spread on a tray and a portion of the solvents was allowed to evaporate under the hood. When the polymer could be picked up without sticking to the fingers, it was thoroughly washed on a corrugated rubber wash mill until free of alkali, or as long as the rubber could be maintained as a continuous sheet on the rolls. If washing was continued until too much of the solvent was lost, the olymer began to crumble and tended to wash away. After wasting was completed, the roduct was air-dried overnight and for 8 hours or longer. finally dried in vacuo at 50 O
8
EMULSION POLYMERIZATION PROCEDURE. A GR-S type polymerization recipe was used for the preparation of this series of butadiene polymers (Table 11), with monomers 100, distilled water 180, Ivory soap flakes 5, potassium persulfate 0.3, and the amount of commercial dodecyl mercaptan (dodecanethiol) indicated in the table. Polymerizations were carried out in 2-quart glass-lined reactors rotated at 35 r.p.m. in a water bath maintained a t 43” C. The monomers were the same as used for the Alfin polymers. The polymerization was stopped a t the desired conversion by the addition of 0.2% hydroquinone (calculated on monomers charged). Then henyl-2-naphthylamine (2% calculated on the pol mer) was ad&d, the latex was coagulated with salt-alcohol, andr the polymer was washed on the wash mill, then dried in vacuo at 50” C.
DETERMINATION OF POLYMER PROPERTIES. Polymers were purified by the method recommended by Kolthoff and Lee (19) before determination of iodine number, perbenaoic acid o x i d e tion, refractive index, density, infrared absorption, and x-ray diffraction. Iodine number and perbenzoic acid titrations were determined as recommended (IS,15). The method of Madorsky and Wood (16) was used to determine refractive index with an Abbe refractometer. I n preparation of t h e test sample a small amount of the dry purified polymer was placed in a circular hole (1.5 inch diameter) cut in a aluminum sheet 0.005 inch thick, which in turn waa placed between two similar aluminum sheets in a press, and the sample was molded 5 minutes a t 270” F. A smooth, clear sheet was thus obtained with a thickness of 0.007 to 0.0095 inch. The density was determined at 25” C. by t h e pycnometer method, with a bar sample weighing about 0.7 gram and having dimensions ’/8 X l / 4 X 8 / , ~ inch, which had been molded in a press 5 minutes at 270’ F. Inherent viscosities were determined from solutions of 0.1000 gram of polymer in 100 ml. of benzene. Viscosities of “unmilled” polymers were determined after vacuum drying at 50” C., as described above. The “milled ” polymers were processed 4 to 5 minutes on a laboratory mill prior t o solution. Solutions of the A l h polymers were diluted before the determination, so that the relative viscosity value was in the range 1.2 to 1.4. The isoprene polymer solutions were allowed to stand 24 hours in the dark, and the butadiene polymer solutions 48 hours in the dark, before filtration and viscosity determinations. A modified Ostwald type viscometer was used at 30’ C., and a kinetic energy correction as recommended by Wall (26)was made. For the infrared absorption studies 1 to 3y0solutions of t h e p f i e d pol mers in benzene were prepared by rolling overnight. ilms cast $om these solutions were used for the measurements by a previously described method ( 6 ) . X-ray diffraction patterns were obtained by usual procedures, using CuKa radiation.
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
102
COMPOUNDING A N D TESTING.The physical properties listed in Tables I V and V were obtained on vulcanizates compounded according to the following recipe: Polymer E P C black ZnO Stearic acid Captax Sulfur
100 50
5 2 1.5 2
The same recipe, with omission of the carbon black, was used for the gum stock vulcanizates. The following vulcanization periods and temperature were used: Polymer B/S 100/0
90/10
80/20 70/30 Polyisoprene
Vulcanization Conditions Min. F. 40/275 501’275 60/275 70/275 40/276
Because of the limited amounts of polymer available, a series of cures could not be run to determine time for optimum cure. The abrasion resistance was measured on the National Bureau of Standards testing machine ( I ) , for which a standard natural rubber stock was given an arbitrary abrasion index of 100. ACKNOWLEDGMENT
The writers are grateful to A. A. Morton for supplying the Alfin catalysts with recommendations as to their use. Dilatometric measurements were made by R. 31. Pierson and E. A. Sinclair. Density and refractive index data aere obtained with the assistance of R. W. Schrock. The x-ray diffraction and infrared data were obtained by P. J. Jones and D. E. Woodford. Compounding data were provided by the research testing laboratory and the Compound Development Department. Test tires were compounded under the supervision of J. H. Fielding. The writers wish to express their appreciation to H. J. Osterhof and The Goodyear Tire & Rubber Company for permission to publish this paper. (1)
Rubber,” A.C.S. Monograph 74, Chap. 3 and 21, New York, Reinhold Publishing Corp., 1937. D’Ianni, J. D., IND. ENG.CHEM.,40, 253-6 (1948). Eberly, K. C., and Johnson, B. L., J . Polymer S c i . , 3, 283-96 (1948).
