Method and composition for inhibiting acrylate ester polymerization

This invention relates to compositions and methods of inhibiting acrylate monomer polymerization at elevated temperatures comprising adding to the acrylate monomer an effective amount for the purpose of (a) a hydroxylamine having the formula ##STR1## wherein R and R' are the same or different and are hydrogen, alkyl, aryl, alkaryl or aralkyl groups, and (b) a para-phenylenediamine or derivative thereof having at least one N-H group. Preferably the phenylenediamine is a para-phenylenediamine having the formula ##STR2## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups with the proviso that at least one of R.sup.1, R.sup.2, R.sup.3 or R.sup.4 is hydrogen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a composition and method for use in inhibiting 
acrylate monomer polymerization at elevated temperatures. 
2. Description of the Prior Art 
It is well known in the art that acrylate monomers readily polymerize and 
that the rate of polymerization increases with increasing temperature. 
Common industrial methods for producing the acrylic monomers typically 
include purification processes such as distillation to remove impurities. 
However, purification operations carried out at elevated temperatures 
result in an increased rate of undesirable polymerization. The 
polymerization of acrylate monomers is undesirable because it causes 
fouling of processing equipment and it renders the compounds unfit for use 
without further treatment. 
Known polymerization inhibitors for acrylates include phenothiazine, 
hydroquinone, the methyl ether of hydroquinone, benzoquinone, and 
methylene blue. Of primary interest is Japanese Pat. No. 47-18820 which 
discloses the use of dialkylhydroxylamine of generic structure 
##STR3## 
(with R and R' as its alkyl radicals), singly or together with other 
sundry polymerization inhibitors, to inhibit polymerization of unsaturated 
compounds of generic structure 
##STR4## 
(where R stands for hydrogen or methyl radical and R' and R" for alkyl 
radicals). Also, May in U.S. Pat. No. 3,408,422 discloses a process for 
stabilizing ethylenically unsaturated polyesters and a composition 
stabilized against premature gelation comprising (1) a hydroxy--containing 
ethylenically unsaturated polyester of a glycidyl polyether of a 
polyhydric phenol and an ethylenically unsaturated monocarboxylic acid, 
and (2) a hydroxylamine compound. 
Phenylenediamines alone or with oxygen are known in the art as 
polymerization inhibitors in acrylate systems. Otsuki et al. in U.S. Pat. 
No. 3,674,651 discloses a process for inhibiting the polymerization of 
acrylic acid using a combination of diphenylamine or its derivatives and 
an oxygen-containing gas, or mixtures of diphenylamine or its derivatives 
with benzoquinone and/or hydroquinone mono-methyl-ether and an 
oxygen-containing gas. Wilder, in U.S. Pat. No. 4,016,198, discloses a 
method of inhibiting polymerization of unsaturated carboxylic acid esters 
and improved unsaturated carboxylic acid ester compositions comprising 
incorporating into the ester composition a combination of 
polyalkyleneamines and certain N-aryl-o or p-phenylenediamines. Also, 
Mullins in U.S. Pat. No. 4,017,544 discloses the use of a class of 
N-(nitroalkyl)-N'-phenyl-p-phenylenediamines to inhibit the polymerization 
of unsaturated carboxylic acid esters. Findeisen in U.S. Pat. No. 
4,267,365 discloses a process for the preparation of certain oligomeric 
acrylic acids wherein the acrylic acid is heated in the presence of 0.001 
to 1% by weight of a polymerization inhibitor consisting of molecular 
oxygen, nitric oxide, a phenol, a quinone, an aromatic amine, a nitro 
compound or diphenylpicrylhydrazyl to a temperature from about 50.degree. 
to 200.degree. C. Clonce et al. in U.S. Pat. No. 4,480,116 discloses an 
improved method for preparing and processing readily polymerizable 
acrylate monomers by employing phenyl-para-benzoquinone, 
2,5-diphenyl-para-benzoquinone, or a mixture thereof. None of these prior 
art references recognizes the unique synergistic mixture of hydroxylamine 
and phenylenediamine or derivatives thereof having at least one N-H group 
as desirable for inhibiting acrylate ester polymerization. 
