Vulcanization of ChlorineContaining Acrylic Elastomers W. C. MAST AND C. H. FISHER Eastern Regional Research Laboratory,
U. S . Department of Agriculture, Philadelphia 18, Pa. available data have been obtained with chloropropyl acrylate copolymers and it appeared likely that the nature of the halogencontaining monomer is an important factor, the purpose of the present work was to prepare and determine the comparative vulcanization characteristics of copolymers of ethyl acrylate and various other monomers having halogen in the molecule. To a large extent the investigation consisted in comparing the ease with which various ethyl acrylate copolymers were vulcanized with two or more standard recipes. Bromine compounds are also suitable for vulcanization purposes ( 6 ) , but chlorine compounds were usually employed in the present study because of their relatively low cost. Polymeric ethyl acrylate can be made amenable to sulfur vulcanization by direct halogenation, but the chlorine in the polymers of the present study was introduced conveniently by polymerizing an alkyl acrylate (usually ethyl) with monomers containing chlorine. I n some instances ethyl acrylate was copolymerized with small quantities of two chlorine-containing monomers. It was assumed in the present work that copolymerization actually occurred when a mixture of two or more monomers was polymerized. Possibly the homogeneous appearance of the polymers and their amenability to sulfur vulcanization indicate that the products were true copolymers. Only the copolym'ers made from low boiling halogen monomers, such as vinyl chloride, 2-chloropropene, and vinylidene chloride, were analyzed for halogen. Approximately 90% of the theoretical chlorine was obtained in nearly all instances.
Earlier investigations showed that the 95% ethyl acrylate-5% 3-chloropropyl acrylate coploymer can be vulcanized readily with (a) sulfur and accelerators, (b) p-quinone dioxime and red lead, ( c ) dinitrobenzene and litharge, (cl) Polyac, and (e) amines and amine condensation products. To obtain additional information in this new versatile method of vulcanization and to determine whether the halogen atom can be used generally instead of olefinic unsaturation for vulcan5zation, various chlorine-containing ethyl acrylate copolymers were prepared and studied. Most of the copolymers vulcanized satisfactorily; this showed that the halogen atom is generally useful for vulcanization purposes. The various copolymers exhibited wide variations in molding characteristics, rate of vulcanization, and properties of the vulcanizates. Modified recipes were found preferable for some of the copolymers. The copolymer of 2-chloroallyl alcohol vulcanized most rapidly. Considerable attention was given to the 95% ethyl acrylate-2-chloroethyl vinyl ether copolymer (designated Lactoprene EV), which yielded vulcanizates having outstanding resistance to oils, oxidation, and heat aging.
C
OPOLYMERS of acrylic esters and dienes such as butadiene have been found (3, 8) capable of undergoing vulcanization with sulfur and certain accelerators. It was observed subsequently (6, 8) that halogen-containing acrylic resins, prepared conveniently (9) by copolymerizing 95 parts of ethyl acrylate with approximately 5 parts of either 3-chloropropyl acrylate or 2-chloroethyl acrylate, also can be vuloanized with sulfur and with certain other agents. Since polymeric ethyl acrylate is not sulfur-vulcanizable it was assumed that olefinic linkages and halogen atoms, respectively, are responsible for sulfur vulcanization of the ethyl acrylate-butadiene and ethyl acrylatechloropropyl acrylate copolymers. Considerable attention (1, 6, 6, 7) has been devoted recently to halogen-containing acrylic copolymers, with the result that a new type of elastomer (designated Lactoptene) having certain outstanding advantages and properties has been developed. Advantages of the halogen-containing acrylic copolymers include: (a) the nondccurrence of cross linkage during polymerization eliminates the necessity of using preventive agents and techniques; ( b ) the halogen-containing monomer, as well as the alkyl acrylate, is a liquid a t room temperature, and hence pressure equipment is not needed; ( c ) the copolymer is saturated, and therefore antioxidants and measures to prevent oxidation are unnecessary; and ( d ) the copolymer is readily soluble in several solvents. Vulcanizates (1, 6, 6, 7') prepared from the ethyl acrylate-chloropropyl acrylate copolymer have the following special properties: resistance to oxidation, long flex life, oil resistance, stability to aging a t normal or elevated temperatures, resistance to cut growth, and low permeability to certain gases. Further study of the preparation and vulcanization of halogencontaining acrylic copolymers seemed desirable in view of the advantages mentioned and the general lack of information on this new method of vulcanization. Since most of the currently
CHLORINE-CONTAINING MONOMERS
