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Rubberlike materials, designated as Lactoprene, were prepared in earlier investigations b y copolymerizing ethyl acrylate with small proportions of butadiene, isoprene, or allyl maleate, compounding the resulting copolymers (assumed to have olefinic unsaturation) with sulfur and acceleraton, and then curing the compounded products. Since it was difficult to prevent cross linkage during polymeriza- tion of mixtures containing butadiene and other polyfunctional monomers, vulcanization of acrylic resins not having olefinic link- ages was attempted. Poiyethyl acrylate and various saturated co- polymers of ethyl acrylate were vulcanized satisfactorily with red
lead and quinone dioxime and also with benzoyl peroxide. The copolymers made from acrylonitrile, cyanoethyl acrylate, chloroethyl acrylate, chloropropyl acrylate, and phenyl acrylate were vulcaniz- able with certain sulfur-accelerator mixtures. The preparation of rubberlike materials b y vulcanizing saturated acrylic resins instead of copolymers of the ethyl acrylate-butadiene type has the follow- ing advantogor: (a) Agents and techniques to prevent cross linkage are not required] ( b ) the polymers and copolymers are soluble, and hence the viscosity of the solutions can be used as an index of the molecular weight) and (e) synthetic rubber cements can be made.
w. c. MAST, c. E. kEHBERG, T. J . DIETZ, AND c. H. FISHER . . Eastern Regional Research Laboratory, Philadelphia, Pa.
HE vulcanization of copolymers (presumed to have ole- finic unsaturation) made from alkyl acrylates and small
lar polyfunctional monomers are described in other papers ( 4 , 9). Although the vulcanizates prepared in this manner were rubbery and seemed suitable as rubber replacements in some fields, poly- functional monomers were generally objectionable because of their tendency to create cross linkages prematurely-that is, during polymerization. After a study of the copolymerization of ethyl acrylate with many polyfunctional compounds had in- c-iicated that cross linkage (or effects ordinarily attributed to it) nearly always occurs when this method is used to produce un- aaturated copolymers, it was decided to attempt the vulcaniza- tion of saturated acrylic resins.
Although olefinic unsatuSation has generally been considered necessary for vulcanization (1 O), it seemed likely that vulcaniza- tion could be effected through some combination of a nonolefinic functional group (ester, cyano, halogen, etc.) and a vulcanizing agent. Acrylic resins contain ester groups and one hydrogen alpha to the carboxyl group that might enter into cross linkage or vulcanization reactions. Acrylic resins containing other functional groups were prepared by copolymerizing ethyl acry- late with small proportions of acrylonitrile, p-cyanoethyl acrylate, y-chloropropyl acrylate, and similar monomers. Vulcanization of these copolymers was attempted with various recipes including benzoyl peroxide and reinforcing agents, sulfur and organic ac- celerators, p-quinone dioxime and red lead, p-dinitrobenzene and litharge (IS), sulfur and litharge, and Polyac (14). The results of this study and certain properties of vulcanizates prepared from saturated acrylic resins are given in the present paper.
The polymerizations were carried out as before (4,9) in round- bottom, threeneck, Pyrex flasks fitted with a thermometer well, reflux condenser, and water-sealed stirrer (ground-glass joints). Steam was passed through the emulsion to distill monomer or volatile impurities, and then coagulation was effected by the addition of a dilute solution of sodium chloride. The polymers were washed with water on a small washing mill and air-dried.
The acrylic esters were emulsion-polymerized more success- fully when proper consideration was given to purity of the mono- mer and the threshold or minimum catalyst concentration re- quired for polymerization. The threshold catalyst concentration was related to the temperature, and only small amounts of cata- lyst (ammonium persulfate) were needed under refluxing condi- tions (approximately 82' C.). The monomers should he freshly
7 proportions of butadiene, isoprene, allyl maleate, and simi-
distilled and, if not used immediately, stored so that the forma- tion of peroxides is minimized. The removal of inhibitors by dilute sodium hydroxide should be followed by several washings with distilled water, dilute sulfuric acid (0.010/,), and finally wltb distilled water.
Generally it is disadvantageous to use more than the threshold concentration of ammonium persulfate. When there is too much catalyst, refluxing may be so violent that the emulsion coagu- lates. When the catalyst concentration is below the threshold value, polymerization may not occur even after hours of refluxing. When carried out properly, polymerization proceeds smoothly a t refluxing temperature with little heating. A steam bath is more satisfactory than a water bath for this type of polymeriza- tion.
The phenyl (a), chloropropyl, methoxyethyl, cyanoethyl, and nitroisobutyl acrylates were prepared in connection with other investigations (11).
The compounding ingredients were milled into the polymers on a small rubber mill. The polymers usually were tacky and easily milled without the addition of plasticizers or softeners. Benzoyl peroxide (Luperco A) was so active as a vulcanizing agent that i t was difficult to prevent scorching on the mill, even when the peroxide was incorporated last.
The compounded mixtures were cured in stainless-steel sand- wich molds having the dimensions 4 X 4 X 0.032 inch or 6 X 6 X 0.075 inch. Cellophane sheets were used in the smaller mold. These were apparently detrimental, since in some instances the tensile strengths were lower.
