Composition comprising at least one dialkyl peroxide or peroxyketal peroxide and at least one unsaturated organic peroxide

Abstract

The present invention relates to a composition comprising at least one organic peroxide selected from the group consisting of dialkyl peroxides, peroxyketal or mixtures thereof and at least one unsaturated organic peroxide. The invention also relates to the use of such a composition for preventing scorching of at least one crosslinkable composition. The invention also relates to a method for crosslinking at least one crosslinkable composition, said crosslinkable composition comprising at least one crosslinkable polymer. The invention also relates to an article, in particular a molded or extruded article, which can be obtained by a cross-linking process.

Description

Technical Field

[0001] The present invention relates to a composition comprising at least one organic peroxide selected from dialkyl peroxides, peroxyketals and mixtures thereof and at least one unsaturated organic peroxide.

[0002] The invention also relates to the use of such a composition for preventing scorching of at least one crosslinkable composition comprising at least one crosslinkable polymer, preferably chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, even more preferably chosen from elastomeric polymers.

[0003] The invention also relates to a process for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer, preferably chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, in the presence of said composition.

[0004] Furthermore, the present invention aims at providing an article, in particular a moulded or extruded article, which is obtainable by the process described in detail below. Background Art

[0005] Polymers and copolymers crosslinked with organic peroxides and / or azo compounds, i.e., thermoplastic polymers, elastomers, and mixtures thereof, generally exhibit better mechanical and physical properties than uncrosslinked polymers or polymers crosslinked by sulfur curing. These properties may include, for example, high heat aging resistance, low compression set percentage, reduced metal contamination, and ease of producing colored products with enhanced color stability.

[0006] However, premature crosslinking (also called scorch) occurring during the manufacturing stage represents a major problem in implementing organic peroxides and azo compounds in crosslinking (also called curing) applications of elastomeric and / or thermoplastic materials.

[0007] The preparation stage usually includes blending or compounding the components and possibly extruding them at usually high temperatures. The operating conditions of the preparation stage often lead to partial decomposition of the peroxide or azo initiator, thereby causing a premature crosslinking reaction, forming gel particles in the bulk of the polymer mixture. The presence of these gel particles is responsible for imparting defects such as non-uniformity and surface roughness to the final product.

[0008] As a result, scorch can reduce the plasticity of the target polymer material so that it can no longer be converted, which can result in the loss of the entire batch. In addition, excessive scorch can in some cases cause the extrusion operation to stop completely.

[0009] Several attempts have been made to suppress the tendency to scorch. For example, it has been proposed to add free radical initiators with a long half-life. However, the disadvantages resulting from the described embodiments are low productivity due to long curing times and high energy costs.

[0010] Additionally, other attempts have relied on the use of various additives as scorch inhibitors during crosslinking of polymer compositions, such as organic hydroperoxides, vinyl monomers, nitrites, aromatic amines, phenolic compounds, mercaptothiazole compounds, sulfides, hydroquinones, and dialkyldithiocarbamate compounds.

[0011] Although these additives serve to extend the scorch resistance time, they still hinder the cure time and / or final crosslink density, resulting in reduced productivity and / or properties of the final product.

[0012] In fact, the crosslink density corresponds to an indication of the properties of the final product, in particular the mechanical properties. Therefore, a decrease in the crosslink density is usually a sign of a decrease in the mechanical properties of the final product.

[0013] Therefore, there is a real need to provide compositions that are able to extend the scorch resistance during crosslinking of polymeric compositions, particularly thermoplastic and / or elastomeric polymeric compositions, without adversely affecting the cure time and / or the final crosslink density.

[0014] In other words, one of the objects of the present invention is to provide a composition capable of effectively crosslinking (or curing) a polymer composition and at the same time imparting good properties in terms of physical and / or mechanical properties to the target product.

[0015] In particular, one of the objects of the present invention is to delay scorch during crosslinking of polymer compositions without causing a significant loss in crosslinking efficiency. Summary of the invention

[0016] The present invention arises in particular from the unexpected discovery by the inventors that blending two types of organic peroxides in a specific ratio can overcome the above-mentioned disadvantages.

[0017] Therefore, the present invention relates to a composition comprising:

[0018] a) at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof,

[0019] b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a),

[0020] c) at least one nitroxide radical,

[0021] Wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04.

[0022] The composition of the invention makes it possible to delay scorch during the crosslinking of polymeric compositions, in particular thermoplastic and / or elastomeric polymeric compositions, without hampering the curing time and / or the crosslinking density.

[0023] In other words, the composition according to the present invention can prolong the scorch resistance of the polymeric composition during crosslinking and ensure sustainability of the curing time and / or crosslinking density.

[0024] Therefore, the composition of the present invention can be effectively used for crosslinking polymer-based compositions while imparting good properties, particularly good physical and / or mechanical properties, to the target product at a satisfactory productivity.

[0025] In particular, the composition of the invention imparts to the final product improved mechanical properties and more particularly enhanced resistance to ageing.

[0026] The present invention also relates to a method for producing the aforementioned composition, comprising mixing:

[0027] a) at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, and

[0028] b) said at least one organic peroxide (b) comprises in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a),

[0029] c) optionally at least one nitroxide radical,

[0030] Wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04.

[0031] The invention also relates to a method for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer, in particular chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, comprising:

[0032] i) mixing the crosslinkable composition, optionally in the presence of a composition comprising:

[0033] a) at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof,

[0034] b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a),

[0035] wherein the weight ratio between the organic peroxide (b) and the organic peroxide (a) is in the range of 0.003 to 0.04, preferably 0.005 to 0.03, more preferably 0.01 to 0.025;

[0036] ii) curing the obtained mixture.

