Organic peroxide for the crosslinking of polyolefins

Abstract

The present invention relates to the use of one or more organic peroxides of formula (I), particularly for the crosslinking of polyolefins, such as elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers, especially those intended for use in photovoltaic applications. The invention also relates to a crosslinkable composition comprising at least one polyolefin and at least one organic peroxide conforming to formula (I). The present invention likewise relates to a process for preparing a polyolefin-based material, preferably an encapsulating material, particularly for photovoltaic cells, comprising at least one crosslinking step of a crosslinkable composition as defined above.

Description

Title of the invention: Organic peroxide for the crosslinking of polyolefins

[0001] The present invention relates to the use of one or more organic peroxides, as defined below, in particular for the crosslinking of crosslinkable polymers, preferably polyolefins, more preferably elastomeric polyolefins (POE) and ethylene and vinyl acetate (EVA) copolymers, in particular intended for use in photovoltaic applications.

[0002] The invention also relates to a crosslinkable composition comprising at least one crosslinkable polymer and at least one organic peroxide as defined below.

[0003] The present invention also relates to a method for preparing a crosslinkable polymer-based material, preferably an encapsulating material, in particular for photovoltaic cells, comprising at least one crosslinking step of a crosslinkable composition as defined above.

[0004] The invention also relates to a crosslinkable polymer-based material that can be obtained by the process described above and a photovoltaic module comprising at least one such material.

[0005] Materials, preferably in the form of films, used for encapsulating photovoltaic cells are commonly designed from polyolefins, such as ethylene vinyl acetate (EVA) copolymers or elastomeric polyolefins (POE).

[0006] In order to acquire satisfactory thermomechanical properties for this application, in particular in terms of good adhesion properties with respect to the substrate of the module, resistance to creep and resistance to degradation in relation to weathering, it is important to proceed with the crosslinking of the polyolefins and to obtain a good crosslinking density.

[0007] Indeed, if the crosslinking density is too low, the resulting material is likely to exhibit, among other things, insufficient resistance to breakage and tearing.

[0008] The crosslinking agents typically used are organic peroxides such as dialkyl peroxides, peroxyesters, peroxyketals, peroxycarbonates, and mixtures thereof. As an example of monoperoxycarbonates, OO-tert-butyl-O-(2-ethylhexyl)monoperoxycarbonate (TBEC) is already known to be used for the crosslinking of polyolefins, in particular for the crosslinking of ethylene vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE).

[0009] During the manufacturing process of the photovoltaic module, the solar cells and their electrical conductors are thus arranged between two layers (or films) These materials are obtained from a polyolefin-based composition and one or more crosslinking agents. Such a manufacturing process involves a single step of laminating the various layers forming the photovoltaic module at a specific temperature for a given period, during which the polyolefin-based composition is crosslinked. The different layers of the module are thus compressed together, and the solar cells become embedded in a crosslinked polyolefin-based material.

[0010] However, the cross-linking of polyolefins with certain organic peroxides can cause yellowing, or even browning in some cases, of the material encapsulating the photovoltaic cells. Such a phenomenon can thus induce a modification of the transmittance of the incident light flux in the solar cells, which in the long run reduces their power.

[0011] Furthermore, the crosslinking of ethylene-vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE), conventionally carried out at present, often leads to materials with mechanical properties, particularly tensile strength and tear resistance, that are likely to decrease over time. Indeed, the crosslinking density can degrade over time under the effect of environmental factors.

[0012] Furthermore, under the effect of ambient temperature and / or humidity, the organic peroxide added to polyolefins, in particular elastomeric polyolefins (POE), to formulate the encapsulation film, can evaporate, thus leading to an insufficient degree of crosslinking of the material intended to encapsulate the photovoltaic cells.

[0013] Finally, some crosslinking agents also have the disadvantage of being synthesized from raw materials solely of fossil origin.

[0014] In view of the above, there is therefore a real need to propose a bio-based crosslinking agent, exhibiting good crosslinking properties for crosslinkable polymers, in particular by giving them a satisfactory crosslinking density, including one that is stable over time, while minimizing the risks of yellowing that may occur during the crosslinking of crosslinkable polymers.