Unlike the copolymers ( 4 , 9) prepared with monomers having two or more olefinic linkages, most of the copolymers of the present work were soluble in organic solvents before vulcaniza- tion. The viscosities of solutions containing about 0.05 gram of polymer per 100 ml. of toluene were determined at 25' C. (con- stant-temperature bath) with modified Ostwald tubes. The natural logarithm of the relative viscosity divided by the con- centration-that is, (In ~r/c)-wns used as an index of the aver- age molecular weight of the polymers (6) . It was shown ex- perimentally that the values for (In ?,/c) were approximately the same when c was 0.05 or extrapolated to 0.
VULCANIZATION OF POLYETHYL ACRYLATE Polyethyl acrylate, prepared as shown in Table I, was com-
pounded by several different recipes and molded at 298' F. (Table 11). The sulfur-Captax-Tuads combination gave unsatisfactory
1022
N d r , 1944 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 1023
The ester group in polyethyl acrylate apparently is responsible Table I. Preparation of Ethyl Acrylate Copolymers by Emulsion Polymriut ion
Ethyl Expt. Acrylate, No. Grama 1 1bOml.
2 142.6
8 142.6
4 b 1470.0 5 142.6 I 136 7 89
8 142.6 0 96
LO 142.6 11 142.6 12 142.6
Copolymerising Monomer, Gronu
None Acrylonitrile, 7 . 6
Acrylonitrile, 7 . 6
y-Chloroprop 1 acr late 76 8-Chloroethy~acry~tee,~. b 8-Chloroethyl acrylate 16 8-Chloroethyl acrylatb, 6;
acrylonitrile. 6 Bensyl aorylate, 7 . 6 Phenyl acrylate, 6 8-Methoxyethyl acr late 7 6 8-C anoqtbyl acrygte, i.b 2-~e-2-nitro-l-propy1
acrylate, 7 . 6
Terdtol Pen- trant
No. 4a, Gram
4
4
4
28 4 4 3 4 3 4 4 4
Water, M1. 800
260
300
3200 300 300 1bO
2bO 1bO 300 300 300
Ammo- nium Per-
sulfat4 Gram' 0.026
0.02
0.046
0 .02 0.016 0.016 0 .12
0 . 0 3 0 . 1 0 . 0 3 0 . 0 3 0 .02
T t y ,
80-92 78-92
78-91
81-90 78-92 82-91 78-9 1
78-92 76-92 80-92 80-92 77-92
Time, Hr. 1 . 6
4 . 2 8
4 . 6
1.26 1 . 6 2 1.78
2 0 .83 1 .83 1.67 1 .67
Yield, % e
87.b 8 .82 3 .96
88.11 3.62 3 .91
90 .5 2.98 3 . 2 4 6 .27
60' 3.b3 88 92 2.'43
91 3 .80 90
91 3 . 6 4 91 4.66
9 3 . 6 1nno1.
for the vuic'anization withbenzoyl peroxide and quinone dioxime, since cross linkage did not occur when polyisobutylene (Vistanex) waa compounded according to these two recipes and molded. The mechanism of the vuIcaniza- tion of polyethyl acrylate is not known, but earlier work by Kharasch and Gladstone (7) with a peroxide and isobutyric acid is suggestive. They observed that isobutyric acid is converted into tetramethylsuccinic acid by treat- ment with acetyl peroxide.. Since the polyacrylic ester chain is somewhat similar to isobutyric acid in. having one hydrogen
alpha to the carboxyl group, possibly cross linkage occurs through the same type of coupling.
Sodium alkyl sulfate. * Triton 720 (8 grams) used: thia emulsifier is a sodium aslt of aryl alkyl polyether sulfonate (1 6).
seeulta, but the Luperco A (benzoyl peroxide) and GMF (qui- none dioxime) recipes gave good vulcanizates. About 4 hours at a98" F. was necessary for vulcanization with the quinone dioxime formula, and the vulcanizates thus prepared (Tables I1 and 111) had moderately high tensile strengths. Cross linkage occurred much more rapidly with benzoyl peroxide (10 to 20 minutes a t 210" F.), but the products were relatively weak. [Cross-linked acrylic resins were produced &o by preparing ethyl acetab solutions of the polymeric acrylic ester and benzoyl peroxide (Lucidol), applying the solution to a surface, allowing the solvent to evaporate, and heating the resulting fdm at about 80" C. for B short time.]
VULCANIZATION OF ETHYL ACRYLATE COPOLYMERS
Ethyl acrylate was copolymerized with various monomers I), and the resulting CoPolYmers were compounded by
different recipes and molded to ascertain whether the cyano, halogen, Phenyl, ether, and nitro groups in the copolymers would facilitate vulcanization. The results show that several functional groizps in the acrylate copolymers are susceptible to cross linkage or vulcanization. It has been believed that olefinic
Expt. No.