It was thought that, in order to be completeIy satisfactory for the preparation of vulcanizable ethyl acrylate copolymers, t h e chlorine-containing monomer should meet the following requirements: (1) It should be actually or potentially inexpensive and available commercially; (2) the boiling point a t atmospheric pressure should be between approximately 50 and 200 C.; (3) it should be capablb of distillation without decomposition or premature polymerization, and (4) capable of copolymerizing readily and satisfactorily with ethyl and other alkyl acrylates; (5) it should not lower the molecular weight of the copolymer seriously; (6) the copolymer formed should be capable of being vulcanized a t a satisfactory rate by several different recipes; (7) it should not cause pitting, bubbling, or blowing during vulcanization; (8) it should not raise the brittle point appreciably; (9) it should not adversely affect the milling and processing ease of t h e copolymer; and (10) the vulcanizates should have satisfactory tensile, elongation, hardness, and other characteristics. This, list of desirable characteristics was based on the properties of copolymers of ethyl acrylate and approximately 5% of t h e chlorine compound. The 5% vinylidene chloride copolymer, for example, cured slowly, whereas the 16% vinylidene chloride copolymers vulcanized satisfactorily. Some of the chlorine compounds copolymerized readily when they constituted only a small proportion of the monomer mixture, but whether copolymers containing large quantities of the chlorine monomer segment (such copolymers were beyond the scope of this study) could be made satisfactorily was not determined. O
107
O
108
INDUSTRIAL AND ENGINEERING CHEMISTRY
TARTX r. HALOGEXRIOYOMERSA N D THEIRDEFICIENT PROPERTIES Monomer Vinyl chloride Vinylidene chloride Allyl chloride 1-Chloropropene 2-Chloropropene 2 3-Dichloropropene Skhloroallyl alcohol 2-Chloroallyl lactate 2-Chloroallyl pelargonate a-Chloroacrylonitrile a-Chlorostyrene 8-Chloroethoxyethyl acrylate 3-Chloropropyl acrylate 2 3-Dichloropropyl acrylate C'hloromaleic anhydride Dimethyl chloromaleate Di-n-butyl chloromaleate Di-2-chloroethyl maleate 2-Chloroethyl vinyl ether
Deficient Properties6 2, 8 2, 6, 7,8 2, 4, 5 2, 4, 5 2, 8
Vol. 40, No. 1
butadiene is polymerized. Sinde cross linkage also might consume double bonds, butadiene should not be so effective in introducing olefinic linkages as its molecular weight would indicate.
Chloropropyl Butadiene Acrylate Equiv.b Equiv. c 0.865 2.38 1. 11 (0.564) 3.06 (1.53d) 0.705 1.94 0.705 1.94 0.705 1.94 o,972 (o,49d) 2 , 6 8 ( 1 , 3 4 d ) 0.583 1.60 0.328 0.90 0.232 0.637 0.617 1,70 0.39 1.07 0.305 0.83 0.364 1.00 0.59 ( 0 . 3 d ) 1 . 6 2 (0.814) 0.409 1.12 0.305 0.83 0.21 0.58 0.196 0.54 0.508 1.39
PREPARATION OF COPOLYMERS
The usual procedure was to polymerize, in emulsicin (Q), t)he mixture of monomers, which usually consisted of 95% ethyl ?, acrylate and 5% chlorine-containing monomer. Larger or 8 smaller proportions of the chlorine compound were used in some .. experiments. The agents and technique previously described 7 (8,9) were used for the emulsion polymerizations i n most in8' .. stances. The refluxing temperature and amount of catalyst or .. .. initiator depend somewhat upon the monomer used. In general, 8 more catalyst was required than when chloropropyl acrylate wax 8 7 employed. Efficient condensers and t'emperatures slightly under 6 refluxing were used in some experiments when low boiling mono.. mers such as 2-chloropropene (boiling point, 22.5" C.) byere used. Numbers refer to properties given i n text: absence of is not necessarily indication that monomer is satisfactory. The vinyl chloride copolymerization was conducted under presb From the standpoint of introducing one chlorine for each molecule of sure in a closed system (sealed tube). At the end of t.he copolybutadiene. e From the standpoint of introducing a n equal quantity of chlorine. merizations the emulsions were d On the hasis of one chlorine equivalent. steam-distilled to remove monomers or other volatile T A B L E 11. \'ULCANIZATION RECIrJEsa*b material. Coagulation was p-Qui- TriethylCalthen effected with brine as none ene cined Zinc Stearic Red Dioxime TetraMapIron previously described ( 6 , 8 ); the Oxide Acid Sulfur Tuads Lead ( G M F ) mine nesia Oxide l'olyac Recipe Rotax copolymers were washed (small 10 A 3 .. 10 2 .. .. .. .. rubber washing mill) with 10 E 0.i 2 2 '1' . . .. .. .. .. 10 L 3 .1. 10 1 .. .. .. .. water and allowed to stand a t 10 D 0,'s 2 2 .. .2. 1 .. 3 .. .. 10 2 1 5 .. room temperature for several 10 E 10 F 0:5 2 2 1 .. 1 5 .. .. days until dry. The viscosity 10 3 .. .. io 2 .. .. 1 .. 10 1 .. .2. .2. 1 .. .. of dilute toluene solutions (0.05 10 .2. .2. 10 ii 5 1 .. .. 2 '1' 2 15 1 .. gram per 100 ml.) was used as J 0.5 .. .. K .. .. .. io 2 2 15 .. .. previously described (6) in L 0:5 .. .. 2 1 .. .. 2 l? .. .. 5 MC 0 5 . . 2 1 . . 1 . . . . conjunction with Huggins' .. .. 2 1 .. .. 1 E N 0.5 .. equation as follows to csti.. .. 1 .. .. .. .. 2 .. 10 3 .. io 2 1 5 .. mate the relative molecular 10 2 .. '1' .. .. .. .. 2 10 3 .. .. 10 2 1 5 .. .. weights: . t
. I
.