[0015] In other words, one of the objectives of the present invention is to propose a bio-based agent that is at least as effective for crosslinking crosslinkable polymers as the crosslinking agents conventionally used at present.

[0016] The present invention therefore relates in particular to the use of at least one monoperoxycarbonate corresponding to the following formula (I):

[0017] [Chem.l]

[0018] Formula (I) wherein:

[0019] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12,

[0020] R2 represents a branched alkyl radical;

[0021] for the crosslinking of at least one crosslinkable polymer, preferably at least one polyolefin.

[0022] The monoperoxycarbonate(s) used according to the invention allows(s) for the effective crosslinking of crosslinkable polymers, preferably polyolefins, in particular polyolefins intended for use in the encapsulation of photovoltaic cells, ensuring them a good crosslinking density, in particular stable over time.

[0023] The monoperoxycarbonate(s) used according to the invention thus has the advantage of having a bio-based origin, of exhibiting good crosslinking properties of crosslinkable polymers, in particular polyolefins, and of reducing the risks of yellowing that may occur during their crosslinking.

[0024] The monoperoxycarbonate(s) used according to the invention have in particular a carbon content by weight predominantly of biological origin in relation to the total mass of carbon of the monoperoxycarbonate.

[0025] The monoperoxycarbonate(s) used according to the invention preferably have a carbon content of biological origin greater than at least 30% by weight, preferably at least 50% by weight, more preferably at least 55% by weight, better at least 60% by weight, relative to the total mass of carbon of the monoperoxycarbonate.

[0026] The monoperoxycarbonate(s) used according to the invention thus makes it possible to obtain polymer-based materials, preferably polyolefin-based, crosslinked materials having good mechanical properties.

[0027] Thus the use of at least one monoperoxycarbonate according to the invention is at least as effective for the crosslinking of polymers, in particular polyolefins, as the crosslinking agents conventionally used in the prior art while being more environmentally friendly and / or safer for the health of users.

[0028] In particular, the use of at least one monoperoxycarbonate according to the invention makes it possible to lead to less evaporation of organic peroxides than other crosslinking agents conventionally used in the prior art.

[0029] Another aspect of the present invention relates to one or more monoperoxycarbonate(s) corresponding to the following formula (II):

[0030] [Chem.2]

[0031] Formula (II) wherein:

[0032] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, preferably as defined below,

[0033] R2a represents a branched alkyl radical comprising a number of carbon atoms strictly greater than 4.

[0034] The invention also relates to a crosslinkable composition comprising at least one crosslinkable polymer, preferably at least one polyolefin, more preferably chosen from the group consisting of ethylene and vinyl acetate (EVA) copolymers, elastomeric polyolefins (POE) and their mixtures, and at least one monoperoxycarbonate corresponding to formula (I) or (II), as defined above.

[0035] The crosslinkable composition according to the invention makes it possible to produce a material, in particular an encapsulation or sealing material, preferably for photovoltaic cells, having thermomechanical properties suitable for the applications sought, with high production.

[0036] The crosslinkable composition according to the invention thus has the advantage of crosslinking during a manufacturing process of a photovoltaic module.

[0037] Similarly, another object of the present invention lies in a crosslinked polymer, preferably a crosslinked polyolefin, capable of being obtained by a crosslinking process using at least one monoperoxycarbonate corresponding to formula (I) or (II) as defined above.

[0038] Furthermore, the present invention relates to a crosslinking process for a composition comprising at least one crosslinkable polymer, comprising at least one crosslinking step of said polymer with at least one monoperoxycarbonate corresponding to formula (I) or (II) as defined above.

[0039] The process according to the invention makes it possible to obtain a high reaction rate, and therefore rapid crosslinking of the polymers, while maintaining a good crosslinking density. Thus, the materials, based on polymers crosslinked with at least one monoperoxycarbonate according to the invention, exhibit good mechanical properties.

[0040] Furthermore, the present invention also relates to a method for manufacturing a material comprising at least one crosslinking step of a crosslinkable composition as defined above.

[0041] The process according to the invention thus has the advantage of leading to a material having good thermomechanical properties and whose possible structural asperities are minimized.