1
2
3
40
6
6
7
B
!d
10
11
12
Table tl. Vulcanization of Polyethyl Acrylate and Ethyl Acrylate Copolymetp
Copolymeriaing Monomers, % None
Aorylonitrile, 6
Acrylonitrile, b
y-Chloropropyl acrylate, 4.8
8-Cbloroethyl acrylate, 5
8-Chloroethyl acrylate, 10
8-Chlp-ethyl aorylate, 6; acrylo- zutrrle, 6
Benayl acrylate, 5
Phenyl acrylate, 6
Methoxyethyl acrylate, 6
8-Cyanoethyl aorylate, 5
2-Me-2-nitro-1-propyl scrylate. 5
Compounding Recipe uinone dioxirnee 9 ensoyl eroxided
S u l f u r J uinone dioximee 8 enroyl peroxided
Sulfur 0
uinone dioxime' 8 enaoyl peroxided Sulfur%/ C&inin?e &oxime8
Quinone dioximee Benioyl peroxided
Quinone dioximeo Benaoyl peroxided Bulfur. Quinone dioximee Benaoyl peroxided Sulfur%/ Quinone dioximee Benroyl peroxided Sulfur* Quinone dioximea Benaoyl peroxided Sulfur. Quinone dioximee Benroyl peroxided Sulfur'
uieone dioxime" 8 enaoyl peroxided Sulfur* Quinone dioximeo Menloyl peroxided Sulfur % I
Sulfur'
Curing Time Tensile a t 298O F.. Strength
240 1390 120 810
240 1320 180 1000 240 850 240 1420 120 870
160h 1610 210c 1240 120 1610 240 870 240 1280 180 1350 120 1050 180 1220 240 1180 180 820
240 1410 120 640 240 < 100 240 960
20 670 240 790 240 1090
80 < 100 240 < 100 120 1670 80 510
120 lono 120 470 180 760
M1n.b Lb./Sq. 1;.
. I . ...
... ...
... ...
... ...
Elon Ultimate ation,
610 440
280 420
1040 340 620
470 960 400 600 880 460 280 720 470 660
480 490
>2400 180 480 780 340 380 680 450 440 860 410 440
t% ...
...
...
...
Shore A Hardneii
56 46
72 13 60 70 62
67 39 84 4b 46 66 60 42 66 46
85 45 40 75 42 50 65 40
66 45 48 31 41
..
..
..
as
..
Tensile Product
710 365
345 420 860 480 460
766 1178 646 435
1126 620 295 880 668 460
676
...
. . .
... ais ... 170 276 615 370 ... ... 750 226 940 190 335 ..
Brittle Point,
O c. - 16 - 16
-11 - 7 - 7 - Q - 8
...
...
... ... - 1b - 9 - 15 - 16 -11 - 14 - 6 - 6
-11 - 10 -17 - 11 - 16 - 17
...
...
... ... - 16 - 13 - 16 - 14 - 13 ... ...
* Prepared 91) desoribed in Table I; brittle point. of vulcanisate determined an deacribed in citation (18). 5 Cured in 4 X 4 X 0.039 inch molds. 1 Compounded: polyme;, 100; iron oxihe, 150: Luperco A (b6n;oyl peroxide), 5.
/ 8 ecimen uneh8foctory for testing. e &red in 6 X 6 X 0.075 inch ~uolds.
Compounded: polynier 100; red lead 10; quinone dioxime 2. sinc oxide 5; stearic acid, 3; Furnex Beads (semireinforcing carbon black). 30.
Com ounded. polymer, 100; Captax (inercap~oben.othisaole), 0.5; rina oxide, 10; ateario acid, 2; sulfur, 2; Furnex Bead., 30; T u a b (tetramethyl- rbiuram h f i d e ) ' 1,.
A Cured at 303O F. i Cured at 312O b'.
1024 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 Vol. 36, No. 11
Table 111. Preparation and Vulcanization of Copolymers of Ethyl Acrylate with Chloropropyl Acrylate or Chloroethyl Acrylates
h g i t o l Tensile Ulti- Shore Ethyl Penetrant Triton Ammonium cz$$&s Strength Lb./Sq. 'Elonga- mate Hard- A 1-nr
Expt. Copolymeridng Monomer, Acrylate, Water, No. 4 720 Persulfate, 'ITme, Temp., NO. Grams Grams M1. O r a d Grads Grams Hr. * C. Min. F. In. tion. ?& ne= c . .- 1 r-Chloropropyl acrylate, 32 630 1125 5 . . 1.70 5 65-92 180 298 500 1030 42 3.033 2b &me, 10 90 300 4 .. 0.04 3.5 76-92 240 298 990 760 42 4.784 3e Same, 44 882 3050 40 .. 0.05 1 81-88 18W 298 1700 4O Same, 45 897 2860 40 .. 0.03 1 80-84 240 298 1200 %3 5.386 5 Same, 150 3000 ml. 5000 60 (paste) 80 0.180 4.5 82-90 {ti$ gi: ici: 420 76 . . . 6 Same, 150 3000 ml. 6000 80 (paste) 30 0.040 3 83-90 18W 298 1890 440 75 . ..
5.273 7 Same. 75 1470 3200 28
8 Same, 200 4000 ml. 6000 80 (paste) 40 0.035 3 8%90 120d 298 ''lo %' ''1 5.062
o.020 78-90 210 312 1240 950 1M)d 303 1610 I B O 312 1210 790 48
9 10 11 12 13 14
BChloroethyl acrylate, 125 Same 26 Same: 20 Same, 60 Same, 50 Same, 25
2375 475 380 1140 950 500
5000 1000 800 2700 2250 1350
45 9 4 80 SO 10
12.5 2.5 2 15 .. ..
