Organic peroxide stabilization with oximes

Peroxydicarbonate compounds are stabilized against decomposition by the presence of an effective amount of one or more oximes of the general formula ##STR1## wherein R.sup.A and R.sup.B are optionally substituted alkyl or alkenyl of up to 22 carbon atoms or phenyl, or form a C.sub.4 -C.sub.8 cycloalkyl ring.

FIELD OF THE INVENTION 
The present invention relates to organic peroxide compositions, and more 
specifically to peroxydicarbonate compositions, in which one or more 
oximes has been added to retard the rate of decomposition of the peroxide 
compound. 
BACKGROUND OF THE INVENTION 
Organic peroxides, such as peroxydicarbonates, are useful as free-radical 
initiators in the polymerization or copolymerization of ethylenically 
unsaturated monomers. 
For example, organic peroxides are used as initiators in the polymerization 
of vinyl halides, such as vinyl chloride or vinyl bromide; vinylidene 
halides such as vinylidene chloride; and other compounds containing 
polymerizable unsaturated units. The products of this well known 
polymerization process have extensive commercial applications. 
The polymerization of vinyl halides or the copolymerization of vinyl 
halides with vinylidene halides is usually conducted in an aqueous medium, 
i.e., emulsion, solution or suspension polymerization. In such 
polymerizations, the monomer or mixture of monomers is dispersed in water 
in the presence of a surfactant and thereafter the polymerization 
initiated with an organic peroxide. This is a well known reaction that has 
been widely reported. 
All organic peroxides are by their nature hazardous materials. Their 
usefulness depends on their ability to decompose into free radicals, shown 
by the following reaction: 
EQU RO--OR'.fwdarw.RO.+R'O. 
The rate of this decomposition reaction at any given temperature depends on 
the structure of R and R'. 
The decomposition reaction is exothermic. If exothermic decomposition were 
to occur during production, storage, or shipment, when the peroxides are 
in a concentrated form, excess pressure development and/or fire or 
explosion could result. Consequently, many organic peroxides must be kept 
refrigerated. 
There have been several reports in recent years of the retardation of the 
rate of decomposition of organic peroxides. 
The Journal of the American Chemical Society, Volume 72, pages 1254 to 1263 
(1950) discloses the use of, for example, ethyl acetoacetate, iodine, 
trinitrobenzene, acetanilide, nitromethane, phenol, hydrogen peroxide, and 
tetralin to retard the rate of decomposition of diisopropyl 
peroxydicarbonate. 
U.S. Pat. No. 4,515,929 (1985) reports aqueous dispersions of organic 
peroxides including peroxydicarbonates, which are stabilized against 
decomposition by the addition of diphenyl peroxydicarbonate or di(alkyl 
substituted) phenyl peroxydicarbonates. 
U.S. Pat. No. 4,552,682 (1985) discloses the use of phenolic antioxidants 
to retard the rate of degradation of aqueous organic peroxide dispersions. 
The use of phenolic antioxidants is undesirable because they result in 
discoloration. 
U.S. Pat. No. 5,155,192 (1992) discloses the use of organic hydroperoxides, 
e.g., tert-butyl hydroperoxide, to retard the rate of decomposition of 
peroxydicarbonates. 
U.S. Pat. Nos. 5,548,046 (1996) and 5,541,151 (1996) disclose the thermal 
stabilization of dialkyl peroxydicarbonates using unsaturated nitrites or 
unsaturated acetylenic compounds. 
SUMMARY OF THE INVENTION 
The present invention relates to the use of certain non-peroxide compounds 
which are effective in retarding the rate of decomposition of organic 
peroxides such as peroxydicarbonates. Thus, one aspect of the present 
invention is a composition containing an organic peroxide compound, such 
as a peroxydicarbonate, and one or more oximes which reduces the rate of 
decomposition of the peroxide compound. Another aspect of the present 
invention is the method of stabilizing a peroxydicarbonate against 
decomposition, comprising adding thereto one or more oximes in an amount 
effective to achieve said stabilization. 
The oximes useful in this invention include those of the formula (I) 
##STR2## 
wherein R.sup.A and R.sup.B are independently of each other hydrogen; 
branched or unbranched, substituted or unsubstituted, alkyl containing 1 
to 22 carbon atoms or alkenyl containing 2 to 22 carbon atoms; phenyl; or 
substituted phenyl; or R.sup.A and R.sup.B taken together with the carbon 
atom to which they are attached can form a substituted or unsubstituted 
cycloalkyl ring containing 4 to 8 carbon atoms; or R.sup.A can be 
--C(R.sup.C).dbd.N--OH wherein R.sup.C can be hydrogen; branched or 
unbranched, substituted or unsubstituted, alkyl containing 1 to 22 carbon 
atoms or alkenyl containing 2 to 22 carbon atoms; phenyl; or substituted 
phenyl; or R.sup.C taken together with R.sup.B and the carbon atom to 
which R.sup.B is attached can form a substituted or unsubstituted 
cycloalkyl ring containing 4 to 8 carbon atoms. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to compositions containing an organic 
peroxide, such as a peroxydicarbonate, and one or more oximes to retard 
the rate of decomposition of the peroxide compound. 
In the foregoing formula (I), the R.sup.A and R.sup.B groups (and the 
cycloalkyl group which R.sup.A and R.sup.B can cooperate to form) can be 
substituted or unsubstituted. When substituted, preferred substituents 
include phenyl, hydroxyl, acyl containing 1 to 4 carbon atoms, alkoxy 
containing 1 to 4 carbon atoms, ethers, esters containing a total of 1 to 
4 carbon atoms, aldehydes containing 1 to 4 carbon atoms, ketones 
containing 1 to 4 carbon atoms, nitro, or halogen (of which fluoro and 
chloro are preferred). The hydrocarbon substituents can be branched or 
unbranched. 
Preferred oximes include acetone oxime R.sup.A .dbd.R.sup.B .dbd.CH.sub.3), 
acetaldoxime (R.sup.A .dbd.H,R.sup.B .dbd.CH.sub.3), 2-heptanone oxime 
(R.sup.A .dbd.CH.sub.3,R.sup.B .dbd.n-C.sub.5 H.sub.11) and 
4-methyl-2-pentanone oxime (R.sup.A .dbd.CH.sub.3, R.sup.B 
.dbd.(CH.sub.3).sub.2 CHCH.sub.2 --). Other preferred oximes include 
2-butanone oxime, cyclohexanone oxime, 1,2-cyclohexanedione dioxime, 
dimethylglyoxime, and 4-fluorobenzaldoxime. 
Liquid oxime can be added directly. Solid oxime can be dissolved in 
inexpensive solvents and then added to the organic peroxide. Solvents 
useful in this regard include alcohols, such as methanol, ethanol, or 
2-propanol; ethers, such as 2-methoxyethyl ether; glycols, such as 
ethylene glycol; esters, such as ethyl acetate; and ketones, such as 
methyl ethyl ketone and diethyl ketone. 
The amount of oxime to use in the compositions of the present invention is 
an amount sufficient to retard the rate of decomposition of the peroxide 
compound. The preferred amount of oxime is a concentration of 0.2 to 5.0% 
by weight of the peroxydicarbonate or other organic peroxide present. When 
the oxime is added as a solution, the amount of the solution to use is 
adjusted according to the amount of oxime present in the solution. The 
exact amount will vary and depend on the organic peroxide compound, and on 
the conditions to which the peroxide composition is to be exposed. 
Peroxide compounds useful in this invention are of the general structural 
formula: 
EQU R.sup.1 --O--C(O)--O--O--C(O)--O--R.sup.2 
wherein R.sup.1 and R.sup.2 can each be an aliphatic, cycloaliphatic or 
aromatic group with 1 to 22 carbon atoms, preferably 2 to 8 carbon atoms. 
R.sup.1 and R.sup.2 may be branched or non-branched, substituted or 
unsubstituted alkyl, alkenyl, cycloalkyl or aromatic groups. 
Examples of R.sup.1 and R.sup.2 groups include phenyl, methyl, ethyl, 
n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, isobutyl, hexyl, octyl, 
neopentyl, 2-ethylhexyl, capryl, lauryl, myristyl, cetyl, stearyl, allyl, 
methallyl, crotyl, cyclohexyl, 4-t-butylcyclohexyl, 4-t-amylcyclohexyl, 
benzyl, 2-phenylethyl, 2-phenylbutyl, .alpha.-carbethoxyethyl, 
.beta.-methoxyethyl, 2-phenoxyethyl, 2-methoxyphenyl, 3-methoxyphenyl, 
2-ethoxyethyl, 2-ethoxyphenyl, 3-methoxybutyl, 2-carbamyloxyethyl, 
2-chloroethyl, 2-nitrobutyl and 2-nitro-2-methylpropyl. 
Specific examples of peroxydicarbonates include diethyl peroxydicarbonate, 
di-n-butyl peroxydicarbonate, diisobutyl peroxydicarbonate, and 
di-4-tert-butylcyclohexyl peroxydicarbonate. Preferably the 
peroxydicarbonate is di-sec-butyl peroxydicarbonate, di-2-ethylhexyl 
peroxydicarbonate, di-n-propyl peroxydicarbonate or diisopropyl 
peroxydicarbonate. 
The peroxide compound may be symmetrical or unsymmetrical i.e., R.sup.1 and 
R.sup.2 may be the same or different. The peroxide may be a homogeneous 
mixture containing symmetric peroxides, asymmetric peroxides such as 
isopropyl-sec-butyl peroxydicarbonate, or a mixture of symmetric and 
asymmetric peroxides such as mixtures of diisopropyl peroxydicarbonate, 
di-sec-butyl peroxydicarbonate and isopropyl-sec-butyl peroxydicarbonate 
as disclosed in U.S. Pat. No. 4,269,726. 
The peroxydicarbonate compounds can be synthesized by conventional 
techniques familiar to one of ordinary skill in the art. 
Peroxydicarbonates are typically prepared by reacting the corresponding 
alkyl chloroformate with aqueous sodium peroxide at low temperatures, 
0.degree.-20.degree. C. See U.S. Pat. No. 2,370,588 and the Journal of the 
American Chemical Society, Volume 72, page 1254 (1950). Other synthetic 
techniques will be familiar to one of ordinary skill in the art. 
Preferably, the peroxydicarbonates useful in this invention include those 
which are a liquid at 0.degree. C. and more preferably a liquid at 
-5.degree. C. Still more preferred are the peroxydicarbonates which are 
liquid down to -20.degree. C. 
The present invention is especially applicable to aqueous dispersions of 
peroxydicarbonates that are useful as initiators in the free radical 
polymerization of ethylenically unsaturated materials, particularly in an 
aqueous medium, e.g., suspension or emulsion polymerization. A dispersion 
of the peroxydicarbonate is prepared by dispersing it in water with a 
suitable dispersing aid, e.g., a surfactant or emulsifying agent. 
Surfactants and emulsifying agents useful in the formation of such 
dispersions are well known in this field and are quite numerous. 
To prepare dispersions in accordance with the present invention, the oxime 
or a solution thereof may be added to an already-formed peroxide 
dispersion, or to the water containing the surfactant, or to the peroxide 
before the dispersion is formed. Dispersions of the present invention 
generally contain 20 to 70% by weight, preferably 30 to 60% by weight of 
the peroxydicarbonate or other organic peroxide compound and 0.2 to 5.0% 
(by weight of the peroxide) of oxime. 
The manner of preparation of peroxide dispersions is known to one of 
ordinary skill in the art. A description of peroxydicarbonate dispersions 
and their preparation can be found in U.S. Pat. No. 4,515,929; U.S. Pat. 
No. 3,825,509; U.S. Pat. No. 3,988,261 and U.S. Pat. No. 4,092,470. 
Peroxydicarbonate compositions of the present invention may also be 
prepared as physical mixtures in the form of liquids, granules, powders or 
flakes. A physical mixture in accordance with the present invention may be 
prepared by mixing a liquid peroxide compound, or a solution of a peroxide 
in a suitable solvent, with the desired amount of a liquid oxime or a 
solution thereof in a suitable solvent in a conventional mixing apparatus. 
The resulting mixture is then, if desired, granulated, pulverized or 
flaked. The oxime may be added either (1) to the chloroformate-containing 
reaction mixture before preparation of the peroxide compound or (2) to the 
unprocessed reaction mixture immediately after preparation of the peroxide 
compound. Either (1) or (2) will ensure that the two components are mixed 
as homogeneously as possible in order to receive the greatest possible 
benefit from the stabilizing effect of the oxime. 
A solution of the present invention may be prepared by combining the 
desired amounts of oxime and peroxide in a suitable solvent. 
Suitable organic solvents include those normally employed for 
peroxydicarbonates such as esters of phthalic acid, an example of which is 
dibutyl phthalate, and aliphatic and aromatic hydrocarbons and mixtures of 
such hydrocarbons, examples of which are hexane, odorless mineral spirits, 
mineral oil, benzene, toluene, xylene and (iso)paraffins such as 
isododecane. Other suitable solvents will be familiar to one of ordinary 
skill in the art. 
Solutions according to the present invention preferably contain at least 
10% by weight and more preferably at least 25% by weight of a 
peroxydicarbonate compound. 
The peroxide compositions of the present invention display numerous 
significant advantages. Chief among these is improved thermal stability, 
both in response to exposure to elevating temperature and in response to a 
given constant temperature. 
Thermal stability of self-reactive substances, in response to elevating 
temperatures, can be determined by measuring the self accelerating 
decomposition temperature or SADT. SADT is one of the recognized tests to 
determine the safe storage and transportation of materials such as organic 
peroxides. Recommendations on the Transport of Dangerous Goods, 9th ed, 
United Nations, NY 1995, Section 11.3.5, page 264!. 
SADT can be directly correlated with the onset temperature as measured in a 
differential thermal analyzer (DTA). The onset temperature is the point at 
which an uncontrolled thermal decomposition starts. The onset temperature 
can be measured by determining the point at which the rate of temperature 
increase in a sealed cell exceeds a certain predetermined value. In 
addition, the onset temperature can be measured by determining the point 
at which the rate of pressure increase in the sealed cell exceeds a 
certain predetermined value. 
Thermal stability in response to a given constant temperature can be 
assessed by means of accelerated aging tests at, for instance, 15.degree. 
C. 
The presence of the oxime in accordance with the present invention 
increases the onset temperature of peroxydicarbonates. Also, the oxime 
does not detract from the effectiveness of the peroxide as a 
polymerization initiator.

The following examples are intended to illustrate the claimed invention and 
are not in any way designed to limit its scope. Numerous additional 
embodiments within the scope and spirit of the claimed invention will 
become apparent to those skilled in the art. 
EXAMPLE 1 
The onset temperature was measured for samples of pure di-2-ethylhexyl 
peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate diluted in odorless 
mineral spirits (OMS), and di-sec-butyl peroxydicarbonate diluted in OMS. 
The onset temperature was also measured for the aforementioned 
peroxydicarbonate samples in the presence of various amounts of several 
oximes. The liquid mixtures were prepared by dissolving the required 
amount of oxime solution in the peroxydicarbonate. 
Using a type of Differential Thermal Analyzer (Radex Solo Thermal Analyzer, 
marketed by Astra Scientific International, Pleasanton, Calif.), with an 
isothermal hold temperature of 30.degree. C. for 15 minutes and then a 
temperature increase of 1.degree./minute to 130.degree. C., the onset 
temperature was measured for a one gram sample of the peroxydicarbonate in 
a sealed cell. The onset temperature was measured both by noting the point 
where the rate of increase (.DELTA.T) of the sample temperature reached 
0.2.degree. C./minute and also, independently, the point where the rate of 
increase in pressure (.DELTA.P) of the closed sample cell reached 1.0 
psi/minute. .DELTA.T is the difference between the oven temperature and 
the sample temperature. .DELTA.P is the difference between a reference 
pre-calibrated pressure and the pressure developed in the sealed sample 
cell. 
Table I presents the results of the tests carried out with samples of pure 
di-2-ethylhexyl peroxydicarbonate without oxime and with, in turn, 
acetaldoxime, 2-heptanone oxime, 4-methyl-2-pentanone oxime, and a 50 wt. 
% solution of acetone oxime in 2-propanol. 
Table II presents the results of similar tests carried out with samples of 
di-2-ethylhexyl peroxydicarbonate in OMS. 
Table III presents the results of similar tests carried out with samples of 
di-sec-butyl peroxydicarbonate in OMS. 
The results show that the presence of oxime increases the temperature at 
which self accelerating decomposition of the peroxydicarbonate will begin. 
This shows that the oxime is an effective stabilizer. The data also show 
that the effect is concentration dependent, with the decomposition 
beginning at a higher temperature when more oxime is present. 
TABLE I 
______________________________________ 
Onset Temperature of Decomposition for 97.2% 
Di-2-ethylhexyl Peroxydicarbonate Unstabilized and 
Stabilized with Oxime 
Onset 
Wt. % of Temperature 
Pure (C..degree.) 
Additive Additive by .DELTA.T 
by .DELTA.P 
______________________________________ 
None 0.0 36.7 41.0 
Acetaldoxime 
0.3 41.9 45.5 
Acetaldoxime 
0.6 45.8 48.7 
Acetaldoxime 
1.0 48.2 50.7 
Acetaldoxime 
2.0 49.8 51.3 
Adetaldoxime 
3.0 51.4 54.4 
Acetaldoxime 
5.1 53.3 56.3 
2-Heptanone 
2.0 47.7 50.7 
oxime 
4-Methyl-2- 
1.9 47.3 50.3 
pentanone 
oxime 
Acetone 0.5 42.7 44.2 
oxime-50* 
Acetone 1.5 49.0 50.1 
oxime-50* 
Acetone 2.5 50.5 52.0 
oxime-50* 
______________________________________ 
*Acetone oxime was added as 50 wt. % solution in 2propanol 
TABLE II 
______________________________________ 
Onset Temperature of Decomposition for 
74.9% Solution of Di-2-ethylhexyl peroxydicarbonate in 
OMS Unstabilized and Stabilized by Oxime 
Onset 
Wt. % of Temperature 
Pure (.degree.C.) 
Additive Additive by .DELTA.T 
by .DELTA.P 
______________________________________ 
None 0.0 38.9 43.6 
Acetaldoxime 
0.3 45.8 47.7 
Acetaldoxime 
0.5 48.1 49.9 
Acetaldoxime 
1.0 50.2 51.6 
Acetaldoxime 
2.0 51.1 52.2 
Acetaldoxime 
3.0 53.9 54.5 
Acetaldoxime 
5.0 55.6 54.6 
2-Heptanone 
2.0 50.1 51.4 
oxime 
4-Methyl-2- 
2.0 49.0 50.3 
pentanone 
oxime 
Acetone 0.5 46.6 47.8 
oxime-50* 
Acetone 1.5 49.0 50.1 
oxime-50* 
Acetone 2.5 53.1 53.5 
oxime-50* 
______________________________________ 
*Acetone oxime was added as 50 wt. % solution in 2propanol 
TABLE III 
______________________________________ 
Onset Temperature of Decomposition for 
75.9% Solution of Di-sec-butyl peroxydicarbonate in 
OMS, Unstabilized and Stabilized by Oxime 
Onset 
Wt. % of Temperature 
Pure (.degree.C.) 