Field, J. E., Woodford, D. E., and GehinaTl. S. D.. J . A p p l i e d Ph?/s., 17, 386-97 (1946).
Firestone Tire and Rubber Co., private cornniunication. Gehman, S. D., Woodford, D. E.. arid Wilkinson, C. S.,1x1). ENG.CHEM.,39, 1108-15 (1947). Hanson, E. E., and Halvorson. G., J . Am. Chem. Soc., 70, 779-83 (1945).
Hart, E. J., and Meyer. A . W.. I b i d . , 71, 1980-5 (1949). Hendricks, S.B., Wildman, 9. G., and Jones, E. J., Arch. Biochem., 7, 427-38 (1945) : Rubber Chem. Techno/., 19, 501-9 (1946).
Kemp, A. l i . , Proc.
Rubber Tech. CoiLf., L o n d o n , 1938, 68-79; Rubber Chem. Technot., 12, 470-81 (1939). Kolthoff, I. &I., and Lee, T. S., J . Polymer S c i . , 2, 206-19 (1947).
Kolthoff, I. M., Lee, T. S., and Maiw. M , A . . Ihid., 2,
Am. Soc. Testing Materials Standards on Rubber Products, A.S.T.M. Designation D 394-47, Method B, p. 105, February 1948.
( 2 ) Beu, K. E., Reynolds, W. B., Fryling, C. F., and McMurray, H. L., J . Polgmer Sci., 3, 465-80 (1948). (3) Davis, C. C., and Blake, J. T., “ChemistIy and Technology of
220-8
(1947). Ibid.,pp. 199-205.
Madorsky, I., and Wood, I,. A , , private corninuiiication. Marvel, C. S.,Bailey, W. J., and Inskeep, G . E., J . Polymer Sci., 1, 275 (1946); Rubber Chem. Technol., 20, 1 (1947).
Meyer, K. H., and Mark, H., ”Der Aufbau del, hochpolymeren organischen Naturstoffe,” pp. 199, 205, Berlin, Hirschwaldsche Buchhandlung, 1930. Morton, A. A., et al., J . Am. C h ~ m Soc., . 68, 93 (1946) ; 69, 160, 161, 167, 172, 950, 1675 (1947); 70, 3132 (1948); 71, 481, 487 (1949). Natl. Bur. Standards, Circ. C461 (November 1947).
Natl. Bur. Standards, private communication. Saffer, A., and Johnson. B. L., IND.ENG.CHEM.,40, 538-41 (1948).
Sckulee: W. A., and Crouch, W. My.,J . Am. Chem.
Soc., 70,
3891-3 (1948).
Shearon, W. H., McKenzie, J. P., and Samuels, M. E., IND. ENG.CHEM., 40, 769 (1948).
Taft, W. K., University of Akron Government Laboratories, private communication, March 11, 1949. Wall, F. T., private communication. Wood, L. A., Proc. Rubber Tech. Conf.,London, 1938, 933-53; Rubber C h e m . Technol., 12, 130-62 (1939).
Wood, L. il., Bakkedahl, N., and Roth, F. L., IND.EXG.CHEM., 34, 1291-3 (1942).
Yanko, J. A , , J . Polyme? Sci., 3, 576-601
LITERATURE CITED
Vol. 42, No. 1
(1948).
RECEIVED June 27, 1940. Presented before the Division of Rubber Chemistry, AMERICANCHEXICAL SOCIETY,Boston, M a s s . , May 23 to 25, 1949. Contribution 168 from The Goodyear Tire R: Rubber Company Research Laboratory. This investigation was carried out under the sponsorship of t h e Office of Rubber Reserve, Reconstruction Finance Corporation in connection with the government synthetic rubber program.
Treatment of Paper astes in Biochemical xidatio Ponds C. C. PORTER AND FRED W. BISHOP Southland Paper Mills, Inc., Lufkin, Ter.
T
HE paper mill with which the authors are connected manufactures groundwood, unbleached and bleached kraft pulp using pine as a raw material. The pulps are converted into newsprint, cylinder board, and kraft wet lap. The newsprint furnish includes 20% bleached kraft and SO% groundwood pulp. The cylinder board may be solid unbleached kraft or unbleached kraft with a bleached liner or unbleached kraft with a small amount of groundwood pulp added. The met lap may be either solid bleached or unbleached pulp. Unbleached kraft pulp is made by the selective saponification of lignin in wood b r digestion with rauqtic soda and sodium
sulfide as the active ingredients. The saponification product is collected from a three-stage, countercurrent vacuum washing system, which discharges clean pulp from one end and concentrated liquor from the other. The sodium lignate, commonly called black liquor, is evaporated, ignited to sodium carbonate, and recausticized to sodium hydroxide for reuse in the digesters. Unbleached kraft pulp is bleached in a three-stage system employing direct chlorination, caustic extraction, and sodium hypochlorite addition, in that order. Groundwood pulp is prepared by mechanically pressing 4foot lengths of peeled logs lengthwise against a revolving grind-
