Accelerator-Activators from Amic Acids M . C. THRODAHL, R. 0. ZERBE, AND D. J. BEAVER' Organic Chemicals Division, Monsanto Chemical Co., .Vitro, W. Va.
ULC.iNIZATIOS of elastomers with thiazole type accelerators like benzothiazyl disulfide often may be enhanced if used in conjunction with a n activator. Types of organic compounds commonly used as accelerator-activators are : aminee, fatty acids and amine soaps of fatty acid*, and dithiocarb,mates Some of these have definite accelerator characteristics in addition to their activating propcities. -4 new class of powerful accelerator-activators has heen found in certain of the amic acid derivatives. Amic acids, or the half amides of dicarboxylic acids, and their Jalts have the following general structure:
Activation of thiazole accelerators in vulcanization of rubber stocks may be effected by several types of conipounds. Two important characteristics desired for accelerator-activators are that such compounds should be (1) low melting (about 100' C.) solids and (2) soluble or easily dispersible in the rubber stock. A new class of accelerator-activators derived from amic acids possesses valuable properties for natural rubber and GR-S. Unsubstituted oxamic acid and its several esters and salts retarded cure and were therefore unsuited as activators. Unsubetituted maleamic acid retarded cure, but the butylamine salt of N-butylmaleamic acid was a strong activator. Unsubstituted succinamic acid and derivatives prepared therefrom were moderate in their activity. The alkylamine salts of N-alkylphthalamic acids were powerful activators. Many of the compounds, particularly the alkylamine salts of N-alkylphthalamic acids, were stable, low melting solids which dispersed readily. Present day economics are favorable for thefie latter compounds.
I
where KI and Rz are hydrogeii, alkyl, aralkyl, or cycloalkyl groups, and h.1 is hydrogen, or a salt-forming group puch a8 a metal, ammonium, or an amine. A4nlic acids were described many years ago when Reissert ( 3 ) reported oxamic acid, CONK*,
I
CONTROL / O
o/o
iu 1804; Aiischuetz ( 1 ) nialeanlic acid, HC-CONH,,
/
COOH in 1890;
/I
&rda
€€CCOO€1 and Wiedemarin (4)succinariiic acid, H$C---COSHz,
I
HZC-COOH
-~
1 Yresent address, Orgarlic Chemical& Division, Monsanto Cheniical Co., S t . Louis. hlo.
ob
5
IO
TIME
IN
(5 20 25 MINUTES 1 2 1 O C .
30
3
Figure 1. Scorch Curles of Natural Kuhher Stocks Activated with Succinamic .4cid Derivatives
2. .-C2H5 - CH(GH $2
z
13
A
/"'O
./a
I.
> 100-
W
A
z
-
0
g
0
50-
-
-6-
- c-
- 6I - c-
a
Figure 3. Modulus TS. Time of Cure of Satirral Itubber Stocks Activated with Butylamine Sal t 4 of iV-Butylamic .icids Shaded area = 500% mudulu* Shaded plu. colid area =700%0 niodulu.
926
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
April 1951
TABLEI.
SCORCH -451) A%CTIVATING CHARlCTERISTICS OXAMIC .4CID DERIVATIVES Base formula
Activator
OF
Parta 100.0 85.0 1.3 1.o 0.6 1.0
Smoked sheet? Zinc oxide Sulfur Stearic acid Bensothiazyi disiilfide Activator
CO?u"*
Srresi-dtrsin Properties UtiUlti.\looney mate mate Scorch" Cure at at tensile, elonga1210 ~ , , 1 . 1 2 o C .LIodulus. . L h . ' S q s Ib.:sq. tion, Xin, M i n . 300% %500% 700% inch "0 10' 20 30
>6R
QOOH
Yo
30
Figure 1. Scorch (:urves of Satural Rubber Stocks Activated with But?lamine Salts of N-Butylamic Acids
10
>GB
S o vulranization effected
20
30;
A 0 0 C 2 H5
40
fiO
CON €Ics I3 b
15 20 25 IN MINUTES AT 121.C.