SUMMARY OF THE INVENTION 
This invention relates to compositions and methods of inhibiting acrylate 
monomer polymerization at elevated temperatures comprising adding to the 
acrylate monomer an effective amount for the purpose of (a) a 
hydroxylamine having the formula 
##STR5## 
wherein R and R' are the same or different and are hydrogen, alkyl, aryl, 
alkaryl or aralkyl groups, and (b) a phenylenediamine or derivative 
thereof having at least one N-H group. Preferably, the phenylenediamine is 
a para-phenylenediamine having the formula 
##STR6## 
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different 
and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups with the proviso 
that at least one of R.sup.1, R.sup.2, R.sup.3 or R.sup.4 are hydrogen. 
This mixture provides an unexpectedly higher degree of polymerization 
inhibition of acrylate monomers than the individual ingredients comprising 
the mixture at elevated temperatures. It is therefore possible to produce 
a more effective acrylate polymer inhibiting composition and method than 
is obtainable by the use of either ingredient alone. Because of the 
enhanced polymer inhibiting activity of the mixture, the concentrations of 
each of the ingredients may be lowered and the total quantity of the 
polymerization inhibitor required for an effective treatment at elevated 
temperatures may be reduced. 
Accordingly, it is an object of the present invention to provide 
compositions and methods for inhibiting the polymerization of acrylate 
monomers at elevated temperatures. It is another object of this invention 
to control fouling of processing equipment due to the polymerization. It 
is a further object of the present invention to provide economically 
effective polymer inhibiting compositions and methods. These and other 
objects and advantages of the present invention will be apparent to those 
skilled in the art upon reference to the following detailed description of 
the invention, which demonstrates the synergism of the compounds 
comprising the instant invention.

DETAILED DESCRIPTION OF THE INVENTION 
The hydroxylamines used with phenylenediamine or derivatives thereof having 
at least one N-H group in accordance with the instant invention correspond 
to the chemical formula: 
##STR7## 
wherein R and R' are the same or different and are hydrogen, alkyl, aryl, 
alkaryl, or aralkyl groups. The alkyl, alkaryl and aralkyl groups may be 
straight or branched-chain groups. Preferably, the alkyl, aryl, alkaryl, 
or aralkyl groups have one to about twenty carbon atoms. Examples of 
suitable hydroxylamines include N,N-diethylhydroxylamine; 
N,N-dipropylhydroxylamine; N,N-dibutylhydroxylamine; 
N,N-butylethylhydroxylamine; N,N-2-ethyl-butryloctylhydroxylamine; 
N,N-didecylhydroxylamine; N,N-dibenzylhydroxylamine; 
N-benzylhydroxylamine; N,N-butylbenzylhydroxylamine; 
N-phenylhydroxylamine; N,N-butylphenylhydroxylamine; 
methylbenzylhydroxylamines; ethylbenzylhydroxylamines; etc. The term 
"methylbenzylhydroxylamines" is meant to include mixtures of 
benzylhydroxylamines and methylbenzylhydroxylamines, such as Mixture B in 
Table III described below. Also, the term "ethylbenzylhydroxylamines" is 
meant to include mixtures of benzylhydroxylamines, such as Mixture A in 
Table III described below. Most preferably, the hydroxylamine is selected 
from the group consisting of N,N-diethylhydroxylamine, 
N,N-dibenzylhydroxylamine, methylbenzylhydroxylamines, and 
ethylbenzylhydroxylamines. 
The phenylenediamine component of the inhibitor mixtures of this invention 
include phenylenediamine and derivatives thereof having at least one N-H 
group. It is thought that ortho-phenylenediamine or derivatives thereof 
having at least one N-H group are suitable for use in accordance with the 
instant invention. However, the preferred phenylenediamine is 
para-phenylenediamine having the formula 
##STR8## 
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different 
and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups with the proviso 
that at least one of R.sup.1, R.sup.2, R.sup.3 or R.sup.4 is hydrogen. 