I
I .
..
..
..
.. .. ..
..
..
10
.. 0
2
.. ..
.. ..
.. 2
.. ,.
2
I . . I
.. 1 .. 1
1 '
..
io . I
10
.. ..
.. .. 2
.. 2
..
..
All recipes are given a s parts per weight for each 100 parts of copolymer;
SRF carbon black except U and V.
.. 1 2 2 2 2
..
..
..
15 15 15
1 1
10
10
15
..
.. .. ..
1
..
1
..
..
. I
3
(n) = V a p ! C
z
1
1
+ 0.3 nP
each recipe contained 30 parts of
The compounding ingredients were dispersed i n the copolymers at, relatively low perature (approximately 125" F.) as previously described and not by the improved milling technique recently recommended (1, 7 ) . In view of recent data demonstrating that acrylic elastomers are degraded or undergo breakdown during cold milling, probably the copolymers i n t,hc milled stock had intrinsic viscosities of approximately one regardless of the intrinsic viscosity of the copolymer before milling. Iforeover, it is 1ikel.y that vulcanizates having improved physical properties would have been obtained if the improved milling technique had been used.
principal standard recipes were A to F. recipes based on sulfur: B, D , ,F, H, J, L, RI, y! V. recipes hased on G M F : A , C, E, G , I, K , P, R, V , W ; recibes based on Polyac: 0, Q ; recipes based on dmtrdbenaene: S; and recipe based on triethylene tetramine: T. C Also contained 5 parts of magnesium phenylstearate. d Also contained 10 parts of magnesium phenylstearate. e Also contained 10 parts of plasticizer KP-140. / Also contained 10 parts oi litharge and 4 parts m-dinitrobenzene. 0 Also contained 80 parts of Kalvsn. b
The halogen monomers used in the present study and certain properties in which they are deficient are given in Table I. Some of the monomers of Table I, such as vinyl chloride and vinylidene chloride, obviously are more effective than chloropropyl acrylate, the previous standard, on the basis of the quantity of chlorine placed in the polymer molecule. The structure of the chlorinecontaining segment, however, appeared to be more important than the quantity. Presumably the structure of the chlorine segment of the polymer chain varied greatly from one copolymer to another. Probably the chlorine of the vinyl chloride copolymers (and copolymers prepared from other monomers having chlorine on the polymerizable vinyl group) is located on the polymer chain, whereas the chloropropyl acrylate copolymers have chlorine in side chains. Since the molecular weight of the halogen monomers is higher than that of butadiene, none of the monomers of Table I is so effective in introducing chlorine as butadiene is in introducing olefinic linkages. Cross linkage usually occurs, however, when
TABLE 111. 570 CHLoROPRoPYL ACRYL.4TE-9570 ACRYLATECOPOLYMER (E 78A)0
ETHYL
Curing Curing Tensile Ultimate Shore A Intrinsic ViscosTime, Temp.. Strength, Elonga- HardRecipe \fin. F. Lb./Sq. In. tion, ness ity Ab 120 298 1610 560 63 5.lC B 180 312 1210 790 48 a Brittle point approximately - 18' C. (0' F.); additional data on thie copolymer have been given (6,8). b Zinc oxide 5 parts instead of 10 parts. 0 Intrinsic viscosity of copolymer.
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1948
109
TABLE IV. VINYLIDENE CHLORIDE COPOLYMERS Copolymer NO.
Vinylidene Chloride,
Vulcanization Intrinsic Viscosity
%
..
6 12 12 3 1.5 24 15 15 15 15 4 4 4 4 4 4 4 6 6 6 8 8 10 12 12 6 6 6 6 6
L-10 L-10 L-10 L-11 L-11 L-12 L-13 L-13 b L-14 L-14b L14b L-15c L-15c
.....