[0037] The process of the invention allows delaying the scorching of the crosslinkable composition without significantly hampering the crosslink density. In other words, no decrease in crosslink density has been observed during the process described above.

[0038] The process according to the invention makes it possible to produce articles having good properties, in particular good physical and / or mechanical properties, while ensuring a satisfactory productivity.

[0039] Therefore, another aspect of the present invention relates to an article, in particular a moulded or extruded article, obtainable by the process described in detail above.

[0040] Another subject of the present invention is the use of the aforementioned composition for curing at least one crosslinkable composition comprising at least one crosslinkable polymer, in particular chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, preferably elastomeric polymers.

[0041] Advantageously, the use of the composition makes it possible to limit the risks of scorching of the crosslinkable composition and to control its curing.

[0042] Preferably, the aforementioned composition is used for preventing scorch of at least one crosslinkable composition comprising at least one crosslinkable polymer as defined previously.

[0043] Other objects and features, aspects and advantages of the present invention will become more clearly apparent by reading the following description and examples.

[0044] In the following, unless otherwise indicated, the limits of the numerical ranges are included in the stated ranges, especially in the expressions "between" and "ranging from to".

[0045] Furthermore, the expression "at least one" used in this specification is equivalent to the expression "one or more".

[0046] In the following, the terms "peroxyketal" and "perketal" are equivalent.

[0047] In addition, the term "polymer" encompasses "homopolymers" and "copolymers", and the term "copolymer" refers to a polymer composed of at least two different monomers in polymerized form. For example, a copolymer according to the present disclosure can be a polymer comprising two different monomers, and a terpolymer is a polymer comprising three or more different monomers.

[0048] Composition

[0049] As previously detailed, the composition of the invention comprises in particular at least one organic peroxide (a) chosen from dialkyl peroxides, peroxyketals and mixtures thereof.

[0050] The dialkyl peroxide may be selected from di-tert-butyl peroxide; tert-butyl cumyl peroxide; 2,5-di(cumylperoxy)-2,5-dimethylhexane; 4-methyl-4-(tert-butylperoxy)-2-pentanol; 4-methyl-4-(tert-amylperoxy)-2-pentanol; 4-methyl-4-(cumylperoxy)-2-pentanol; 4-methyl-4-(tert-butylperoxy)-2-pentanone; 4-methyl-4-(tert-amylperoxy)-2-pentanone; 4-methyl-4-(cumylperoxy)-2-pentanone peroxy)-2-pentanone; 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; 2,5-dimethyl-2,5-di(tert-amylperoxy)hexane; 2,5-dimethyl-2-tert-butylperoxy-5-hydroperoxyhexane; 2,5-dimethyl-2-cumylperoxy-5-hydroperoxyhexane; 2,5-dimethyl-2-tert-amylperoxy-5-hydroperoxyhexane; 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxy) isopropyl)-benzene; 1,3,5-tri(tert-butylperoxyisopropyl)benzene; 1,3,5-tri(tert-amylperoxyisopropyl)benzene; 1,3,5-tri(cumylperoxyisopropyl)benzene; bis[1,3-dimethyl-3-(tert-butylperoxy)butyl]carbonate; bis[1,3-dimethyl-3-(tert-amylperoxy)butyl]carbonate; bis[1,3-dimethyl-3-(cumylperoxy)butyl]carbonate; di-tert-amyl peroxide; dicumyl peroxide; tert-butyl Peroxy-m-isopropenyl-cumyl peroxide; tert-amyl cumyl peroxide; tert-butyl-isopropenyl cumyl peroxide; 2,4,6-tri(butylperoxy)-s-triazine; 1,3,5-tri[1-(tert-butylperoxy)-1-methylethyl]benzene; 1,3,5-tri-[(tert-butylperoxy)-isopropyl]benzene; 1,3-dimethyl-3-(tert-butylperoxy)butanol; 1,3-dimethyl-3-(tert-amylperoxy)butanol; and mixtures thereof.

[0051] Other dialkyl peroxides that may be used alone or in combination with other free radical initiators contemplated by the present disclosure are selected from those represented by the following formula (I):

[0052]

[0053] wherein R4 and R5 may be independently in the meta or para position and are the same or different and are selected from hydrogen or a straight or branched chain alkyl group having 1 to 6 carbon atoms. Dicumyl peroxide and isopropylcumyl peroxide are illustrative.

[0054] Preferably, the dialkyl peroxide is selected from compounds having the following formula (II):

[0055]

[0056] in:

[0057] R1 and R'1 independently represent a linear or branched, preferably branched, C3-C 10 alkyl,

[0058] R2 and R'2 independently represent a linear or branched, preferably a branched C3-C 10 alkyl.

[0059] More preferably, according to formula (II):

[0060] - R1 and R'1 are the same and represent a linear or branched, especially a branched C3-C 10 Alkyl, and

[0061] - R2 and R'2 are the same and represent a linear or branched, preferably a branched C3-C 10 alkyl.

[0062] Even more preferably, according to formula (II):

[0063] -R1 and R'1 represent branched C3-C 10 Alkyl, especially branched C3-C6 alkyl,

[0064] -R2 and R'2 are the same and represent a branched C3-C 10 Alkyl, especially branched C3-C6 alkyl.

[0065] Preferably, the group R'2-OO-R'1 may be in the meta-position or para-position on the phenyl ring defined in formula (II).

[0066] The dialkyl peroxide corresponding to formula (II) is preferably selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof.

[0067] The dialkyl peroxide is preferably selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, a dialkyl peroxide represented by formula (I), a dialkyl peroxide represented by formula (II), and a mixture thereof.