0.355 0.215 0.010 0.015 0.16 0.100
6.5
1125 2.25 4.5 2
a Compounded with sulfur and accelerators (footnote a of Table 11) unleen otherwise indicated. b Methyl acrylate (30 grams) and n-butyl acrylate (70 grams) were also used aa oo-monomers, c The copolymers prepared in experiments 3 and 4 were combined. d Compounded with quinone dioxime and red lead (footnote 8 of Table 11).
82-88 82-88 82-91 81-92 78-82 75-92
... 240 240 240 240
{ ttE
... 298 298 298 298 298 298
... 1290 1440 1430 740 1120 1300
. . . 900 840 860 800 820 530
46 42 48 48
2: 829 3.255 5.079 1.968 3.284
unsaturation is necessary for vulcanization with sulfur, but our findings indicate that cyano, halogen, and phenoxy groups are also adequate in acrylic resins when suitable vulcanization agents are used. We have not ascertained whether these groups are suswptible to vulcanization in the absence of ester groups such as those found in acrylic resins.
The cyano group in the acrylonitrile copolymer did not de- crease the time required for quinone dioxime vulcanization (ex- periments 2 and 3, Table 11) or significantly improve the proper- ties of the vulcanizates. It was possible, however, to vulcanize the acrylonitrile copolymer with sulfur. The acrylonitrile seg- ments in the polymer chain raised the brittle point and incrcased the hardness.
The cyano group in the cyanoethyl acrylate copolymer was advantageous. It decreased the timc required for vulcanization with quinone dioxime and permitted sulfur vulcanization (ex- periment 11, Table 11). I t did not appear to raise the brittle point.
Acrylic resins containing halogen were prepared by using either r-chloropropyl or 6-chloroethyl acrylate as copolymerizing monomers. The halogen in the polymers was beneficial in that i t decreased thc time required for the quinone dioxime vulcani- zation and resulted in good sulfur vulcanizates. Moreover, it did not adversely affcct the brittle points of the vulcanizates. Copolymers made from ethyl acrylate and either chloroethyl or chloropropyl acrylate have been prepared several times in this laboratory and given considerable study (Table 111).
The phenyl group of benzyl acrylate seemed ineffective for vulcanization purposes, but the - - phenyl group of phenyl acrylate per- mitted sulfur vulcanization. Thc quinone dioxime and benzoyl perox- ide vulcanizates prepared from the phenyl acrylate polymers were un- satisfactory, perhaps because of the antioxidant character of the phenyl ester group.
Vulcanizatea of poor quality were obtained from the resins contain- ing the ether and nitro groups (Table 11). The possibility that molecular weight as well as specific effects of functional groups was re- sponsible for the differences in prop- ertiea of the vulcanizates of Table I1 is diewased below.
EFFECT OF MOLECULAR WEIGHT
Ethyl acrylate was emulsion-polymerized under various con- ditions to obtain polymers of different molecular weight (Table IV). Polymers of relatively high molecular weight (w indi- cated by viscosity measurements) could be prepared oonven- iently by refluxing the reaction mixture and using low con- centrations of ammonium persulfate (experiment 6, Table IV) . The (In q,/c) values ranged from 2.6 to 6.3, an indication that the polymer of experiment 6 had an average molecular weight con- siderably higher than that of the polymer of experiment 1.
The vulcanizates prepared from the seven polymers of Table I V t e r c roughly similar in spite of the considerable differences in average molecular weight. These results suggest that the plateau of the curve showing the relation between the properties and molecular weight (8) has been reached for polyethyl acrylate and that further increase in molecular weight would not be bene- ficial from the standpoint of tensile strength, ultimate elongation, and Shore A hardness.
Viscosities of toluene solutions of most of the copolymers shown in Table I were determined to ascertain whether the mono- mers used with ethyl acrylate had a pronounced effect on mo- lecular weight. Moreover, it was hoped that viscosity data would indicate whether the properties of the vulcanizates (for example, the low tensile strength of the nitroisobmtyl acrylate product, item 12 in Table 111) could be attributed to differences in molecular weight. Since a copolymer having (In q,/c) value as low as 2.43 (experiment 7, Table I) gave a satisfactory vul- canieate and the other copolymers had even higher (In v , / c )
Table IV. Emulsion Polymerizations of Ethyl Acrylate and Properties of the Vulcanizatesb
Tergttol Ammo- Pene- nium Vulcanizatee
Ethyl trant Per- Tenaile Ultimate Shore A Grama Grams O C. Hr. Grama lb./sq. in. tion, % produot ness
E%!. Acrylate, No. 4. Temp., Time, eulfate. ( ! ) O strength. elonga- Tensile hard-
1 2d 3 4 5 61 7
680 540 560 955 835 200 760
ao 20 20 30 30 3 60
72-81 66-7 62-75 62-90 62-85 82-92 62-81
30 .s 0 . 5 0.75 0.5 1.25 0.75
0.30 0.45 0.43 0.60 0.50 0.003 0.70
2.578 3.020 3.552 4.110 4.285 6.284 4.267
1220 1270 * 1290 1330 1280 1380 1400
520 560 480 480 490 480 470
634 710 620 638 626 662 668
53 52 80 61 63 58 63
a Except where indicated, 2 liters of water were used. pol merieation yieAds wars 89 to 997 * Compounded: polyethyl acrylate, 100; red lead, io; $nc oxide, 5; stearic acid, 3; GMF, 2; and Furner
a Viscosities determined w t h solutions containing approximately 0.05 gram per 100 ml. of toluene. d 4.15 liters of water used. ' Cured for 3 hours a t 298" F. f SO0 ml. of water used.