4:36 4.36 4.36 4.36 4.44 4.44 4.44
4.44
4.44 4.44 4.44 4.76 4.76 4.76 4.53 4.53 3.99 3.75 3.75 4.56 4.56 4.56 4.79 4.79
No. 1532, 3 1535 1575 1536, 7, 76 1538, 9 1540, 1 1753 1750 1749 1747 1828 1854 1873 1839 183 1832 1827
~~
B
S AA"&"B&
A & B
T F D B
F I
Wd
P/
FP
Fh
E
U
K V
K J
K K J F J K K J
Pitt.ed with recine minutes a t 298O ~ . . ~. ~ A when cured 120 ._ b 0.5% 2-bromoethyl acrylate also used.
0
Time, min. a t 298' F. 120 120 120 120 120 120 120 30 30 30,60,120 120 120 120 120" 120' 120' 120 120 120 120 120 120 120 120 120 120 120 120 120 60
Recipe A&B
~~~~~
F.
1% 3-chloro ropy1 also used. d 10 parts Z n 8 zinc ozide also used.
Tensile Strength, Lb./Sq. In. Pitted 1030 720 Pitted Pitted Pitted 1160 1150 950 Pitted 320 1780 1730 Pjtted Pitted Pitted 1300 970 1650 1150 1420 1360 1410 1380 1710 490 1400 1170 1290 1850
Ultimate Elon ation,
Shore A Hardness
540 930
32 42
&
Brittle P:int, C.
..
..
..
..
.. ..
iio
46 51 48
1 io0
47 74 64
620 1000
..
..
..
390 510 ,
.. ..
I .
-9
.. .. .. 65
620 510 580 720 650 510 400 280 470 1100 640 560 480 350
..
- 10
76 53
..
.. ..
-7
-5 fl
.. ..
55 59 56 60
Cured a t 312O F. f 5 Darts -~.. iron oxide also -. .. used. _ .. 2 parts triethyIGe tetramine a180 used. h 3 parts triethylene tetramine also used.
.
0
TABLE v. 8-CHLOROPROPENE COPOLYMERS Polymer No. H-45 L-20
L-21
Additional Monomer
%
Chloropro ene,
8
10
........
10
....... *
Intrinsic Viscosity 4.35
6
4.86
Chldropropyl acrylate, 2
3
3.60
L-37 L-38 L-39 L-40 L-42 L-44
Chloropropyl Chloropropyl Chloropropyl ChloroDronvl Chloropro&l Chloropropyl
3 3 3
1r;sbl.
8 3 3
4126 2.55 4.87
L-45 L-49
Chloropropyl acrylate, 4 Chloropropyl acrylate, 2
2 3
5.26 5.52
4. isoprene, 1 2; isoprene, 1 3; isoprene, I 2 4 4
..
Vulcanization Time, min. a t Recipe 298" F. F 30 30 120 30 A 30,60,120 Ka 120 E 60 E 120 F 120 J 30 E 120 F 120 W 30 F 60 F 60 F 60 F 30 F 60 F 60 E 60 F 120 L 120 120 30 F 120
P
3.77
L-33
acrylate, acrylate, acrylate, acrvlate. acrylate; acrylate,
No.
2 M-75b Chloroallyl alcohol, 1 a 1 part triethylene tetramine used in addition. b Crescent tear, 192 pounds per inch; break set, 23.5%; Bashore resilience, 5.
5
Tensile Strength Lb./Sp. 1;. I190 1240 Pitted 1600 Pitted 1230 1110 960 1210 1360 1240 1370 1210 1200 1240 1330 1280 970 1200 1150 1280 1560 1280 1200 930
Ultimate Shore ElonpaA tion, % Hardness 900 41 740 55 830 if0 860 920 730 300 850 860 430 580 570 660 760 870 730 590 530 230 580 340 820
..
40
Brittle Point, C.
.. .. ..
-3
..
-9
..
-11 13 -12 12
-
.. .., .... .. .. .. ..