IO
TIME
viilcanization rRi.cwd
40' 60
com2
927
>6n
00 cI T 1I
110
10 20
900
233
224.5
885
X o vulcanization effected
30: 40
f j0
65
65
IO> 20 30
,ij
10
85
60
110
10 20
30 40
60
S o tulcanization effected
30 105 125 185
110 170 270
236 565 950
N o rulcanization 100 85 805 230 1080 300 1240 3.55
620 1185 2020
900 865 840
effected 440 1970 2365 2435
940 886
850 830
01
a > indicates thatscorching v o u l d occur in a time greater t h a n 65 minutes. t h i s was t h e duration of t h e t e s t period.
in 18~10:arid i\?cti:in
i c j ptitti:il:iinir acid,
0
I
IO TIME
I
I
30
40
J
-COOH
1886. Tlici conipouritis t i i s c u r d i l l this paper include tliese amic acids and derivatives thereof. Trro iniportant characttxristicd are desirable in accrleratoractivator..
w
c.
z
8 5c
Iphthalamic acid, p\~-COS(CsH,,
j,,
i~
n-liitc
(/-coos
f 0
I
5 TIME
I
10
IN
I
I
I
25 15 20 MINUTES AT 121'C.
I
30
Figure 6. EfTect of Fineness of Butylamine Salt of \ Hiitjlphthalaiiiic. icid on Scorch of hntrrral Iiiihlwr Stocl.
sllid nielting ut, 189" C., showed mild activatiiig prupr.1.tir.s at the vulcanizing temperature of 112" C. At 155" (!.: hu\\-c~vcr, this compound was considerably more effcctivv. Tlitb ziiic salt of dic~clohcsq-lphthalaniicacid WHP sonie\\.hat nie>rc' :icrive than rhc free acid, b u t the differences bct,ween t l i f ~ m \vvw siiinll. Of thc ciic?ciohesylaniiii(, derivatives only the iiliiit.
125
gm150[ loo
P !
TIME IN MINUTES AT 121.C.
Figure 7. Scorch Curves of Natural Rubber-Carbon Blacli Stocks Activated with Alkylamine Salts of .\-Allqlphthalamic .\cids
Figure 8. Scorch Curves of Natural Rubber-Whiting Stocks Activated with Butylamine Salt of ,V-Butylphthalamic Acid
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1951 TABLE I\-,
S C o R C l € .4XU
. % C T I \ h T I S G CHARACTERISTIC$ .$CID I~ERIYITIVES
PHTH4L.IXIC
OF
( B a s e forinitla same a s s h o w n i n Table I ) Stress-Strain __Properties Alooney UltiRrorrh mate at ?lire a t 1 2 1 ~c,, 1 4 2 ~c , , A m , Lb. S q Inch >fin. llin. 300Yc 500Co 700'; inch
&' $:
.\ r t i vat o r
30
5j
--COS[C~HI;)~
?R
165
10
20 30 40 60
165 160 165 160
10
40 60
80 210 215 230 220
10) 2o ~. 30' 40 60
10.5 I25 133
20 30
--C'OOH.IIS(C~H~I)? 68
220 235 380
110 10.5
40 ti0
R80
760 138.j
Utimate
"'t"p0Y-
1620 1980 2595
880 910 823
X n vulraniaation effected
530 490
435 530
2113 1893 l6li 2013
3110 3400 3035 2900
780 830
735 2745 3420 3320 320.5
780 735 775 i6i 780
l!r0
387
630 600
2520 2563
575
269,: 2275
64.;
?;
So viilcanisation effected 230 802 1970
300 355
''5
1080 1240
2365 2435
885
850 830
929