Beads. 30; curing time was 4 h o w at 298O F.: molded specimens were 4 X 4 X 0.032 inch.
November, 1944 I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY 1025
polyethyl acrylate. When compounded with tho quinone dioxime formula (footnote ', Table 11) and
Cure a t parts Per 100 Polymer Tensile Ultimate cured for 60 minutes a t 298' F., a vulcanizate with Expt. 298°F.. Red Furnet strength F:$$t the following properties ww obtained: tensile
428 strength, 780 pounds per square inch; ultimate 1 300 5 1 30 1190 360 66 2 240 5 2 30 1190 660 49 784 elongation, 640%; Shore A hardness, 47; tensile
40' product, 500; and brittle point, about -50' C. 3 300 10 1 36 1110 860 66 4 180 10 2 30 1240 610 66 766 5 240 10 ? 40 1230 8 240 10 2 60 1360 440 70 698 6 Pr ared in experiment 5 Tabie 111 Coin ounded: polymer, 100; stearic acid. 3.0;
Table V. Vulcrnization of Polyethyl Acrylate0
No. Min. lead CMF Beads Lb./Sp. 1;. %
400 65 492 ( -58' F.). HEAT AGING
2110, 63; test specimens were)( X 4 X 0:032 incg. Vulcanizates prepared by the sulfur and quinone
dioxime recipcs were heated in an oven a t 150' C.
values, i t appeam that some specific effect ot the functional group was more important than molecular weight.
The methoxyethyl acrylate copolymer was not completely soluble in toluene. Whether this was due to cross linkage or waa charaoteristic of this part,icular copolymer is not knowa
VULCAMIZATION WITH OUINONE DIOXIME
The dects of variations in the quinone dioxime (GMF) recipe were studied briefly because this vulcanization method produced satisfactory vuloanizates with polyethyl acrylate and several ethyl acrylate copolymers. Moreover, vulcanization could be achieved in less time with quinone dioxime than with sulfur. Harder and less elastic vulcanirates were obtained by using 1 instead of 2 parts of quinone dioxime (Table V). Use of 5 parts of red lead rather t,han 10 softened the vulcanizate without causing any significant decrease in tensile strength. The effect of larger proportions of Furnex Beads is shown by experiments 4, 5, and 6, Table V. The vulcaniaate prepared with 50 parts of black was harder and stronger but less elastic than the standard vulcanizate (experiment 4) having 30 parts of black.
Pitting sometimes occurred when curing temperatures higher than 248" F. were used. In some instances pitting at 307" F. was not wvere, but badly pitted vulcanizates were produced at, 312' F. Some of the undercured specimens prepared a t 298" F. were pitted, although the vulcanizates cured for a longer time at this temperature were satisfactory. Possibly the tendency of products compounded with the quinone dioxime recipe to pit at temperatures much above 298" F. is related to the exothermic reaction between &he dioxime and red lead (1) . Products com- pounded according to the sulfur-Rotnx-Tuads recipe showed less tendency to pit, and satisfactory vulcanizates were prepared a t temperatures as high as 320" F. (75 pounds steam pressure).
EFFECT OF CARBON BLACK
In B preliminary study of the effect of carbon black, it was oh- served that greater tensile strengths were obtained when Kosmos, Gastex, and Pelletex were used (50 parts per 100 parts of poly- mer) instead of Furnex Beads. The elongation and hardness values, however, were less:
Tensile Ultimate Expt. Carbon hlodulua Strength Elon a- Shore -4 Tensile 3o.a Black Lb./Sq. 1;. Lb./Sq. 1;. tion,% Hardness Product
1 FurnexBeads 970 600 ) 1200 620 69 744 2 Konmoa40 1460 600 ) 1630 640 67 826
61 689 480 'lo 55 710
3 Dixie20 11101800~~ 1130 1450
680 54 717 4 Gaatex 6 Pelletex 1130(400%) 1410 a Copolymer WBB pre ared from 96% ethyl acrylate and 6 7 chloropropsl
acr lata. Compounded? copolymer 100. Rotax 0.6- z n 6 !Os stearic d, 2; sulfur, 2; Tuads, 1; and'semi;einforci;g black, ab. &red iii 4 X 4 X 0.082 inch molds at 298O F. for 4 houra.