VULCANIZATION RECIPES
The vulcanization recipes are referred to in the text and tables by the letters shown in Table 11. Most of the recipes of Table I1 are based on primary vulcanizing agents (2, 4, 12) used previously to vulcanize natural and certain synthetic rubbers. The recipes, all of which vulcanize the 3-chloropropyl acrylate copolymers, may be classified as follows: (a) sulfur and accelerators, ( b ) p-quinone dioxime ( 3 ) and oxidizing agents, (c) dinitrobenzene, ( d ) Polyac (10, I f ) , and (e) amines or amine condensation products. Amines (or amine condensation products) effect rapid vulcanization of chloropropyl acrylate copolymer even when used as the sole agent. When amines are included with other vulcanizing agents, they usually accelerate the curing and alter the properties of the vulcanizates. Calcined magnesia or iron oxide was used as an additional ingredient in some instances to accelerate the vulcanization or to prevent pitting. When the standard recipes, particularly recipes A and B of Table 11, failed to produce satisfactory vulcanizates, the formulas
were modified. Frequently it was possible to obtain satisfactory vulcanizates in this manner from copolymers that behaved unsatisfactorily with the standard recipes. [Since completion of the work described in this paper, more suitable recipes for vulcanizing certain chlorine-containing acrylic copolymers have been developed and described (I, 6, ?).] The suitability of the different copolymers was necessarily judged on the basis of currently known vulcanizing recipes. As a basis for comparison, copolymers of ethyl acrylate and 3chloropropyl acrylate were chosen (Table 111). These copolymers ( 6 t o 10% chlorqpropyl acrylate) have been made and vulcanized many times, and considerable information is available concerning some of their properties (6, 7 , 8 ) . The compounding ingredients referred to by trade names are: G M F (quinone dioxime); Kalvan (small particles of coated calcium carbonate) ; plasticizer KP140 (tributoxyethyl phosphate); Polyac [agent used by Sturgis and Trepagnier ( f f ) ] ;
INDUSTRIAL AND ENGINEERING CHEMISTRY
110
Vol. 40, No. 1
In addition to curing slowly and requiring special recipes, Chlorothe vinylidene chloride copolyVulcanization Brittle ethyl Intrinsic Tensile Ultimati 3 Shore A Hardness Point, mer vulcanizates had relatively Polymer Vinyl ViscosTime, Temp., Strength, ElongaOF. Lb./Sq. In. tion, % c. No. Ether, % ity No. Recipe min. high brittle points, The brittle 1140 770 40 L-35 5 4.01 1973 F 120 298 points depended primarily on 1974 E 30 298 1310 640 46 -13 298 1260 560 50 L-36 10 3.35 1983 E 60 the proportion of vinylidene 1PR4 F 120 -.. 298 1200 500 51 L-51 5 5 40 fl?? ?! 298 1110 660 45 chloride in the copolymer 298 1300 500 46 -14 298 1250 450 47 -16 (Table IV). Preliminary ex312 1480 880 39 -20 298 1270 600 50 -20 periments indicated that sol312 1480 750 44 -14 vent resistance was improved 298 1250 610 47 -2 1 M-47 5 298 1020 660 50 by copolymerization with 5:OO 298 1050 620 51 .. M-54 5 M-716 4 298 950 750 45 .. vinylidene chloride. 1520 700 36 .. Small quantities of chloroM-81 5 .. 870 730 47 propylacrylate or2-bromoethyl a Also oontained 1%2-chloroallyl alcohol. acrylate m-ere used in addition to vinylidene chloride in the preparation of copolymers L14 and L15 (Table IV) for the purpose of increasing the curing rate. Rotax (mercaptobenzoth'iazole) ; and Tuads (tetramethylthiuram This resulted in little improvement. disulfide).
TABLE VI. CHLOROETHYL VINYLETHERCOPOLYMER
..
..
..
2-CHLOROPROPENE COPOLYMERS
VINYLIDENE CHLORIDE C O P 0 LYM E R S
Vinylidene chloride copolymerized readily with ethyl acrylate, and the resulting copolymers had high molecular weights as judged by the intrinsic viscosities (Table IV). The copolymers cured slowly by most of the recipes tried, and only the copolymers containing relatively high proportions of vinylidene chloride vulcanized satisfactorily. The strong tendency of the vinylidene chloride copolymers to pit or blow during vulcanization was overcome in many .instances by using calcined magnesia and triethylene tetramine. Iron oxide was used successfully in several experiments to idcrease the curing rate. Several recipes (I, K, T, U, and V of Tables I1 and IV), developed particularly for vinylidene chloride copolymers, have not been studied with other copolymers.
TABLEVII. COPOLYAIER
OF
The 2-chloropropene-ethyl acrylate copolymers had high molecular weights and resembled the vinylidene chloride copolymers, in that vulcanization occurred slowly and its vulcanixates had relatively high brittle points (Table V). I n spite of the low rate of curing, several recipes were used successfully to vulcanize the chloropropene copolymers. Chloropropyl acrylate, isoprene, and 2-chloroallyl alcohol were used as additional monomers in the preparation of ethyl acrylate2-chloropropene copolymers (experiments L33 to M75, Table V). These more complex copolymers also were vulcanized satisfactorily. 2-CHLOROETHYL VINYL ETHER COPOLYMERS
Chloroethyl vinyl ether copolymerized readily with ethyt
95% ETHYLACRYLATE AND 5% 2-CHLOROETHYL VINYL ETHER",^
After Aging 3 Days a t 300° F. Tensile Ultimate Shore A Crescent Tensile Shore A Strength, Elongation, Hardness Tear, Bashore Break cret, strength, Elongation, hardness Lb./In. No. Recipe Lb./Sq. In. % Resilience % lb./sq. in. % 61 20550 A 60 1380 660 169 6 41.6 2053 B 60 Pitted ..... .. 2056 C 120 1580 440 179 6 27 24io 50 94 135 1170 690 2057 D 180 5 17.3 1220 230 63 1390 710 77 2058 0 120 6 13.8 1150 610 37 Q Pitted 2054 Designated Ad) 79E20 and prepared on a pilot plant scale by the Chemioal Engineering and Development Division of this laboratory. Vulcanized a t 298' F.. Sample required c.ooling before removal from mold. Vulcanization
Time, mn.