More preferably, the alkyl, aryl, alkaryl and aralkyl groups have one to 
about twenty carbon atoms. The alkyl, alkaryl and aralkyl groups may be 
straight or branched-chain groups. Exemplary para-phenylenediamines 
include p-phenylenediamine wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 
are hydrogen; N,N,N'-trialkyl-p-phenylenediamines, such as 
N,N,N'-trimethyl-p-phenylenediamine, N,N,N'-triethylphenylene-p-diamine, 
etc.; N,N-dialkyl-p-phenylenediamines, such a 
N,N-dimethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine, etc.; 
N-phenyl-N',N'-dialkyl-p-phenylenediamines such as 
N-phenyl-N'-N'-dimethyl-p-phenylenediamine, 
N-phenyl-N',N'-diethyl-p-phenylenediamine, 
N-phenyl-N',N',-dipropyl-p-phenylenediamine, 
N-phenyl-N',N'-di-n-butyl-p-phenylenediamine, 
N-phenyl-N',N'-di-sec-butyl-p-phenylenediamine, 
N-phenyl-N'-methyl-N'-ethyl-p-phenylenediamine, 
N-phenyl-N'-methyl-N'-propyl-p-phenylenediamine, etc.; 
N-phenyl-N'-alkyl-p-phenylenediamines, such as 
N-phenyl-N'-methyl-p-phenylenediamine, 
N-phenyl-N'-ethyl-p-phenylenediamine, 
N-phenyl-N'-propyl-p-phenylenediamine, 
N-phenyl-N'-isopropyl-p-phenylenediamine, 
N-phenyl-N'-butyl-p-phenylenediamine, 
N-phenyl-N'-isobutyl-p-phenylenediamine, 
N-phenyl-N'-isobutyl-p-phenylenediamine, 
N-phenyl-N'-sec-butyl-p-phenylenediamine, 
N-phenyl-N'-tert-butyl-phenylenediamine, 
N-phenyl-N'-n-pentyl-p-phenylenediamine, 
N-phenyl-N'-n-hexyl-p-phenylenediamine, 
N-phenyl-N'-(1-methylhexyl)-p-phenylenediamine, 
N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, 
N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, etc. Preferably, the 
para-phenylenediamine is selected from the group consisting of 
N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, 
N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, and 
para-phenylenediamine wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are 
hydrogen. 
The present invention is applicable to readily polymerizable acrylate 
monomers. The term "acrylate monomer" as used herein is intended to 
include acrylic acid, methacrylic acid and the various esters of acrylic 
acid and methacrylic acid. Such acrylate esters can include n-alkyl, 
secondary and branched-chain alkyl esters of acrylic acid and methacrylic 
acid. Exemplary esters of acrylic acid include methyl acrylate, ethyl 
acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl 
acrylate, sec-butyl acrylate, 2-methylbutylacrylate, 3-methylbutyl 
acrylate, 2-ethylbutyl acrylate, 1,3-dimethylbutyl acrylate, pentyl 
acrylate, hexyl acrylate, 2-ethylhexyl acrylate, heptyl acrylate, 
1-methylheptyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, 
hexadecyl acrylate, etc. Exemplary esters of methacrylic acid include 
methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl 
methacrylate, butyl methacrylate, isobutyl methacrylate, sec-butyl 
methacrylate, tert-butyl methacrylate, hexyl methacrylate, octyl 
methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, decyl 
methacrylate, etc. Preferably, the acrylate ester is n-butyl acrylate. 
The total amount of hydroxylamine and phenylenediamine or derivatives 
thereof having at least one N-H group used in the compositions and methods 
of the present invention as a polymerization inhibitor is that amount 
which is sufficient to effect inhibition of polymerization and will, of 
course, vary according to the particular acrylate monomer and conditions 
under which it is used. At higher temperatures, larger amounts are 
generally required. Preferably, the total amount of hydroxylamine and 
phenylenediamine or derivatives thereof having at least one N-H group is 
from about 1 ppm to about 10,000 ppm based upon the weight of the acrylate 
monomer. Most preferably, the total amount of the aforesaid compounds is 
from about 1 ppm to about 1000 ppm based upon the weight of the acrylate 
monomer. The relative concentrations of hydroxylamine and phenylenediamine 
or derivatives thereof having at least one N-H group are generally in the 
range of about 5 to about 95 weight percent hydroxylamine and about 95 to 
about 5 weight percent phenylenediamine or derivatives thereof having at 
least one N-H group based on the total combined weight of these 
components. Preferably, the molar ratio of hydroxylamine to 
phenylenediamine or derivatives thereof having at least one N-H group is 
about 1:10 to about 10:1 and, most preferably, the molar ratio is about 
1:5 to about 5:1. 
