CA1191988A - Process for crosslinking and, if desired, foaming natural or synthetic homo- and/or copolymers - Google Patents

Abstract

ABSTRACT

A process is provided for crosslinking, foaming, or both of polymers at temperatures above 150°C using at least one azo ester and/or azo ether in combination with at least one crosslinking intensifier having at least two reactive carbon-carbon double or triple bonds.

Description

PROCESS FOR CROSSL,IN~ING AND, IF DESIRED, FOAMING NATUR~L~L OR SYNTHETIC HOMO- AND/OR COPOLYMERS

~ACKGROUND OF THE INVENTION
The invention pertalns to the method, of crosslinking homo- and/or copolymers using symmetric or unsymmetric azo esters or syn~netric or unsymmetric azo ethers with the aid of crosslinking intensifiers.
U.S.4,129,531 has as its goal the crosslinking and foaming of polymers with the aid of azo esters; US Patent No.
3,776,885 pertains to the corsslinking of polymers with azo ethers.
SUMMARY OF_THE INV-ENTION
The present inv.ention is directed to a process of crosslinking or simultaneously crosslinking and foaming a ~ 8 natural or synthetic homo- or copolymer or a mi.Yture thereof ha-~ir.g -CH2- and/or CH-groups comprising:
mi.~ing with a 100 parts by weight of said ~olymer (i) 0.02 to abo~t 3.0% by weight of at least one member selected from the group consisting of an azo ester, an azo ether, and a mi.~ture thereof and (ii) 0.05 to about 10% by weight of at least one crosslinking intensifier ha~7ing at least two reactive carbon-carbon double or triple bonds, and heating the polymer mi.~ure at a temperature above 150C but not to the point where the polymer will substantially degrade and at a pressure of from about 0 to ahout 300 psia until crosslinking or crosslinking and foaming are effected.
DETAILED DESCRIPTION OF THE INVENTION
Within the framework of this invention it was found that combinations oE smaller amounts of azo esters (e.g., Formula I below) or azo ethers (e.g., Formula II below) CH3-C - N = N - C - CH3 ~ I-N = N - ~
CH3-COO OOC-CH3 C~l3-O O-CH3 (I) (II) with crosslinking intensifiers (e.g., triallyl cyanurate, triallyl trimellitate,etc.) are e~cellently suitable for crosslinking of polymers, and provide considerable aclvantages, as described hereinafter, compared to the use of azo esters or azo ethers alone, thus in the absence of crosslinlcing intensi.fiers.

~ ~9~

Unless otherwise indicated, percentages are percent by weight.
1. In the present invention a considerable reduction is possible in the quantity of azo ester or azo ether required to produce a degree of crosslinking while with azo esters or azo ethers alone the same degree of crosslinking can only be obtained by using a considerably larger amount of these azo compounds. For e~ample, in the crosslinking of polyethylene when using a combination of 0.~% azo ester (I) and 0.3% triallyl cyanura~e, a crosslinking degree of 74% was achieved, whereas when using large amounts of the azo ester (I) alone, such as 1.5%, 2%, 3%, 4% and 5%, crosslinking degrees of only 71%, 76%, 80%, 81% and 82%, respectively, were yielded.
lS It is even possible to reduce the quantity of azo compound below 0.1%, e.g., to 0.05% or 0.02%, and nevertheless achieve good degrees of crosslinking. For example, polyethylene at 200C was crosslinked to the e~Ytent of 81% using a combination of 0.5% triallyl cyanurate and 0.05% 2,2'-azo-bis-(2-aceto~y-4-methylpentane).

2. In accordance with this invention the combination of azo crosslinkers and crosslinking intensifiers can even give the possibility of achieving a good degree of crosslinking i~ the azo crosslinlcer alone produced no crosslinking whatsoever. For e.~cample, ethylene-propylene copolymer (= E:PR, saturated type) was crosslinked to the e~tent of 7~% using a combination of 1.5% azo ester (I) and 0-7/O triallyl cyanurate as a crosslinking intensifier, while no appreciable crosslinking was achieved with the azo ester alone. Specifically, 1.5% azo ester (I) alone resulted in a crosslinking degree of only 0.7%, and 5% of (I) gave a crosslinking degree of only 1.5%.

3. In accordance with this invention the combination of an azo compound and a crosslinking intensifier permits crosslinking of sensitive polymers and copolymers such as polypropylene. For e~ample, 5% of triallyl trimellitate and 1% of 2,2'-azo-bis-(2-aceto~y-4-methylpentane) were able to crosslink polypropylene to the e.~tent of 67% at 200C and 78%
at 180C, whereas no crosslinking occurs with the azo compound alone and pero.~ide crosslinkers degrade polypropylene.

4. An additional advantage of the system in accordance with this invention as compared to the use of azo esters or azo ethers alone lies in the "kicker" effect of the crosslinking intensifier, which reduces the start-up temperature by about 20C.

5. Using the system in accordance with this invention it is possible, under unpressurized or practically unpressurized conditions (below 5 bar) to obtain non-foamed, bubble-free polymer molded articles (e.g., pipes) with a good degree of crosslinking. In this case particularly favorable results are achievecl if azo esters or azo ethers are used in - ) -very small amounts (about 0.02 to 0.2%) in the combination in accordance with this invention.

6. As compared to pero~ide type crosslinking agents, this invention offers the advantage that mixing with the polymer at higher temperatures is possible without scorching, which is especially important in the case of polymers with a high softening point, e.g., high density polyethylene or polypropylene.
In accordance with this inventi.on crosslinking can be carried out at temperatures above 150C, wherein the upper limit depends on the thermal stability of the polymer.
The ~oaming ability of the azo esters or azo ethers, which give off molar quantities of nitrogen upon thermal degradation, is also retained when crosslinking intensifiers are used. If the crosslinking is carried out in accordance with the invention under application of pressure, no foaming takes place. When small amounts of azo compound are used (for e~amp,le, less than 0.2%), the simultaneous use of J~ c~r/~ ~,"
c-roFs1inkin-~ intensifiers make it possible to perform bubble-free crosslinking even under nonpressurized conditions, as described hereinbefore.
The sy~Lmetric or unsymmetric azo esters or azo ethers used as crosslinking agents are used individually or in combination in total amounts of 0.02 to 3.0 Wt-%7 preferably O.l to 2.5 wt:-%, especially preferably 0.4 to l.5 wt %, based on the polymer to be used.

.

It is also possible to combine one or more of the azo compounds used in accordance with this invention with one or more crosslinking-promoting free radical forming agents such as pero~ides, azides and diazoacetates, hherein the total amounts of the crosslinking agent combinations fall within the ranges mentioned hereinbefore.
It is also possible to use the azo cornpounds in accordance with the invention in themselves, or their-combinations with one or more other free radical forming agents, together with foaming agents (e.g., azodicarbonamide, azobisisobutyronitrile).
The amounts oE crosslinking intensifiers which are used individually or in combination fall within the overall range of 0.05 to 10 wt-%, preferably from 0.1 to 5 wt-%, and especially preferably from 0.2 to 2 wt-%, based on the polymer to be crosslinked.
The relationship of the quantity of crosslinking intensifiers or their combinations to the quantities of azo compound or their combinations with other free radical forming agents can assume any desired value. Preference is given to weight ratios of crosslinking intensifiers to azo compound of 0.5 to 10:1, preEerably 0.75 to 2:1 and especially preferably about 1:1. At such ratios the highest crosslinking degree is made possible with a simultaneous marked decrease in ~.he amount of crosslinking agent and crosslinki.ng intens:i.fier.

The sum of crosslinlcing i.ntensi.fier and azo compound is not critical. In general it amounts to at least 0.4 wt-%, based on the polymer to be crosslinked and can be as high as 13.0%; preference is given to 0.5-7.5 wt-% based on the polymer.
Obviously, instead of an individual crosslinking intensifier, any desired mi~tures of two or more crosslinking intensifiers can be used.
As the symmetric or unsymmetric azo esters or azo ethers, those customarily employed for the crosslinking of polymers may be used, as described for e.Yample in U.S. Patent 4,129,531 and in US Patent No. 3,776,885. The following preferred compounds of General Formula III (symmetric or unsymmetric) and IV (unsymmetric), individually or in combination, have proven particularly suitable:
R~ R2 R6 R2 Rl C - N = N - C - R1 R5 - C - N = N - 1 -l l 14 R - O O - R R O - R
(III) (IV) In Formulas III and IV the substituents R, R1, R2, R4, R5 and R6 have the following meanings:
R is selected from the group consisting of linear or branched alkyl of 1 to 11 carbons, substituted or unsubstitutecl cycloalkyl of 5 to 6 carbons, substituted or unsubstitutecl phenyL, substituted or unsbustituted aralkyl of

7 to 15 carbons, and R3-Co-, wherein the substituent is alkyl of 1 to 10 carbons, R3 is selected from the group consisting of H, linear or branched alkyl of 1 to 10 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubstituted aralkyl of 7 to 15 carbons, wherein the substituent is alkyl of 1 to 10 carbons, Rl and R2 are independently selected from the group consisting of linear or branched alkyl of 1 to 10 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubstituted aralkyl of 7 to 15 carbons, wherein the substituent is alkyl of 1 to 10 carbons, RlR2C- can joi~ together to form a group selected from substituted or unsubstituted cycloalkyl of 5 to 6 carbons wherein the substituent is alkyl of 1 to 10 carbons, -OR and Rl can join together to form a member selected from the group consisting of -OCO-CH2-CH2- and -OCO-CH2-CH2-CH2-, R4, R5 and R6 are independently selected from the group consisting of linear or branched alkyl of 1 to 10 carbons, substituted or unsubstitutecl cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubsti.tuteci aralkyl of 1 to 10 carbons, wherein the substituent is alkyl of 1 to 10 carbons, R5R6C- can join together to form a member selec~ed from the group consisting oE substituted or unsubstituted cycloalkyl of 5 to 6 carbons wherein the substituent is alkyl of 1 to 10 carbons In General Formula III, the groups R, R1, R2, R3, R1R2C
and RRl on ~he left hand side of the molecule are generally identical to the corresponding groups on the right hand side of the molecule, but they may also be different, and either one or several of the groups may be different Thus it is also possible that R O- on the left hand side will represent an ether group and on the right hand side an ester group (R3-Coo-), and thus a mixed azo-ester-ether will be present Preferred alkyl substituents in the aforementioned R Rl R2 R3 R4 R5 and R6 are C1_6 alkyl, especially methyl, ethyl and propyl Examples of preferred gro~lps R, Rl, R2, R3, R4, R5 and R6 are: alkyl groups, such as C1 6 alkyl, especially methyl, ethyl and propyl an~ aralkyl with Cl 10 alkyl groups such as benzyl or phenethyl.
Suitable symmetrical azo esters o~ Formula III are, for example: 2,2'-azo-bis-(2-acetoxypropane), 2,2'-azo-bis-(2-acetoxybutane), 2,2'-azo-bis-(2-acetoxy-3-methylbutane), 3,3'-azo-bis-(3-acetoxy-2,4-dimethylpentane), ~,2'-azo-bis-(2-acetoxy-~-methylpentane, 1,1'-azo-bis-(1-acetoxy-cyclohe~ane), l,l'-azo-bis~ acetoxy-l-phenylethane, 1,1'-azo-bis-(l-acetoxy-2- or 3- or 4- or 2/3-or 2/4- or 2/3/4-1ni~ture-methyl-cyclohe~:clne) J
1,1'-azo-bis-(l-acetoxy-3,3,5-trimethyl-cyclohexarle), y,y'-azo-bis-(y-valerolactone), 7yy~C>~7~o ~ ~
2,2'-azo-bis-(2- ~--~r-~yrt~-~), r~
2,2'-azo-bis-(2-for~yloxybutane), 2,2'-azo-bis-2-formyloxy-4~methylpentane), l,l'-azo-bis-(l-formyloxy-cyclohexane), 2,2'-azo-bis-(2-propionoxypropane), l,l'-azo-bis (l-propionoxy-cyclohexane), 2,2'-azo-bis-(2-benzoyloxypropane), l,l'-azo-bis-(l-benzoyloxycyclohexane), 2,Z'-azo-bis-(2-isobutyryloxybutane), 2,2'-azo-bis-(2-pivaloyloxypropane), 2,2'-azo-bis-(2-isobutyryloxy-4-methylpentane), and l,l'-azo-bis-(l-isobutyryloxy-cyclohexane).
Suitable unsymmetric azo esters of Formula III are, for example: 2-l2'-acetoxypropyl-(2')-azo]-2-acetoxybutane, 1-~2'-acetoxybutyl-(2')-azo]-1-propionoxy-cyclohexane, 2-acetoxy-2'-propionoxy-2,2'-azo-bis-propane, l-formyloxy-l'-acetoxy-2,2'-azo-bis-cyclohexane, [2-acetoxy-4 methyl pentyl-(2)]-l'-acetoxy-cyclohexyl-(l')]
-diazene.
Suitable symmetric azo ethers of Formula III are, for example: 2,21-azo-bis-(2-methoxypropane), 2,2'-azo-bis-(2-methoxybutane), 2,2'-azo-bis (2-methoxy-4-methylpentane), 1,1'-azo-bis~ methoxy-cycloheYane), 1,1'-azo-bis-(1-metho,cy-3,3,5-trimethyl-cyclohexane), 2,2'-azo-bis-(2-echoxypropane), 2,2'-azo-bis-(2-ethoxy-4 -methyl-pentane), 1,1'-azo-bis-(1-etho~y-cyclohe.Yane), 1,1'-azo-bis-(1-ethoxy-3/4-mixture-methyl-cyclohe.Yane), 2,2'-azo-bis-(2-isopropoxy propane), 2,2'-azo-bis-(2-isopropoxybutane), 1,1'-azo-bis-(1-isopropoxy-cyclohexane), 2,2'-azo-bis-(2-propoxybutane), 2,2'-azo-bis-(2-buto.Yypropane), 2,2'-azo-bis-(2-butoxy-4-methylpentane), 1,1'-azo-bis-(1-butoxy-cyclohexane), 2,2'-azo-bis-(2-pheno.Yypropane), 1,1'-azo-bis-(1-pheno~Yy--cyclohexane) Suitable unsymmetric azo ethers of Formula III are, for example: 2-[2'-methoxy-propyl-(2')-azo]-2-methoYybutane (equivalent to [2'-methoxypropyl-(2')~-(2-methoxybutyl-(2)]
-diazene), 1-[2'-methoxy-butyl-(2')-azo~-1-ethoxy-cyclo-hexane, 2-methoxy-2'-ethoxy-2,2'-azo-bis-propane, l-methoxy-l'-isopropoxy-l 31 ~ - azo-bis-cyclohexane, [2-ethoxy-4'-methylpentyl-(2')]-[1-ethoxy-cyclohexyl-(1)]
-diazene, 2-isopropoxy-2'-butoxy-2,2'-azo-bis-butane Suitable mixecl azo ester ethers of Formula III are, for example 2-prol)ionoxy-2'-propoxy-2,2'-azo-bis-propane, L9~