in Table L- and Figurc 2. Thcsc compounds \\ere of greatest interest among itll the aniic: iicid derivatives tested. I n addition t o being the most powerful activators, they were readily dispcrsed in the rubber stock and were low melting. The butyl homolog was ideal, nicking at 95' t o 100' C., folloiveii by the isopropyl (120" to 121' C.) and the ethyl derivative (decompoacd a t 128' (2,). I n activating properties little difference was observed between thc ethyl and butyl homologs although the butyl derivatives W:LS slightly fastc%ras judged b y Mooney scorch tc The isopropyl derivative was the least activo o f the three homologs b u t was still a n effective activator. Dispersion was judged to be slightly better with the butyl homolog. The graphic conip:rrisoii,q of modulur: agaiwt time of cure (Figure 3) and Mooney .worth (Figure 4) for thc three Ijutylamine salts o f butyl substit.utet1 :iniic acids were taken from Tables 11, 111, and V and Figures 1 and 2. Stiuss-straiii results indicated only a slight :idvantage for the phthalamic dcrivativtt ovcr the succirianiic anti ma.lPamic itnalogs, imt. t.he 1Iooney scorch curves clearly differentiatmethe thrre analogs; the phthalamic was most scorchy, follo\\-td by thc. wccinamic and maleamic, respecti vcl y . Compounding Variations. The butylaminc salt of S-butylphthalamic acid was selected for further compounding study. A measure of its act,ivity is illustratrd by t,he data in Table VI and Figure 5. .\< l i t t l c as 0.2 part gave significant activation. .
b
)--CoN(C,H,,),
-Cook€.HX(C,H,,),, showed t,he kind of properti?. desired for this type activator, although the nielting point n~ 172" t o 174" C. This compound also eshihited awelrl:iting properties of its o x n . The alkylaminr salts of .~~-:rlk.lphthalainicacids are described
-
R-Grnii~) G € T b
c.,
142" 3Iin.
265 320 315 350 315
965 1185 1095 1055 1060
3365 3740 3685 3600
10 20 30 40 60
130 320 320 320 290
450 I055 1116 1125 I005
1540
i68b
10
265
20 30
310 295 295 280
BO Coritrol
Stress-Strain Properties Air boliib aged 4 hours a t 121' C.. 1-naged Stocks 80 Ib. jsq. i n c h -~ .~ __.__ UltiCltiUltiUltitilate IIiate mate mate Rlodulii-. ti.nsile. elongaLb, ~lod11l1,s ,sg, I;rl, rensile, ehngaLb./Sq. I n c h__ lh.,'sy. tinn, Ih./nq. tion, 300% 500cj, 700% inch % 300% 500% 70OmG inch 00
10 20 30 40 60
40
10
20 30 40 60
-
parisons ehoi&in Table \'I1 and Figure 6. During a ~ p a rof t the milling operation the rubber stock was heated sufficiently to Irlelt the activator (900 to g j c c.). ~t apparently n~:idclittle difference whether thc particlc size \vas through 200 n i d or retained on 8 mesh. The use of the alkylamine %Its of .V-alkylphthalamic acids in a fine thermal type c:irbon back (P-33) st,ock gave results coni-
30 105 130 145
750 740 710
3925 3935 3835 1665 3595
3460
1685 3425 3790 3615 3460
910 1120 1020 1045 I005
3240 3695 3500 3355 3385
3775 3985 3580 3660 3475
143
510 1380 1690 1743
S o vulcanization effected 685 875 195 270 2420 830 220 t00 2250 795 220 565 2365 780 170 515
475 535 575
3393
3615
700
435 410 345 335 365
1500 1430 1265 1325 1245
725 665 725 700 700
335 390 345 325 325
1355 1165 1090 1070
755 740 720 73.5 720
430 365 335 300 285
1425 1300 1210 1135 '225
720
, ,
.. .
,.
... ..
,
:. : : ,
,
,
., .. .
,
...
. . .. ... , ,
... li75 ..