EFFECT OF MONOMER STRUCTURE
Vulcanizates of polymethyl acrylate were harder, stronger, and less rubbery than those prepared from polyethyl acrylate. The samples of vulcanized polymethyl acrylate had brittle points of approximately 0" C. Poly-n-butyl acrylate, prepared under the conditions shown in Table I, was softer and tackier than
for periods up to 5 weeks and examined to deter- mine their resistance to aging a t elevated temperatures. Heat increasod the tensile strength and hardness of both vulcanizates but decreased the elongation and permanent set :
-Permanent Set- 10 min.,
Aged at Tensile Ultimate Shore A 75% 160° C., Strength Elonga- Hard- elqnga- A t
Sainplea Days Lb./Sq. 1;. tion, % ness tron hreak 1 b 0 1680 370 66 25 6 20 .4
1 2170 260 81 .. 22 2 2130 200 84 . . 4 2240 190 83 . . . . 8 1930 90 89 . . . .
2c 0 1700 1 2100 4 2430 7 2330
14 2120 2160
36 2320 28 21 2200
480 110 80 50 50 80 40 60
68 7 . 1 82 2 . 4 80 10 .0 92 3 . 1 97 0 98 . .
100 * . 98 ..
a Specimens were heated in an oven at 150° C.; they were tough instead of brittle at end of teat:
b Polymer re ared in experiment 7 Table IV. Compounded. polymer 100: red 1-8, 83; ZnO, 5; stearic &id, 3; quinone dioxime,'2; Furne; Beads, 30. .Cured 240 minutee at 298' F. in 6 X 6 X 0.075 inch molds.
Polymer prepared in experiments 3 and 4 Table 111. Com ounded. fjplymer, 100; Rotax, 0.6; zinc odde,,b; steariiacid, 2; sulfur, 2; %de, 1;
urnex Beads, 30. Cured a t 298O F. in 6 X 8 X 0.076 inch molds.
These results show that vulcanized iicrylie resins are rather re- sistant to heat, and suggest that acrylic resins might be useful where rubbery materials are required to withstand relatively high temperatures. It should be possible to improve the heat- aging characteristics of vulcanized acrylic resins by making tip- propriate changes in the compounding recipe. These changes might include the uee of antioxidants, softeners or plasticizers, decreasing the proportion of sulfur and vulcanizing agents, and loading with more suitable reinforcing agents.
BLENDS WITH OTHER SYNTHETIC ELASTOMERS
-4 copolymer made from ethyl acrylate and 5 % 7-chloropropyl acrylnte blended readily with Butyl rubber on a small rubber mill. Increasing the proportion of Butyl rubber increased the tensilc strength and lowxed the brittle point:
Butyl Rubber, Cure nt Tensile Ultimate Brittle
Expt. % of 288O F., Strength Elonga- Shore A Tensile Point, No.' Gumb hfin. Lb./Sq. 1;. tion, % Hardness Product .a C.
513 -18 I 0 180 500 ? 20 240 1050 830 46 870 -22 I 35 240 1370 900 48 1230 -48 4 80 120 1410 920 40 1300 -49 6 100 180 2340 790 41 1860 - 8 5
1030 4?
a Butyl rubber A contained 1.6 b Blends were compounded as ~ l l o w s : gum stoc!, 100; Captax. 0.5:
Cured in
arts sulfur and 5 arts BnO.
ZnO. 6; stesrig acid, 2: sulfur, 2: Furnex Beads, 30: Tunds, 1. 4 X 4 X 0.032 inch molds.
Apparently blending with Butyl rubber (and presumably cer- tain other synthetics) cotistitutes a convenient method of lower- ing the brittle points of polyethyl acrylate vulcanizates. Other methods of lowering the brittle point consist in using plasticizers or in copolymerizing ethyl acrylate with suitable monomerfi, such as n-butyl acrylate.
1026 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 Vol. 36, No. II.
Table VI. Vulcenization of Ethyl Acrylate-Chloropropyl Acrylate Copolymer with Various Agentsa
Compound No. 1 s 2 3 4 6 b 6 7 8 9 fO 11 12 Recipe, parts
Rotax- ZnO Steario acid Sulfur Furnex Beads Tuads Plaatici~er SC Red lead pi;ui:e diosime
Cumate Polyac Te ~ 1 . 0 8
&nitrobensene
. . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . . . . . . . . . 10 .. . . . . . . . . . . . . . . . . . . . . . . 80
The tear strorigth by the crescent test test is about 220 pounds per inch. The permanent set is frequently 20% or leae. The brittle point is approximately Om, -15', or -50' C., depending upon whether methyl acrylate, ethyl acrylate, or n-butyl acrylate is the principal monomer.