2-aceto.~y-2-ethoxy-2,2'-dzo-bis-butane, 2-formylo.Yy-2'-metho.Yy-2,2'-azo-bis-(4-methylpentane), l-acetoxy-l'-methoxy-l,1'-azo-bis-cyclohe.Yane, l-formyloxy-1'-n)ethoYy-l,l'-azo-bis-cyclohexane, 2-formyloxy-2'-propoxy-2,2'-azo-bi.s-butane, 2-acetoxy-2'-isopropoxy-2,2'-azo-bis^propane.
Suitable unsymmetric azo esters of Fornlula IV are, for example: 2-tert.-butylazo- (or ~ert.-alllylazo- or cumylazo)-2-acetoxy-4-methyl-pentane, 2-tert.-butylazo- (or tert.-amylazo-or cumylazo)-2-propionoxy-butane, 1-tert.-butylazo (or tert.-amylazo-or cumylazo)-1-formyloxy-cyclohexane, 2-tert.-butylazo- (or tert.-amylazo- or cumylazo)-2-isobutyryloxy-propane, 1-tert.-butylazo- (or tert.-amylazo- or cumylazo)-l-acetoxy-cyclohexane, y-tert.-butylazo-(or tert.-amylazo- or cumylazo)-~-valerolactone, 2-(1-methylcyclohexylazo)-2-acetoxybutane, 1-(t-octylazo) -l-acetoxycyclohexane and 2-(t-hexylazo)-2-acetoxy propane.

Suitable unsymmetric azo ethers of Formula IV are, for example: 2-tert.-butylazo- (or tert.-amylazo-or cumylazo)-2-methoxy-4-methyl-pentane, l-tert.-butylazo- (or tert.-amylazo- or cumylazo)-1-methoxy-cyclohexane, 2-tert.-butylazo- (or tert.-amylazo- or cumylazo)-2-ethoxy-butane, I-tert.-butylazo- (or tert.-amylazo- or cumylazo)-1-:isopropoxy cyclohexane, 2 tert.-butylazo- (or tert.-arnylazo- or cumylazo)-2-propo.~ybutane, 2-tert.-butylazo- (or tert._amylazo- . or cumylazo)-2-buto.~ypropane, 2-tert.-butylazo- (or tert.-amylazo- or cumylazo)-2-pheno.Yypropane, l-tert.-butyl-azo-(or te~t.-arnylazo-or culrlylazo)-l~phenoxycyclohe.Yane, ~e f~ ~c/~7~f~y~
, 1-(1-~0~4e-=~f~-e-}-e~)-1-metho.~ycyclohe.~ane, 2-(t-octylazo)-2-metho.~ybutane and 2-(t-hexylazo)-2-metho.Yypropane.
Suitab].e crosslin~ing intensifiers include all compounds ~ith at least two reactive (= polymerizable) carbon-carbon double- and/or carbon-carbon triple bonds in the molecule, either individually or as a mixture. Suitable crosslinking intensifiers are, for example di-, tri- or polyallyl compounds, for example cyanurates (such as triallyl cyanurate, triallyl isocyanurate, di.allyl isocyanurate), allyl esters of divalent, trivalent or polyvalent carboxylic acids (such as triallyl trimellitate, triallyl trimesinate, diallyl succinate, -glutarate, -adipate, diallyl phthalate, diallyl diglycol dicarbonate), divalent, trivalent or polyvalent N-allyl-substituted acid amides or imides (e.g., N,N,N',N' tetraallyl adipic acid diamide), allyl ethers on the basis of divalent, trivalent or polyvalent alcohols (such as trimethylolpropane triallyl ether), allyl esters of dibasic, tribasic or polybasic inorganic acids (such as triallyl phosphate), allyl-substituted amino group-bearing ~ 9~

s-triazines (such as 2-butylamino-4,6-cliallyl-o.~y-s-triazine).
Di-, tri- or polymethallyl compounds corresponding to the above mentioned di-, tri- or polyallyl compounds, are for example trimethallyl cyanurate.
Di-, tri- or polycrotyl compounds corresponding to the above mentioned di-, tri- or polyallyl compounds, are for example tricrotyl cyanurate.
Di-, tri- or polymethacryl esters, are for example, ethylene glycol-dimethacrylate, hexanediol-(1,4)-dimethacrylate, trimethylolpropane-trimethacrylate.
Di-9 tri- or polyacryl esters corresponding to the above mentioned di-j tri- or polymethacrylate esters, are for example diethylene glycol diacrylate.
Polyenes (= polymers with double bonds), are for eYample polybutadiene rubber (~ 1,2- or 1,4-polybutadiene).
Di-, tri- or polyvinyl compounds are for example divinylbenzene, butanediol-(1,4)-divinyl ether, trimethylolpropane-trivinyl ether, divinyl succinate, trivinyl isocyanurate, 1,2,4-trivinyl cyclohexane.
Compounds with triple bonds, are for example dipropargyl phthalate, tripropargyl trimellitate.
Di-, tr:i- or polymaleimides, are for example m- or p-phenylene-bis-(malei.mide), 1,6-bls-maleimido-he.Yane, 4,L~'-methylene-bis-phenyl-maleimide, tris-(4-maleimi.do-phenyl)-methane, tris-, tetrakis- or pentakis-male:imides of Formula V
CH = CH CH - CH CH ~ CH
(~ C C C C C
5O/ \ ~ ~O O~ O O// \ / ~O
N N N

I~CH2~--~CH2 ~ ~ ,3 n in which n = 1,2 or 3.
Examples of compounds with different double or- triple bonds in the molecule, are acrylate, allyl methacrylate, diallyl maleate, dipropargyl maleate, 1,3-bis-(allylo.Yy)-propyl-(2)-methacrylate, l-allyloxy-2-2 -dimethylolbutane-dimethacrylate, 2,2-bis-(allyloxymethyl) -butyl-(l)-methacrylate, N-allylmaleimide and N-vinylmaleimide.
All polymers or copolymers of compounds with -CH2-and/or -CH- groups capable of crosslinking by free radical forming agents, and obtained either synthetically or naturally, as well as any desired mixtures of these can be used in the practice of this invention. Such compounds include, for example, high pressure polyethylene of low density, low pressure polyethylene of high and low density, chlorinated polyethylene, chlorosulfonated polyethylene, polypropylene, polybutylene-(1), poly-[4-methylpentene-(1)], polyvinyl chloride, polyvinyl aceta~e, polyacrylic acid esters, ethylene-vinyl acetate copolymers, ethylene~propylene copolymers, ethylene-propylene-diene terpolymers, ethylene-butylene copolymers, ethylene-propylene-butyiene S copolymers, ethylene-vinyl ch:Loride copolymers, vinyl chloride-vinyl acetate copolyrners, vinyl chloride-vinylidene chloride copolymers, ethylene-carbon monoxide [sic]
copolymers, natural rubber (polyisoprene), polybutadi.ene, polychloroprene (neoprene), synth,atic polyisoprene, ethylene-propylene-ethylidene norbornene (or cyclopentadiene or hexadiene or butadiene) copolymer, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, butadiene-styrene-acrylonitrile copolymer, styrene-isoprene block polymer, butyl rubber (isobutylene-isoprene copolymer), silicone rubber, saturated polyesters, polyamides J
polyurethanes, polyethers and polyacetals.
Examples of suitable organic peroxides include the following:
~ ~ J~
(a) dialkyl peroxides, e.g., ~ l peroxide, tert.-butyl-cumyl peroxide, ~, ~'-bis-(tert.butylperoxy) 1,4-(or 1~3)-diisopropylbenzene, 2,5-bis-(tert.-butylperoxy) -2,5-dimethyl-hexane or -hexyne-(3), 3-(tert.-butylperoxy) -3-pher~yl-phthalide;
(b) perketals, e.g,, 1,1-bis-(tert.-butylperoxy)-3,3, 5-trimethylcyclohe.Yane, 4,4-bis-(tert.-butylperoYy) -pentanoic acid n-butylester;

9~

(c) mixed dialkylperoxide perketals, e.g., 3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxanonane;
(d) per-esters, e.g., tert.~butyl perbenzoate, tert.-butyl per-3,5,5-tri-methylhexanoate, tert.-butylper-2-ethylhexanoate;
(e) monoperoxycarbonate esters, e.g., 00-ter~.-butyl o-2-ethyl-he.Yyl monoperoxycarbonate, 00-tert.-butyl o-myristyl monoperoxycarbonate, decamethylene bis(oo-t-butyl monoperoxycarbonate);
(f) diacyl peroxide, e.g., 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2-methylbenzoyl peroxide, benzoyl peroxide, 2,~!-dichlorobenzoyl peroxide;
(g) ether peroxides, e.g., 2-tert.-butylperoxy-2 -hexoxy-propane, 2,5-bis-[2-butyloxypropyl-(2)-peroxy]-2,5 -dimethylhexane;
(h) ketone peroxide-per-esters, e.g., bis-[2-(2-ethylhexanoylperoxy)-butyl-(2)]-peroxide, bis-(2-lauroylperoxy)-butyl-(2)-pero~ide, bis-(2-benzoyl-peroxy)-butyl-(2)-peroxide;
(i) tert.-alkylperoxyketone peroxides, e.g., 3,5-di-tert.-butylperoxy-3,5-dimethyl-1,2-dioxacyclopentane.
Examples of suitable organic azides include the following:
(a) di- or polysulfonyl azides, e.g., decane-1,10-bis-(sulfonazide), octadecane-1,9-18-tris-(sulfonazide), tris-(p- or m-azidosulfonylphenyl)-iso-cyanurate, benzene-l,3-disulfonazide;
(b) di- or polyazidoformates, e.g., tetramethylene-bis-(azidoformate), bis(~-azidoformylo~Yyethyl) -terephthalate;
(c) aryl bis-(azides), e.g., 2,6-bis-(4-azidobenzene)-cyclohe.~anone.