[0068] The dialkyl peroxide is preferably selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof.

[0069] Even more preferably, the dialkyl peroxide is selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof.

[0070] The peroxyketal may be selected from 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane; 1,1-di(tert-butylperoxy)cyclohexane; n-butyl 4,4-di(tert-amylperoxy)valerate; ethyl 3,3-di(tert-butylperoxy)butyrate; 2,2-di(tert-amylperoxy)propane; 3,6,6,9,9-pentamethyl-3-ethoxycarbonylmethyl-1,2,4,5-tetraoxacyclononane; n-butyl-4,4-bis(tert-butylperoxy)valerate; ethyl-3,3-di(tert-amylperoxy)butyrate; and mixtures thereof.

[0071] The peroxyketal is preferably selected from n-butyl-4,4-bis(tert-butylperoxy)valerate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane and mixtures thereof.

[0072] Preferably, the perketal is n-butyl-4,4-bis(tert-butylperoxy)valerate.

[0073] The organic peroxide (a) is preferably selected from the dialkyl peroxides as defined above, especially those selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, the dialkyl peroxide represented by formula (I), the dialkyl peroxide represented by formula (II) and mixtures thereof.

[0074] The organic peroxide (a) is preferably selected from dialkyl peroxides, in particular those selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof, more preferably those selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof.

[0075] The composition according to the invention further comprises at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain.

[0076] Preferably, the organic peroxide (b) comprises in its structure at least one side chain containing one or more ethylenic unsaturations, more preferably one ethylenic unsaturation.

[0077] Preferably, the side chain is a straight or branched C2-C 10 , more preferably a C2-C4 unsaturated hydrocarbon moiety.

[0078] The side chain may be a straight or branched C2-C 10 , more preferably a C2-C4 unsaturated hydrocarbon moiety.

[0079] Preferably, the side chain is a straight or branched C2-C 10 , more preferably C2-C4 alkylene.

[0080] More preferably, the side chain is ethylene.

[0081] In other words, the organic peroxide (b) may contain in its structure at least one linear or branched C2-C 10 Unsaturated hydrocarbon part, preferably straight chain or branched C2-C 10 , more preferably a main chain substituted with C2-C4 alkylene.

[0082] The organic peroxide (b) may be selected from compounds having the following formula (III) or (IV):

[0083] R6-OO-R6'(III) or

[0084] R6'-OO-R6'(IV)

[0085] in:

[0086] -R6 represents a straight chain or branched chain, preferably a branched chain C3-C 10 Alkyl, preferably C3-C6 alkyl;

[0087] -R'6 represents a straight chain or branched C2-C 12 alkyl:

[0088] - is substituted by at least one aromatic ring, in particular at least one benzene ring, which is substituted by at least one side chain, preferably a linear or branched C2-C 10 , more preferably C2-C4 unsaturated hydrocarbon partial substitution, or

[0089] - at least one side chain containing one or more ethylenic unsaturations, preferably a linear or branched C2-C 10 , more preferably C2-C4 unsaturated hydrocarbon partial substitution,

[0090] Preferably, R'6 represents a straight or branched C2-C substituted by at least one aromatic ring, especially at least one benzene ring. 12Alkyl, which is separated by at least one side chain containing one or more ethylenic unsaturations, preferably a linear or branched C2-C 10 , more preferably partially substituted with C2-C4 unsaturated hydrocarbons.

[0091] Preferably, R6 represents a branched C3-C 10 Alkyl, even more preferably branched C3-C7 alkyl, even more preferably a C4 group, even more preferably a tert-butyl group.

[0092] Preferably, the alkyl group of R6' is a linear or branched C3-C5 group, even more preferably a linear or branched C3 group.

[0093] Preferably, the side chain of R6' is isopropenyl, vinyl or allyl, more preferably isopropenyl.

[0094] The aromatic ring of R6' can be C6-C 12 A membered ring, preferably a benzene ring.

[0095] The organic peroxide (b) is preferably 1-(2-tert-butylperoxyisopropyl)-3-isopropenylbenzene.

[0096] The weight ratio between the organic peroxide (b) and the organic peroxide (a) is in the range of 0.003 to 0.04, preferably 0.005 to 0.3, even more preferably 0.01 to 0.025.

[0097] The composition according to the invention further comprises at least one nitroxide radical.

[0098] The nitroxide radical may be selected from 2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 2,2,5,5-tetramethylpyrrolidine-1-oxyl, bis(1-oxy-2,2,6,6-tetramethyl-piperidin-4-yl)sebacate, 1-piperidinyloxy-4,4'-(1,10-dioxo-1,10-decanediyl)bis(oxy)bis(2,2,6,6-tetramethyl-), 2,2,6,6-tetramethyl-1-4-hydroxypiperidin-1-oxymonophosphonate, 3-carboxy-2,2,5,5-tetramethylpyrrolidin-1-oxyl and mixtures thereof.

[0099] The nitroxide radical is preferably selected from 2,2,6,6-tetramethylpiperidin-1-oxyl (commonly sold under the name TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (commonly sold under the name 4-hydroxy-TEMPO), 1-piperidinyloxy-4,4'-(1,10-dioxo-1,10-decanediyl)bis(oxy)bis(2,2,6,6-tetramethyl-) (commonly known as di-TEMPO sebacate) and mixtures thereof.

[0100] The nitroxide radical is preferably 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy.

[0101] The weight ratio between the nitroxide radical and the organic peroxide (a) is preferably in the range of 0.008 to 0.50, more preferably 0.02 to 0.2, and even more preferably 0.03 to 0.12.