[0042] Similarly, another object of the invention relates to the material comprising at least one crosslinked polymer, preferably crosslinked polyolefin, with at least one monoperoxycarbonate according to the invention.

[0043] The material obtained is preferably a solar cell encapsulation material.

[0044] The invention also relates to a photovoltaic module comprising such a material encapsulating solar cells.

[0045] The photovoltaic module exhibits improved properties thanks to the presence of the encapsulating material.

[0046] Other features and advantages of the invention will become clearer upon reading the description and examples that follow.

[0047] In what follows, and unless otherwise indicated, the bounds of a domain of values ​​are included in that domain.

[0048] The expression "at least one" is equivalent to the expression "one or more".

[0049] Use of at least one monoperoxycarbonate of formula (I)

[0050] The monoperoxycarbonate(s) used in accordance with the present invention correspond(s) to the following formula (I):

[0051] [Chem.l]

[0052] Formula (I) wherein:

[0053] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, preferably less than or equal to 10,

[0054] R2 represents a branched alkyl radical.

[0055] Preferably, in formula (I), R2 represents a branched alkyl radical in C3-Ci0, more preferably in C4-C8.

[0056] Preferably, in formula (I), R2 represents a branched alkyl radical at C4, C5 or C8, more preferably at C4.

[0057] Preferably, in formula (I), Ri represents a linear alkyl radical in CrCi2, more preferably in C2-Ci2, even more preferably in C4-Ci2, better in C6-C12.

[0058] Preferably, in formula (I), Ri represents a linear alkyl radical in Ci-Cio, more preferably in C2-CiO, even more preferably in C4-CiO, better in C6-CiO.

[0059] According to a preferred embodiment, in formula (I): • Ri represents a linear alkyl radical in C1-C12, more preferentially in C2-C12, even more preferentially in C4-C12, and even better in C6-C12, • R2 represents a branched alkyl radical in C4-Ci0, more preferentially in C4-C8.

[0060] According to a preferred embodiment, in formula (I): • Ri represents a linear alkyl radical in C1-C1O, more preferentially in C2-C1O, even more preferentially in C4-C1O, and even better in C6-C1O. • R2 represents a branched alkyl radical in C3-Ci0, more preferentially in C4-C8.

[0061] According to a preferred embodiment, in formula (I), Ri represents a linear alkyl radical in C4-Ci0, preferably in C6-Ci0, and R2 represents a branched alkyl radical in C3-C10, preferably in C4-C8.

[0062] Preferably, the monoperoxycarbonate(s) of formula (I) correspond(s) to the following formula (II):

[0063] [Chem.2] —O—O—Ç—O—R1 $ (H)

[0064] Formula (II) wherein:

[0065] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, as defined previously in formula (I) and

[0066] R2A represents a branched alkyl radical comprising a number of carbon atoms strictly greater than 4, preferably a branched alkyl radical in C5-C10, more preferably in C5-C8, better in C5 or C8.

[0067] Preferably, the monoperoxycarbonate(s) of formula (I) correspond(s) to the following formula (I'):

[0068] [Chem.3] O RZ 'Z '"0' \-x ■■■••■■"" Z in

[0069] Formula (!') in which:

[0070] R2 represents a branched alkyl radical as defined previously in formula (I).

[0071] Preferably, in the formula (!'), R2 represents a branched alkyl radical in C3-Ci0, more preferably in C4-C8, better in C4, C5 or C8, even better in C8.

[0072] Preferably, the monoperoxycarbonate(s) is / are chosen from the group consisting of:

[0073] [Chem.4] O XAA V "o" x -

[0074] OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC),

[0075] [Chem.5]

[0076] OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC),

[0077] [Chem.6]

[0078] OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC),

[0079] and mixtures thereof.

[0080] More preferably, the monoperoxycarbonate is OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC).

[0081] As previously stated, an object of the present invention relates to the use of at least one monoperoxycarbonate corresponding to formula (I), as defined previously, for the crosslinking of at least one crosslinkable polymer, preferably a polyolefin.

[0082] For the purposes of this invention, "polyolefin" means a polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc.

[0083] By "derived from", for the purposes of the present invention, the motifs of the main chain of the polymer and / or the adjacent chains (or pendant chains) of the polymer result from the polymerization or copolymerization of the monomers from which the polymer is manufactured.

[0084] Preferably, the polyolefin is chosen from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures.

[0085] Preferably, the polyolefin is chosen from the group consisting of elastomeric polyolefins (POE) or ethylene and vinyl acetate (EVA) copolymers.

[0086] For the purposes of this invention, "polyolefin elastomer" (POE) means an elastomer polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc.

[0087] For the purposes of this invention, "elastomer" means a polymer capable of undergoing uniaxial deformation at room temperature, preferably of at least 20% for a period of fifteen minutes, and of returning to its original shape, preferably with a residual deformation of less than 5% compared to its original shape, when this stress is no longer exerted.

[0088] The thermoplastic and / or elastomer polymers used according to the invention can be defined as natural or synthetic polymers that have thermoplastic and / or elastomeric properties and that can be crosslinked (cured) by the action of a crosslinking agent. In Rubber World, "Elastomer Crosslinking with Diperoxyketals," October 1983, pages 26-32, and in Rubber and Plastic News, "Organic Peroxides for Rubber Crosslinking," September 29, 1980, pages 46-50, the crosslinking action and crosslinkable polymers are described. Polyolefins suitable for the present invention are described in Modern Plastics Encyclopedia 89, pages 63-67, 74-75.

[0089] By way of example of polymers and / or elastomers, one may mention linear low-density polyethylene, low-density polyethylene (LDPE), high-density polyethylene (HDPE), chlorinated polyethylene, ethylene-propylene-diene terpolymers (EPDM), ethylene-vinyl acetate (EVA) copolymers, polyolefin elastomers, for example ethylene-propylene copolymers, ethylene-butene copolymers, silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene copolymers (NBR), styrene-butadiene copolymers (SBR), chlorosulfonated polyethylene or fluoroelastomers, ethylene-(meth)methyl acrylate copolymers, ethylene-glycidyl methacrylate copolymers and their mixtures.

[0090] According to one embodiment, the crosslinkable polymers are devoid of chlorine functional groups and carboxylic acid functional groups, of preference devoid of halogen functional groups and carboxylic acid functional groups.

[0091] Polyethylene may include homopolymers and copolymers such as linear low-density polyethylene, low-density polyethylene (LDPE), high-density polyethylene (HDPE), chlorinated polyethylene, ethylene-propylene-diene terpolymers (EPDM).

[0092] Preferably, the crosslinkable polymers are chosen from the group consisting of polyethylene, ethylene-vinyl acetate (EVA) copolymers, ethylene-butene copolymers, polyethylene, rubber, ethylene-propylene-diene terpolymers (EPDM) and their mixtures, more preferably chosen from the group consisting of ethylene-vinyl acetate (EVA) copolymers.

[0093] Ethylene and vinyl acetate (EVA) copolymers suitable for the present invention are, for example, the ethylene-vinyl acetate copolymers sold respectively under the trade names "Evatane® 24-03, 24-03 SA, 28-03, 28-05, 28-25, 28-40, 28-150, 28-420, 28-800, 33-15, 33-25, 33-45 PV, 33-400, 34-50 PV", by SK Chemicals.

[0094] The vinyl acetate content of the ethylene-vinyl acetate copolymers suitable for the present invention can vary: for example, these copolymers can be low vinyl acetate or high vinyl acetate.

[0095] Preferably, the invention relates to the use of at least one monoperoxycarbonate of formula (!') or (II), as defined above, for the crosslinking of at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and mixtures thereof, in particular elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers.

[0096] Preferably, the invention relates to the use of at least one monoperoxycarbonate selected from the group consisting of:

[0097] OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC),

[0098] OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC),

[0099] OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC),

[0100] preferably OO-tert-butyl-O-octyhnonoperoxycarbonate (TBOC) for the crosslinking of at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures. Monoperoxycarbonate of formula (II)

[0101] As previously stated, an object of the present invention relates to one or more monoperoxycarbonate(s) corresponding to the following formula (II):

[0102] [Chem.2] R—O^O—C---O---R, $ (II)

[0103] Formula (II) wherein:

[0104] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, as defined previously in formula (I) and

[0105] R2a represents a branched alkyl radical comprising a number of carbon atoms strictly greater than 4.