Suitable foaming agents inclu10 azodicarbonamide, azobisisobutyronitrile, azobisisobutyri ~, ~J'~,;~ ~C?/e~,'c7gJ~
, acid diethyl ester, 4,4'-azo-bis-(4-~ e~ acid), diazoaminobenzene, p,p'-hydro~Yybis-(bensenes'ulfonyl) -hydrazide, benzenedisulfonyl hydrazide, diphenylsulfone-3, ~,or~o 3'-disulfohydrazide, N,N-~nitro~a-pentamethylenetetramine, p,p'-azo-bis-(benzenesulfonyl semicarbonamide), 5-morpholyl-(4)-1,2,3,4-thiatriazole, trihydrazinotriazine, NaHCO3 ~ carbonic acid.
In accordance with this inventiorl crosslinking can also be carried out in the presence of fillers (e.g., carbon black, calcium carbonate, talcum, calcium silicate, aluminum silicate (kaolin) or silicic acid (SiO2)), glass fibers, pigments, ant.io~Yidants or other additives, such as e.Ytenders, plasticizers, flame retardants, antistatic agents, and .
lubricants.

~ ertain polymers, such as high density polyethylene, ifthey contain double (or trip:l.e) bonds in their molecules, may assert the function of both a polymer and a crosslinking intensifier.
.5 The energy supply necessary for crosslinking can be accomplished (a) by direct contact of the polymer to be crosslinked with a preheated material (e.g., steel, molten metal, molten salt, water, air, nitrogen), (b) by electromagnetic radiation (e.g., IR, UHF (= microwave), Y-ray, gamma rays), or (c~ by corpuscular radiation (e.g., alpha or beta rays (= electron beams)). It should be noted that certain types of energy radiation, e.g., gamma or beta rays, also bring about crosslinking in the absence of crosslinking àgents; however, the presence of free radical forming agents and crosslinking intensifiers improve the degree of crosslinking.
The invention will be further illustrated by means of the following e.Yamples.

Examples ~. Crosslinking The polymer to be crosslinked is homogeneously mixed (e.g., in a E3anbury mi.Yer or on a mill) or in the form of a powcler with the crosslinking agent(s), if desired with acldition of a solvent (acetone, clichloromethane), which is evaporated beEore the crosslinking process. Then the miYture - ~o -is heated ~o crosslink the polymer and left at the crosslinking temperature for a certain time.
B. Determination of the Degree of Crosslinking by Ext:rac~ion The crosslinked polymer, cut into strips after cooling is packed into an accurately weighed fine wire mesh, and after repeated weighing of the wire mesh and polymer, e~tracted for 1 hour with boiling xylene (80 ml xylene for 1 g crosslinked polymer) in a 100 ml Erlenmeyer flask under reflux. Then the wire mesh and the contents are washed with hot xylene, dried completely at 150 to 160~C to dry the xylene (1 hr), and the weight loss, which corresponds to the polymer portion clissolved out, determined by weighing again.
The difference from the weight of the polymer before extraction indicates the fraction of undissolved polymer, its quantity expressed as a percent of the original total polymer mixture, and the degree of crosslinking.
C. The following abbreviations are used for the initiators used in the examples.
(a) aæo esters or azo ethers LUAZ0 AP = 2,2'-azo-bis-(2-acetoxypropane)(= sym. azo ester) LUAZ0 ABA = 2,2'-azo-bis-(2-acetoxybutane)(= sym. azo ester) LUAZ0 ~MP = 2,2'-azo-bis-(2-acetoxy-4-methylpentane)(= sym.
azo ester) IUAZ0 AC = :L,l'-a20-bis-(l-acetoxy_cyclohexane)(= sym. azo ester) L.UAZO VL = ~,y'-azo-bis-(y-valero:Lactone)(= sym. azo es~er) sym. azo ether = 1,1'-azo-bis-(l~methoxy-cyclohexane) unsym. azo ester = 1-tert.-butylazo-l~aceto.~y-cyclohexane unsym. azo ether = 1-tert.-butylazo-1-metho.~y-cyclohexane (b) peroxides peroctoate = tert.-butyl peroxy-2-ethylhexanoate (per ester) perbenzoate = tert.-butyl peroxybenzoate (per es~er) LUPERO~ 231 = l,l-bis-(tert.-butyl peroxy)-3,3,5-trimethyl cyclohexane (perketal) ]0 dicup = dicumyl peroxide (dialkyl peroxide) LUPEROX 101 = 2,5-bis-(ter~.-butylperoxy)-2,5-dimethylhexane (dialkyl peroxide) LUPERO~Y 130 = 2,5-bis-(tert.-butylperoxy)-2,5-dimethylhexyne -(3) (dialkyl peroxide) D. The crosslinking intensifiers are abbreviated as follows:
TAC = triallyl cyanurate isoTAC = triallyl isocyanurate diIso AC = diallyl isocyanurate 2-butylam-DAC
2-n-butylamino-4,6-diallyloxy-s-triazine 2-octylam-DAC = 2-n-octylamino-4,6-diallyloxy-s-triazine 2 stearylam DAC = 2--stearylamino-4,6-diallyloxy-s-triazine TAPA = triallyl phosphate TATM = triallyl tr:imellitate DAP = di.allyl phthalate DADDC ~ diallyl diglycol dicarbonate DA~l = diallyl maleate . TRIDA = trimethylol.propane diallyl ~efs TRIM = trimethylolpropane trimethacrylate 5 ED~ = ethylene glycol dimethacrylate m-PBMI = m-phenylene-bis-(maleimide~
E~ample 1 High pressure, low density polyethylene powder (melt index 70 g/10 min; density 0.918~ is crosslinked for 40 min at 215C using the symmetric azo es~er LUAZ0 AP
(2,2'-azo-bis-(2-acetoxypropane~ as crosslinking agent with the aid of TAC (triallyl cyanurate~ as crosslinking intensifier under atmosphere pressure.
This e~ample illustrates the rule that the most effective activation of the azo ester is achieved by a quantity of TAC (crosslinking intensifier~ equal to approximately half or double its amount.
It is noteworthy that 0.4% azo ester alone has a cross-linking degree of 28%, but the combination of 0.4% azo ester 20 + 0 . 2% IAC gives a crosslinking degree of 74%, which is as high as in the case when 1,5% azo ester is used alone. It is even more remarkable that a combination of 0. 8% azo ester +
0.6% TAC gives a crosslinking degree of 81%~ quite as high as that which can be achieved with 4% or 5% azo ester alone (81%
25 and 82%) respectively.

All samples heated in the presence of L~!AZO AP showed a fine-pore foam structure.

_ _ . . . . _ . _ Additives Degree of Crosslinking _ _ _ _ _ _ .
a) no additives 6%
b) 0.1% L.UAZO AP 11%
0.3/0 " 25%
0 4% !~ 28%
1() 0.5/0 " 2~.%
0.6% " 33%
0 . 8% ~ 60%
1 % ~ 62%
1.5% " 71%
2 % " 76%
3 % LUAZO AP 80%
4 % " 81%
5 % " 82%
c) 0.1% TAC 10%
0.:15% " 11%
0.2% " 12%
0.3% " 14%
0 4% " 18%
0.5% ~ 20%
0. 6% " 22%
0 . 8% ~ 25%
1 % " 27%
1.5% " 29%
2 % " 36%
30d ) 0 . 2% LUAZO AP + 0.15% TAC 48%
0.2% ~ 0.2 % ll 38%
e) 0.4/~ LUAZO AP + 0. 1% TAC 61%
0 . ~% ~I + 0 . 2% ll 74%
0.~% ll ~ 0 . 3% ll 7~%
0 ll% ~ -t O . 0~% 1l 59~
f) 0.5% LUAZO AP + 0.25% TAC 64%
0.5'~0 " + 0.5% " 4~%
0.5% " + I. % " 73%
0.5/0 " + 1.5% " 58%
~0 0.5% " + 2 % " 50%

~ 3.~

0.5% ~ t 2.5~/~ " 53%
0.5/~ " ~ 3 % " 53%
0.5% " + 4 % " 63%
g) 0. 6% LUAZO AP + 0.3% Tac 74%
5 0.6% " + 0.4% " 52%
0.6% ~ + 0.6% ~ 52%
0.6% ~' + 0.8% ~' 75%
0 . 6% ~ /o ~ 7 6%
h) 0.8% LUAZO AP + 0.4% TAC 79%
100.8% " + 0.6% " 81%
0.8% " + g% " ~-%
0.8% " + 1 % " 79%
0.8% " + 1.5% " 70%
i) 1 % LUAZO AP + 0.1% TAC 64%
151 % " + 0.4% " 69%
1 % " + 1 % " 68%
1 % " + 1.5% " 4~%
1 % " + 2 % " 71%
j) 2 % LUAZO AI' ~ 0.1% TAC 81%
2 % " ~ 0.~% " 71%
2 % " + 1 % " 77%
2 % " + 1.5% " 63%
2 % " + 2 % " 70%

E~ample 2 Ethylene-propylene copolymer, saturated type (AP rubber) with a Mooney viscosity ML 1 + 4 (100C) of 45 is crosslinked for 40 min at 215C using the LUAZO AP as a crosslinking agent with the aicl of TAC as a crosslinking amplifier in the presence and absence of carbon black as a filler under atmospheric pressure. The crossllnking and determination of the degree of crosslinking were carried out as described initially. However, the crosslinking agents were incorporatecl on a hot roller.

- ~5 -This e.~ample illustrates particularly clearly the greac advantage of combined use of azo ester and crosslinking intensifier, since AP r~bber shows no crosslinking with the azo ester alone. The experi.ment also shows that the filler, carbon black, does not interfere. All of the samples e), f), g), h), i) and j) heated in the presence of LUAZ0 AP
developed a fine-pore foam.

.
Azo ester and/or carbon black Degree of 10 crosslinking intensifier Crosslinking a) no addi~ive 0.7%
b) 3 % carbon black 2.8%
c) 0.7% TAC 7 %
d) 0.7% TAC + 3% carbon black 18 %
e) 1.5% LUAZ0 AP 0.7%
f) 5 % LUAZ0 AP 1.9%
g) 1.5% LUAZ0 AP + 3% carbon black 0.9%
h) 5 % LUAZ0 AP + 3% carbon black 1.4%
i) 1. 5% LUA20 AP + 0.7% TAC 78 %

j) 1.5% LUAZ0 AP + 0.7% TAC + 3% carbon black 74 %

E~Yample 3 Ethyl.ene-vinyl acetate copolymer powder (EVA) with a vinyl acetate fraction of 33%, an ethylene fraction of 67%
and a melt inde~ of 25 g/10 min (at 190C) is crosslinked for 40 rnin at 220C usino the two symmetrical azo esters, IUAZO
.~P or LUAZ0 AP, as crosslinking agents with the addition of TAC as a crosslinking amplifier under atmospheric pressure.
To de{ermine the degree of crosslinking, 1 hour e~ctraction with an 80-fold vo1ume of boi:l.ing .~ylene was carried out twice (instead of only once).
This e~ample shows that with this polymer, which is more difficult to crosslink, the ma~imum achievable degree of crosslinking is lower than in E.Yamples 1 or 2. However, in this case as well the simultaneous use of the crosslinlcing intensifier TAC presents distinct advantages.
A11 samples heated in the presence of LUAZO AP developed a fine-pore foam.