The term "elevated temperatures" as used herein means temperatures at and 
above the boiling point of the particular acrylate monomer utilized. Of 
course, since the boiling points of the various acrylate monomers are 
different, the elevated temperatures will vary depending upon the boiling 
point of the particular acrylate monomer utilized at the particular 
pressure at which the acrylate monomer is added. For example, the boiling 
point of n-butyl acrylate is about 294.degree. F. at 760 mm pressure, so 
the elevated temperature for n-butyl acrylate would be 294.degree. F. and 
above at 760 mm pressure. 
The methods and compositions of the present invention can control the 
fouling of processing equipment, such as equipment used in the separation 
and purification processes of acrylate monomers, which is due to or caused 
by the polymerization of the acrylate monomers. The instant invention is 
useful as a process inhibitor, which is employed during the preparation 
and processing of the acrylate monomer. The invention can be utilized 
under normal pressure (760 mm), under superatmospheric pressure or under 
reduced pressure. The hydroxylamine and phenylenediamine or derivatives 
thereof can be provided to the acrylate monomer by any conventional 
method. The components can be added to the acrylate monomer as a single 
composition containing the inhibitor compounds or the individual 
components can be added separately or in any other desired combination. 
The composition may be added as either a concentrate or as a solution 
using a suitable carrier solvent which is compatible with the acrylate 
monomer. 
To demonstrate the synergism which is provided by the inventive combination 
of compounds, the data set forth below was developed. The following 
examples are included as being illustrations of the invention and should 
not be construed as limiting the scope thereof. 
EXAMPLES 
Polymerization inhibition of n-butyl acrylate was evaluated by the reflux 
test method. A round-bottom flask equipped with a condenser, a magnetic 
stirrer, and gas inlet and outlet tubes was flushed with nitrogen for ten 
minutes. Freshly distilled n-butyl acrylate (20 mL-vacuum distilled at 
about 40.degree. C. to remove MEHQ inhibitor) with the additive being 
tested was added to the flask and the apparatus was again flushed with 
nitrogen for ten minutes. The mixture was heated at reflux (294.degree. 
F.) for two hours whereupon a 10 mL aliquot of the mixture was added to 90 
mL of methanol in a calibrated centrifuge tube. The amount of polymeric 
liquid that settled was recorded. The less polymer observed, the more 
effective the treatment. The results are reported in Table I below. It is 
believed that the fluctuations in the mL of polymer for the lower dosages 
in Table I may have been due to a malfunctioning pipette that was 
determined to be over-dosing at the low dosages after most of these 
experiments were conducted. 
TABLE I 
______________________________________ 
PDMBPDA DEHA No. Ave. mL 
ppm ppm Tests mL Polymer Polymer 
______________________________________ 
25 0 4 2.3, 3.0, 3.5, 5.5 
3.6 
0 25 4 4.5, 3.5, 3.5, 3.3 
3.7 
12.5 12.5 1 0.03 0.03 
10 15 1 4.5.sup.a 4.5.sup.a 
10 15 11 2.8, 0, 0.5, 0, 0, 0, 
0.4 
0, 0, 0, 0, 1.6 
12 0 2 0.5, 2.9 1.7 
8 0 1 4.3 4.3 
0 16 1 3.3 3.3 
0 12 1 1.9 1.9 
0 10 1 1.9 1.9 
9 3 1 0 0 
6 6 2 0, 0.5 0.25 
3 9 1 0.1 0.1 
0 0 3 .sup.b .sup.b 
______________________________________ 
PDMBPDA = N--phenylN'--(1,3dimethylbutyl)-p-phenylenediamine 
DEHA = N,N--diethylhydroxylamine 
.sup.a This data point was generated during one of the very first 
experiments that were run using the abovedescribed reflux test method and 
the technician conducting the experiment was still learning the technique 
therefore, it is believed that thi s data point is inaccurate, especially 
in view of the further data generated using 10 ppm PDMBPDA and 15 ppm DEH 
reported above. 
.sup.b Mixture became so viscous that it was not possible to obtain a 10 
mL aliquot. 
The results reported in Table I indicate that combinations of 
N-phenyl-N'(1,3-dimethylbutyl)-p-phenylenediamine and 
N,N-diethylhydroxylamine showed a synergistic effect in inhibiting 
polymerization at elevated temperatures. 