The polymers are readily milled with- out softeners or plasticizers. Different compounding recipes can be used, and several blacks and pigments, such IW
iron oxide, zinc oxide, and calcium car- bonate, can be used as reinforcing
leu 14u JOU 14u & ;;J 6UU 14u JOC 298 iii 298 298
uuring time, min. Curing temp., F. 312 298 298 298 2:; Tenaile lb/sq in. 1::: f,ll70, 12:: 2: f,63,: 1::: fif lit! f f z Modul& si 606%
............................. agents. The copolymers are soluble in I 298 organic solvents, and synthetic rubber
Ultimate elonga- The vulcanizates have the advantages 48 46 40 40 66 40 43 43 41 38 35 47 of resistance to oxygenandaging,which Shore A gardneas
^"? 240
wv yvI _l._ llu .A0 370 .. 1240
790 690 690 880 650 940 740 790 700 920 560 610
- . . lo g80 1340 l Z 8 O cements can be prepared from them.
tion, 7 one would expect to find inessentiallp
After 10 min. 2 1 . 4 3 4 . 9 saturated materials. The acrylic else- tomers contain a high proportion of
Permanent set, %
Tenaile product
At break 13.7 . . . . . . 2 6 . 6 . . . . . . . . . . . . . . 9.56 soi sii 7 i 4 994 1460 i o i i iiii io i i eoi 760 780
- . _ a 100 parts ao olymer (prepared in experiment 8, Table I11 used.
b doompounded uuxturea cured in 6 X 6 X 0.076 inch molda.
With exoeption of experiments 1 oxygen and are resistant to some oils, particularly those that are paraffinic.
Although in some respects vulcanimd acrylic resins do not compare favorably with certain other synthetic elastomere,
they have several advantages. The monomers can be made from several raw materials, including whey (61, molwes, corn, sugar, Petrolem, and Coal. Moreover, more than twice as much Bcrylic elastomer as elastomers of the butsdime types can be made from carbohydrates.
bnd 6 oompounfed plitturea werq cured in 4 X 4 X. 0.023 inch mdds.
MISCELLANEOUS VULCANlZAflON RECIPES
Samples of copolymer prepared from ethyl acrylate and chloropropyl acrylate (experiment 8, Table 111), were vulcanized with various agents, and the vulcanizates were compared with products obtained with the standard quinone dioxime and sulfur- Rotax-Tuads recipes.
Both Cuprax and Cumate (cupric salt of mercaptobenzothia- zole and cupric diethyldithiocarbamate, respectively) were ef- fective in promoting sulfur vulcanization (Table VI, experiments 6, 7, and 8). The combination of Cuprax and Tuads gave vul- canizetes that were superior to those obtained with combinations of Rotax and Tuads, Rotax and Cumate, and Cuprax and Cu-
and gave vulcanizates which compared favorably with those prepared by other recipes. The dinitrobenzene litharge combina- tion also gave satisfactory vulcanizates (experiment 11, Table VI). The vulcanizate obtained with Tegul OS, an organic sulfur compound, Rotax, and Tuads (experiment 10) had high elongation but relatively Iow tensile strength.
Considerable quantities of plasticizers were used in experiments 2, 3, and 4. In the presence of increased amounts of carbon black the plasticizer decreased tensile strength and hardness while increasing the elongation. Witcarb R (calcium carbon- ate) functioned as a reinforcing agent when used instead of carbon black.
Although the study of compounding and vulcanization is still in the preliminary stage, the results obtained show that certain
6ed with a variety of agents.
r i I i I P ~ o o L O A D E O STOCKS
0 GR-5, DlNSMORE ------- m O R - ~ , S T U R G I S A N D
'OQ0 T R E PAGN I ER -. -
mate. Polyac (14) caused vulcanization in the absence of sulfur eLACTOPRENE -
saturated acrylic resins cap be vulcanized, reinforced, and modi- % ELONGATION
Figure 1. Stredtrain Curves PROPERTlES OF VULCANIZED ACRYLIC RESINS
As Figure 1 shows, the copolymer of ethyl acrylate and 5% chloropropyl acrylate has a tensile strength of approximately 1700 Pounds Per Square inch (cured in 6 x 6 x 0.075 inch without cellophane sheets) and an elongation of 500%. Higher tensile values may be obtained by sacrificing elongation and presumably with different blacks or higher loading, 88 shown above, The stress-strain curve of a quinone dioxime vulcani- zate is roughly comparable with those of other synthetic elasto- mer8 (9) up to about 400% elongation (Figure 1).
Another advantage of acrylic elastomer is that the polmen- sation can be carried out in simple equipment. Since ethyl acrylate boils at 99' C. at atmospheric pressure, high-preesure reaction vessels are not needed. The time required is short, and polymerization is carried to completion. Polyfunctional mone mers are not required, and consequently premature cross linkage and its attendant disadvantages are avoided. Any one of 8ev. era1 acrylic esters can be used, or two or more acrylic esters csn be copolymerized.
Nwember, 1944 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 102P
LITERATURE CITED (1) Bruce, P. L., Lyle, R., and Blake, J. T., IND. ENQ. Cmm., 36,
(2) Dinsmore, R. P., Chem. Eng. Newe, 21, 1798 (1943). 4) Filaohione, E. M., Lengel, J. H., and Fisher, C. H., J. Am.
(4) Fisher, C . H., Mast, W. C., Rehberg, C. E., and Smith, L. T.,
(5) Fisher, C. H., Rstchford, W. P., and Smith, L. T. , Ibid., 36, 229
(6) Flory, P. J., J . Am. Chem. SOC., 65, 372 (1943). (7) Kharamh, M. S., and Gladstone, M. T., Ibid., 65, 15 (1943). 18) Mark, H . , Am. Scientist, 31 (2). 97 (1943). (0 ) Mast, W. C., Smith, L. T., and Fisher. C. H., IND. ENO. CHEM..