AdditivesDegree of crosslinking .
(A) with LUAZO AMP
a) without additives6%

b) 0.1% LUAZO AMP 13%
0.2% LUAZO AMP 18%
0.5% " 19%
l % " 21%
2 % " 28%
4 % " 37%
5 % " 38%

c) 0.5% TAC 6%
l % " 7%
2 % " 8%

d) l % LUAZO -~P + 0.5~O T;~C 39%
1 % " ~ 1 % " 50%
1 % " ~ 2 % " 54%
(B) with LUAZO AP
5 a) without additives 6%
b) 0.1% LU.~ZO AP 10%
0.2% " 12%
0.5% " 19%
1 % " 21%
2 % LUAZO AP 33%
4 % " 4~1%
5 % " 49%
c) 0.5% TAC 6%
151 % " 7%
2 % " ~%
cl) 0.5% LUAZO AP ~ 0.5% TAC 54%
0.5% " ~ 1 % " 34%
e) 1 % LUAZO AP t 0.5% TAC 53%
201 % " ~ 1 % " 64%
1 % " + 2 % " 62%

. . ~
Example 4 Low density, high pressure polyethylene powder (melt index 70 g/lO min; density 0.918) is crosslinked for 40 min at 215C using three symmetrical azo esters (LUAZO AP, LUAZO
AC, LUAZO VL) or an unsymmetric azo ester with TAC as a crosslinking intensi:Eier under atinospheric pressure.
Th:is example shows that the crosslinking degrees of 0.6%
azo ester -~ 0.3% TAC (81%, 82%) fall in the same order of magnitude as the crosslinking degrees of 2 to 3% azo ester alone. Thus. combination with half its quantity o:E TAC makes :it possible to recluce the azo ester quantity to about 1/5 of its original vaLue whi.le achieving an equal degree of crosslinking.
All samples heated in the presence of the azo ester displayed a fine pore foam.

Additives Degree of Crosslinking ~ ) with LUAZO AP

a) 0.6% LUAZO AP 47%
2 /O " 77%
3 % " 84%
b) 0.3% TAC 19%
c) 0.6% LUAZO AP + 0.3% TAC 81%
(B) with LUAZO AC

a) 0. 6% LUAZO AC 14%
2 % " ~4%
3 % " 75%
b) 0.3% TAC 19%
c) 0.6% I,UAZO AC + 0.3% TAC 81%
(C) with LUAZO VL

a) 0.6% LUAZO ~iL 30%
2 % " 89%
3 % " 85%
b) 0.3% TAC ' 19%

c) 0.6% L.UAZO VL + 0.3% TAC 82%
(D) with unsy~metric azo ester a) 0.6'~/o urlsy~netrie azo ester 31%
2 % " " " 84%
3 % " " " 84%

- _3 b) 0.3J~ TAC 19%

c) 0.6% unsyn~ietri~ azo ester -t 0.3% TAC 81%

Example 5 Low density, high pressure polyethylene powder (melt inde~ 70 g~10 min; density 0.918) is crosslinked for 40 min at 205C using the symmetrical azo ester LU.~ZO ABA (2,2'-azo -bis-(2-aceto.~ybutane) in the presence of triallyl isocyanurate (IosTAC) as a crosslinking intensifier under atmospheric pressure. The sample heated in the presence of LUAZO ABA devel.oped a fine-pore foam structure.

, = . ~ . _ _ . . . _ _ _ Additives Degree of crosslinking . .. ~
a) no additives 15%
b) 0.6% LUAZO ABA 12%
c) 0.3/O IsoTAC 15%
d) 0.6% LUAZO ABA + 0.3% IsoTAC 54%

xample 6 Low density, high pressure polyethylene powder (melt inde~ 70 g/l() min; density 0.918) is crosslinked for 40 min at 215C using the symmetrical azo ester, LUAZO AP, as a crosslink:ing agent ancl TAC as crosslinking intensifier in the presence of azodicarbonami.de as a foaming agent at atmospher:ic pressure.

This e~ample shows ~hat the combination of azo compound crosslinking intensifier brings about good crosslinking even in the presence of a foaming agent; b), d) and e) were foamed.

Additives Degree of crosslinking a) no additives 12%
b) 0.6% LUAZO AP 19%
c) 0.3% TAC 23%
d) 0.6% LUAZO AP + 0.3% TAC 74%
e) 0.6% LUAZO AP ~ 0.3/O TAC + 5%
azodicarbonamide 79%

E~ample 7 Low density, high pressure polyethylene powder (melt inde~ 70 g/10 min; density 0.918) is crosslinked for 40 min at 215C using the symrnetrical azo ester LUAZO AP and LUAZO
VL with the aid of various crosslinking intensifiers at atmospheric pressure.
All samples crosslinked in the presence of LUAZO AP and LUAZO VL were fine-pore foams.

_ _ _ _ Degree of crosslinking 2~

(L) with LUAZO AP

a) no additives 9%

b) 0.5,~ I.U.~ZO AP 28%
0.6% " 33%
A) a) 0.2% 2-butylam-DAC (butylam) 16%
0 3% " 18%
0.5% " 19%
1 % " 28%
2.3% " 38%
b) 0.5% LUAZO AP -~ 0.2% butylam 38%
0.5% " ~ 0.5% " 53%
0 . 5% -r 2.3% ' 73%
c) 0.6% LUAZO AP + 0.3% butylam 78%
B) a) 0.2% 2-octylam-DAC (octylam) 18%
O 5% ~ 1 9%
l % " 27%
2.X~Io " 24%
b) 0.5% AP ~ 0.5% octylam 62%
0.5% AP ~ 2.8% " 74%
C) aj 0.3% diisoAC 20%
0.6% AP t 0.3% diisoAC 70%
D) a) 0.3% butanediol-(1,4)-divinyl ether 11%
b) 0.6% AP + 0.3% butanediol-(1,4)-divinyl ether 60%
E) a) 0.3% diallyl phthalate (DAP) 12%
b) 0.6% AP + 0.3% DAP 54%
F) a) 0.3% TAPA 14%
b) 0.6% AP + 0.3% TAPA 65%
G) a) 0.3% diallyl diglycol dicarbonate (DADDC) 25%
b) 0.6% AP -t 0.3% DADDC 55%
H) a) 0.3% cliallyl maleate 13%
b) 0.6% AP + 0.3% diallyl maleate 55%
(II) with LUAZO VL
a) no additi.ves 10%
b) 0.6% IUA~O VL (=VL) 14%
A) a) 0.3% TAC 18%
b) 0.6% VL ~ 0.3% TAC 78%
B) a) 0.3% isoTAC 15%
b) 0.6% VL + 0.3% isoTAC 82%

119:~ 9~

C) a~ 0.3% diisoAC 20%
b) 0.6% VL + 0.3% diisoAC 76%
D) a) 0.3% 2-butylam-D.~C (=bu~ylam) 18'~o b) 0.6% VL ~ 0.3~/O butylam 61%
5 E) a) 0.3% 2-oc~ylam-DAC (= octylam) 18%
b) 0.6% VL ~ 0.3/0 octylam 67%
F) a) 0.3% 2-stearylam-DAC (= stearylam) 10%
b) 0.6% VL + 0.3% stearylam 50%
G) a) 0.3% TAPA 12%
b) 0.6% VL + 0.3% TAPA 64%
H) a) 0.3% butanediol-(l,4)-divinyl ether9/O
b) 0.6% VL + 0.3% butanediol-(l,4)-divinyl ether 28%
I) a) 0.3% trimethylolpropane-diallyl ether (TRIDA) 8%
b) 0.6% VL + 0.3% TRIDA 18%
J) a) 0.3% diallyl phthalate (DAP) 12%
b) 0.6% VL + 0.3% DAP 58%
K) a) 0.3% diallyl diglycol dicarbonate (DADDC) l5%
b~ 0.6% VL + 0.3% DADDC 77%
L) a) 0.3% diallyl maleate 13%
b) 0.6% VL + 0.3% diallyl maleate80%
M) a) 0.3% ethylene glycol dimethacrylate (ED~) 7%
b) 0.6% VL + 0.3% EDMA 43%
N) a) 0.3% trimethylolpropane trimethacrylate (TRIM) 20%
b) 0,6% VL + 0.3% TRIM 54%
O) a) 0.3% m-phenylene-bis-(maleimide) (mPBMI) 71%
b) 0.6% VL, + 0.3% m-PBMI 84%

_ample 8 Hot vu1canizab1e silicone rubber (Silopren VS 60E 2302, containing methyl anci vinyl groups) is crosslinked for 40 min - :J3 -at ~20C with a n~lTIber of: dZ.O esters and azo ethers as crosslinking agents with the aid of 0.3% TAC as a crosslinking intensifier at a~mospheric pressure.
Crosslinking agents and crosslinking intensifiers were incorporated into the rubber on a hot roller at 70C. The crosslinking and determination of the degree of crosslinking were carried out as described initially (thus 1 g crosslinked rubber is e.~tracted wi~h 80 ml boiling ~ylene for 1 hr.).
The azo compoun~ containing specimens were fine-pore 10 foams.

_ _ .9dditives Degree of crosslinking . _ _ a) no additives 1%
b) 0.6% I.UAZO AP ~ 0.3% TAC 74%
c) 0.6~, LIJAZO AMP ~ 0.3% TAC 77%
d) 0.6% unsy~metric azo ester -~ 0.3% TAC 64%
e) 0.6% syn~metric azo ether + 0.3% TAC 78%
f) 0.6% unsyn~metrie azo ether + 0.3% '['AC 63%
_ _ _ _ _ _ _ __ Example 9 H:igh pressure, low density polyethylene powder (melt incle.Y 70 g/10 min; density 0.918) :is crosslinked for 40 min at various temperatures (180, 190, 200C) with the aid of ~5 two symmetrical azo esters (LUAZO AMP and LUAZO ABA) and an - 3~, -unsymmetrical azo ether as crosslinking agents and wiLh the aid of TAC as crosslinlcing int:ensifier under atmospheric pressure.
This e.~ample shows that in the case of lower temperatures as well (180, 190, 200C), a considerable increase in the degree of crosslinking in comparison to the azo cornpound alone can be achieved with half the quantity of TAC (0.3%).
A11 sa~ples crosslinked in the presence of the azo compound were fine-pore foams.
This e.Yample, Example 9, represents a supplement to E~ample 4.

Additives Degree of crosslinking at i80 190 200 without additives 5.2% 5.8% 6.5%

(A) a) 0.6% unsymmetric azo ether 11 % - -b~ 0.3% TAC 10 % - -c) 0.6% unsyl~metric~-azo ether ~ 0.3% TAC 52 %

(B) a) 0.6% L.UAZO AMP 11 % 49 /O
b) 0.3% TAC 10 % 15 %
c) 0.6% LUAZO AMP -~ 0.3% TAC 43 % 64 %

(C) a) 0.6% LUAZO ABA - - 8 %
b) 0.3"/0 I'AC - - 18 %
c) 0.6% L,UAZO ABA ~ 0.3% TAC - - 65%

_xample 10 In all of ~he preceding e.~ampl.es the crosslinking was carried out in the absence of pressure (thus at latm), and a foamed material was always obtained. In the present example, Example lO, polye~hylene is crosslinked under pressure For this purpose, low density, high pressure polyethylene powder (melt index 70 g/10 min; density 0.918), containing 0.6%
symmetrical azo ester LUAZO AP as crosslinking agent and 0.3n/0 TAC as crosslinking intensifier, incorporated homogeneously, was crosslinked in a cylinder between two movable, precisely fitted pistons under pressure for 2 hrs at 215C. The cylinders with the pistons were located between two steel plates, pressed together at the corners by four screws with nuts. The pressure was generated by tightening the nuts. The nuts were retightened several times during the crosslinking period.
In this manner a thin, white, non-foamed, but crosslinked polyethylene plate was obtained, whose crosslinking degree was 84%.
Example 11 Low density, high pressure polyethylene powder (melt index 70 g/10 min; density 0.918) was crosslinked for 40 min at 180C or 190C using combinations of two or three azo compounds with TAC as a crosslinking intensifier under atmospheri.c pressure.

The samples crossl.inked in the presence of the azo compounds were fine-pore foams.

Additives Degree of crosslinking at . ~
without additives 5.2~ 5.8%
0.3% TAC 10 ~ 15 %
a) 0.3% symmetric azo ether +)8 ~ 31 %
O.3% unsymmetric azo ether) 0.3% symmetr.ic azo ether +) O.3~ unsymmetric azo ether +) 53 ~60 0.3% TAC
b) 0.3~ LUAZO AMP + ) 7 % 44 O.3% symmetric azo ether) 0.3% LUAZO AMP +
O.3% symmetric azo ether +)45 % 60 0.3% TAC
c) 0.3% LUAZO AMP ~ ) ~ 12~ %
0.3% unsymmetric azo ether) 0.3% LUAZO AMP +
0.3% unsymmetric azo ether +) ~51 %
0.3~ TAC
d) 0.2% LUAZO AMP + 0.2% LUAZO) ABA + O.2% unsymmetric azo ) ether - 11 %
0.2% LUAZO AMP -~ ) 0.2% LUAZO ABA + ) 61 %
O.2~ unsymmetric azo ether +) 0.3~ TAC
e) 0.2% LUAZO AMP + 0.2% ) 46 %
symmetric azo ether +
0.2% unsymmetric azo ether ) O.2% LUAZO AMP +
0.2% symmetric azo ether +) 96 %
0.2% unsymmetric azo ether +) 0.3% TAC

.~

(f ) O. 2 7~ sy~nnetric azo ether ~) O.2% unsy~metric azo ether f ) - 12 %
0.2% unsymmetric azo ester 0.2% sym~etric azo ether +
, 0.2% unsymmetric azo ether +) - 62 %
0.2% unsymmetric azo ester +) 0.3% TAC
_ Example 12 Low density, high pressure polyethylene powder (0.918) with a melt index of 70 g/10 min. was crosslinked for 40 min at 185C using the symmetrical azo ether l,1'-azo-bis~
methoxy-cyclohexane) as crosslinking agent with the aid of TAC as a crosslinking intensifier at atmospheric pressure.
This e.~ample is a supplement to Example 4 and E~ample 9, in which a symmetrical azo ether was lacking.
With quantities as small as 0.6% azo ether and 0.9% TAC, the same degree of crosslinking (76%) is achieved with quantities as large as 3, 4, or 5% azo ether alone. If the amount of TAC is increased to 1.2%, the degree of crosslinking increases to 83%, which cannot even be achieved with 5% azo ether. An increase in the quantity of triallyl cyanurate in the combinations with azo ether in this example thus led to a distinct rise in the degree of crosslinking.
All samples crosslinked in the presence of the symmetrical azo ether were fine-pore foams.

.$i . . ~,, - 3~ -~9~313 Azo ether and/or eross-Degree of erosslinkina linkirlg intensifier a) wlthout adcliti~es 5%
b) 0 6% syn~netric azo ether 13%
[l,1'-azo-bis-(l-meth o.~y-cychlohe.~cane)]
1 ~/O syn~metric azo ether 31%
2 % " " " 64%
3 % " " " , 75%
~I % " " " 76%
5 % " " " 76%
c) 0.2% TAC 12%
0.3% " 15%
0.6% " 12%
0.9% " 17%
15 1.2% " 19%
d) 0.6% syl~metric azo ether + 51%
0.2% TAC
,, 0.6% sym~metric azo ether t 58%
0.3% TAC
20,, 0.6% sym~metric azo ether ~ 72%
0.6% TAC
,, 0.6% sym,metric azo ether -~ 76%
0.9% TAC
,,. ~ 0.6% sym,metric azo ether ~ 83%
l.2% TAC
. .

L~cample 13 Low density, high pressure polyethylene powder (0.918) with a melt inde.~ of 70 g/lO min. was crosslinked using LUAZO
AP as a erosslinking agent with the aid of TAC as a erosslinking intensiEier for 40 min. at 215C in the presenee of the fillers earbon blaek, ealeium earbonate or aluminum silieate, at atmospherie pressure.
While the Eillers CaCO3 and Al silicate reduee the degree of erosslinking, earbon blaelc brings about a slight inerease in the degree of erosslinlcing. All samples - 39 ~

crosslinked in the presence of t~e azo ester were fine-pore foams.

Filler, azo ester, crosslinking. Degree of crosslinking intensifier without additives &%
0.6% LUAZ0 AP (without filler) 37%
0.3% TAC (without filler) 14%
1.2% " (without filler) 26%
0.6% LUAZ0 AP + ) 70%
0.3% TAC (without filler) ) 0.6% LUAZ0 AP + ) 75%
1.2% TAC (without filler) 15 (A) with 3% carbon black a) 3% carbon black 11%
b) 3% carbon black ~ ) 55%
0.6% LUAZ0 AP
c) 3% carbon black ~ 0.3/0 TAC 19%
3% carbon black + 1.2% TAC 28%
d) 3% carbon black + ) 76%
0.6% LUAZ0 AP + 0.3% TAC ) 3% carbon black + ) 80%
0.6% LUAZ0 AP + 1.2% TAC
(B) with 3% calcium carbonate (CaC0 ) a) 3%3CaC03 8%
b) 3% CaC03 ~ 0.6% LUAZ0 AP 11%
c) 3% CaC0 + 0.3% TAC 9%
3% " 3 + 1.2% " 13%
d~ 3% C,aC0 + 0.6% LUAZ0 AP t ) . 60%
0.3% TA~ ) 3% CaC0 + 0.6% LUAZ0 AP + ) 61%
1.2% TA~ ) (C) with 3% aluminum silicate (Al-silicate) a) 3% A].-silicate 6%
b) 3% A].-silicate + 0.6% ) LUAZC) AP ) 12%
c) 3% A].-silicate ~ 0.3% TAC 8%
3% ~ + 1.2% " 10%

d) 3% Al-silicate + 0.6% ) 32%
LUAZO AP + 0.3% TAC
3% Al-silicate -t 0, 6% ) 73%
LUAZO AP + 1.2% TAC

Example 14 High density granular polyethylene (0.950 to 0.953) with a melt index of 1.7 to 2.3/lO min. was cross].inked with LUAZO
AP as a crosslinking agent and TAC as a crosslinking intensifier for 40 min. at 220C under atmospheric pressure.
Crosslinking and determination of the degree of crosslinking were performed as described initially, but the 1 hr extraction was performed wi~h an 80-fold volume of boiling xylene, twice (instead of only once).
This e~ample shows that high density polyethylene can also be crosslinked using a combination of azo compound -t crosslinking intensifier, and good degrees of crosslinking achieved. All samples were fine-pore foams.

A7.o esters and crosslinking Degree of crosslinking intensifiers 0.4% LUAZO AP -~ 0.2% TAC 54%
" + 0 4% " 66%
~ -t O . 6% " 73%
" + 0.8% " 74%
0.6% LUAZO AP -t O . 3% TAC 54%
" ~ 0.4% " 63%
" + 0.6% " 65%
" + 0.8% " 68%

.. ~

" ~ l % " 78%
~ ~ 1.2% " 79%
0.8% LUAZO AP ~ 0.2% T~C 57%
~ 0.4% ~ 58%
5~ ~ 0.6% ~ 60%
+ 0.8% ~ 7~%
+ 1 % ~ ~7%
" ~ 1.2% " 73%
~ + 1.6% ~ 78%
1% LUAZO AP ~ 0.2% TAC 54%
" ~ 0.~% " 55%
" ~ 0.5% " 62%
+ 0.6% ~ 64%
~ + 0.8% ~ 74%
~ + l % ~ 76%
" + 1.2% " 77%
+ 1.6% ~ 78%
" + 2 % " 80%

Example 15 A miYture of equal parts by weight of high pressure, low density, polyethylene powder (0.918) with a melt index of 70 g/10 min. and ethylene-vinyl-acetate copolymer powder (EVA) with a melt index of 25 g/lO min. (at 190C), containing 33%
vinyl acetate and 67% ethylene were crosslinked for 40 rnin at 220C using LUAZO AP as crosslinking agent and TAC as crosslinking intensifier under atmospheric pressure.
Crosslinking and determination of the degree oE crosslinking were carried out as described initially, but the l-hr extraction wi.th 80-Eold volume of boiling xylene was carried out twice (instead oE just once).
This exclrrlple shows that the mi.Yture of polyethylene ~
EVA can be crosslinked even better by azo ester + TAC (degree of crosslinking 70%) than polyethylene alone (degree of crosslinking 62%) . All cross].inked samples (j), k)~ 1)) were fine-pore foams.

Polymer, azo ester, cross- Degree of cross-linking intensifier linking ..... . . .. _ .. ., .. . ., . . . _ _ a) polyethylene, without additives 4%
b) EVA, without additives 4%
10 c) polyethylene + 5%
EVA, wi thout additives d) polyethylene + 0.5% LUAZO AP 2~%
e) EVA + 0.5% " 24%
f) polyethylene + 10%
EVA ~ 0.5% LUAZO AP
g) polyethylene + 1 % TAC 18%
h) EVA + 1 % " 10%
i) polyethylene + 21%
EVA + 1 % TAC
j ) polyethylene + 0 . 5% LUAZO AP + 62%

k) EVA + 0. 5% LUAZO AP + 57%
% TAC 57%
; ; 1) polyethylene + ) 70%
EVA 1 % TAC ) 70%

_ . ., ~, , . . .

Example 16 HLgh pressure, lo~ density pol~7ethylene powder (0.918) with a l-nelt index of 70 g/lO min. was crosslinked for 40 min.
at 215C using various combina~ions of azo compound(s) +
pero.~ide(s) as crosslinking agent and one or more different S crosslinking intensifiers under atmospheric pressure.
This e,Yample shows that combinations of azo compound +
crosslinking intensifier -~ peroxide also yield good degrees of crosslinking. The samples were fine-pore foams.

Azo compound, peroxide, Degree of crosslinking crosslinking intensifier _ _ _ a) 0.3% L,UAZO AP + 0.3% 90%
peroctoate + 0.3% TAC

iS b) 0.3% LUAZO AP + 0.3% 73%
perbenzoate + 0.3/~ TAC

c) 0.3% LIJAZO AP + 0.3% 80%
dicup -~ 0.3% TAC

d) 0.3% LUAZO AP -~ 0.3% 80%
LUP. 101 + 0.3% TAC

e) 0.3% LUAZO AP + 0.3% 76%
LUP. 130 + 0.3% TAC

f) 0.3% LUAZO AP + 0.3% 76%
LUP. 231 -~ 0.3% TAC

g) 0.3% LUAZO AP + 0.3% 77%
LUP. 231 + 0.3% butylam-DAC

h) 0.3% LUAZO AP + 0.3% dicup +)68%
0.15% TAC + 0.15% dlallyl maleate i) 0.3% LUAZO AP + 0.3% ) 57%
clicup + 0.15% TAC -~ ) 0.15% isoTAC

j) 0.3% LUAZ0 AP + 0.3% ) 60%
LUP. 231 ~ 0.15% TAC + 0.15%) diallyl maleate k~ 0.3% LUAZ0 AP + 0.3% ) 65%
LUP. 231 -~ 0.15% TAC
+ 0.15% isoTAC
1) 0.3% LUAZ0 AP ~ 0.3% ) 62%
LUP. 231 ~ 0.15% TAC +
O.15% D~DDC
m) 0.3% LUA70 AP + 0.15% ) 70%
peroctoate ~ 0.15% LUP.
130 + 0.3% TAC
n) 0.3% LUA7.0 AP + 0.15% ) 76%
LUP. 130 + 0.15% LUP.
231 + 0.3% TAC
o) 0.15% LUAZ0 AP + 0.15% ) 60%
LUAZ0 VL ~ 0.3% LUP. 231 ~ 0.3% TAC
p) 0.15% LUAZ0 AP ~ 0.15% asym.) 79%
20azo ester -~ 0.15% peroctoate) 0.15 LUP. 130 ~ 0.3% TAC

Example l?
Low density, high pressure polyethylene powder (0.918) with a melt inde~ of 70 g/10 min. was crosslinked for 40 min.
at 220C using 0.6% of the azo ester LUAZ0 AP as crosslinking agent and 0.3% high molecular weight 1,2-polybutadiene oil (Lithene AH) as crosslinking intensifier under atmospheric pressure. The samples crosslinked in the presence of LUAZ0 AP were fine-pore foams.

1- !

Azo ester and/or cross-Degree of crosslinking linking intens:ifier-. . ~
a) without additives 12%
b) 0.6% LUA~O ~P 30%
c) 0.3% 1,2-polybutadiene oil 9%
d) 0.6% LUAZO AP t 0.3% )56%
1,2-polybutadiene oil .

Example 18 A PVC paste, prepared from 70% paste PVC with a K value of 70 by tr:iturating with 30% dioctyl phthalate, was crosslinked with different azo compounds and TAC for 40 min.
at 180C and 190C under atmospheric pressure.
a) Crosslink1ng: The PVC paste to be crosslinked was homogeneously mi.Yed with the crosslinking agent.
Crosslinking was performed as initially described.
b) Determination of the degree of crosslinkin~
e~traction: The PVC, cut into strips after cooling, was packed into an accurately weighed wire mesh basket, and after repeated weighing oE the wire mesh and PVC, ex-tracted for 1 hr with boiling tetrahydrofuran (85 ml tetrahydrofuran per l g PVC) in a :lO0 ml Erlenmeyer flask under reflux. Then the wire mesh containing the une~tracted crosslinked PVC fraction 2S was rewashed w:ith hot tetrahydrofuran, dried briefly at room temperature, then dried for l hr at 140C in a drying oven.

- ~16 -Then t:he weight loss corresponding to the dissolved out polymer fraction ~as determined by weighing repeatedly. The difference from the weight of the polymer before e~traction gives the undissolved polymer fraction, whose quantity, e~pressed as a percentage of the original tocal polymer amount, i.ndicates the degree of crosslinking.
The crosslinking degrees in e.Ycess of 100% can be e.Yplained by the partial incorporation of dioctyl phthalate into the polymer during the crosslinking reaction. The 0 samples were fine-pore foams.
c) Crosslinki~ results:

Crosslinking agent and Degree of crosslinking crosslinking intensifier based on PVC + DOP PVC +
+ initiator initiator (A) non-s~abilized PVC at 180C
a) 0.1% LUAZO AMP + 75% 107%
0.05% TAC
0.1% LUAZO AMP + 70% 100%
O .1 % TAC
0.1% LUAZO AMP + 57% 81%
0.2% TAC
b) 0.2% t,UAZO AMP + 71% 101%
0.05/O TAC
0.2% LUAZO AMP ~ 76% 107%
0.1~, TAC
0.2% LUAZO AMP + 72% 102%
3() 0.2% TAC
'~ (B) stabilized PVC at 190C
stabilizer:

0.17% Ba/Cd stearate 0.3 /O epozidized soy bean oil (Edenor 81) 0.3% triphenyl phosphite based on 70% PVC powder +
30/O dioctyl phthalate a) 0.2% LUAZO AP + 0.1% TAC 81% 115%
b) 0.5% LUAZO AP + 0.1% TAC 71% 101%

EYample 19 High pressure, low density polyethylene powder (melt inde~Y 70 g/lO min; density 0.918) is crosslinked for 40 min.
at 215C using crosslinking agent combinations, all of which contain stearylazidoformate in addition to an azo ester and/or pero~ide, with the simultaneous presence of TAC or TAC
+ butylam-DAC as crosslinking intensifiers under atmospheric pressure.
This e.Yample shows that in the presence of stearylazidoformate crosslinking degrees are achieved whi.ch are just as good as those achieved in its absence. It likewise shows that stearylazidoformate does not interfere in any combination.
The LUAZO VL containing samples were fine-pore foams.

Additives Degree of crosslinking a) 0.3% LUAZO VL + 0.3% TAC 58%
b) 0.6% LUAZO VL + 0.3% TAC 78%

c) 0.3% L~JAZO VL + 0.3/O stearyl- 76%
azidoformate -~ 0.3% TAC

d) 0.3~/(. LUAZO VL -~ 0.3% stearyl- 78%
azidoformate + 0.15% TAC +
0.15% butylam-DAC

e) 0.2% LUAZO VL -~ 0.2% LUP. 231 + 73%
0.2% stearyla~idoEormate -~
0.8% TAC

10 E.~ample 20 Five different types oE synthetic rubber are crosslinked for 40 min at 220C using four symmetrical azo esters, one symmetrical. azo ether, an unsymmetrical azo ester and an unsymmetrical azo ether as crosslinking agents with the aid lS of TAC as a crosslinking intensifier under atmospheric pressure. Crosslinking agents and crosslinking intensifiers were incorporated into the rubber on a hot roller at 70C.
The crosslinking and determination of the degree of crosslinking were carried out as described initially (i.e., 1 g crosslinked rubber is eYtracted with 80 ml boiling .~ylene for l hr).
In all cases azo compound + TAC bring about good crosslinking, wherein the degrees of crosslinking are considerably above the blank value (rubber heated with additive). The AP rubber Buna AP 201 cannot be crosslinked by azo compounds alone; only the combination with a cross-linking intensifier makes crosslinking possible. The a70 compound containing samples were fine-pore foams.

E ample 21 Low density, high pressu:re polyethylene powder (melt index 70 g/10 min; density 0.918) is crosslinked with 0.6%
L.UAZO AP as crosslinking agent with the aid of 0.3% TAC as crosslinking amplifier in cornparison to 0.6% LUAZO AP under atmospheric pressure (A) for 40 min at various temperatures and (B) at 215C for various lengths oE time.
Part (A) of this example serves for determining the take off temperature. It shows that the combination of 0.6% LUAZ0 AP + 0.3% TAC takes off at 20C lower (at 200C) than 0.6%
LUAZO AP alorle (at 220C). It also shows that the maximum crosslinking degree of the combination is higher than that of LUAZO AP alone.
Part (B) of this example serves for determining the minimum crosslinking time. It shows that the combination of 0.6% LUAZO AP + 0.3% TAC requires an approximately 5 minutes shorter min:imum crosslinking time (ca. 20 min) than LUAZO AP
alone (ca. 25 min). It also shows that the maximum crosslinking degree of the combination is higher than that of LUAZO AP alone.
The samples crosslinked with LUAZO AP or with the comb:ination LUAZO AP t TAC were fine-pore foams.

~3~

~ I C~ ,~
3 ~ ! ~~
(_` .-- Cl`C`1 3' 1 1 1 1 Lr) ;I~ ;.Q ~
CC '~`~0~ L'~ )--'~:a ~ x ~ ^;) 1~! j j a) cl I ~ X
~ I ~ ~;
3 ~
. ^ L~
~ ~ :`1 1 1~ C i ~ o~ ~ ~ O--¦ ~1 ~ ^ 1 ~1 ~ L'`1 a~ 00 ~ ~
~ ~ ¢ I `~D X Ci~ X ~ I X I I ~1 ~
a~ I ).- ~, ~J I
L_~ ! s:~ c 1 I c c ~c ~ I o o I C ~ ~ ~
Y ~ o o ~ ~ ,~ o~ o~ o~ o~ C C
~1 ~ L X 1~ ~ ~ ~
¢ ~ ~ c ~n ~o 5 ;J a D
L_~ ~ ~ r ,~
O ~ v ~
~ ~ I I S~ aJ
o o o a) a~ 1 L~ ~ ~ I C
OC ~ o`~ ~ o~
~J ~ r~ J ~ ~1 al~ ¢ ~ X

O O O ~ C:
~J
¢ C~
¢ ¢ ¢ O E-~ I I I
E~ a) o o , t~
o ~ ~~ ~ o~! aJ O L'~ a~ ) C
. c~ Yl N N ~ r~
l O ~ O ~ t~ O
~ ~ u~ O O O N .5~
~ ~\ + ac~ c.) c) t_) + ~ ~J v ~ O
J ~ + + + ~1 ¢ ''I ¢ a) o a.J u~ Q, .,~ ~,, ' t,~ ). ~ Ll E
JJ JJ ~
G ~ ~ C ¢ ~ ¢ ~ ~ ~ ~J ~ ¢ ~I
ta v ~ ~ O
) ~ O O O O ~ ' Ei ' O L~
l ~ ~ ~ ¢ ~ O ~ O
¢ ¢ ¢ ¢~ E~ ¢ o ~ u~
~ ~ ~ + ~ ~ ~ ~ ~ ~ V~
o ~a 3 ~ 1 ,~
C~ . O ~ ) 1 L 1~
C ~J r 0~ 0~ 0~ 0~ 0~ 0~ o 0~ ~0~ ¢ ¢ ¢
O J~ D O ~9 J ~ C
~J ~ '~ u 3 o 1~ o o o ~ + o a~ o ~ ~ ~ c ~ c c ~r~ ::~ 3 3 N ,~ ~ ,~ ~
c~ :~5 ~ I _~ J L'`) ? ! ~

Crosslinking degrees achieved with 0.6% LUAZO ~L~p 0 3% TAC 0.6% LUAZO AP) -~0.3% TAC

S ~
(A) crosslinking temperatures:
140C 0 % 0 % 0 %
150C 0 % 0 % 0 %
160C 0 % 0 % 0 %
170C 0 % o % o %
180C 6.9% 6.4% 7.1%
190C 5.9% 6.6% 6.9%
200C 5.6% 7.~% 35 %
210C 8.7% 12 % 71 %
220C 32 % 16 % 80 %
230C 56 % 21 % 77 %
240C 63 % 23 % 73 %
(B) crosslinking times:
5 minutes 3.6% 3.2% 4.3%
" 4.1% 3.9% 4.9%
" 4.0% ~.3% 5. 1%
" 6.1% 7.1% 45 %
" 41 % 9.6% 68 %
" 35 % 12 % 73 %
" 40 % 9.5% 68 %
" 58 % 8.1% 66 %
" 39 % 11 % 68 %
" 32 % 11 % 67 %
" 30 % 16 % 83 %
" 30 % 17 % 67 %

, _ _ Example 22 Granular hlgh density polyethylene (0.950-0.953) with a melt inde~ of 1.7 to 2.3/10 rnin. is crosslinked with LUAZO
AMP or the unsyrnmetric azo ether 1-tert.-butylazo-1-metho~y -cyclohe.~ane as crosslinking agent with the aid of TAC as ~ ~ 9 ~

crosslinking intensifier in the Monsanto rheometer at 195C
until the maYimum degree of crosslinking has been achieved (ca. 2 hr). The measured values will be e~plained in the following table:
T5 = scorched time = vulcanization starting time ~
time in min to reach 5% of the ma~imal crosslin~ing.
T90 = time in min required to reach 90% of the ma~imal crosslinking.
TM50 = torsional force applied at the ma.~imal crosslinking to the oscillating disc of the Monsanto rheometer at a sensitivity setting of 50. The magnitude of the TM50 va]ue makes a statement regarding the crosslinking degree of polyethylene; the TM50 values are relative quantities.

Since the inherent viscosity of the polyethylene mi~ture heated to 195C has a TM50 vaLue of 14, such a value of 14 corresponds to a non-crosslinked polyethylene.
This e~ample shows that the viscosity (as an indirect measure of the degree of crosslinki.ng) in the presence of TAC
is higher, and in addition, bubble-free crosslinked products are obtained.

Azo compound, cross- T5 T90 TM50 Appearance 10 linking intensifier min. min. of the crosslinked polyethylene ~) non-crosslinked poly- - - 14 ethylene at the be-ginning of cross-linking b) O. 6% LUAZO AMP 3.5 54 52 foamed . c) 0.6% unsy~metric azo 2.5 43 65 foamed ether d) 0.6% LUAZO .~lP + o.6% 3. 8 62.5 59 bubble-free TAC

e) O .6% unsy~metrie azo 2.5 40.5 67 bubble-free ether + O. 6% TAC

25 _ _ _ Example 23 -Polypropylene powder (melt index 0. 6g/10 min at 230C
and 2.16 kp load) is crossl.inked for 40 min using (A) various amounts of LUAZO AMP with cooperation of 5%
triallyltrimellitate (TATM) as crosslinking intensifier at 200C~ ancl (B) using 5% TATM + 1% LUAZO AMP at different ) - ) ternperatures (175 to 205~C) under nitrogen. The determina-tion of the degree of crosslinking is carried out as described initially, i.e., by e~traction for l hr with an 80-fold volume of boiling .Yylene under reflu.~.
S E.~perimental series (A) shows that crosslinking takes place only upon adding quantities of between 0.4% and about 2.5% LUAZO .-~`IP~ and e~perimental series (B) shows that crosslinking no longer occurs above 200C.

.
Azo ester~ crosslinking inten- Degree of crosslinking sifier (A) at 200C with varlous amounts of LUAZO AMP:
a) witho~lt additives 0.1%
b) 0.09% LUAZO AMP 0.1%
0.11% " %
0,5 % " 0.0%
% " 0.0%
2 % " 0.0%
3 % " 0.0%
4 % " 0.0%
5 % " 0.0%
c) 5 % TATM + 0.09% 0.3%
LUAZO AMP
d) 5 % TATM + 0.11% 1 %
LUAZO AMP (equivalent to 0.05% LUP. 101) e) 5 % TATM + 0.2% 8 %
LUAZO ~IP
f) 5 % TATM + 0.3% 14 %
LUAZ() AMP
g) S % TATM ~ 0.4% 60 %
LUAZ() AMP
h) 5 % TATM ~ 0.5% 67 %
LUAZ() AMP
i) S ,' TAI'M -t 0 75% 66 %

- 5~ -~ 8 LUAZO AMP
j) 5 % TATM + l % 67 %
LUAZO ~P
k) 5 % TATM + 2 % 48 %
LUAZO .~IP
l) 5 % TATM ~ 3 /O 24%
LUAZO ~P
m) 5 % TAT~ 4 % 5 %
LUAZO A~P
n) 5 % TATM ~ S % 0.2%
LUAZO AMP
(B) at different temperatures (175 to 205C) with 1%
LUAZO ~IP
a) 5 /O TATM ~ 1 % 78 %
LUAZO AMP (at 175C) b) 5 % TATM ~ 1 % 78 %
LUAZO AMP (at 180C) c) 5 % TATM ~ I % 75 %
LUAZO AMP (at 185C) d) 5 % TATM + l % 74 %
LUAZO .~MP (at 190C) e) 5 % TATM + 1 % 67 %
L~AZO AMP (at 200C) f) 5 % TATM + 1 % 3 %
LUAZO AMP (at 205C) ~ ... __ E ample 24 Polypropylene powder (melt index 0.6 g/10 min. at 230C
and 2.16 kp load) is crosslinked using 1% LUAZO AMP with the aid of 5% of different crosslinking intensifiers for 40 min at 180C under nitrogen in the absence and presence of 0.1%
of the antioYidant, 0,0'-di-tert.-butyl-p-cresol (TBK). The determination of the degree of crosslinking is carried out as described in.itial:Iy, i.e., by extraction for 1 hr with an 80 old volume of boi:Ling xylene uncler reflux.
This exaIllple shows that in addition to triallyltrinlellitate, other (but not all) crosslinking - ;5 -intensifiers are suitable for the crosslinking of polypropyl.ene, both in the absence and in the presence of an antioxidant.

_ Azo ester, crosslinking inten~ Degree of crosslinking sifier (A) with l~/o LU~ZO .~P ~ 5/O of different crosslinking inten-sifiers:

a) 5/O TATM 78%
b) 5% TAC 71%
c) 5% TAPA 72%
d) 5% diallyl glutarate 0%
e) 5% diisoAC 49%
f) 5% DAP
g) 5% TRIM 65%
h) 5% EDMA 63%
i) 5% m-PBMI 67%

0 (B) with 1% LUAZO AMP + 5% of different crosslinking inten-sifiers + 0.1% TBK anti-oxidan~ (Ant.):
a) 5% TATM + Ant. 18%
b) 5% TAC + Ant. 79%
c) 5% TAPA + Ant. 70%
d) 5% TRLM + Ant. 75%
e) 5% EDMA + Ant. 76%
f) 5% m-PBMI + Ant. 62%

xample 25 In this example, the symmetrical azo ester LUA~O AMP is used in very small amounts as free radical forming agent.

~ 3 ~ ~

High pressure, low intensity polyethylene powder (melt inde~ 70 g/10 min; density 0.918) is crosslinked for 40 min.
at 200C using a combination of very small amounts of the sy~netrical azo ester LUAZO ~IP as a free radical forming agent and TAC as crosslinking intensifier, at atmospheric pressure.
This e.Yample shows that in the presence of a crosslinkoing intensifier even very small amounts of azo compound bring about good degrees of crosslinking. It is remarkable that better crosslinking takes place (77% compared to 81%) in the presence of smaller amount of TAC (0.5/~) than in the presence of larger amounts (1% or 2%) TAC.
The crosslinked product was not foamed.

Additives Degree of crosslinking a) without additives 6.5%
b) 0.01 % LUAZO AMP 6.0%
0.02 /O " 6.3%
0.03 % " 7.1%
~ % " 8.0%
0.043% " 8.5%
0.05 % " g.9%
0.1 % " 48 %
0.2 % " 61 %
0.5 % " 67 %
1 % " 75 %
2 % " 77 %
c ) O . 1 % 'rAC 10 %
0 5 ~)/o " 22 %
1 % " 25 %
2 % " 43 %
cl) 0.1 % TAC + 0.05 LUAZO AMP 41 %
e) 0.5 % " ~ 0.043% " " 77 %

0.5 % " + 0.05% " " 81 %
E) 1 % ~ t 0.02% " " 46 %
1 % " + 0.043% " " 70 %
1 % " -~ 0.05% " " 73 %
5g) 2 % " + 0.05% " " 74 %
.. . .. . . _ _ Example 26 In this example an unsymmetric azo ester and an unsymmetric azo ether are used in very small amounts as free radical forming agents.
Low density, high pressure polyethylene powder (melt index 70 g/10 min; density 0.918) is crosslinked for 40 min.
at 220C using a combination of TAC as crosslinking intensifier and very small amounts of the unsyrnmetric azo ester 1-tert.-butyazo-1-acetoxy-cyclohexane or the unsymmetric azo ether l-tert.-butylazo-l-methoxy-cyclohexane under atmospheric pressure.
This e.~ample shows that the crosslinking intensifier TAC
is activated just as well by small amount of unsymmetric azo compounds as by the symmetrical azo ester LUAZO AMP of the preceding example, Example 25.
This crosslinked product was not foamed.

Additives Degree of cross linking __. _ _ _ _ a) without additives 10%
t~) 0.5% TAC 26%
1 /O " 36%
.30 (A) with unsyl~netrlc azo ester:

- sx -a) 0.05% unsymmetric azo ester 11%
0. 1% ~ 10%
0.2% " 13%
0 5% " 10%
1 % ~ 63%
2 % ~' 71%
3 % ~ 83%
b) 0 5% T.~C ~ 0.05% unsy~metric- azo ester 31%
. , c) 1 ~/O TAC + 0. 05% unsy~metric azo ester 51%
1 % " ~ 0.1 % " 78%
1 % " ~ 0.2 % " 77%
;,j~ (B) with unsymmetric azo ether:
, a) 9 05/O unsymmetric azo ether l7%
150.2 % t~ 39%
0.5 % " 79%
% ~I 78%
2 % " 71%
3 % I~ 70%
,,2~0 b) 0. 5% TAC ~ 0.05% unsy~metric azo ether 80%
~, c) 1 % TAC + 0.05% unsym~netrie azo ether 73%
1 % " + 0.1 % " 74%
1 % " + 0.2 % " 70%

Example 27 In this e.Yample a symmetric azo ether and four symmetric azo esters are used in very small amounts as free radical forming agents at different temperatures.
Low density, high pressure polyethylene powder (melt indeY 70 g/10 min; density 0.918) is crosslinked for 40 min.
at 190C, 200C, 210C, or 220C using combinations of TAC as crosslinking intensifier and very small amounts of the symmetrical a.zo compounds mentioned in the following (azo ethers ancl azo esters) at atmospheric pressure.

This e.Yample shows that syI~netrical azo ethers and azo esters when used in ~ery small amounts are also capable of activating crosslinking intensifiers and supplying very good degrees of crosslinking which reach or exceed those of 2% to 5% of the azo compounds alone.
The crosslinked product was not foamed.

Additives Degree of crosslink-ing (a~-~t 190C [with l 1'-azo-bis-(l-metho~y -cyclohexane)~:
a) without additives 6%

b) 0.5% IAC 11%
1 % ' 18%
c) 0.05% symmetric azo ether 9%
d) 1 % TAC + O.05% symmetric azo ether 76%

(B) at 190C [with 2J2 -azo-bis-(2-acetoxy -4-methyl-pentane)~:
a) without additives 6%

b) 0.5% TAC 11%
1 % 18%
c) 0.05% LUAZO AMP (symmetric azo ester) 7%

d) 0.5% TAC + 0.05/O LUAZO AMP 48%
l % ~ 0.05% 58%

(C) at 200C [with 2 2'-azo-bis-(2-acetoxy-4 -methyl-pentane)l:

a) without additives 6.5%
b) 0.. 5% TAC 22%

11~1988 c) 0.05/O LIJAZO .~IP 8%
0 1 % " 648oo/o G.5 /O " 67%
2 % " 77%
d) 0.5/O TAC + O.05% LUAZ() AMP 81%
(D) at 210C [with 2,2'-azo-bis-(2-acetoxy -propane)]:
a) without additives 9%
b) 0.5/0 TAC 28%
1 % " 35%
c) 0 05% LUAZO AP (symmetric azo ester)8%
0.2 % " 9%
1 1%
1 % " 16%
2 % " 70/O
d) 1 % TAC + 0.05% L.UAZO AP 48%
1 % " ~ 0.1 % " 7~%
(E) at 210C ~with 2,2'-azo-bis-(2~acetoxy -butane)]:
a) without additives 9%
b) 0.5% TAC 28%
1 % " 35%
c) O.05% LUAZO ABA lsymmetric azo ester) 8%
0 . 1 % ", 9/
0.2 % 9 D/
0.5 % " 9%
1 % " 59%
2 % " , 72%
d) 0.5% TAC ~ 0.05% LUAZO ABA 42%
% " -t O, 05% ~ 71%
(F) at 220C [with 1,1'-azo-bis-(1-acetoxy 3~ -cyclohexane)]:
a) without additives 10%

~ 9~

b) 0~5% TAC 26%
1 % " 36/~
c) 0.05% LUAZO AC (symmetric azo ester) 10%
0.1 % " 11%
50.2 % " 10%
0 5% " 11%
1 % " 11%
3 % " 66%
5 % " 72%
10d) 1 % TAC -~ 0.05% LUAZO AC 45%
1 % " ~ 0.1% " 67%

_ _ . . _ .
Example 2_ Low density, high pressure polyethylene powder (melt index 70 g/10 min; density 0.918) is crosslinked for 40 min.
at 215C with LUAZ0 AP and LUAZO VL as crosslinking agents with the aid of TAC as crosslinking intensifier in the presence of the antioxidants TBK antioxidant (0,0-di-tert.
-butyl-p-cresol) and PADAT antioxidant (2-(p-phenylamino -anilino)-4,6-diallyloxy-s-triazine) at atmospheric pressure.
This e.~ample shows that good degrees of crosslinking are also achieved in the presence of antioxidants in the crosslinking of polyethylene.
All samples crosslinked in the presence of azo esters were fine-pore foams.

w . ~
Addltives Degree of crosslinking a) 0.3/~ TAC 16%
b) 0. 6% LUAZO ~P 33%
c ) O . 6% LUAZO AP + 0.3% TAC 73%
d) 0.6% LUAZO ~P ~ 0.3% TAC ~ 0.1% TBK-Ant. 51%

e) 0. 6% LUAZO AP + 0.3% TAC + 0.1%
PADAT-Ant. 80%

f) 0.6% LUAZO ~P + 0.3% TAC + 0.3%
P~D~T-Ant. 6 6%
g) O . 6% LUAZO VL 30%
h) 0. 6% LUAZO ~L + 0.3% T.~C 77%
i) 0.6% LUAZO VL + 0.3/O l'AC ~ 0.1% TBK-Ant. 56%

j) 0.6% LUAZO VL -~ 0.3% TAC -~ 0.1%
PADAT-Ant. 75%

k) 0.6% LUAZO VL + 0.3% TAC + 0.3/0 PADAT-Ant. 74%

Examples 29-38 General Experimental Procedures The crosslinkable compositions used in Examples 29-38 0 were all prepared by the following procedure:
100 parts by weight of resin were fluxed in a C.W.
Brabender Plasti-corder mixer with a Roller-S type mixing head. Unless otherwise specified, a blade speed of 50 rpm and a mixing head temperature of 140C were used. The desired azo :initiator and co-agent were then added to the flu.Yecl res:in. The cornposition was then allowed to rnix for three (3) minutes. The sarnple was then removed from the mixing heacl and quickly pressed into plaques, utilizing a - 6:~ -room temperature Carver Laboratory Press (Model C), and then the plaques were allowed to cool ~o room temperature.
Crosslinking determinations on the plaques were carried out using the Monsanto Oscillating Disk Rheometer and swell ratio measurements.
The Monsanto Rheometer test procedure consists of a wncured sample enclosed under positive pressure in a heated die cavity containing a biconical disk. The disk is oscillated (100 cycles/min) through an arc of 3. The force or torque required to oscillate the disk is recorded as a function of time. This shear modulus is proportional to the e.~tent of cross1ink:ing ancl is a representation of the cure reaction. The shear modulus increases as percent crosslinking increases. The test variables recorded from the rheometer curve were as follows:
MH - Maximum torque (in-lbs), a measure of crosslinking attained.
ML - Minimum torque (in-lbs), a measure of viscosity of the compound and an indicator of scorch. Increased ML values are indicative of scorch.
MH-ML - Difference between maxiumum and minimum torque values. Th:is value is useful in determining extent of crossl:inlcing.
TC90 - ('ure time (minutes), time to reach 90% of maximum torque as clel-ined by (M~l-MI) 0.9 ~ ML.