Further tests were conducted using other phenylenediamines (PDA) and 
hydroxylamines (R.sub.2 NOH). These tests used the procedure described 
above for Table I data and the results are reported in Table II below. 
TABLE II 
______________________________________ 
mL Polymer 
PDA ppm R.sub.2 PNOH ppm in 2 Hrs. 
______________________________________ 
PDMPPDA 25 None -- 3.0 
PDMPPDA 12.5 N,N--diethyl- 
12.5 0.0 
hydroxylamine 
p-PDA 25 None -- a 
p-PDA 12.5 N,N--diethyl- 
12.5 0.0 
hydroxylamine 
TMPDA 25 None -- a 
TMPDA 12.5 N,N--diethyl- 
12.5 a 
hydroxylamine 
PDMBPDA + 12.5 + None -- a 
p-PDA 12.5 
None -- N,N--dibenzyl- 
25 a 
hydroxylamine 
PDMBPDA 12.5 N,N--dibenzyl- 
12.5 0.03 
hydroxylamine 
None -- N,N--diethyl- 
12.5 a 
hydroxylamine + 
+ 
N,N--dibenzyl- 
12.5 
hydroxylamine 
______________________________________ 
a Mixture became thick and viscous and removal of an aliquot was 
impractical. 
PDMPPDA = N--phenylN'--(1,4dimethylpentyl)-p-phenylenediamine 
pPDA = pphenylenediamine [C.sub.6 H.sub.4 (NH.sub.2).sub.2 
TMPDA = N,N,N',N',--tetramethylp-phenylenediamine 
PDMBPDA = N--phenylN'--(1,3dimethylbutyl)-p-phenylenediamine 
The results reported in Table II indicate that 
N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine and p-phenylenediamine 
[C.sub.6 H.sub.4 (NH.sub.2).sub.2 ], both of which have N-H groups, 
exhibited synergism in inhibiting polymerization when used in combination 
with N,N-diethylhydroxylamine at elevated temperatures. However, the 
phenylenediamine without a N-H group, 
N,N,N'N'-tetramethyl-p-phenylenediamine, failed to show synergism with 
N,N-diethylhydroxylamine. Also, another hydroxylamine, 
N,N-dibenzylhydroxylamine, showed synergism when used in combination with 
N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine. But the test runs 
where two phenylenediamines and two hydroxylamines were used respectively 
showed no synergism. 
Additional testing was conducted to further evaluate the synergistic 
combination of the instant invention utilizing the reflux test method 
described above. Two mixtures were prepared for these additional tests. 
Mixture A was prepared by placing 15.9 g (0.15 mol) of anhydrous sodium 
carbonate, 7.0 g (0.1 mol) of hydroxylamine hydrochloride, 11.5 mL (12.5 
g, 0.1 mol) of benzyl chloride, 15 mL (16 g, 0.1 mol) of ethylbenzyl 
chlorides (about 30% ortho and 70% para isomers) and 130 mL of methanol in 
a 1-L round-bottomed flask. This mixture was heated and stirred at reflux 
for four hours, whereupon the methanol was removed by distillation. The 
remaining viscous mixture was stirred with 50 mL of water to yield a 
clear, colorless aqueous layer and a hazy organic layer. Separation of the 
layers resulted in 22.8 g (98% of theory) of crude dibenzylhydroxylamines 
(by gas chromatography--mass spectrometry analysis this mixture consists 
of N-monobenzylhydroxylamine, N-monoethylbenzylhydroxylamine, 
N,N-dibenzylhydroxylamine, N-benzyl-N-ethylbenzylhydroxylamine, and 
N,N-diethylbenzylhydroxylamine, plus other unidentified materials). The 
starting chlorides were virtually not present in the resulting product. 
Acidification of the barely basic aqueous layer yielded substantially no 
CO.sub.2. Mixture B was prepared using the same procedure as described 
above for preparation of Mixture A, but 6.3 (0.05 mol) benzyl chloride, 
7.0 g (0.05 mol) of o-methylbenzyl chloride, 7.0 g (0.5 mol) of 
m-methylbenzyl chloride, and 7.0 g (0.05 mol) of p-methylbenzyl chloride 
were used in place of the benzyl and ethylbenzyl chlorides, resulting in 
20.5 g (87%) yield of N-monobenzylhydroxylamine, 
N-monomethylbenzylhydroxylamine, N,N-dibenzylhydroxylamine, 
N-benzyl-N-methylbenzylhydroxylamine, and N,N-dimethylbenzylhydroxylamine, 
plus other unidentified materials. The results are reported in Table III 
below. 