[0102] The composition may comprise at least one organic peroxide selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof and at least one nitroxide radical selected from 2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl and mixtures thereof in a weight ratio of 0.008 to 0.50, more preferably 0.02 to 0.2, even more preferably 0.03 to 0.12.

[0103] The weight ratio between the nitroxide radical and the organic peroxide (b) is preferably in the range of 0.05 to 50, more preferably 0.15 to 16 and even more preferably 0.5 to 6.

[0104] The composition may comprise 1-(2-tert-butylperoxyisopropyl)-3-isopropenylbenzene and at least one nitroxide radical selected from 2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy and mixtures thereof in a weight ratio of 0.05 to 50, more preferably 0.15 to 16, even more preferably 0.5 to 6.

[0105] The composition may further contain at least one crosslinking accelerator, in particular selected from compounds containing at least one double bond, which may be difunctional or polyfunctional, such as difunctional vinyl monomers, difunctional allylic monomers, polyfunctional vinyl monomers or polyfunctional allylic monomers. These compounds are described in International Application WO 02 / 28946 and can accelerate the crosslinking rate without negatively affecting the scorch resistance or the crosslinking density.

[0106] The composition according to the invention may further comprise at least one crosslinkable polymer, preferably chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, more preferably chosen from elastomeric polymers.

[0107] The thermoplastic and / or elastomeric polymers of the present invention can be defined as natural or synthetic polymers having thermoplastic and / or elastomeric properties and which can be crosslinked (cured) under the action of a crosslinking agent. Crosslinking and crosslinkable polymers are described in Rubber World, "Elastomer Crosslinking with Diperoxyketals", October 1983, pages 26-32 and Rubber and Plastic News, "Organic Peroxides for Rubber Crosslinking", September 29, 1980, pages 46-50. Polyolefins suitable for use in the present invention are described in Modern Plastics Encyclopedia 89, pages 63-67, 74-75.

[0108] The crosslinkable polymer can be selected from low density linear polyethylene, low density polyethylene, high density polyethylene, chlorinated polyethylene, ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-octene copolymer, ethylene-butyl acrylate copolymer (EBA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EBA), silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene copolymer (NBR), styrene-butadiene copolymer (SBR), chloroprene rubber (CR), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene block copolymer (SBS), chlorosulfonated polyethylene, fluoroelastomer, copolymer of ethylene and methyl (meth)acrylate, and copolymer of ethylene and glycidyl methacrylate, and combinations thereof.

[0109] The polymer is preferably an elastomeric polymer, more preferably selected from ethylene-propylene-diene terpolymers (EPDM).

[0110] The organic peroxide (a) preferably accounts for 1.6 to 4.8 parts, advantageously 2 to 4 parts, per 100 parts by weight of the crosslinkable polymer.

[0111] The organic peroxide (b) preferably accounts for 0.015 to 0.8 parts, advantageously 0.05 to 0.3 parts, per 100 parts by weight of the crosslinkable polymer.

[0112] The total content of the organic peroxide (a) and the organic peroxide (b) may be 1.62 to 5.6 parts, preferably 2.05 to 4.3 parts, per 100 parts by weight of the cross-linkable polymer.

[0113] The nitroxide radicals are preferably present in an amount of 0.04 to 0.8 parts, advantageously 0.15 to 0.3 parts, per 100 parts by weight of the crosslinkable polymer.

[0114] Preferably, the composition may comprise:

[0115] a) at least one organic peroxide (a) selected from dialkyl peroxides, in particular those selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dialkyl peroxides represented by formula (I), dialkyl peroxides represented by formula (II) and mixtures thereof,

[0116] b) at least one organic peroxide (b) which contains in its structure at least one unsaturated side chain, in particular those selected from compounds of formula (III), in which R'6 preferably represents a linear or branched C2-C substituted by at least one aromatic ring, in particular at least one benzene ring 12 Alkyl, which is separated by at least one side chain containing one or more ethylenic unsaturations, preferably a linear or branched C2-C 10 , more preferably C2-C4 unsaturated hydrocarbon partially substituted, the organic peroxide (b) is different from the organic peroxide (a),

[0117] c) at least one nitroxide radical,

[0118] wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range of from 0.003 to 0.04;

[0119] d) at least one crosslinkable polymer, in particular chosen from elastomeric polymers.

[0120] According to this aspect, the weight ratio between the organic peroxide (b) and the organic peroxide a) ranges from 0.003 to 0.04, preferably from 0.005 to 0.03, even more preferably from 0.01 to 0.025.

[0121] More preferably, the composition may comprise:

[0122] a) at least one organic peroxide (a) selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof, even more preferably selected from those selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof,

[0123] b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, in particular 1-(2-tert-butylperoxyisopropyl)-3-isopropenylbenzene, said organic peroxide (b) being different from the organic peroxide (a),

[0124] c) at least one nitroxide radical,

[0125] wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range of 0.003 to 0.040;

[0126] d) at least one crosslinkable polymer, especially chosen from elastomeric polymers, even more preferably from ethylene-propylene-diene terpolymers (EPDM).

[0127] According to this aspect, the weight ratio between the organic peroxide (b) and the organic peroxide (a) ranges from 0.003 to 0.04, preferably from 0.005 to 0.03, even more preferably from 0.01 to 0.025.

[0128] Method for making the composition

[0129] Another subject of the present invention is a process for producing a composition as defined previously, said process comprising the steps of mixing:

[0130] - at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof,

[0131] - at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a),

[0132] - optionally at least one nitroxide radical,

[0133] The weight ratio between the organic peroxide (b) and the organic peroxide (a) is in the range of 0.003 to 0.04, preferably 0.005 to 0.03, even more preferably 0.01 to 0.025.