..
..
0
b t
TABLEVIII. %
2,3-Dichloropropene,
NO.
L-18
10
0
..
L-19
5
0
1.80
M-72
2
0
..
L-28 L-29
0
0
10 5
1194
Polymer
L-3Ze
L-508 a
b
2,3-DICHLOROPROPENE
2-Chloroallyl Alcohol,
0
0
%
3
3
See also experiment M-71, Table VI. 1 part triethylene tetramine also used. 2% 3-ohloropropyl acrylate also used.
Intrinsic Viscosity
No. 1914
19117
1.44
2.64
..
..
L .
1978 1979
AND
..
..
..
*. ..
..
..
.. ..
2-CHLOROALLYL ALCOHOL^ COPOLYMERS
Curing Time, Min. a t 298' F. 30 30 30 120 30 30 120 30, 60, 120 60 120 120 120 120 120 30 120 60 60 30 120
Recipe E
F
E
E F B F 0 F
F J
w
E
F J
w
X
J b
Y L
Tensile Strength Lb./Sq. Ih. 2020 1670 1400 1710 1220 1420 1165 Pitted 80 120 380 1120 1030 980 1020 1340 1160 1100 1410 1400
Ultimate Elongation,
%
110 130 160 270 230 710 690
....
>1100 >1100 900 640 620 >1100 220 450 480 550 260 500
Shore A Hardness
Brittle Point.
c.
-5 -3 - 13
- 10
..
31
40 34 44
50
40 59 45 46 44 56 47
.. .. .. .. ..
.. ..
..
..
. I
- 10 - 14 .. ..
January 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEIX.
Expt.
MISCELLANEOUS COPOLYMERS OF ETHYL ACRYLATE
Monomer, %
NO.
H-19-1 Vinyl chloride, 3 H-19-1 H-19-2 Vinyl chloride, 6 H-19-2 H-19-3 Vinyl chloride, 9 H-19-3 E-182 2-Chloroallyl lactate, 5 E-182 E-183 2-Chloroallyl lactate, 10 E-183 E-183 L-16 Chloroethyl maleate, 5 L-16 L-17 Chloroethyl maleate, 2 L-17 Chloroethyl maleate, 3, chloropropyl acrylate, 3 L-34 L-34 L-34 L-34 2-Chloroallyl pelargonate, 20 L-47 2-Chloroall 1 pelargonate, 10 L-48 E-263 Dimethyl cxloromaleate, 5 E-264 Dimethyl chloromaleate, 10 E-264 E-240 Dichloro-n-propyl acrylate 5 Chloromaleic anhydride, 3,'chloropropyl acrylate, 2 L-23 L-23 L-31 L-31 E-207 a-Chlorostyrene, 5 E-207 E-188 Chloroacrylonitrile, 2 E-189 Chloroacrylontrile. 5 p2hloroethoxyethyl acrylate, 5 E-89 E-89 M-50 n-Butyl chloromaleate, 10 M-50 n-Butyl chloromaleate, 20 M-51 M-51 M-100 1-Chloro-1-propene M-101 E-174 Dichloroisopropyl acrylate, 10 E-174 E-175 Diohloroisopropyl acrylate, 5 E-175 a 3 parts triethylene tetramine also used. b 2 parts triethylene tetramine also used. 0.5 part triethylene tetramine also used.
Intrinsic Viscosity 2.49 1.74 2.87 3.01 2.49 4.61 5.12 4.22
2.85 2.40 2.67 2.16 5.25 3.60 3.36 5.29 3.81 Insol.