TABLE III 
______________________________________ 
Molar Ratio 
PDMBPDA Hydroxylamine 
PDMBPDA: 
ppm ppm Hydroxylamine 
mL Polymer 
______________________________________ 
25 None -- 5.0 
23 2 DEHA 4:1 1.5 
21 4 DEHA 2:1 0 
19 6 DEHA 1:1 0 
15 10 DEHA 1:2 0 
11 14 DEHA 1:4 0 
20 5 Mixture A 
4:1 4.0 
17 8 Mixture A 
2:1 3.5 
13 12 Mixture A 
1:1 1.5, 2.0 
19 19 Mixture A 
1:1 a 
9 16 Mixture A 
1:2 a 
5 20 Mixture A 
1:4 a 
0 25 Mixture A 
-- a, a, 4.5 
20 5 Mixture B 
4:1 a 
17 8 Mixture B 
2:1 1.9 
13 12 Mixture B 
1:1 0, 2.0 
19 19 Mixture B 
1:1 0.5 
10 15 Mixture B 
1:2 0.1, 0.15 
9 16 Mixture B 
1:2 0.5 
5 20 Mixture B 
1:4 a 
0 25 Mixture B 
-- a, 2.4 
______________________________________ 
a Mixture became too viscous to be able to remove a 10mL aliquot. 
PDMBPDA = N--phenylN'--(1,3dimethylbutyl)-p-phenylenediamine 
DEHA = N,N--diethylhydroxylamine 
Polymerization inhibition of n-butyl acrylate was also evaluated by the 
viscosity test method, using an oil bath regulated at 285.degree. F. with 
a Thermo-Watch. Double distilled (under vacuum at about 35.degree. C. with 
about 12 inches distance from the flask to the condenser) n-butyl acrylate 
(10.0 mL) was placed in a 17 mL tube and 50 uL of 0.25 wt% xylene 
solutions of additives were added. The tubes were capped with a rubber 
septum, which was wired on. Two needles were inserted in the septum and 
argon was purged through for 30 sec., whereupon the needles were removed. 
The tubes were then placed in the oil bath and the viscosities of the 
solutions measured at appropriate times by inverting the tube and 
observing the time needed for the 7 mL bubble to reach the top of the 
inverted tube. The time required to obtain a viscosity of 20 sec. was 
calculated for each tube by interpolating between the two points that 
bracketed the 20 sec. viscosity using a semilog evaluation. If a viscosity 
of 20 was not reached in 5 days of testing, the data were extrapolated to 
obtain the time to reach a viscosity of 20 sec. If the reaction proceeded 
so fast that a viscosity of 20 sec. was missed, again the first two 
viscosity points were extrapolated to obtain the time to a viscosity of 20 
sec. The viscosity at the beginning of the test period was less than 1 
sec. Usually two to five viscosity determinations were made per tube. The 
results are reported in Table IV below. 
TABLE IV 
______________________________________ 
Additive mL of Air Time (a) 
______________________________________ 
None 0 112, 121 
DEHA 0 114, 113 
PDMBPDA 0 1258, 886 
DEHA (25 ppm) & PDMBPDA 
0 416, 935 
(25 ppm) 
None 0.2 137, 125 
DEHA 0.2 115, 113 
PDMBPDA 0.2 1271, 675 
DEHA (25 ppm) & PDMBPDA 
0.2 2052, 1784 
(25 ppm) 
______________________________________ 
(a) Values for None and DEHA only were approximated from one point using 
relative viscosity = 1 at time = 1 as the other point. 
DEHA = N,N--diethylhydroxylamine 
PDMBPDA = N--phenylN'--(1,3dimethylbutyl)-p-phenylenediamine 
While this invention has been described with respect to particular 
embodiments thereof, it is apparent that numerous other forms and 
modifications of this invention will be obvious to those skilled in the 
art. The appended claims and this invention generally should be construed 
to cover all such obvious forms and modifications which are within the 
true spirit and scope of the present invention.