- 6~J -TS2 - Scorch time (minutes), time required for torque ~o increase two inch-pounds above ~IL.
The cure temperature Eor examples 29-38 was 196C
Swell ratio measurements were obtained by immersing a 0.5 gram sample of the rheometer cured composition in closed 6 oz jars contai.ning xylene for 24 hrs in a circulating air oven at 110C. Afterwhich the gel was removed and weighed using a pre-tared closed weighing boLtle so the ~ylene present in the gel would not evaporate. The gel is then dried for 24 hrs at 110C and then weighed. The following calculation is used to determine the swell ratio.
r( Weight of gel ) ~1l ~ K
Swell Ratio = 1 -~L Weight of dried poiymer ~ -K - ratio of density of polymer to solvent at immersion temperature.
For High Density Polyethylene K = 1.17 For Ethylene-Propylene Diene (EPDM) rubbers K = 0.99.
Examples 29-32 High Density Polyethylene (HDPE) resin (density 0.962) (Union Carbide DMDJ7008) with a melt flow index of 8.0 was utilized in the following examples listed in Table l. The preparation and crosslinking determination test followed are the same as in the general experimental procedures.

Examples 29 10 31* _ 3~*
_mpositions (parts by weight) IIDPE 100 100 lO0 100 2-t~Butylazo-2 -me thoxy-4 -methylpentane 2.0 2.0-2,2' .~zobis(2-acetoxypropane) - 2.3 2.3 Triallyl Cyanurate - 2.0 2.0 MH-ML (in-lbs) 10 37 0 33 Tc9~ (mins) 13.0 6.0 - 39.0 TS2 (mins) 3.61.6 - 6 0 lO Swell Ratio - 9.9 - 8.6 *Examples 31 and 32 rheometer cured at 204C

Examples 29 and 31 show that 2-t-Butylazo-2-methoxy-4 -methylpentane and 2,2'-azobis (92 acetoxypropane) yield inefficient cures in this particular HDPE resin.
Incorporation of a co-agent, i.e., triallyl cyanurate, yield significant improvements, over the non co-agent cure systems as indicated by examples 30 and 32.
High Density Polyethylene (HDPE) resin (density 0.960) (Phillips Petroleum Company) with a melt flow index of 30.0 was utilized in the following examples listed in Table 2.
The preparation and crosslinking determination tests followed are the same as in the General Experimental Procedures.

- b~) -TA~3LE 2 Examples 33 3~ 35'i 36*

Compositions (parts by weight) HDPE 100 lO0 lO0 100 2-t-Butylazo-2-metho~y-4 5 -methylpentane 2.0 2.0 - -2.2'~Azobis(2-acetoYypropane) - - 2.3 2.3 Triallyl Cyanurate - 2.0 - 2.0 MH ML (in-lbs) 46 78 40 69 Tc90 (mins) 11.0 7.5 53.0 33.0 TS2 (mins) 2.3 1.8 6.0 6.0 Swell Ratio 23.0 5.9 25.0 6.2 *Examples 35 and 36 rheometer cured at 204C

The incorporation of a co-agent, e.g., triallyl cyanurate, signif:icantly improves the crosslink density as indicated by the higher MH-ML values and lower swell ratio's for examples 34 and 36 as compared to examples 33 and 35.
Ethylene-Propylene-Diene (EPDM) rubber (specific gravity 0.86) with a Mooney Viscosity (ML-8, 100C) of 30 and a 5-ethylidene-2-norbornene content of 4-5% was ~Itilized in the following examples listed in Table 3. The mixing temperature and the blade speed were room temperature and 30 rpm, respectively and the swelling and drying temperatures were 25C and 60C, respectively, otherwi.se the same procedure as described in the General Experimental Procedure was followed.
~5 _ __ __. __ Exarnples Compos:itions (parts by we:ight?

5 2-t-Butylazo-2-methoxy-4-methyl -pentane 2.0 2.0 Triallyl Cyanwrate - 2.0 MH~ML (in lbs) 39 72 TC90 (mins) 17.0 11.0 10 TS2 (mins) 2.0 l.8 Swell Ratio 9.0 4.7 Incorporation of a co-agent, i.e., triallyl cyanurate, signlficantly increased the corque values and lowered the swell ratio, indicating a high crosslink density for example 5 38 as compared to exarnple 37.
o~
A resin blend of polyvinyl ~ ~ and chlorinated polyethylene (Blane No. 79 105E, Blane Division of Reichhold Chemicals Inc.) was utilized in the following example listed in Table 4. The miYing temperature was 160C, otherwise the same procedure as described in. the General Experimental Procedure was followed.
Table ~

Ex amp l e Composition (parts by weight) Blane No. 79-105E 100 2-t-Butylazo-2-1llethoxy-4-rnethylpentane 0.5 Triallyl Cyanllrate 3.5 - 6(S -M}I-ML (in lbs) 36 Tc90 (mins) 32.0 TS2 (mins) 1.8 Blends of Polypropylene (Density of 0.903), melt flow inde.~ oE 4.0) and ethylene-propylene diene (EPDM) rubber ~ith a Mooney Viscosity (ML-8, 100C) of 30 and a 5-ethylidene-2-norbornene content of 4-5/O were crosslinked with (l) 2-t-Butylazo-2-metho~y-4-methylpentane and (2) 2,2'-Azobis(2-aceto~ypropane) as well as a mixture of both azo-ester initiators With only a change in the mi~ing temperature to 160C and the rheometer cure temperature to 218C, the e~amples, in Table 5, were prepared and Monsanto Rheometer tested as ciescribed in the General Experimental Procedure.

Table 5 E~ample 41 42 ~3 Compositions (parts by weight) Polypropylene 25 25 25 25 Ethylene-Propylene Diene Rubber 75 75 75 75 2-t-Butylazo- 2-me~hoxy-4-methyl ~pentane 2.0 2 0 - 1.0 2,2'-Azobis(2-àceto~ypropane) - - 2.0 1.0 Triallyl Cyan-lrate - 2.0 2.0 2.0 ~9 ~H-ML (in lbs) 10 20 33 27 Tcgo (mins) ~, 0 3 2 30 5 22.5 TS2 (mins) 1 3 1.1 6 0 1.6 The results illustrate that the resin blend is crosslinlced and further that crosslinking co-agents, i.e., triallyl cyanurate, enhance the crosslinking reaction as illustrated in examples 40-42.
Due to their inherent chemical inertness, different azo initiators can be blencled to obtain specific processin~
advantages. Thus, by using a mi.Yture of azo initiators, example 43, one can extend the scorch time or increase the rate of cure Typical commercial organic peroxide crosslinlcing agents ~dicumyl peroxide; 1,4 and 1,3-di(2-t-b-utylperoxyisopropyl) benzene and 2,5-di(t-butylperoxy)-2,5-dimethylhe~ane] were run under similar conditions as examples 40-42. The organic peroxide cure systems yielded no measurable torque values even in the presence of triallyl cyanurate.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process of crosslinking or simultaneously cross-linking and foaming a natural or synthetic homo-, copolymer or a mixture thereof having -CH2-and/or -CH- groups comprising:
mixing with a 100 parts by weight of said polymer (i) from about 0.02 to about 3.0% by weight of at least one member selected from the group consisting of an azo ester, an azo ether, and a mixture thereof and (ii) from about 0.05 to about 10% by weight of at least one crosslinking intensifier having at least two reactive carbon-carbon double or triple bonds, and heating the polymer mixture at a temperature above about 150°C but not to the point where the polymer will substantially degrade and at a pressure of from about 0 to about 300 psia until crosslinking effected.

2. The process of Claim 1 wherein the azo ester and azo ether have the following formulas and wherein, R is selected from the group consisting of linear or branched alkyl of 1 to 11 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, substituted or unsubstituted aralkyl of 7 to 15 carbons, and R3-CO-, wherein the substituent is alkyl of 1 to 10 carbons, R is selected from the group consisting of H, linear or branched alkyl of 1 to 10 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubstituted aralkyl of 7 to 15 carbons, wherein the substituent is alkyl of 1 to 10 carbons, R1 and R2 are independently selected from the group consisting of linear or branched alkyl of 1 to 10 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubstituted aralkyl of 7 to 15 carbons, wherein the substituent is aralkyl of 1 to 10 carbons, R1R2C- can join together to form a group selected from substituted or unsubstituted cycloalkyl of 5 to 6 carbons wherein the substituent is alkyl of 1 to 10 carbons, -OR and -R1 can join together to form a member selected from the group consisting of -OCO-CH2-CH2- and R4, R5 and R6 are independently selected from the group consisting of linear or branched alkyl of 1 to 10 carbons, substituted or unsubstituted cycloalkyl of 5 to 6 carbons, substituted or unsubstituted phenyl, and substituted or unsubstituted aralkyl of 1 to 10 carbons, wherein the substituent is alkyl of 1 to 10 carbons, R5R6C- can join together to form a mumber selected from the group consisting of substituted or unsubstituted cycloalkyl of 5 to 6 carbons wherein the substituent is alkyl of 1 to 10 carbons.

3. The process of Claim 1 or 2 wherein at least one other free radical crosslinking agent is included.

4. The process of Claim 1 or 2 wherein at least one other free radical crosslinking agent is included, selected from organic peroxides with the exception of hydroperoxides and per-acids.

5. The process of Claim 3 wherein at least one other free radical crosslinking agent is included, selected from organic azides.

6. The process of Claim 1 wherein the reaction is carried out in the presence of additional foaming agents.

7. The process of Claim 1 wherein the reaction is carried out in the presence of fillers.

8. The process of Claim 1 wherein the reaction is carried out in the presence of antioxidants.

9. The process of Claim 1 wherein the polymer is a polymer blend selected from the group consisting of (i) polypropylene and ethylene-propylene diene rubber and (ii) polyvinyl chloride and chlorinated polyethylene.

10. The process of Claim 1 wherein the polymer is selected from the group consisting of high pressure polyethylene of low density, low pressure polyethylene of high and low density, chlorinated polyethylene, chlorosulfonated polyethylene, polypropylene, polybutylene-(1), poly-[4-methylpentene-(1)], polyvinyl chloride, polyvinyl acetate, polyacrylic acid esters, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, ethylene-butylene copolymers, ethylene-propylene butylene copolymers, ethylene-vinyl chloride copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, ethylene-carbon monoxide [sic] copolymers, natural rubber (polyisoprene), polybutadiene, polychloroprene (neoprene), synthetic polyiso-prene, ethylene-propylene-ethylidene norbornene (or cyclo-pentadiene or hexadiene or butadiene) copolymer, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, butadiene-styrene-acrylonitrile copolymer, styrene-isoprene block polymer, butyl rubber (isobutylene-isoprene copolymer), silicone rubber, saturated polyesters, polyamides, polyurethanes, polyethers, and polyacetals.

11. The process of Claim 1 wherein the intensifier is selected from the group consisting of polyallyl cyanurates, polyallyl esters of polyvalent carboxylic acids, polyvalent N-allyl-substituted acid amides or imides, polyallyl ethers of polyvalent alcohols, polyallyl esters of polybasic inorganic acids, and polyallyl substituted amino group-bearing s-triazines.

12. The process of Claim 11 wherein the intensifier of polyallyl cyanurates is selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, and diallyl isocyanurate.

13. The process of Claim 11 wherein the intensifier of polyallyl esters is selected from the group consisting of triallyl trimellitate, triallyl trimesinate, diallyl succinate, diallyl glutarate, diallyl adipate, diallyl phthlate, diallyl diglycol dicarbonate.

14. The process of Claim 11 wherein the intensifier of polyvalent N-allyl-substituted acid amides or imides is N,N,N',N'-tetraallyl adipic acid diamide.

15. The process of Claim 11 wherein the intensifier of polyallyl ethers of polyvalent alcohols is selected from the group consisting of trimethylolpropane and triallyl ether.

16. The process of Claim 11 wherein the intensifier of polyallyl esters of polybasic inorganic acids is triallyl phosphate.

17. The process of Claim 11 wherein the intensifier of polyallyl substituted amino group-bearing s-triazines is 2-butylamino-4,6-diallyl-oxy-s-triazine.