4:44
5.28 4.60 4.80
Vulcanization Recipe F 1900~ E l9Olb F 1896 E 1897 E le03 F 1902 A 1692 B 1693 E 1760 B 1695 A 1694 E 1912 F 1905 1913 E F 1906 E 1927 F 1931 J 1962 1963 F 2050 F 2051 F 1952 E 1953 F 1951 F 1919 E 1918 F 1911 F 1928 E 1924 E 1774 F 1775 1726,7,1768 1 A B&E 1728,9,30 B: D & E A 1507 B 1506 E 2037c F 2036 F 2034 E 2035 A&D 2061 2 2059,'60 A&D 1678 A B 1679 A 1680 B 1681
acrylate, yielding polymers of high molecular weight. The 2-chloroethyl vinyl ether copolymers (Table VI) cured more slowly than the standard chloropropyl acrylate copolymer but more rapidly than the vinylidene chloride and 2-chloropropene copolymers. The tensile, elongation, hardness, and tear strength values of the chloroethyl vinyl ether vulcanizates were satisfactory. Unlike vinylidene chloride and 2-chloropropene, the presence of the ether segment in the polymer molecule had little effect on the brittle point (Table VI). The presence of 1% of 2-chloroallyl alcohol (experiment M71,Table VI) in the copolymer apparently was not beneficial. In addition to the advantages mentioned, chloroethyl vinyl ether has a satisfactory boiling point (109' C.) and has most of the qualifications desired in a halogen-containing monomer. Although chloroethyl vinyl ether copolymerizes readily with ethyl acrylate, i t can be stored and shipped in the absence of polymerization inhibitors. The principal advantage of this property is that redistillation or other means of removing an inhibitor immediately prior t o the copolymerization is not required. In view of the advantages of chloroethyl vinyl ether as the halogen-oontaining monomer, copolymers of 95% ethyl acrylate and 5y0 2-chloroethyl vinyl ether were made on a pilot plant scale by a rubber manufacturer and the Chemical Engineering and Development Division of this laboratory. This copolymer called Lactoprene EV ( E for ethyl acrylate and V for vinyl ether), has been investigated extensively (1,7). Suitable curing recipes in addition t o those given in Table VI and a description of the properties of the vulcanizates are included in recent publications (1,.)'7 As shown by data in Table VI1 and in another paper (I),some of the Lactoprene EV vulcanizates have exceptional resistance to aging or deterioration a t temperatures as high as 149' C.
.
(300' F.)
111
No.
w
Time, Min. a t 298O F. 60 120 60 60 120 60 120 180 60
iao
180 120 120 120 120 120 120 30 30 120 60 30 120 120 120 30 120 120 120 120 120 60-180 60-120 180 360 120 120 120 120 30 60 120 30: 60: 120 180 180 180 180
Tensile Strength Lb./Sq. Ih. 240 1440 290 Pitted 1440 340 1.160 Pitted 1.630 Pitted Pitted 1110 750 1160 620 1180 620 1140 1230 Pitted 980 650 1160 790 430 1310 1320 1150 1350 1870 1590 Pitted Pitted 1630 1360 Pitted Pitted Pitted Pitted Pitted Pitted 1450 1310 1500 1220
Ultimate Elon ittion.
$b
1100 570 1100
Shore
A
Hardness 50 63 50
..
1100 480
830
57 45 54
265
52
..
SO0
1100
820
1100 790 1100 380 630
iio
.. ..
66
44 49 45 46 37 48 39
..
1230 900 1150 1100 620 620 720 500 130 180
57 35 42 40 43 45 50 45 50 81 78
ii0
61 50
..
560
..... . .. ai0 470 480 730
.... *. 8 .
.. 51 55 47
2.3-DICHLOROPROPENE AND 2-CHLOROALLYL ALCOHOL COPOLYMERS
These two monomers appeared to lower the molecular weight somewh3 when copolymerized with ethyl acrylate, but the extent of this phenomenon was not serious for the low proportions of chlorine-containing monomers (10% or less) used in the present work. Dichloropropene and chloroallyl alcohol also tended to raise the brittle points of their ethyl acrylate copolymers (Table VIII). The dichloropropene-ethyl acrylate copolymers cured slowly and in most instances unsatisfactorily. The 95% ethyl acrylate3% dichloropropene-2% chloropropyl acrylate copolymers (experiments L32 and L50, Table VIII) were more suitable for vulcanization. The Zchloroallyl alcohol copolymers cured more rapidly than any thus far examined i n this laboratory (Table VIII). Vulcanizates were obtained even when the copolymer contained only 2% of the chloroallyl alcohol segment. Presumably the rapid curing is related in some manner to the structure of the chloroallyl alcohol segment, which possibly is as follows:
--CHZCH-CH,
I 6OOEt
8'
-CHzCH--
I
\
bHzOH '\ COOEt
MISCELLANEOUS E T H Y L ACRYLATE COPOLYMERS
Data obtained with various ethyl acrylate copolymers are given in Table IX. Vulcanizstes suitable for testing were obtained from most of the copolymers, but only pitted or defective products were obtained from the chloroacrylonitrile, di-n-butyl chloromaleate, and 1-chloropropene copolymers.
112
INDUSTRIAL AND ENGINEERING CHEMISTRY
A soft sticky polymer u*;ts obtained when a mixture of ethyl acrylate and 1-chloropiopene was polymerized. Even if a true copolymer was formed, it seems likely that the molecular weight was low. The polymerization of ethyl acrylate with chloromaleic anhydride was not entirelv satisfactory because of premature coagulation of some of the copolymer (approximately 60%). Probably this objection could be eliminated by the use of other conditions of polymerization. Some of the monomers of Table IX, such as vinyl chloride, dimethyl chloromaleate, chloromaleic anhydride, and chlorostyrene, raised the brittle points oi their copolymers. This feature is considered objectionable, although the brittle point can be lowered by plasticization or the use of additional monomers such as n-butyl or n-octyl acrylate. Some of the copolymers of Table IX, such as those made with 2,3-dichloropropyl acrylate, P-chloroethoxyethyl acrylate (CH,: CHCOOCHzCH~OCH&H~C1)and di-2-chloroethyl maleate, would appear to warrant further investigation when the monomers become more accessible.