37 (1944).
Chem. SQC., 66, 494 (1944).
IND. ENO. CREM., 36, 1032 (1944).
(1944).
36, 102’7 (1944).
(10) Powers, P. O., “Synthetic Resins and Rubbers”, N e w York,
(11) Rehberg, C. E., and Fisher, C. H . , J. Am. Chem. Soc., 66, 1203
(12) Selker, M. L., Winepear, G. G., and Kemp, A. R., IND. ENO.
(13) Sturgis, B. M., Baum, A. A., and Vincent, J. R., Ibid., 36, 348
John Wiley & Sons, 1943.
(1944).
CHEW., 34, 157 (1942).
119441. (14) Stur&:‘l%. M., and Trepagnier, J. H., Rubber Age (N. Y.), 54
(15) Van Antwerpen, F. J., IND. ENO. CXIUM., 35, 126 (1943). (4), 326 (Jan., 1944).
PRESENTED before the Engineering Section at the fall meeting of the Ameriasn Association for the Advanoement of Science, Cleveland. Ohio. 1844.
COPOLYMERS OF ETHYL ACRYLATE AND ALLYL MALEATE
Rubberlike materials were made by copolymerizing emulsified ethyl acrylate with small proportiona of allyl maleate and vuluniz- ins the resulting unsaturated acrylic rraina with aulfur and accelera. ton and with other agents in the absence of sulfur. Acrylonltrilo (preferably about 6%) and dodecyl mercaptan had a benelclal effect, posaibly because of their tendency to decrease croas linkage. Ammonium peraulfate was preferable as polymerization catrlyatr a small amount cauaod polymerization to proceed amoothly. Benzoyl
peroxide waa ala0 effective but produced properties, such as in- solubility and toughness, that are sometimes attributed to cross linkage. Although not so active aa benzoyl peroxide, hydrogen peroxide waa moderately satikctory. Sodium perborate had no advantage. Nonsulfur vulcanization gave promiaing results. Com- binationa of quinone dioxime, quinone dioxime dibenzoate, red lead, and lead peroxide produced vulcanizater with considerably higher tensile strength and somewhat greater hardneaa than did aulfur.
W. C. MAST, LEE T. SMITH, AND C. H. FISHER Eastern Regional Research Laboratory,
U. S. Department of Agriculture, Philadelphia, Pa.
ECAUSE of their flexibility and certain rubberlike charac- teristics, acrylic resins have been used in place of rubber for R some purposes (4, 6, 7). Since i t seemed reasonable that
the value of acrylic resins as rubber replacements would be en- hanced by vulcanization, an investigation of the preparation and properties of vulcanized or cross-linked acrylic polymers was in- augurated in this Laboratory. An earlier paper (8) described pre- liminary results, which showed that vulcanizable polymers could be prepared by copolymerizing acrylic esters with small propor- tions of polyfunctional monomers such aa butadiene, isoprene, and allyl maleate. The copolymers prepared were compounded with sulfur, vulcanization accelerators, and carbon black, and vulcanized with the equipment and techniques ordinarily used in processing natural and synthetic rubbers. These vulcanizates were more rubberlike than the unvulcanized acrylic resins and ap- peared to warrant further study.
The present paper describes the results of investigating certain vsriables in the production of vulcanized acrylic resins. To sim- plify the study and decrease the numerous possibilities afforded in copolymerization, compounding, and curing operations, ethyl acrylate and allyl maleate were selected as the acrylic and poly- fiinctional monomers. Ethyl acrylate was chosen because its polymers are softer and more rubbery than the other acrylic res- ina examined in the preliminary study. To provide information on suitable monomer concentrations and conditions of poly- merization, uniform compounding and curing conditions were i r e d in most experiments.
The monomers were eniulsion-polymerized because this opera- tion can be carried out conveniently both in the laboratory and plant, and also because emulsion polymerization ordinarily yields polymers of relatively high molecular weight. Hydrogen perox- ide (27.5%) and benzoyl peroxide were used to initiate poly- merization in the earlier experiments, but ammonium persulfate was employed after its advantages as catalyst were discovered.
Batisfactory copolymers were prepared with Triton K 60 (IO) as emulsifying agent and hydrogen peroxide aa catalyst, but an appreciable amount of polymer tvea usually precipitated during this reaction, necessitating the laborious removal of resin from the stirrer and vessel. Controlling the rate of polymerization offered some difficulties when hydrogen peroxide was used. Triton K 60 could not be employed with ammonium persulfate or sodium perborate catalysts because of precipitation or loss of emubifying action.
Tergitol Penetrant No. 4 (IO) worked satisfactorily with am- monium persulfate, sodium perborate, benzoyl peroxide, or hy- drogen peroxide. Little if any polymer precipitated from the emulsion during polymerization. Moreover, the polymer emul- sion could be completely broken merely by adding a dilute solu- tion of sodium chloride.
Acrylonitrile and dodecyl mercaptan were used in some of the experiments to decrease or prevent cross linkage (I). Polymeri- zation seemed easier to control in the presence of dodecyl mer- captan when hydrogen peroxide was used aa catalyst.
The copolymers were prepared, compounded, cured, and