[0134] Method for crosslinking a crosslinkable composition

[0135] Another aspect of the present invention relates to a method for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer, in particular chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, comprising:

[0136] i) optionally, a step of mixing at least one crosslinkable composition comprising at least one crosslinkable polymer in the presence of:

[0137] - at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, and

[0138] - at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain; said organic peroxide (b) being different from said organic peroxide (a),

[0139] - at least one nitroxide radical,

[0140] - wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04,

[0141] ii) a step of cross-linking the composition obtained.

[0142] The invention also relates to a method for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer, in particular chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, comprising:

[0143] i) optionally, a step of mixing at least one crosslinkable composition comprising at least one crosslinkable polymer in the presence of:

[0144] - at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, and

[0145] - at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain; said organic peroxide (b) being different from said organic peroxide (a),

[0146] - optionally at least one nitroxide radical,

[0147] - wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04,

[0148] ii) a step of cross-linking the composition obtained.

[0149] In other words, the present invention relates to a process for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer, in particular chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, comprising:

[0150] i') a step of crosslinking said at least one crosslinkable composition in the presence of:

[0151] - at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, and

[0152] - at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain; said organic peroxide (b) being different from said organic peroxide (a),

[0153] - at least one nitroxide radical,

[0154] - wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04.

[0155] The present invention therefore relates to a method for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer as defined below, the method comprising:

[0156] i') a step of crosslinking said crosslinkable composition in the presence of a composition as defined above.

[0157] The cross-linking step may be preceded by a step of mixing:

[0158] - said crosslinkable composition, and

[0159] - at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, and

[0160] - at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain; said organic peroxide (b) being different from said organic peroxide (a),

[0161] - at least one nitroxide radical,

[0162] - wherein the weight ratio between the at least one organic peroxide (b) and the at least one organic peroxide (a) is in the range from 0.003 to 0.04.

[0163] The composition obtained comprises said at least one crosslinkable polymer as defined previously, said at least one organic peroxide (a) chosen from dialkyl peroxides, peroxyketals and mixtures thereof, and said at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from the organic peroxide (a), wherein the weight ratios are as described below.

[0164] In other words, the composition obtained is the mixture obtained in the mixing step i) of the process.

[0165] Preferably, the method comprises the step of cross-linking the mixture obtained in the mixing step i).

[0166] The crosslinkable composition preferably comprises at least one crosslinkable elastomeric polymer, more preferably chosen from ethylene-propylene-diene terpolymers (EPDM).

[0167] The crosslinkable composition may additionally contain at least one additive, for example a carbon black filler, a process oil, a mold release agent, an antioxidant and / or a heat stabilizer.

[0168] The crosslinkable composition may be a polymer masterbatch, preferably an elastomeric masterbatch, which may comprise one or more of the aforementioned additives.

[0169] Preferably, the polymer masterbatch may comprise at least one elastomer and one or more additives selected from the group consisting of carbon black, polyethylene glycol, at least one process oil (e.g., a liquid saturated hydrocarbon such as 352), at least one antioxidant (e.g., 2,2,4-trimethyl-1,2-dihydroquinoline, also known as TMQ), at least one mold release agent, at least one thermal stabilizer, and combinations thereof.

[0170] Advantageously, the mixing step may be carried out in any conventional manner.

[0171] The curing (or cross-linking) step may be carried out at a temperature between 140°C and 250°C and more preferably between 160°C and 220°C.

[0172] The process may further comprise converting the obtained composition (or the mixture obtained in step (i)) into a moulded or extruded article before, during or after the crosslinking step, preferably before or after the crosslinking step.

[0173] The method preferably comprises extruding the obtained composition to form an uncured preformed article and curing the uncured preformed article.

[0174] use

[0175] Another subject of the present invention is the use of the above-mentioned composition comprising a) at least one organic peroxide (a) chosen from dialkyl peroxides, peroxyketals and mixtures thereof and b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from the organic peroxide (a); wherein the weight ratio between said at least one organic peroxide (b) and said at least one organic peroxide (a) is within the range of 0.003 to 0.04, to cure at least one crosslinkable composition comprising at least one crosslinkable polymer as described herein.

[0176] The crosslinkable polymer is preferably selected from thermoplastic polymers, elastomeric polymers and mixtures thereof, more preferably selected from elastomeric polymers, even more preferably selected from ethylene-propylene-diene terpolymers (EPDM).

[0177] Preferably, the crosslinkable composition is an elastomeric masterbatch.

[0178] In particular, the aforementioned composition is used to control the curing of at least one crosslinkable composition comprising at least one crosslinkable polymer, especially those chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, more preferably from elastomeric polymers, even more preferably from those chosen from ethylene-propylene-diene terpolymers (EPDM).

[0179] Preferably, the aforementioned composition is used for preventing scorch of at least one crosslinkable composition as defined previously.

[0180] Products

[0181] The invention also relates to an article, in particular a moulded article or an extruded article, obtainable by the process defined above.

[0182] More preferably, the present invention relates to an extruded article obtainable by the above process.

[0183] The article is preferably an elastomeric article.

[0184] In other words, the article is obtainable by the process as previously defined for crosslinking at least one crosslinkable composition comprising at least one crosslinkable elastomer.

[0185] The article is preferably selected from cables or wires.