Vol. 40, No. 1
fore, cost and availability are important factors in theselection of the halogen-containing monomer. When additional monomers of this type become available it is likely that they will be found useful in preparing vulcanizable polymers. ACKNOWLEDGMENT
The authors are grateful to C. S. Marvel, The B. F. Goodiich Company, Rlerck & Co., Naugatuck Chemical Company, National Aniline and Chemical Company, Shell Development Company, and The Rohm & Haas Company for supplying various monomers and other materials. The contributions and assistance of T. J. Dietz, W. E. Palm, R. L. Dean, W. W. Howerton, Mari0n.B. Dixon, C. E. Rehberg, and M. L. Fein of this laboratory are gratefully acknowledged. LITERATURE CITED
Diets, T. J., Mast, W. C., Dean, R. L., and Fisher, C. H., IND. ENG.CHEM.,38, 960 (1946).
Fisher, C. H., Mast, W. C., and Smith, L. T., Ibid., 36, 1032 (1944).
DISCUSSlON OF RESULTS
The experiments of Table I X and of some of the preceding tables indicate that halogen in the polymer generally facilitates vulcanization or cross linkage and that many halogen-containing polymers are amenable to sulfur and other types of vulcanization. Presumably nonacrylic polymers containing halogen also will be found vulcanizable by agents and techniques similar to those used with acrylic polymers. Some of the findings herein described may be applied in the preparation of cross-linked or modified coatings, laminates, and adhesives. Although most of the copolymeh examined (Tables I1 to IX) were vulcanizable, each copolymer had its own pecularities, which in many instances casused it to respond best to modified or special recipes. This suggest that suitable recipes can be found eventually for most halogen-containing polymers. There-
Fisher, H. L., Ibid., 31, 1351 (1939). Haworth, J. P., and Baldwin, F. P., Ibicl., 34, 1301 (1942). Leeper, H. M.,Govt. Evaluation Lab., Office of Rubber Reserve, Univ. of Akron CR 619 (1945). Mast, W. C., Dietz, T. J., and Fisher, C. H., I n d i a Rubber W o r l d , 113, 223 (1945).
Mast. W. C.. Diets. T. J.. and Fisher. C. H.. in areDaration. Mast] W. C : , Kehberg, C. E., Dieti; T. J., a i d &her, C. H., IND.ENG.CHEM., 36, 1022 (1944).
Mast, W. C., Smith. L. T., and Fisher, C. H., Ibid., 37, 365 (1945).
Sturgis. B. M . , Baum, A . A., and Vincent, J. R., Ibid., 36, 349 (1944).
Sturgiu, B. M . , and Trepagnier, J. H., Rubber Age (N. Y.), 54, 325 (1944).
War Production Board, Office of Rubber Director, No. 113.1 (Nov. 5 , 1942). RECEIVED October 25, 1946. Presented before the division of Paint, Varnish, and Plastics Chemistry a t the 109th Meeting of the AMEBICAN CHEMICAL SOCIETY, ritlantic City, N. J.
Permeation through and Sorption of Water Vapor by High Polymers PAUL M. HAUSER AND A. DOUGLAS McLARENI E. Z . du Pont de Nemours and Company, Znc., Buffalo,N . Y .
A
REICENT study ( 5 ) of the water vapor transmission by synthetic polymers indicated that the steady state permeability P of a film can be broken down into two factors represented by D , the diffusion constant, and S , the solubility coefficient-that is, P = DS (1) This equation is derived on the assumption that both Fick’s law and Henry’s law apply. I n the previous work P and D were determined by high vacuum technique and S was computed. The work of King ( 7 ) , Rouse (IO), and others demonstrated, however, that D is a function of the water content of a polymer film in many cases and is therefore not a constant. I n view of these findings it seemed desirable actually to measure S and P and calculate D to determine the relative humidity, temperature, 1
Present address, Brooklyn Polytechnic Institute, Brooklyn, N. Y .
and thickness range of application of this expression for a number of polymeric materials. In addition it seemed desirable to observe the behavior of a laminate of a good vapor barrier on a film of high transmissivity and water sorption in order to note the time requirements for the steady state to be reached. This was especially worth while since previous results ( 5 ) on samples of the same films (vinylidene chloride-acrylonitrile copolymer on cellulose) pointed toward a failure to observe Fick’s law with respect to coating thickness (Equation 2) when a vacuum technique waB used. PERMEABILITY MEASUREMENTS
The transmission of water vapor through films was determined by modifications of well known cup methods (4, IS). The permeability constant P was calculated from the definition:
