CA1132295A - Crosslinking of polymers with azo-esters - Google Patents

Abstract

A B S T R A C T

A method is provided for crosslinking polymers at temperatures above 170°C using azo-esters having the formula:

(I) wherein R3 is -OOC-R. alkyl, cycloalkyl or aralkyl; R1 and R2 are independently selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl wherein each of the groups may have alkyl branching; R1 and R2 can join together to form R1R2 where the group is selected from -(CH2)4-, -(CH2)5-, alkyl-substituted tetramethylene, or alkylsubstituted pentamethylene;
and R and R1 can join together to form RR1 where the group is selected from -CH2-CH2, -CH2-CH2-CH2-, alkylsubstituted -CH2-CH2- or alkylsubstituted -CH2-CH2-CH2-, and R is lected from the group consisting of H, lower alkyl, cycloalkyl, aryl and aralkyl.

Description

~ 2 1. FIELD OF INYENTION
This invention relates to a method of crosslinking or simultaneously crosslinking and-foaming of polymers using a high decomposition temperature azo-ester crosslinking agent.

2. DESCRIPTION OF THE PRIOR ART
Prior to the present invention, azo compounds gener-ally were thought to be unable to abstract a hydrogen atom from a carbon atom and, hence, were unable to perform as a cross-linking agent for polymers. U.S. Patent 3,152,107 was the first published exception to this general rule; it described the crosslinking effect of unsymmetrical aromatic azo compounds wherein one side of the azo group (-N=N-) is attached directly to the aromatic nucleus and the other side of the azo group is attached to an aliphatic radical with a strongly electrophilic group like a carbonamide group attached to the ~-carbon atom thereof. Examples of such compounds are as follows:
f H3 CH3 f H3 C6H5-N=N-f CH3 C6H5-N-N-I-CH2-CH-CH3 C6H5-N-N

These azo compounds have not been found commercially acceptable hitherto, probably because of their relatively high price and their color which is presumably due to the presence of the chromophoric azo group attached to the aromatic ringi this color represents a severe disadvantage in many applications because decomposed residue of the crosslinking agent causes undesirable discoloration of the polymer.
U.S. patent 3,776,885 is a second exception to the above-mentioned general rule; it describes aliphatic symmetri-cal and asymmetrical azo-ethers having the following structures:

3~13~9~

Rl _ C - N - N - I - Rl and R2 _ 1 - N = N - 1 - R5 R - 1 1 - R Rl ~ R6 (II) (III) These azos are good crosslinking agents for polymers in the temperature range of 120 to 230C. Nevertheless, when com-paring these azo-ethers (II) and (III) with the azo-ester (I) of the present invention, the azo-ester has a higher decompo-sition temperature although they are analogously structured, i.e., made from the same ketone. Other differences of the azo-ester (I) of the present invention are their simpler and cheaper preparation, lower volatility, solid state (in many instances), and low or lack of toxicity. For example, the azo-ether, 2,2'-azo-bis(2-methoxy-propane) is a toxic liquid while the corresponding azo-ester, 2,2'-azo-bis(2-acetoxy-propane) is a colorless power melting at 103C; similarly the azo-ether, l,l'-azo-bis(l-methoxy-cyclohexane) is an orange-yellow oil solidifying at about 0C while the corresponding azo-ester, l,l'-azo-bis(l-acetoxy-cyclohexane) is a colorless powder melting at 91-94C.
Organic peroxides and diperoxides are normally used as crosslinking agents for crosslinking polymers. Peroxides, however, cannot be used when the softening temperature of the polymer is above the decomposition temperature of the peroxide because the peroxide would decompose before being completely mixed with the polymer. On the other hand, the high decompo-sition temperature of the azo-ester of this invention makes it possible to mix them with such polymers having a softening temperature higher than the decomposition temperature of the peroxides such as dicumyl peroxide, ~,~'-bis(t-butylperoxy)-p(m)-diisopropylbenzene, 2,5-dimethyl-2,5-bis(t-butylperoxy)-~ ~ 3 ~9 S

hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-(3), di-t-butylperoxide, etc. Azo-esters can effect foaming during crosslinking in the absence of pressure; peroxides cannot.
Crosslinking with the azo-ester under pressure, however, gives compact unfoamed polymers in the same way and in the same order of magnitude as when peroxides are used.
The commercially available azo compounds used techni-cally as initiators are symmetrical azonitriles of the general structure:

Rl C - N = N - C - Rl (IV) C - N C _ N
The most known representative of the azonitriles is 2,2'-azo-bis-isobutyronitrile. The azonitriles have a decomposition temperature range of about 60 - 80C below that o-F the above-mentioned crosslinking peroxides and about 80 - 110C below that of the azo-ethers (II) and (III) and the azo-ester (I) of the present invention. These azonitriles cannot effect cross-linking reactions in polymers (see Example 4~ infra).
STATEMENT OF INVENTION
The present invention provides a method of cross-linking polymers such as polyethylene or ethylene-vinylacetate copolymer at hi~h temperatures over 170C which are free from, or at least reduce, the problems associated with the use of prior art crosslinking agents. Saturated and unsaturated homo-and copolymers are crosslinked under pressure in the range of O to 300 psia and at a temperature above 170C, but not to the point where the polymer will substantially degrade, in the presence of 0.51~ to 20% of the azo-ester (I) crosslinking agent. This azo-ester (I) can be used singularly or in combi-nation with other crosslinking agents such as another azo-L3'~29~i ester, azo-ether or peroxide. Further, the azo-ester can be used in combination with another crosslinking agent as men-tioned supra and a foaming agent.
The azo-ester crosslinking agent of this invention has the following formula:

R1 C - N = N - C - Rl (I) R - col R3 in which R3 is selected from the group consisting of -OOC-R, alkyl, cycloalkyl and aralkyl;
R is selected from the group consisting of H, lower alkyl, cycloalkyl, aryl and aralkyl;
Rl and R2 are independently selected from the group I consisting of alkyl, cycloalkyl, aryl and aralkyl wherein each of the groups may have alkylbranching;
Rl and R2 can join together to form RlR2 where the group is selected from -(CH2~4-, -(CH2)5-, alkylsubstituted tetramethylene, or alkylsubstituted pentamethylene; and R and Rl can join together to form RRl where the group is selected from -CH2-CH2, -CH2-CH2-CH2-, alkyl-substituted -CH2-CH2- or alkylsubstituted -CH2-CH2-CH2-.
The azo-ester (I) is a good crosslinking agent for polymers that will also simultaneously foam the polymer under atmospheric pressure.
DETAILED DESCRIPTION OF INVENTION
The preferred moieties of R, Rl, R2 and R3 of the present invention are the alkyl of 1-4 carbons, cycloalkyl of 3 to 6 carbons, aryl of 6-10 carbons and aralkyl of 7-11 carbons. All of these moieties may be substituted with non-interfering substituents such as alkyl or halogen such as ~3229~

chloride or bromide. Examples of the preferred aryl moieties are phenyl and naphthyl. Examples of the preferred aralkyl moieties are benzyl, phenyl-alkyl or naphthyl-alkyl.
The azo-ester (I) of the present invention is a good crosslinking agent for polymers at high temperatures above 185C. This azo-ester starts to show crosslinking activity from about 170C depending upon the nature of the substituents of the azo compound. The upper limit of this temperature range is controlled by the degrading temperature of the particular polymer or copolymer. The optimal temperature range for cross-linking is between lS0 - 230C. The azo-ester (I) is used in amounts of 0.5 - 20%, preferably 2 - 7% by weight in a reaction time of 10 - 100 minutes. The pressure in the reactor can range from 0 to 300 psi. For crosslinking, two of the species of the azo-ester of this invention can be used in combination with each other, with azo-ethers, and with peroxides. Azo initiators form nitrogen when they decompose. Hence, they can act also as blowing agents as long as no pressure is applied.
In order to obtain a crosslinked foamed polymer with the desired cellular structure, the azo-ester (I) can be combined with another crosslinking agent having a somewhat lower decomposition temperature such as a peroxide, an azo-ether (such as in U.S. patent 3,776,885), and an azo-ester with appropriate substituents giving them a lower decomposition temperature. The azo-ester (I) can also be combined with crosslinking peroxides having rather low decomposition temper-atures, such as perketals and percarbonate-esters. The azo-ester (I) can also be combined with typical blowing agents, such as azodicarbonamide, sulfohydrazines, NaHC03 plus carbox-ylic acids, etc. This azo-ester (I) can also be combined in a mixture with both a crosslinking agent having a lower decompo-~13~29~i sition temperature and a blowing agent.
Examples of the azo-esters (I) of the present invention are:
1. 2,2'-azo-bis(2-formyloxy-propane~, 2. 2,2'-azo-bis(2-acetoxy-propane), 3. 2,2'-azo-bis(2-propionoxy-propane),

4. 2,2'-azo-bis(2-benzoyloxy-propane),

5. l,l'-azo-bis(l-formyloxy-cyclohexane),

6. l,l'-azo-bis(l-acetoxy-cyclohexane),

7. l,l'-azo-bis(l-propionoxy-cyclohexane~,

8. l,l'-azo-bis(l-benzoyloxy-cyclohexane),

9. 2,2'-azo-bis(2-formyloxy-4-methyl-pentane),

10. 2,2'-azo-bis(2-acetoxy-4-methyl-pentane),

11. 2,2'-azo-bis(2-acetoxy-butane),

12. l,l'-azo-bis(l-acetoxy-l-phenyl-ethane),

13. l,l'-azo-bis(l-acetoxy-methyl-cyclohexane),

14. 1,1'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclohexane),

15. y,~'-azo-bis(~-valerolactone),

16. 2,2'-azo-bis(2-acetoxy-3-methylbutane),

17. 1,1'-azo-bis(l-acetoxy-4-methylcyclohexane)

18. l-t-butylazo-l-acetoxycyclohexane

19. 2-t-butylazo-2-acetoxybutane

20. 2-t-butylazo-2-acetoxy-4-methylpentane

21. 2-t-butylazo-2-acetoxy-5-methylhexane, and

22. 1-t-butylazo-1-acetoxy-3,3,5-trime~hylcyclohexane Examples of polymers that can be either crosslinked or crosslinked and foamed with the azo-ester (I) are:
polyethylene, ethylene-vinylacetate-copolymer, ethylene-propylene-copolymer (EPM), ethylene-propylene-diene-copolymer (EPDM), styrene-butadiene-rubber, acrylonitrile-butadiene-styrene-rubber, PVC and similar polymers.

~ 9 5 A crosslinkable polymer composition can contain besides the polymer and the crosslinking agent other normally present agents for crosslinking compositions, such as coagents, promotors, reinforcing materials, fillers (charcoal, TiO2, CaC03, calcium silicate, and aluminum silicate), antioxidants, etc.
This invention will be more clearly understood by the following specific examples in which, unless otherwise stated, parts (or percent) are by weight.
EXAMPLES
These examples illustrate the crosslinking of polymers and copolymer with various azo crosslinking agents of the generic formula I.
The polymer to be crosslinked was mixed homogeneously as a powder with 5 percent by weight of the crosslinking agent in a solvent such as acetone or dichloromethane. The solvent was then evaporated from the mixture; mixing of polymer powder and crosslinking agent was also possible without using a sQlvent; the residue was crosslinked for 40 minutes at temper-atures about 200C at atmospheric pressure. The amount ofcrosslinking agent used in each example was always equal to 5 percent by weight (relative to the 100% pure crosslinking agent) rather than being equivalent to each other because the use of equivalent amounts of crosslinking agents for their comparative evaluation does not give a very substantial statement.
The determination of the degree of crosslinking was carried out in the usual manner as follows. The crosslinked polymer was cut into strips, wrapped in a steel net having fine meshes and extracted for one hour by refluxing with xylene (80 ml xylene for 2 grs. crosslinked polymer). The steel net ~1~3;2Z95 was then rinsed with warm xylenei the xylene was e~aporated completely at 150C and the loss of weight which corresponded to the dissolved portion of polymer was determined. From this finding, the undissolved polymer portion gave the degree of crosslinking (expressed in percent of the original polymer weight).
EXAMPLE I
(Example of orientation):
Low density, high pressure polyethylene powder (density = 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of the following crosslinking agents for 30 minutes at 190C under atmospheric pressure:
Degree of Crosslinking agents (not e~uivalent amounts) crosslinking a) 5% dicumylperoxide 78%
b) 5% 2,5-bis(t-butylperoxy)-2,5-dimethyl-hexyne-(3) 79%
c) 5~ 1,3,5-tris(2-(t-butylperoxy)-propyl-(2))-benzene 92%
20 d) 5% l,l'-azo-bis(l-methoxy-cyclohexane) (-azo-ether) 95%
e) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 5%
f) 5% l,l'-azo-bis(l-acetoxy-l-phenyl-ethane) 27%
The azo-ester e) was crosslinked again, but this time at a temperature 20C higher, namely 30 minutes at 210C under atmospheric pressure:
9) 5% l,l'-azo-bis(l-ace~oxy-cyclohexane) 86%
These tests demonstrate that the azo-esters of the invention are able to reach crosslinking degrees of the same magnitude as peroxides and azo-ethers but only at higher temperatures.
EXAMPLE II
Low density, high pressure polyethylene powder ~13~ZZ9~

~density - 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of the following crosslinking agents for 40 minutes at 205C under atmospheric pressure:
Degree of Crosslinking agents (not equivalent amounts) crosslinking a) 5% 1,1-bis(t-butylperoxy)-3,3,5-trimethyl-cyclohexane 82%
b) 5~ t-butyl-perbenzoate 85%
c) 5~b dicumylperoxide 82%
10 d) 5% a,a'-bis(t-butylperoxy)diisopropyl-benzene 89%
e) 5% 2,5-bis(t-butylperoxy)-2,5-dimethyl-hexyne-(3) 83%
f) 5~ l,l'-azo-bis(l-methoxy-cyclohexane) (-azo-ether) 71%
9) 5% 2,2'-azo-bis(2-acetoxy-propane) 78%
h) 5% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) 74%
i) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 75%
j) 5~ y,~'-azo-bis(~-valerolactone) 64%
Hence, the crosslinking degrees of the azo-esters are also at 205C of the same order of magnitude as those of the peroxides, which are all used industrially as crosslinking ~c e agents (perbenzoate, however, only in the prcrcnc~ of fillers), and as that of the azo-ether f). The value of 64% for the azo-valerolactone of j) is rather low. The % crosslinking of the azo-esters of 9), h) and i) lies between that of the peroxides and that of the azo-ether of f). The polyethylene crosslinked with the azo compounds of f) ~ j) was fine-porously foamed.
EXAMPLE III
Low density, high pressure polyethylene powder (density - 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of the following crosslinking agents for 40 minutes at 210C under atmospheric pressure:

~3'~

Degree of Crosslinking agents (not equivalent amounts) crosslinking a) without crosslinking agent 10%
b) 5% lauroylperoxide 65%
c) 5% t-butyl-peroctoate 76%
d) 5% 1,1-bis(t-butylperoxy)-3,3,5-trimethyl-cyclohexane 77%
e) 5% t-butyl-per-3,5,5-trimethyl-hexanoate 69%
f) 5% 3,3-bis(t-butylperoxy)butyric acid-ethylester 75%
9) 5% dicumylperoxide 75%
h) 5% 2,5-bis(t-butylperoxy)-2,5-dimethyl-hexane 74%
i) 5% 2,5-bis(t-butylperoxy)-2,5-dimethyl-hexyne-(3) 79%
j) 5~ l,l'-azo-bis(l-methoxy-cyclohexane) (=azo-ether) 71%
k) 5% 2,2'-azo-bis(2-acetoxy-propane) 75%
1) 5% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) 71%
m) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 79%
n) 5% 1,1'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclohexane) 71%
o) 5% l,l'-azo-bis(l-acetoxy-l-phenyl-ethane) 40%
The percent of crosslinking obtained with the azo-esters (k, 1, m, n) has the same order of magnitude as that obtained by the azo-ether (j) and the peroxides. The cross-linking degree of the azo-ester o) of only 40% is conspicuous.
The polyethylene crosslinked with the azo compounds j) to o) was fine-porously foamed.
EXAMPLE IV
Low density, high pressure polyethylene powder (density = 0.915 - 0.918) with a melting index of 17 - 22 grs./
10 min. was crosslinked with 5% of each of the following cross-linking agents for 40 minutes at 210C under atmospheric pressure:

Degree of Crosslinking agents (not equivalent amounts) crosslinking a) without crosslinking agents 2.7%
b) 5% 2,2'-azo-bis-isobutyronitrile 4.3%
c) 5% di(3,5,5-trimethylhexanoyl)peroxide 63%
d) 5% t-butyl-peroctoate 55%
e) 5% 1,1-bis(t-butylperoxy)-3,3,5-trimethyl-cyclohexane 80%
f) 5% t-butyl-per-3,5,5-trimethylhexanoate 46%
10 9) 5% t-butyl-perbenzoate 82%
h) 5% 3,3-bis(t-butylperoxy)butyric acid-ethylester 74%
i) 5% dicumylperoxide 81%
j) 5% ~,~'-bis(t-butylperoxy)diisopropyl-benzene 54%
k) 5% 2,5-bis(t-butylperoxy)-2,5-dimethyl-hexane 81%
1) 5% ~,5-bis(t-butylperoxy)-2,5-dimethyl-hexyne-(3) 84%
m) 5~ l,l'-azo-bis(l-methoxy-cyclohexane) (azo-ether) 73%
20 n) 5% l,l'-azo-bis(l-phenoxy-cyclohexane) (azo-ether) 78.5%
o) 5% 2,2'-azo-bis(2-acetoxy-propane) 63%
p) 5% 2,2'-azo-bis(2-acetoxy-butane) 59%
q) 5% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) 78.5%
r) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 70%
s) 5% l,l'-azo-bis(l-acetoxy-methylcyclohexane) 70%
t) 5% 1,1'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclohexane) 86%
u) 5% l,l'-azo-bis(l-acetoxy-l-phenyl-ethane) 60%
30 v) 5% ~,~'-azo-bis(~-valerolactone) 41%
Azo-esters u), p) and v) show a relatively low %
crosslinking. The degree of crosslinking of the other azo-esters amounts again to the same order of magnitude as that of the azo-ethers (m and n) and that of the peroxides usable as ~L32~5 crosslinkers (e, 9, h, i, j, k, 1), at which j), with 54%
crosslinking is out of place. The 2,2'-azo-bis-isobutyro-nitrile (b) belonging to the group of azo compounds with terti-ary carbon atoms shows, as expected, no crosslinking ability, whereas the two peroxides c) and d) having similar low initi-ation temperatures like azobisisobutyronitrile effect cross-linking of more than 50%. Note the high degree of crosslinking of 86% obtained by the azo-ester t). The polyethylene cross-linked with the azo compounds m) to v) was fine-porously foamed.
EXAMPLE V
This example gives a comparison of the decomposition temperatures of azo-esters, azo-ethers and peroxides. Low density, high pressure polyethylene powder (density = 0.915 -0.918) with a melting index of 17 - 22 grs./10 min. was cross-linked with 5% of each of the following crosslinking agents for 40 minutes at 170C, 180C, 190C, 200C, 210C and 220C under atmospheric pressure:
Crosslinking agents Degree of crosslinking at 20 (not equivalent amounts) 170C 180C 190C 200C 210C 220C
a) without cross-linking agent0.23%1.9%2.6% 2.8% 3.4% 4.0%
b) 5% dicumyl-peroxide 88.5% 88% 93.5% 92% 91% 94%
c) 5% l,l'-azo-bis-(l-methoxy- 1.6% 29.5% 79.5%82.5% 75% 74%
cyclohexane) d) 5% 2,2'-azo-bis-(2-acetoxy-4-10.5%28.6% 81% 79% 82% 81%
methyl-pentane) e) 5% l,l'-azo-bis-(l-acetoxy- 2.1% 2.2% 2.0% 2.6% 4.0% 77%
cyclohexane) In this experiment the dicumylperoxide had already crosslinked below 170C, the azo-ether c) between 180C and ~3Z295 190C; but the azo-ester e) not before 210 - 220C. The azo-ester d), however, had crosslinked already between 180 - 190C
(just as the azo-ether c) had); this is the effect of a common rule for azo initiators that alk~l-substitution in ~-position to the carbon atom connected with the azo group causes an increase of activity (i.e., decrease of decomposition tempera-ture); such ~-position represents the 4-position in the azo-ester d) or the 3- and 5-positions in the cyclohexane ring (see azo-ester t) in Example 4). The polyethylene crosslinked with the azo compounds c) to e) was fine-porously foamed.
EXAMPLE VI
Low molecular ethylene-vinylacetate-copolymer powder (EVA-powder) with an ethylene portion of 37% and a vinylacetate ~` portion 63% and a melting index at 190C of approx. 25 grs./
min., containing 6~ precipitated silicic acid, was crosslinked with 5% of each of the following crosslinking agents for 40 minutes at 220C under atmospheric pressure:

Degree of Crosslinking agents (not equivalent amounts) crosslinking 20 a) without crosslinking agent 25%
b) 5% lauroylperoxide 27%
c) 5% t-butyl-peroctoate 49%
d) 5% dicumylperoxide 79%

e) 5% l,l'-azo-bis(l-methoxy-cyclohexane) (azo-ether) 80%
f) 5% 2,2'-azo-bis(2-acetoxy-propane) 74%
9) 5% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) 76%
h) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 46%

i) 5% y,y'-azo-bis(y-valerolactone) 85%
With the exception of h) the percent of crosslinking of the azo-esters was in the same range as that of the azo-ether e) and of dicumylperoxide d). The azo-ester h), having ~13229S

here only a low effectiveness, has always been very effective in polyethylene crosslinking. Note the good crosslinking effect of the azovalerolactone i) for EVA (85%). The EVA
crosslinked with the azo compoun~s e) to i~ was fine-porously foamed.
EXAMPLE VII
Low density, high pressure polyethylene powder (density _ 0.918) with a melting index of 70 grs./10 min. was crosslinked with combinations of the following azo compounds (azo-esters) (total quantity of crosslinking agent 5%) for 40 minutes at 215C under atmospheric pressure:
Degree of Crosslinking agents (not equivalent amounts) crosslinking a) 2.5~ 2,2'-azo-bis(2-acetoxy-propane) + 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) 79%
b) 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) ~ ~.5% ~,~'-azo-bis(~-valerolactone) 78%
c) 1.7% 2,2'-azo-bis(2-acetoxy-propane) ~ 1.7% l,l'-azo-bis(l-acetoxy-cyclohexane) 74%
+ 1.7% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) Combinations of the inventive azo-esters gave the same good degrees of crosslinking as each of these azo-esters when used individually. The polyethylene was fine-porously foamed.
EXAMPLE VIII
Low density, high pressure polyethylene powder (density = 0.918) with a melting index of 70 grs./10 min. was crosslinked with double combinations of peroxides having high decomposition temperatures and azo-esters (a, b, c) and a combination of an azo-ether effective as crosslinking agent and an azo-ester (d) in comparison with 1 peroxide (f), 1 azo-ester (g) and a combination of 2 azo-esters (e) (total quantity of crosslinking agents 5%) for 40 minutes at 215C under atmos-~3~22~S

pheric pressure;
Degree of Crosslinking agents (not equivalent amounts~ crosslinking a) 2.5% dicumylperoxide + 2.5% 2,2'-azo-bis(2-acetoxy-propane~ 80%
b) 2.5% 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexyne-(3) 75%
+ 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) c) 2.5% 1,3,5-tris(2-(t-butylperoxy)-propyl-(2))-benzene + 2.5% 2,2'-azo-bis(2-acetoxy-4-methyl- 75%
pentane) d) 2.5% l,l'-azo-bis(l-methoxy-cyclohexane) (=azo-ether) 73%
+ 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) e) 2.5% 2,2'-azo-bis(2-acetoxy-propane) + 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) 84%
f) 5% dicumylperoxide 86%
9) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) (azo-ester) 82%
Combinations of crosslinking agents of different structures (peroxide, azo-ether, azo-ester) also give good degrees of crosslinking situated a little lower than those obtained with peroxide or azo-ester alone or with 2 azo-esters.
The polyethylene was fine-porously foamed, except f) (5%
dicumylperoxide) which gave a polyethylene essentially unfoamed with exception of some bubbles because dicumylperoxide forms gaseous products, like methane, on thermal decomposition in polyethylene.
EXAMPLE IX
Low density, high pressure polyethylene powder (density - 0.918) with a melting index of 70 grs./10 min. was crosslinked with double combinations of foaming agent (azo-dicarbonamide) and azo-ester, and further with triple combi-nations of foaming agent (azodicarbonamide), peroxide having a high decomposition temperature or azo-ether and azo-ester for 3Z~9 S

40 minutes at 225C under atmospheric pressure (total quantity of crosslinking agents of 5%). In comparison crosslinking was performed under the same conditions with 2 peroxides, 2 azo-esters, the foaming agent azodicarbonamide and azobisisobutyro-nitrile as single agents:
Degree of Crosslinking agents (not equivalent amounts)crosslinking a) 1.5% azodicarbonamide + 5% 2,2'-azo-bis(2-acetoxy-propane) 66%
b) 1.5% azodicarbonamide + 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 68%
c) 1.5% azodicarbonamide + 2.5% dicumylperoxide 77%
+ 2.5% 2,2'-azo-bis(2-acetoxy-propane) d) 1.5% azodicarbonamide 2.5% 2,5-dimethyl-2,5-bis(t-butylperoxy)- 75%
hexyne-(3) + 2.5,~ l,l'-azn-bis(l-acetoxy-cyclohexane) e) 1.5% azodicarbonamide + 2.5% l,l'-azo-bis(l-methoxy-cyclohexane) 75%
(=azo-ether) + 2.5% 2,2'-azo-bis(2-acetoxy-propane) f) without additions 8%
9) 1.5% azodicarbonamide 30%
h) 5% azobisisobutyronitrile 15%
i) 5% dicumylperoxide 79%
j) 5% 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexyne-(3) 91%
k) 5% 2,2'-azo-bis(2-acetoxy-propane) 73%
30 1) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 70%
In the presence of the foaming agent (azodicarbon-amide) the obtained degrees of crosslinking were somewhat lower than without a foaming agent. The azodicarbonamide containing compositions a) to e) and g) were coarse-porously foamed, h), k) and 1) fine-porously foamed, i) and j) unfoamed with exception of some bubbles and f) unfoamed.

1~32295 EXAMPLE X
Low density, high pressure polyethylene powder (density - 0.915 - 0.918~ with a melting index of 17 - 22 grs./
10 min. was crosslinked with double combinations oF foaming agent (azodicarbonamide) and azo-ester, and further with triple combinations of foaming agent (azodicarbonamide), peroxide haYing a high decomposition temperature or azo-ether and azo-ester for 40 minutes at 225C under atmospheric pressure and under the same conditions with 2 peroxides, 2 azo-esters, the foaming agent azodicarbonamide and azobisisobutyronitrile as single agents. The total quantity of crosslinking agents amounted in all cases to 5~.
Degree of Crosslinking agents (not equivalent amounts)crosslinking a) 1.5% azodicarbonamide ~ 5% 2,2'-azo-bis(2-acetoxy-propane) 26~
b) 1.5% azodicarbonamide + 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 43%
c) 1.5% azodicarbonamide + 2.5% dicumylperoxide 67%
+ 2.5% 2,2'-azo-bis(2-acetoxy-propane) d) 1.5% azodicarbonamide 2.5% 2,5-dimethyl-2,5-bis(t-butylperoxy)- 78%
hexyne-(3) + 2.5% l,l'-azo-bis(l-acetoxy-cyclohexane) e) 1.5% azodicarbonamide 2.5% l,l'-azo-bis(l-methoxy-cyclohexane) 78%
(-azo-ether) + 2.5% 2,2'-azo-bis(2-acetoxy-propane) 30 f) without additions 5%
9) 5% azobisisobutyronitrile 4%
h) 5% dicumylperoxide 79%
i) 5% 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexyne-(3) 89%
j) 5% 2,2'-azo-bis(2-acetoxy-propane) 74%
k) 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 79%

~13Z~S

As in Example IX the degree of crosslinking in the presence of the foaming agent (azodicarbonamide) was lower than without the foaming agent. The azodicarbonamide containing compositions of a) to e) were coarse-porously foamed; 9), j) and k) fine-porously foamed; h) and i) unfoamed except for some bubbles; and f) unfoamed.
EXAMPLE XI
Low density, high pressure polyethylene powder (density = 0.918) with a melting index of 70 grs./10 min. was crosslinked with different quantities (0.2% - 5%) of one of the inventive azo-esters, namely the 2,2'-azo-bis(2-acetoxy-propane) and in comparison with dicumylperoxide for 40 minutes at 220C under atmospheric pressure:
Degrees of crosslinking obtained with:
Amount of 2,2'-azo-bis- dicumyl-crosslinking agents(2-acetoxy-propane) peroxide 0 % 0.5% 0.5%
0.2% 7 %
O . 4% 25 %
0.5% 28 % 72 %
0.6% 33 %
0.8% 60 %
1.0% ~2 % 70 %
1.5% 71 %
2 % 7~ % 71 %
3 % 80 % 72 %
4 % 81 % 77 %
5 % 82 % 58 %
Whereas dicumylperoxide reaches almost the maximal degree of crosslinking in a concentration of 0.5%, the azo-ester does this in concentrations of 1-1.5%. The polyethylene crosslinked with the azo compound was fine-porously foamed.

~32Z~S

EXAMPLE XII
This experiment illustrates the crosslinking of poly-ethylene with l,l'-azo-bis(l-formyloxy-cyclohexane) (R = H) which had not yet been used in the existing examples and with the analogous acetoxy product, l,l'-azo-bis(l-acetoxy-cyclo-hexane) (R = CH3) at different temperatures. Low density, high pressure polyethylene powder (density _ 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of the above mentioned azo compounds for 40 minutes at 190C, 200C, 210C, 220C, and 230C under atmospheric pressure:
Degrees of crosslinking obtained with Crosslinking5% l,l'-azo-bis(l- 5% l,l'-azo-bis(l-Temperatureformyloxy-cyclohexane)acetoxy-cyclohexane) lgOC 2.7% 3.7%
200C 4 . 0% 4.0~
210C 13.5% 78 %
220C 79 % 82 %
230C 78 % 74 %
This experiment shows that the formyloxy compound has a higher decomposition temperature than the acetoxy compound.
The difference in the decomposition temperatures may be almost 10C. In both cases the polyethylene was fine-porously foamed.
EXAMPLE XIII
Low density, high pressure polyethylene powder (density = 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of four crosslinking agents (two peroxides and two azo-esters) for 40 minutes at temperatures from 120C to 220C under atmospheric pressure. This experi-ment shows the temperature differences between the decompo-sition temperature of the azo-esters and that of the cross-linking peroxides having a high decomposition temperature. The degree of crosslinking at the decomposition temperature is ~3Z~95 underlined:
Degrees of crosslinking obtained with 5% of each of the following 4 crosslinking agents at the tempera-tures given at the left side:
Cross- 5% dicumyl- 5% 2,5-bis(t- 5% 2,2'-azo- 5% l,l'-azo-linking peroxide butylperoxy)- bis(2- bis(l-Temper- 2,5-dimethyl- acetoxy- acetoxy-ature hexyne-(3) propane) cyclohexane) (LUPEROX 130) 120C 9.5% 0.05%
130C 62 % 0.1 %
140C 62 % 33 %
150C 86 % 56 %
160C 91 % 78 %
170C 91 % 7~ % 0.3% 2.5%
180C 91 % 78 % 3 % 5 %
190C 88 % 78 % 5 % 5 %
195 C - - 18 %
200C 76 % 87 % 65 % 5 %
205C - - 71 % 5 %
210C - - 80 % 80 %
220C - - 80 % 80 %
EXAMPLE XIV
This experiment illustrates the determination of the decomposition temperature of y,~'-azo-bis(~-valerolactone) in crosslinking of polyethylene. For comparison the three azo-esters, 2,2'-azo-bis(2-acetoxy-4-methyl-pentane), 2,2'-azo-bis-(2-acetoxy-propane) and l,l'-bis(l-acetoxy-cyclohexane) were also tested.
Low density, high pressure polyetnylene powder (density ~ 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of the four above mentioned azo-esters for 40 minutes at 180 - 230C under atmospheric pressure:

~ ~ 3~

Crosslinking agents Degree of crosslinking at (not equivalent amounts) 180 C 190C 200C 210C 220C 230C
a) 5~ 2,2'-azo-bis-(2-acetoxy-4- 39% 70% 69% 63% 63% 60%
methyl-pentane) b) 5% 2,2'-azo-bis-(2-acetoxy- 3% 7% 44% 69% 70% 78%
propane) 10 c) 5% r,r'-azo-bis-(y-valerolactone) 4% 4% 4% 82% 78% 74%
d) 5% l,l'-azo-bis-(l-acetoxy- 0% 3% 4% 5% 70% 78%
cyclohexane) The polyethylene was fine-porously foamed.
EXAMPLE XV
By this experiment the minim~m-~Yosszin~ing-time necessary to obtain a good degree of crosslinking was ascer-tained. As a representative for all the azo-esters of this invention the 2,2'-azo-bis(2-acetoxy-propane) was used as crosslinking agent. Low density, high pressure polyethylene powder (density - 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of this azo-ester at 215C for 5, 10, 15, 20, 25, 30, 35 and 40 minutes under atmospheric pressure:
CrosslinkingDegrees of crosslinking obtained with O
times5% 2,2'-azo-bis(2-acetoxy-propane) at 215 C
5 minutes 0.5%
10 minutes 72 %
3015 minutes 75 %
20 minutes 77 %
25 minutes 75 %
30 minutes 75 %
35 minutes 75 %
40 minutes 75 %
The maximum degree of crosslinking was obtained in about 10 minutes.

3~ ~ S

EXAMPLE XVI
In the present example, polyethylene was crosslinked under pressure. For this purpose low density high pressure polyethylene powder (density - 0.918) with a melting index of 70 g/lO min. containing 5% 2,2'-a~o-bis(2-aeeto~y-propane), homogeneously worked in, was crosslinked under pressure in a cylinder between two movable pistons exactly fitted in at 240C
for 3 hours. The cylinder and pistons were between two metal sheets pressed against each other by means of 4 bolts and nuts.
During crosslinking the nuts were tightened several times.
By this procedure a thin crosslinked bubbZefree poly-ethylene plate was obtained being 70% crosslinked.
EXAMPLE XVII
This experiment illustrates the determination of the decomposition temperature of 2,2'-azo-bis(2-acetoxy-butane) and of 2,2'-azo-bis(2-acetoxy-3-methyl-butane) in crosslinking of polyethylene. For comparison the 2,2'-azo-bis(2-acetoxy-propane) was also tested.
Low density, high pressure polyethylene powder (density = 0.918) with a melting index of 70 grs./10 min. was crosslinked with 5% of each of the three above mentioned azo-esters for 40 minutes at temperatures between 160-230C under atmospheric pressure:

, - , 3L~ 35 Degrees of crosslinking obtained with 5% of each of the following 3 crosslinking agents at the temperatures given at the left side:
5% 2,2'-azo- 5% 2,2'-azo- 5% 2,2'-azo-bis-Crosslinking bis(2-acetoxy- bts(2-acetoxy- (2-acetoxy-3-Temperatures propane) butane) methyl-butane) 160C o % o % 0 %
170C 0.3% 3.5% 0.5%
180C 0.5% 5 % 1.0%
190C 9 % 6 % 69 %
200C 78 % 68 % 73 %
210C 82 % 80 % 72 %
220C 78 % 72 % 67 %
230C - 69 %
The polyethylene was fine-porously foamed.
EXAMPLE XVIII
Five different synthetic rubbers were crosslinked with two peroxides (one perketal and one dialkylperoxide) and four azo-esters for 40 minutes at 220C at atmospheric pressure. Of the crosslinking agents 5% of each were used, they were worked into the rubber by means of a roll at about 80 - 100C.
The determination of the degree of crosslinking was carried out in the same way as described before for poly-ethylene, thus by extraction with 40 to 80 times the volume amount of boiling xylene. Under these conditions the untreated rubber dissolved almost completely (to 99% - 100%), thus showing a degree of crosslinking of 0 - 1%.

- 23 -~32~5 Crosslinking Degrees of crosslinking of the following agent (not 5 rubbers:
equivalent Buna~l) Buna~2) Buna~3) Buna~4) Buna~5) a~ounts) AP 201 AP 241AP 258huls 1502CB 10 a) 5% l,l-bis(t-butylperoxy)-3,3,5-trimethyl-79% 85% 68% 76% 98%
cyclohexane 10 b) 5% dicumyl-peroxide 53% 91% 79% 94% 98%
c) 5% 2,2'-azo-bis(2-acetoxy-1.5% 55% 74% 93% 98%
propane) d) 5% 2,2'-azo-bis(2-acetoxy-0.8% 63% 78% 93% 98%
butane) e) 5~ y,y'-azo-bis-(y-valerolactone) 1.6% 70% 65% 75% 97%
20 f) 5% l,l'-azo-bis-(l-acetoxy- 0.1% 83% 82% 91% 97%
cyclohexane) 1) Buna~AP 201: Ethylene-Propylene-Rubber.
2) Buna~AP 241: Ethylene-Propylene-Ethylidenenorbornene-Rubber, very fast.
3~ Buna~AP 258: Ethylene-Propylene-Ethylidenenorbornene-Rubber, extremely fast.
4) Buna~h~ls 1502: Styrene-Eutadiene-Rubber.
5) Buna~CB 10: Polybutadiene-Rubber.
The ethylene-propylene-rubber (= Buna~ AP 201), con-taining no double bonds, was not crosslinked at all by the azo-esters. The other four rubbers, containing double bonds, were crosslinked by peroxides and azo-esters to almost the same degree.
The rubbers treated with the azo-esters were intensively foamed.
EXAMPLE XIX
In this example polyethylene was crosslinked with 5%
azo-ester or peroxide in the presence of 5% carbon black. Low density, high pressure polyethylene powder (density = 0.918) B~ 24 s with a melting index of 70 grs./10 min. was mixed with 5%
carbon black and 5% crosslinking agent (azo-ester or peroxide) and afterwards crosslinked 40 minutes at 215C under atmos-pheric pressure:
Crosslinking agent Degree of (not equivalent amounts) Crosslinking a) without carbon black and crosslinking agent 5%
b) 5% carbon black, without crosslinking agent 10%
c) 5% carbon black ~ 5% 1,1-bis(t-butylperoxy)-3,3,5-trimethyl- 65%
cyclohexane d) 5% carbon black ~ 5% dicumylperoxide 84%
e) 5% carbon black + 5% 2,2'-azo-bis(2-acetoxy-propane) 84%
f) 5% carbon black + 5% 2,2'-azo-bis(2-acetoxy-butane) 85%
9) 5% carbon black + 5% 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) 72%
h) 5% carbon black + 5% l,l'-azo-bis(l-acetoxy-cyclohexane) 75%
i) 5% carbon black t 5% y,y'-azo-bis(y-valerolactone) 81%
All azo compounds tested in this example gave good degrees of crosslinking with e), f), and i) crosslinking was as good as with dicumylperoxide. Thus, carbon black has no adverse effect on crosslinking of polyethylene with azo-esters.
EXAMPLE XX
Low density polyethylene was crosslinked with 10 meq.
of the following crosslinking agents at 204.5C on the Monsanto Rheometer 100:

Crosslinking Agents l-t-butylazo-l-acetoxycyclohexane*
MH (in-lb~ 3.50 ML (in-lb) 1.08 MH-ML (in-lb) 2.42 Tcgo (min) 199.0 Ts2 (min) 140.0 *(see U.S.P. 4,029,615) MH is the maximum torque; ML is the minimum torque value; MH-ML is the difference in maximum and minimum torque 10 values (i.e., the degree of crosslinking). Tcgo is the time to 90% of MH-ML (degree of crosslinking). TS2 is the time to 2 inch-pound above ML (i.e., scorch time).
The polymer to be crosslinked was mixed homogeneously with the crosslinking agent by means of a C. U. Brabender mixer (roller style, fixed blade head) fitted with a liquid constant temperature circulator. The polymer was melted at 110-C prior to the addition of crosslinking agent.
This experiment shows that l-t-butylazo-l-acetoxy-cyclohexane is not an efficient crosslinking agent at 204.5C.
EXAMPLE XXI
Low density polyethylene was crosslinked with the following unsymmetrical azo-ester for 40 minutes at 235C under 4QQ psi pressure:
Quantity of . Degree of Crosslinking Age_ Crosslinking AgentCrosslinking l-t-butylazo-l-5% acetoxy-cyclohexane 86%
This experiment shows that unsymmetrical azo-esters are efficient crosslinkers of low density poly-ethylene at 235C.
The degree of crosslinking was determined as follows:

~L~3~5 The crosslinked polymer was cut into strips, placed in a wire cage, and extracted 3 hours by refluxing at 110C with xylene (80 ml xylene for 2 gms crosslinked polymer). The cage was rinsed with xylene, and dried at 150C. The lOSâ of weight was determined. From the results, the undissolved portion gives the degree of crosslinking, expressed in % of the original polymer weight.
EXAMPLE XXII
This example describes the crosslinkage and foaming of PVC at atmospheric pressure.
70% PVC powder of pasty consistency having a K value of 70 were stirred with 30% dioctyl phthalate (DOP) to form a paste. From 1 to 2 grams of said PVC paste were mixed with 5%
of the crosslinking agent (azo compound or peroxide) in a porcelain dish which was maintained in a drying cabinet for 40 minutes at the below indicated temperature which ranged between 170 and 215C.
In order to determine the degree of crosslinkage by extraction about 1 gram of the crosslinked polymer was cut into strips, wrapped into a precisely weighed wire mesh, and the total weight was determined by precise weighing. The ex-traction of the non-crosslinked portions was effected in a 100 ml. Erlenmeyer flask by heating for 1 hour with 85 times the volume (about 85 ml.) of tetrahydrofurane at reflux. There-after wire mesh and contents were washed with tetrahydrofurane, dried for a short time at room temperature and then for 1 hour at 120C. in the drying cabinet. After cooling the wire mesh was again weighed on the analytical balance. The degree of crosslinkage indicates how many percent of insoluble (i.e.
crosslinked proportions are present in the total crosslinked material. The degree of crosslinkage may be calculated from ~ ~ 3~ ~9 S

the weight of the insoluble components of the crosslinked material (weight of crosslinked material dried after ex-traction) multiplied by 100 and divided by the original weight of the crosslinked material.
(A) Crosslinkage at 170 to 175C.
Initiator Degree of Crosslinkage based on Relative to PVC
PVC ~ DOP PVC
+ initiator ~ initiator 10 (a) without initiator 0.2% 0.3,~
(b) 5~ dicumylperoxide 20% 27%
(c) 5% 2,2'-azo-bis(2-acetoxy-butane) 39% 53%
(d) 5h 2,2'-azo-bis(2-acetoxy-4-methylpentane) 59% 81%
(e) 5% l,l'-azo-bis(l-methoxy-cyclohexane), 25% 34%
(azo-ether) Samples c, d and e were foamed with fine pores.

(B) Crosslinkage at 190C. with varying amounts of 2,2'-azo-bis(2-acetoxy-propane):
Initiator Degree of Crosslinkage based on Relative to PVC
PVC ~ DOP PVC
I initiator + initiator (a) without initiator 0.2% 0.3%
(b) 0.2% 2,2'-azo-bis(2-acetoxy-propane) 54% 74%
(c) 0.5% " 59% 81%
(d) 1% " 64% 88%
(e) 1.5h " 64% 88%
(f) 2% " 65% 89%
(9) 3% " 63% 86%
(h) 4% " 63% 86%
(j) 5% ~l 62% 85%

~3~

With as little as 0.2% azo-ester a good degree of crosslinkage could be achieved; amounts of 1 to 2~ azo-ester resulted in a maximum degree of crosslinkage at the temperature of 190C.
employed. Samples (b) to (i) were foamed with fine pores.

(C) Crosslinkage with 3% 2~2'-azo-bis(2-acetoxy-propane) at 190C. and with varying crosslinking periods Initiator Crosslinking Degree of Crosslinkage based on Relative to PVC Period PVC ~ DOP PVC
+ initiator + initiator (a) 3% azo-ester 2.5 minutes 0.1% 0.14%
(b) " 5 minutes 0.1% 0.14%
(c) " 7.5 minutes 0.2% 0.3%
(d) " 10 minutes 43% 59%
(e) " 15 minutes 65% 89%
(f) " 20 minutes 68% 93%
(9) " 25 minutes 68% 93%
(h) " 30 minutes 67% 92%
(i) " 35 minutes 64% 88%
~j) " 40 minutes 63% 86%
(k) without 40 minutes 0.2% 0.3%
initiator A period of from 10 to 15 minutes was sufficient to reach a good degree of crosslinkage. After a period of only 20 minutes the maximum degree of crosslinkage was reached. Samples (d) to (j) were foamed with fine pores.

Some of the azo compounds used in the Examples were prepared as follows:
Preparation of l,l'-azo-bis(l-methoxy-cyclohexane):

N = N

2.62 9 of sodium (0.114 mols) were added to 100 ml of methanol. To the sodium methylate solution thus obtained, a solution of 10 9 of l,l'-azo-bis(l-chloro-cyclohexane) t0.038 mols) in 75 ml of n-hexane was added at 20C while stirring.
Subsequently, the stirring was continued for 90 minutes at 25-30C and the reaction mixture was poured into 400 ml of water while being stirred. The organic phase was washed with 500 ml of water and dried with K2C03. The hexane was remo~ed com-pletely at 40C in vacuo. Yellow oil was obtained which solidifies when stored at 0C, and which contains 89% of 1,1'-azo-bis(l-methoxy-cyclohexane); yield: 6.2 g (57% of theory).
Preparation of l,l'-azo-bis(l-phenoxy-cyclohexane):

N - N

35 g of sodium phenolate x3H20 (0.21 mol) were sus-pended in 400 ml of n-hexane. Afterwards 26.3 g of l,l'-azo-1 3'~295 bis(l-chloro-cyclohexane) (0.10 mol) - di ssol ved in 100 ml of n-hexane - were added at 20C while stirring. To complete the reaction, the mixture Was stirred for 3 hours at 20C and for 3 hours at 30C. While being stirred it was poured into 400 ml of water, stirring was continued for 15 minutes and the aqueous phase separated. The organic phase was washed twice with 1 N
sodium hydroxide and subsequently washed With water and dried with K2C03. The hexane was removed completely in vaeuo at 40C
and the yellow residue was recrystallized from acetone. White 10 powder was obtained having a melting point of 115-120C con-taining 53% of l,l'-azo-bis(l-phenoxy-cyclohexane); yield:
7.5 9.
Preparation Of l,l'-azo-bis(l-acetoxy-methylcyclohexane):
a) Methylcyclohexanone-azine:

CH3~ _ N - N ~ G~cH3 To 111 g of a methylcyclohexanone-isomer mixtUre (consisting of 61% 3-methyl-cyclohexanone, 31% 4-methyl-cyclo-hexanone and 8% cyclohexanone) (1.00 mol) was added 50 9 of hydrazine-hydrate, 50% (0.50 mol) at about 20-40C while 20 stirring and cooling in a 4-necked flask, Which was furnished with a reflux condenser, stirrer, dropping funnel and thermo-meter. Stirring was continued for 6 hours at 20C. The whole reaction mixture was poured into a separation funnel, which was closed and kept 40 hours at room temperature. The lower aque-OUs phas.e was separated; the upper phase was washed three times With 70 ml of water and dried With about 5 9 of MgS04x3H20.
The obtained 103 9 of raw azine were distilled under reduced pressure at l9ooc/3oto~fr yielding 74 9 (68% of theory) of the methyl-cyclohexanone-azine-mixture as a yellow oil.

1~ ~3Z295 b) l,l'-azo-bis(l-chloro-methylcyclohexane) N _ N

Cl Cl 21 9 of the above mentioned methylcyclohexanone-azine (0.0965 mol) were dissolved in 150 ml of CC14 in 4-necked flask, furnished with reflux condenser, stirrer, thermometer and chlorine inlet tube. While stirring and excluding atmos-pheric moisture about 2.6 liters of chlorine gas (about 0.105 mol) were bubbled through the solution at 10-15C; stirring was continued for 10 minutes at 10-15C; and subsequently a slow stream of nitrogen was blown through the entire apparatus, in order to react all the chlorine with the azine. Afterwards the CC14 was removed under reduced pressure at 60-70C yielding 60 g of the l,l'-azo-bis(l-chloro-methylcyclohexane) as a reddish brown oil with a purity of 51%.
c) l,l'-azo-bis(l-acetoxy-methylcyclohexane) CH3~N = N~CH3 .

CH3 C00 oOC-CH3 28.4 9 of the above mentioned l,l'-azo-bis(l-chloro-methylcyclohexane) were added in portions while stirring and cooling to a suspension of 41 9 of anhydrous sodium acetate in 300 ml of acetic acid at about 20C. Stirring was continued for three hours at room temperature, subsequently, the mixture was poured into 1.51 of water and stirred for a further 30 minutes. For better separation of phases, the azo compound was dissolved in 100 ml of ethyl acetate and the total mixture allowed to separate in a separation funnel. After separation of the lower aqueous phase, the organic phase was washed with 9~

NaHC03-solution to alkaline reaction and then dried with MgS04x3H20. The acetic ester was removed ~ va~uo at 60C. In the flask remained 51 g of l,l'-azo-bis(l-acetoxy-methylcyclo-hexanone) as a dark reddish brown oil with a slight smell and a purity of 55%.

Preparation of 1,1'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclo-hexane) a) 3,3,5-trimethylcyclohexanone-azine ~ = N - N = ~ H3 701 g of 3,3,5-trimethyl-cyclohexanone (5~0 mol) and 200 ml of isopropanol were filled into a 4-necked flask, furnished with reflux condenser, stirrer, dropping funnel and thermometer. 125 9 of hydrazine-hydrate, 80% (2~0 mol) were added at temperatures beneath 40C while stirring and cooling.
Stirring was continued for 3 1/2 hours at 85C. The mixture was poured into 1 liter of water while stirring and settled in the separating funnel. After separation of the lower aqueous phase, the organic phase was shaken with 500 ml of water;
hereby the azine separated as a solid white product, which was sucked off, washed again and dried in the air. By this process 64 g (11.5% of theory) of 3,3,5-trimethylcyclohexanone-azine were obtained as a white powder with a melting point of 135-137C.
b) l,l'-azo-bis(l-chloro-3,3,5-trimethyl-cyclohexane) C ~ CH3 / ~ CH3 ~ N ~ N ~

CH3 Cl Cl CH3 ~ 2 ~ ~

55.3 9 of the above mentioned 3,3,5-trimethylcyclo-hexanone-azine (0.20 mol) were dissolved in 400 g of CC14 in a 4-necked flask, furnished with reflux condenser, stirrer, thermometer and chlorine inlet tube. At 10-20C about 15 9 of chlorine gas (about 5.3 liters, 0.21 mol) were slowly bubbled through the mixture while stirring, cooling and excluding atmospheric humidity. Stirring was continued for 10 minutes and then a slow flow of nitrogen was blown through the entire apparatus, in order to cause all of the chlorine to react with the azine. The CC14 was removed in va~uo at 60C thus giving 50 g (72~ of theory) of the raw dichloro-azo compound as an orange powder. After recrystallization from n-pentane 27 9 (38% of theory) of the pure 1,1'-azo-bis(l-chloro-3,3,5-trimethyl-cyclohexane) were obtained as a nearly white, yellow-ish powder without a smell, with a melting point of 149-151C
and a purity of 98.1%.
c) l,l'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclohexane) ~ N - N--26.5 g of the above mentioned l,l'-azo-bis(l-chloro-3,3,5-trimethyl-cyclohexane) (0.075 mol) were added in portions while stirring and cooling to a suspension of 32 g of anhydrous sodium acetate (0.39 mol) in 280 ml of acetic acid at about 20C. The mixture was stirred for 3 hours at room temperature, then poured into 1.5 liters of water while stirring, during which the acetoxy-azo compound separated as clear fine crystal-line substance, and then stirred again for 30 minutes. After filtration by sucking, washing with water and drying in the ~322~3S

air, the l,l'-azo-bis(l-acetoxy-3,3,5-trimethyl-cyclohexane) was obtained as a fine light-grey powder w;th a yield of 29.7 g (98% of theory) and a melting point of 109-113C. After recrystallization from acetone, 16 9 of the white crystalline azo compound with a melting point of 111-115C and an assay of 104~ (determined iodometrically) were obtained.
Preparation of l,l'-azo-bis(l-acetoxy-cyclohexane) in one step from the cyclohexanone-azine:

O = N - N = O t NaOOC CH3 0 N = N ~

22 9 of cyclohexane-azine (0.114 mol) were dissolved in 300 ml of acetic acid in a 4-necked flask, furnished with CaC12-tube, stirrer, thermometer and chlorine inlet tube. Then 38 9 of anhydrous sodium acetate (0.464 mol) were added. The mixture was stirred for 10 minutes and then 8.5 g of chlorine (about 3 liter 0.12 mol) were slowly bubbled through the sus-pension at 20C excluding atmospheric humidity. Subsequently a slow stream of nitrogen was blown through the entire apparatus and stirring was continued for 30 minutes at 20C. While stirring, the reaction mixture was poured into 2 liters of water - during which the azo compound separated as a fine crystalline product; then stirring was continued for another 30 minutes; the product was separated and washed well with water and dried in the air. By this process 25 9 (71% of theory) of the l,l'-azo-bis(l-acetoxy-cyclohexane) were obtained as a nearly colourless, light yellowish, crystalline powder with a melting point oF 91-94C and a purity of 99%.

2~3S

Preparation of 2,2'-azo-bis(2-acetoxy-4-methyl-pentane) in one step from methyl-isobutyl-ketone-azine:
CH3 CIH3 ICH3 fH3 +C12 CH3 ICH3 ICH3 fH3 H3 CH CH2 C-N-N-C CH2 CH CH3 ~NaOOC-CH3 CH3 CH CH2 1C-N-N-C CH2 CH CH3 in HOOC-CH3 CH3 COO OOC CH3 30 9 of methyl-isobutyl-ketone-azine (0.153 mol) were dissolved in 400 ml of acetiC acid in a 4-necked flask, furnished with CaC12-tube, stirrer, thermometer and chlorine inlet tube. 50 9 of anhydrous sodium acetate (0.61 mol) were added to the flask; it was stirred 10 minutes and 11.6 9 (about 4.1 liters) of chlorine (0.164 mol) slowly was bubbled through the suspension at 20C under exclusion of atmospheric humidity.
Subsequently a sloW stream of nitrogen Was blown through the entire apparatus and stirring was continued for 1 hour at 20C.
The reaction mixture was poured into 1.5 liters of water while stirring, during whiCh the azo compound separated as oil;
stirring was continued for another 30 minutes; the mixture was settled in a separation funnel and the lower aqueous phase was separated. The upper azo phase was washed with NaHC03-solution until an alkaline reaction occurred. After separation of the aqueous phase, the azo compound was dried With MgS04 x 3H20.
20 Thus, 31.5 9 (64% of theory) of the 2,2'-azo-bis(2-acetoxy-methyl-pentane) were obtained as a yellowish oil With a moder-ate smell and a purity of 97~.
Preparation of l,l'-azo-bis(l-formyloxy-cyclohexane) in one step from cyclohexanone-azine:

O = N - N = ~ ~ NaOOC-H ~ N = N
in HOOC-H ¦ ¦ .

H-COO OOC-H
64 9 anhydrous sodium formate (0.94 mols) were added to 300 ml anhydrous formic acid in a 4-necked flask furnished :~Ll 3~2~ ri with CaC12-tube, stirrer, thermometer and chlorine inlet tube.
Then 44 9 (0.228 mols) of cyclohexanone-azine were added at 20C by stirring which was continued for 10 minutes; the mixture was cooled to 0C and 17.6 9 (about 6.2 liters; 0.248 mols) of chlorine were slowly bubbled through the suspension at 0C (cooling with ice/sodium chloride) excluding atmospheric humidity. Subsequently, a slow stream of nitrogen was blown through the entire apparatus; stirring was continued for 1 1/2 hours in the following manner: 15 minutes at 0C, 15 minutes at +5C, 15 minutes at +10C, 15 minutes at +15C, 15 minutes at +20C and 15 minutes at+25C. While stirring, the reaction mixture was poured into 2 liters of water during which the azo compound separated as a white fine crystalline product; then stirring was continued for 20 minutes; the product was sepa-rated and washed with water. The azo compound was suspended in 800 ml of 8% sodium bicarbonate solution, stirred for 20 minutes, filtered by vacuum, washed well with water and dried in the air. By this process 49.5 9 (77% of theory) of the l,l'-azo-bis(l-formyloxy-cyclohexane) were obtained as a snow-white, odourless crystalline powder with a melting point of 97-99.5C and a purity of 99.5%. The azo compound was not shock sensitive, did not show any signs of decomposition up to 200C and had no explosive properties (in the pressure vessel test a value of < 1 mm was found). After repeated re-crystallizations from acetone, colourless crystals with a melting point of 99-100.5C were obtained.
Elementary analysis: C14 H22 N2 4 ; MW - 282.33 calc.: 59.55% 7.85% 9.92% 22.67%
found: 59.89% 7.82% 10.00% 22.29%
(0 ascertained from difference) (See: D.C. Noller, et al, Ind. & Eng. Chem. 56, No. 12, 18-27 (1964))-s Preparation of 2,2'-azo-bis(2-acetoxy-butane) in one step from methyl-ethyl-ketone-azine:

fH3 CH3 l C12 1CH3 f~l3 CH3-cH2-C=N-N=C-CH2-CH3 t NaOOC-CH3 CH3-CH2- -N=N-f-CH2-CH3 in HOOC-CH3 CH3-COO OOC-CH3 114 9 anhydrous sodium acetate (1.39 mols) were added to 900 ml anhydrous acetic acid in a 4-necked flask furnished with CaC12-tube, stirrer, thermometer and chlorine inlet tube.
Then 96 9 of methyl-ethyl-ketone-azine (0.684 mols) were added at 20C by stirring. Stirring is continued for 10 minutes and 48.6 9 (about 17.2 liters) chlorine (0.684 mols) were slowly bubbled through the suspension at 22-28C by stirring excluding atmospheric humidity. When approximately 4/10 of these 17.2 liters of chlorine were introduced, an additional 114 9 of anhydrous sodium acetate (1.39 mols) were added slowly within 5-10 minutes. Stirring was continued for 1 hour at 30C. ~hile stirring, the reaction mixture was poured into 2250 ml of water and stirring was continued for 15 minutes.
After separation of the aqueous phase, the liquid azo compound was washed with 300 ml of a 6% NaHC03-solution while stirring 30 minutes. After separation from the aqueous phase, the same bicarbonate wash was repeated. It was followed by a wash with 210 ml NaCl-solution, 14% and drying with 20 9 MgS04. The 2,2'-azo-bis(2-acetoxy-butane) obtained was having a greenish, brownish agreeable ketone-like smelling liquid having a yield of 121 9 (68% of theory) and a purity of 99%; density = 1.007 at 20C; nD - 1.4360.

~l3Z'~95 Preparation of 2,2'-azo-bis(2-acetoxy-3-methyl-butane) in one step from methyl-isopropyl-ketone-azine:
fH3 fH3 fH3 fH3 ~C12 CH3 fH3 ICH3 ICH3 CH3-CH - C=N-N=C - CH-CH3 ~NaOOC-CH3 CH3-CH - f-N=N-C - CH-CH3 in HOOC-CH3 CH3-COO OOC-CH3 76 9 anhydrous sodium acetate (0.926 mols) were added to 600 ml anhydrous acetic acid in a 4-necked flask furnished with a CaC12-tube, stirrer, thermometer and chlorine inlet tube. Then 38.3 9 of methyl-isopropyl-ketone-azine (0.228 mols) were added at 20C by stirring. Stirring was continued for 10 minutes and 16.2 9 (about 5.7 liters) chlorine (0.228 mols) were slowly bubbled through the suspension at 22C while stirring and excluding atmospheric humidity. Stirring was con-tinued for 1/2 hour at ~22C, 1/2 hour at ~26C and 1 hour at 30C. The reaction mixture was poured on 1200 ml of ice water while stirringi stirring was continued for 15 minutes and the azo compound solidified. It was filtered by suction, washed with water and dissolved in 150 ml pentane. This pentane solution was washed twice with 200 ml NaHC03-solution, 6% for 30 minutes while stirring, once with 210 ml NaCl-solution, 14%, dried with Na2S04 and the pentane evaporated in va~uo at 20 to 30C yielding the 2,2'-azo-bis(2-acetoxy-3-methyl-butane) as a weakly greenish, strongly smelling, crystalline product; yield:
26 9 (40% of theory), melting point: 55-62C; purity: 98%.
By recrystallization from the 10-fold quantity of aqueous ethanol, 45%, the pure azo compound was obtained as a white odourless fine-crystalline product with a melting point of 62 to 64C.
Elementary analysis: C14 H26 N2 4 ; MW - 286.36 calc.: 58.72% 9.15% 9.78% 22.35%

found: 58.24% 8.90% 10.34% 22.52%
(O ascertained from difference)

Claims (7)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. The process of crosslinking or simultaneously crosslinking and foaming a polymer selected from the group consisting of polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene-styrene rubber, ethylene-propylene-ethylidene-norbornene rubber, and polybutadiene rubber comprising:
(a) mixing with 100 parts by weight of said polymer 0.5 to 20% by weight of a composition including at least one azo-ester crosslinking and foaming agent of the formula:

(I) in which R is selected from the group consisting of H, lower alkyl, cycloalkyl, aryl and aralkyl;
R1 and R2 are independently selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl wherein each of the groups may have alkyl branching;
R1 and R2 can join together to form R1R2 group where the group is selected from -(CH2)4-, -(CH2)5-, alkylsubstituted tetramethylene or alkyl-substituted pentamethylene;

R and R1 can join together to form RRl group where the group is selected from -(CH2)2-, -(CH2)3-, alkylsubstituted -(CH2)2- or alkylsubstituted -(CH2)3-; and R3 is selected from the group consisting of -OOC-R, alkyl, cycloalkyl and aralkyl; and (b) in the absence of an activator which lowers the decomposition temperature of the cross-linking and foaming agent when the composition is heated, heating the polymer mixture at a temperature above 170°C but not to the point where the polymer will substantially degrade and a pressure of 0 to 300 psia until cross-linking or crosslinking and foaming are effected.

2. The process of Claim 1, wherein the polymer mixture is heated in a temperature range of 180° - 230°C at atmospheric pressure.

3. The process of Claim 1, wherein the composition comprises an azo-ester in combination with a member selected from an azo-ether or peroxide.

4. The process of Claim 1, wherein the composition comprises two different azo-esters of formula (I).

5. The process of Claim 1, wherein the composition is 2,2'-azo-bis(2-acetoxy-propane).

6. The process of Claim 1, wherein the composition is 2,2'-azo-bis(2-acetoxy-butane).

7. The process of Claim 1, wherein the composition is one azo-ester of formula (I) and at least one member selected from the group consisting of a foaming agent, azo-ether and organic peroxide.