[0186] The following examples are given as illustrations of the present invention. Example

[0187] I. Initiators tested

[0188] The following is a list of initiators used in the examples described below:

[0189] A. Organic peroxide (a) (Component A)

[0190] 1,3-Bis(tert-butylperoxyisopropyl)-benzene (CAS 2212-81-9) was used in the following examples.

[0191] Synthesis of Component A

[0192] 1,3-Bis(tert-butylperoxyisopropyl)-benzene

[0193] Peroxides consisting mainly of 1,3-bis(tert-butylperoxyisopropyl)benzene (CAS 2212-81-9), commercialized by Nouryon BV A sample of 14S-FL was purified by repeated recrystallization from ethanol.

[0194] The purification was performed in a beaker placed in a water bath.

[0195] The procedure is as follows:

[0196] ●Dissolve the product to be purified in anhydrous ethanol.

[0197] • Allow stirring at a temperature between 45°C and 55°C for about 15 min.

[0198] • Collect the solution in a beaker and cool to 4°C by immersing in a water / ice bath.

[0199] • Remove most of the solvent by keeping the solids at the bottom of the beaker.

[0200] - Wash the solid twice with about 10 / 15 g ethanol in the same beaker (for 50 g treated peroxide).

[0201] • Repeat the dissolution / crystallization cycle (3 cycles total).

[0202] • The product was then filtered on a Büchner funnel using filter paper on a perforated plate.

[0203] • Evaporate the residual ethanol from the purified peroxide and keep the sample under a fume hood at room temperature for 24 h.

[0204] The purified peroxide was analyzed by gas chromatography and exhibited a 1,3-bis(tert-butylperoxyisopropyl)-benzene (CAS 2212-81-9) content of 99.8%.

[0205] 1,3 and 1,4-bis(tert-butylperoxyisopropyl)-benzene

[0206] The isomeric mixture of 1,3 and 1,4-bis(tert-butylperoxyisopropyl)-benzene sold by Sigma-Aldrich / Merck lot number 09212EN (CAS: 25155-25-3) was purified by repeated recrystallization in ethanol with a purity of 96%.

[0207] The purification was performed in a beaker placed in a water bath.

[0208] The procedure is as follows:

[0209] ●Dissolve the product to be purified in anhydrous ethanol.

[0210] • Allow stirring at a temperature between 45°C and 55°C for approximately 15 min.

[0211] Collect the solution in a beaker and cool to 4°C by immersing in a water / ice bath.

[0212] • Remove most of the solvent by keeping the solids at the bottom of the beaker.

[0213] - Wash the solid twice with about 10 / 15 g ethanol in the same beaker (for 50 g treated peroxide).

[0214] - Repeat the dissolution / crystallization cycle (3 cycles in total).

[0215] The product was then filtered on a Büchner funnel using filter paper over a perforated plate.

[0216] • Evaporate the residual ethanol from the purified peroxide and keep the sample at room temperature under a fume hood for 24 h.

[0217] The purified peroxide was analyzed by gas chromatography and showed a 1,3-bis(tert-butylperoxyisopropyl)-benzene (CAS 2212-81-9) content of 63.0% and a 1,4-bis(tert-butylperoxyisopropyl)-benzene (CAS 2781-00-2) content of 36.4% for a total amount of an isomer mixture of 1,3 and 1,4-bis(tert-butylperoxyisopropyl)-benzene (CAS: 25155-25-3) of 99.4%.

[0218] B. Unsaturated organic peroxide (b) (component B)

[0219] 1-(2-tert-Butylperoxyisopropyl)-3-isopropenylbenzene (CAS 96319-55-0) was used in the following examples.

[0220] Synthesis of Component B

[0221] The diol (meta-isomer from Sumitomo) was dehydrated off one alcohol group under a vacuum of 40 mbar for 300 min at 150° C. using adipic acid (2:1 ratio) to extract water.

[0222] The resulting mixture was cooled to 40-50°C and heptane was added. The aqueous phase was removed and the organic phase was distilled under a vacuum of 40 mbar to recover the monoalcohol monoolefin intermediate.

[0223] GC-MS analysis showed a purity of more than 95%.

[0224] The intermediate unsaturated alcohol was reacted with a 45% solution of TBHP in n-heptane (obtained by extracting a commercial grade TBHP with n-heptane) in the presence of p-toluenesulfonic acid. TBH70X preparation) to prepare a mixture containing monounsaturated dialkyl peroxide.

[0225] The mixture was washed with caustic solution and water to remove unreacted TBHP and acid catalyst.

[0226] The n-heptane was removed by evaporation in a laboratory evaporator at 50° C. under a vacuum of 40 mbar for 2 hours.

[0227] The final product was then purified on a silica gel column using acetonitrile as the eluting solvent.

[0228] The eluted fractions containing the desired product were treated on a rotary laboratory evaporator at 50° C. under a vacuum of 40 mbar for 2 hours until the solvent was removed.

[0229] The purified product was analyzed by GC-MS analysis which gave an assay of 99.0%.

[0230] C. Nitrogen oxide free radical (component C)

[0231] 4-Hydroxy-TEMPO supplied by the company Sigma 3V under the name Tempoxy LO and having a purity of 99.5% was used.

[0232] II. Experimental protocol

[0233] Procedure for mixing rubber and preparing rubber sheets

[0234] The following procedure was used to mix the rubber and prepare the rubber compounds for crosslinking testing. A Brabender with a 50 mL capacity bowl was used. It is equipped with a jacket capable of running the mixture at room temperature or under heating oil. The mixer is equipped with a removable sigma-type blade. A small strip of rubber compound "EPDM MB" (see detailed recipe in Table 1) is slowly added to the bowl at a mixing speed of 20 to 25 rpm. Add to the Brabender The total amount of rubber in the bowl was equal to the weight required to provide a rubber volume of 48 ml so that there was sufficient volume to add the peroxide based curative to the rubber, the mixer having a volume capacity of -50 ml.

[0235] The mixer speed was then reduced to 15 RPM and the peroxide formulation used for this experiment, which was weighed on a minimum three digit balance for good accuracy at a low pressure, was slowly added to the mixed rubber. Pre-weighed in cup.

[0236] The speed is then increased to 25 RPM for three minutes. Thereafter, the mixer speed is reduced to 10 rpm and the mixer head is loosened and removed. Once the blades are no longer turning, the rubber around the blades is safely removed and placed in a On polyester sheet. There is a small amount of rubber, which is located at the head of the mixer blade in the inner hollow part of the mixing chamber, which is finally removed. Reassemble the mixer head with bolts and start the mixer motor again at 20rpm. The last removed rubber (which is trapped in the mixing chamber) is first added to the rotating blade, and then the rubber removed from the blade is added. This provides a more uniform elastomer mix. The speed is then increased to 25RPM and maintained at this level for 3 minutes. After this time, the mixer speed is set to 10rpm, and the mixer head is loosened and removed. Once removed, the mixer blade stops moving, and all rubber is safely removed from the bowl and blades of the mixer again.

[0237] The hot rubber is then formed into a tight ball and placed between two The sandwich is placed in a heated hydraulic powered Carver press, which can be set between room temperature and 60°C, depending on the elastomer and peroxide curative used. The rubber ball is flattened between two heavy Wearing nitrile gloves, open the press and remove the Polyester sheet sandwich. Remove the top sheet and roll the rubber into a tube. Re-clip it in the middle and flatten it again. Roll the sheet again, but at 90 degrees to the original rolling direction, and flatten it again. Repeat the operation for a third time and carefully flatten it to a thickness of about 1 / 8 inch. Place the sandwich on the bench top and cover it with a metal sheet, where the rubber is cooled. Then take it out and store it in a tightly sealed polyethylene bag. Then cut these sheets with scissors or use a sharp metal circular punch to prepare small flat circular sheets of uncured rubber for rheometer curing and Mooney scorch evaluation.

[0238] Rheometer Program

[0239] The following procedures are used for moving die rheometer and RPA (Rubber Process Analyzer) evaluations. For Alpha Technologies MDR rheometers, test method ASTM D5289-12 "Standard Test Method for Rubber Property-Vulcanization Using Rotorless Cure Meters" is used. Test method ASTM D6204 is used with an arc of 0.5 or 1.0 degrees and an oscillation frequency of 100 cpm at a cure temperature suitable for the curing agent system, such as 190°C for the following examples.

[0240] When performing rheometer evaluation, approximately 5 to 6 grams of elastomer (depending on the density of the final compound) is used to completely fill the upper and lower dies of the rheometer. Uncured rubber is cut from the pressed sheets formed by the above procedure. The rubber is cut into small discs approximately 1.25 inches in diameter and placed between two The sandwich structure was then placed in a rheometer for testing according to standard ASTM D5289.

[0241] The measured value denoted MH-ML is the difference between the maximum values ​​of the torque (expressed in dN m) obtained from the curve recorded by the rheometer. It indicates the level of crosslinking density.

[0242] Mooney Scorch Procedure

[0243] The scorch time (TS05) was measured at 135° C. with the aid of a Mooney MV 2000 viscometer (Alpha Technologies) according to the test method ISO 289-2:2020 “Rubber, unvulcanized-determinations using ashearing-disc viscometer—Part 2: Determination of pre-vulcanization characteristics”.

[0244] Example 1

[0245] In this example, the EDPM masterbatch elastomer formulations in Table 1 were mixed with various cure systems and the mixtures were then tested with the aid of a rheometer and a Mooney scorch viscometer. Table 2 provides a summary of the three cure systems in the EPDM masterbatch formulations.

[0246] [Table 1]

[0247]

[0248] [Table 2]

[0249]

[0250]

[0251] The results obtained in EPDM rubber compounds containing 3.2 phr of organic peroxide show an improvement in the scorch time measured at 135° C. when using a mixture of organic peroxides A and B, compared to the formulation containing component A as the only organic peroxide.

[0252] Furthermore, the results for Composition 3 show that too high a ratio of organic peroxide B to organic peroxide A results in a significant loss in crosslink density.

[0253] The results therefore show that the composition according to the invention makes it possible to delay scorch during the crosslinking of EPDM compositions without having a deleterious effect on the final crosslink density.

[0254] Example 2

[0255] The protocol described in Example 1 was repeated, except that as component A an isomeric mixture of 1,3 and 1,4-bis(tert-butylperoxyisopropyl)-benzene was used.

[0256] [Table 3]

[0257]

[0258]

[0259] Example 2 also shows an improvement in the scorch time value without a significant change in the rheological crosslink density when organic peroxide A is 1,3- and 1,4-bis(tert-butylperoxyisopropyl)-benzene (CAS: 25155-25-3) and when the mixture contains component B.

[0260] Example 3

[0261] The protocol described in Example 1 was repeated except that the 231 (1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane) was used as component A.

[0262] [Table 4]

[0263]

[0264]

[0265] Example 3 shows an improvement in the scorch time value when organic peroxide A is 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane (CAS: 6731-36-8) and when the mixture includes component B without a significant change in the rheological crosslink density.

[0266] The results for Composition 8 show that too high a ratio of organic peroxide B to organic peroxide A results in a significant loss in crosslink density.

[0267] These results demonstrate that the composition according to the invention makes it possible to delay scorch during the crosslinking of EPDM compositions without having a deleterious effect on the final crosslink density.