Additive Additive by .DELTA.T 
by .DELTA.P 
______________________________________ 
None 0.0 37.6 39.4 
Acetaldoxime 
1.1 39.8 43.5 
Acetaldoxime 
3.0 47.0 47.4 
Acetaldoxime 
5.0 47.6 51.5 
2-Heptanone 
3.0 45.1 45.7 
oxime 
4-Methyl-2- 
3.1 44.6 46.4 
pentanone 
oxime 
Acetone 1.5 39.6 42.7 
oxime-50* 
Acetone 2.5 42.6 44.8 
oxime-50* 
______________________________________ 
*Acetone oxime was added as 50 wt. % solution in 2propanol 
EXAMPLE 2 
The effect of the presence of acetaldoxime, representative of the oxime 
group, on the storage stability at 15.degree. C. of pure di-2-ethylhexyl 
peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate diluted in odorless 
mineral spirits (OMS), and di-sec-butyl peroxydicarbonate diluted in OMS, 
was determined as an accelerated aging test. The purity (active oxygen 
content) of the peroxydicarbonate was measured after 4, 11, 18 and 25 
days. The results, presented in Table IV, show that the oxime is an 
effective stabilizer of peroxydicarbonates. The initial purity values were 
corrected for the presence of the oxime additive. 
TABLE IV 
__________________________________________________________________________ 
Purity vs. Time at 15.degree. C. for 
Peroxydicarbonates Stabilized with Acetaldoxime 
% 
Wt. % of Purity* 
Peroxide 
Additive 
Start 
4 days 
11 days 
18 days 
25 days 
__________________________________________________________________________ 
97.2% Di-2- 
None 97.2(100) 
47.7(49.1) 
22.6(23.3) 
14.3(14.7) 
10.3(10.6) 
ethylhexyl 
0.5 96.7(100) 
89.8(92.9) 
55.5(57.4) 
29.4(30.4) 
18.6(19.2) 
peroxy-di- 
1.0 96.2(100) 
90.4(94.0) 
73.1(76.0) 
42.1(43.8) 
25.6(26.6) 
carbonate 
3.0 94.4(100) 
86.4(91.5) 
80.7(85.5) 
71.3(75.5) 
55.8(59.1) 
(pure) 
74.9% Di-2- 
None 74.9(100) 
39.0(52.1) 
16.6(22.2) 
9.8(13.1) 
6.7(8.9) 
ethyl-hexyl 
0.5 74.6(100) 
66.7(89.4) 
45.5(61.0) 
24.3(32.6) 
14.4(19.3) 
Peroxy-di- 
1.0 74.2(100) 
68.8(92.7) 
56.8(76.5) 
38.5(51.9) 
25.3(34.1) 
carbonate 
3.0 72.7(100) 
65.6(90.2) 
59.3(81.6) 
53.1(73.0) 
43.7(60.1) 
in OMS 
5.0 71.4(100) 
61.5(86.1) 
55.0(77.0) 
50.9(71.3) 
45.7(64.0) 
75.9% di- 
None 75.9(100) 
34.1(44.9) 
5.6(7.4) 
1.3(1.7) 
0.9(1.2) 
sec-butyl 
0.5 75.5(100) 
47.7(63.2) 
13.4(17.7) 
4.8(6.4) 
3.9(5.2) 
Peroxydi- 
1.0 75.1(100) 
56.0(74.6) 
21.2(28.2) 
8.1(10.8) 
4.8(6.4) 
carbonate 
3.0 73.6(100) 
65.2(88.6) 
48.2(65.5) 
30.3(41.2) 
17.6(23.9) 
in OMS 
__________________________________________________________________________ 
*Percent of nondecomposed material relative to the initial amount of 
product is in parenthesis.