,
2645 2916 2815 2730 2730
610 640 650 630 650
1035 2375 2705 2525 2345
175
2315 2700 2785 2745 252.5
600 665 666 680
1065 1815 1676 1390
685 700 680
600 665 655 045 fi30
593
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
930
Smoked s h e r t i Zinc oxide Sulfur Stearic acid Benzothiaayl disulfide
(-'ill.? a1 1420 C ' . , JIin
Vol. 43, No. 4
Rutylainine Salt oi .\--Biitylpiithalainic Acid. Part .~. ~0.5 1.0 -___-~ 0 200 mpsh 8 niesh 200 mesh 8 mesh 3 0 0 5 AIodulii., Lh ' 9 s Inch
C u i e a!
142"
c
hlill
300'7, 3Iodiiliii. Lb 'Sq.I n c h 10
20 30 10 60
40 60 60 11.5
ti0
10 20 30 40
60 10 20 30 40 t,0
so 1!J i 193
1R R
Zoo
2n0 190 160
I70 1 ,in
165 330 395 485
500% I I o d u l u s , 1,h. 5 0 . I n c h 220 4i0 7817 77: on.; 775 -, -t -i ) 8.5 3 750 625 7-10 920 605 64.5 77.5
790 1340 1520 1710
70076 M o d u l i i a , 1.h. 'Sq.Inch 710 1835 2933 3305 2765 3105 3365 2780 3100 2910 :3310 2505 3085 2380 2575
I Ii
20 30 40
40 ..
150 180 150 135
1470 2150 2055 2205
Ultimate Tensile Strength. 1410 2795 3250 3455 3140 3380 3230 3290 30x0 3240
20 a0 40 H0
835
740
790 765 760
,3 . ) ~-~ ,a,,
210 1 5,i
8 4 .i 9o:i 920 825 i.10
m n RJG.7
330n 2210 3120
Lb./SQ. Inch 3205 3610 3985 3802 3595 3445 3360 3290 3405 356,i
Ultimate Elunpation, % 78.5 . _.
1U
1 (I.-,
220 2-15
795 . _.
74.5
i.;n
725
745 730
73.7
745
7-10 7.55
i23 73,i
70.5 7 10 73:
Nu vulcanization cffpcred Hiise formula
partrhle t u the pre~~ioriely descrihed stocks. 'I'nblr VI11 anii Figure i show that the ethyl, isopropyl, and butylamine malogs are very active: the but,yl is strongest of the group. Cse of 1.6 Iiarts benzothi:izyl disulfide ns a control did not give a stock which would scorch in less than 25 minutes a t 121O C. The lnitylamine salt of S-l~utylphthalamicacid n-as found to he 11 powerful activator for ~V-c~cIohr:syl-2-henzothiazole sulfenainide. AP S h O W l l in Table I X and Figure 8 as little as 0.25 part of the wctivator gave a rapid iiicirase in rntje of CUIP. ACKNOWLEDG3IEUT
'lhau1hor.q nish t o thank the M o n m i t o Cheiiiicnl permission t o publish this paper. were prepared by T. W. Bart-
All the nmic acid derivatives
(1890). :%:
-\suhan,
Der.,
19,
1402
lhd.,
37,
3721
(1886). ' 6 ) lieisaert,
(1904). ( 4 1 Serda and Wiedemann, Ibid., 23, 3284 (1890).
( 'ii, for
Activaior. Part
0
('lire a t 1210 Mm.
c..
:0i 4 ,i
60
Swoked sheet 1'43 black Zinc oxide stearic acid
Partfi 100 3 !L
7
1
Base formula
Parts
3
f'araflux Benaothiazyl disulfid? Activator S::lfur
i1 , 6 1
1
B
Stress-Strain (Cnuge9__ _ _ _ _ . Propertie,< .~~ 1 1-lti.-.l.t.i Cure a t
1210
c.,
Min.
hlodulus, Lb./Sq. I n c h 300% 500% 700%
inate
&ate
inch
%
g7Q2: ' zo"[&-
S o \--ulcanization effected S o vulcanization effected 20 30
210 430 110 320
740 1325 'j9.5 li9S
20 30 20 30
80.5 3185
303 393
990 1390
2700 3460
2140
3276
3226 3900 940 4125
830 770 73.5
33ft7
790 7.5.5
3825
806