Claims

1. A composition comprising: a) at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a), c) at least one nitroxide radical, The weight ratio of the organic peroxide (b) to the organic peroxide (a) is in the range of 0.003 to 0.

04.

2. The composition according to claim 1, characterized in that The weight ratio between the organic peroxide (b) and the organic peroxide (a) ranges from 0.005 to 0.03, preferably from 0.01 to 0.

025.

3. The composition according to claim 1 or 2, characterized in that The dialkyl peroxide is selected from compounds having the following formula (II): in: - R1 and R'1 independently represent a linear or branched, preferably branched, C3-C 10 alkyl, - R2 and R'2 independently represent a linear or branched, preferably a branched C3-C 10 alkyl.

4. A composition according to any one of the preceding claims, characterized in that The dialkyl peroxide is selected from dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)-benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof, preferably selected from 1,3-bis(tert-butylperoxyisopropyl)-benzene, 1,4-bis(tert-butylperoxyisopropyl)-benzene and mixtures thereof.

5. A composition according to any one of the preceding claims, characterised in that The peroxyketal is selected from 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane; 1,1-di(tert-butylperoxy)cyclohexane; n-butyl 4,4-di(tert-amylperoxy)valerate; ethyl 3,3-di(tert-butylperoxy)butyrate; 2,2-di(tert-amylperoxy)propane; 3,6,6,9,9-pentamethyl-3-ethoxycarbonylmethyl-1,2,4,5-tetraoxacyclononane; n-butyl-4,4-bis(tert-butylperoxy)valerate; ethyl-3,3-di(tert-amylperoxy)butyrate; and mixtures thereof.

6. A composition according to any one of the preceding claims, characterised in that The organic peroxide (b) may be selected from compounds having the following formula (III) or (IV): [Chemistry 3] R6-OO-R6'(III) or R6'-OO-R6'(IV) in: -R6 represents a straight chain or branched chain, preferably a branched chain C3-C 10 Alkyl group, preferably C3-C6 alkyl group. -R'6 represents a straight chain or branched C2-C 12 alkyl: - is substituted by at least one aromatic ring, in particular at least one benzene ring, which is substituted by at least one side chain, preferably a linear or branched C2-C 10 , more preferably C2-C4 unsaturated hydrocarbon partial substitution, or - at least one side chain containing one or more ethylenic unsaturations, preferably a linear or branched C2-C 10 , more preferably C2-C4 unsaturated hydrocarbon partial substitution, Preferably, R'6 represents a straight or branched C2-C substituted by at least one aromatic ring, especially at least one benzene ring. 12 Alkyl, which is separated by at least one side chain containing one or more ethylenic unsaturations, preferably a linear or branched C2-C 10 , more preferably partially substituted with C2-C4 unsaturated hydrocarbons.

7. A composition according to any one of the preceding claims, characterised in that The organic peroxide (b) is 1-(2-tert-butylperoxyisopropyl)-3-isopropenylbenzene.

8. A composition according to any one of the preceding claims, characterised in that The at least one nitroxide radical is selected from 2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 2,2,5,5-tetramethylpyrrolidine-1-oxyl, bis(1-oxy-2,2,6,6-tetramethyl-piperidin-4-yl)sebacate, 1-piperidinyloxy-4,4'-(1,10-dioxo-1,10-decanediyl)bis(oxy)bis(2,2,6,6-tetramethyl-), 2,2,6,6-tetramethyl-1-4-hydroxypiperidin-1-oxymonophosphonate, 3-carboxy-2,2,5,5-tetramethylpyrrolidin-1-oxyl and mixtures thereof.

9. A composition according to any one of the preceding claims, characterised in that The composition further comprises at least one crosslinkable polymer, preferably chosen from thermoplastic polymers, elastomeric polymers and mixtures thereof, more preferably chosen from elastomeric polymers.

10. The composition according to claim 9, characterized in that The crosslinkable polymer is selected from low density linear polyethylene, low density polyethylene, high density polyethylene, chlorinated polyethylene, ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-octene copolymer, ethylene-butyl acrylate copolymer (EBA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EBA), silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene copolymer (NBR), styrene-butadiene copolymer (SBR), chloroprene rubber (CR), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene block copolymer (SBS), chlorosulfonated polyethylene, fluoroelastomer, copolymer of ethylene and methyl (meth)acrylate, and copolymer of ethylene and glycidyl methacrylate, and combinations thereof.

11. A method for making a composition comprising mixing: a) at least one organic peroxide (a) selected from dialkyl peroxides, peroxyketals and mixtures thereof, said peroxide (a) being as defined in any one of claims 1 to 5, b) at least one organic peroxide (b) comprising in its structure at least one unsaturated side chain, said organic peroxide (b) being different from said organic peroxide (a), said peroxide (b) being as defined in any one of claims 1, 2 and 6 to 8, c) a nitroxide radical as defined in any one of claims 1 to 8, The weight ratio between the organic peroxide (b) and the organic peroxide (a) is in the range of 0.003 to 0.04, preferably 0.005 to 0.03, more preferably 0.01 to 0.

025.

12. A method for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer as defined in claim 9 or 10, the method comprising: i) a step of subjecting the crosslinkable composition to crosslinking in the presence of a composition as defined in any one of claims 1 to 8.

13. Use of a composition as defined in any one of claims 1 to 8 for crosslinking at least one crosslinkable composition comprising at least one crosslinkable polymer as defined in claim 9 or 10.

14. Article, preferably a moulded article or an extruded article, obtainable by the process as defined in claim 12.

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