[0106] Preferably, R2A represents a branched alkyl radical in C5-C10, more preferably in C5-C8, better in C5 or C8.

[0107] Preferably, Ri represents a linear alkyl radical in Ci-Cio, plus preferentially in C2-Ci0, even more preferentially in C4-Ci0, better in C6-Ci0

[0108] Preferably, the monoperoxycarbonate(s) of formula (II) correspond(s) to the following formula (II'):

[0109] [Chem.7]

[0110] Formula (II') wherein:

[0111] R2A represents a branched alkyl radical as defined previously in formula (II), preferably a C5-C10 branched alkyl radical, more preferably a C5-C8 branched alkyl radical, better a C5 or C8 branched alkyl radical.

[0112] Preferably, the monoperoxycarbonate(s) of formula (II) or (IF) is or are chosen from the group consisting of OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC) and their mixtures.

[0113] More preferably, the monoperoxycarbonate(s) of formula (II) or (II') is or are chosen from the group consisting of OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC) or OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC).

[0114] Preferably, the present invention relates to the use of at least one monoperoxycarbonate corresponding to formula (II) and selected from the group consisting of:

[0115] OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC),

[0116] OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC),

[0117] and their mixtures;

[0118] for the crosslinking of at least one polyolefin, preferably chosen from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures.

[0119] Even more preferably, the invention relates to the use of at least one monoperoxycarbonate corresponding to formula (II) and selected from the group consisting of OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC) or OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), for the crosslinking of at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures. Monoperoxycarbonate synthesis process

[0120] The monoperoxycarbonate of formula (I) according to the invention can be prepared by reacting at least alkyl chloroformate of formula RrO-(C=O)Cl, with Ri as defined above, and at least one organic hydroperoxide of formula R2-O-OH with R2 as defined above.

[0121] In other words, the process for the synthesis of a monoperoxycarbonate of formula (II) comprises at least one reaction step (a2) of alkyl chloroformate, as defined above, and at least one organic hydroperoxide of formula R2-O-OH with R2 as defined above.

[0122] The reaction step (a2) can take place at a temperature ranging from -10 to 30°C.

[0123] The reaction step (a2) can take place in the presence of a nonpolar solvent.

[0124] Alkyl chloroformate can be prepared by reacting at least one alcohol Rr OH, with Ri as defined above, with COC12, preferably at a temperature ranging from 5 to 30°C, in the presence or absence of a solvent, such as benzene.

[0125] Alkyl chloroformate can alternatively be prepared by reacting at least one alcohol of formula RrOH, with Ri as defined above, with phosgene, preferably at a temperature ranging from -15°C to 0°C. Crosslinkable composition

[0126] As previously stated, the crosslinkable composition comprises: - at least one crosslinkable polymer, preferably at least one polyolefin, as defined above and - at least one monoperoxycarbonate corresponding to formula (I), as defined above, preferably corresponding to formula (I'), (II) or (II').

[0127] The monoperoxycarbonate corresponding to formula (I), (I'), (II) or (II') may be present in a content ranging from 0.1 to 5 by weight, preferably from 0.2 to 1.5, more preferably from 0.3 to 1, more preferably from 0.4 to 1, more preferably from 0.4 to 0.7 by weight, relative to 100 parts by weight of the crosslinkable polymer as defined previously.

[0128] Advantageously, the crosslinkable composition comprises: - at least one monoperoxycarbonate chosen from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), - at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene vinyl acetate (EVA) copolymers and their mixtures, in particular elastomeric polyolefins (POE) or ethylene vinyl acetate (EVA) copolymers.

[0129] The crosslinkable composition may further comprise at least one additional organic peroxide other than monoperoxycarbonate of formula (I) as described above.

[0130] Preferably, the composition further comprises at least one additional monoperoxycarbonate different from the monoperoxycarbonate of formula (I) as described above.

[0131] Preferably, the additional monoperoxycarbonate is also different from OO-tert-butyl-O-(2-ethylhexyl)monoperoxycarbonate (TBEC).

[0132] The monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), preferably corresponds to the following formula (III):

[0133] [Chem. 8] (III)

[0134] Formula (III) wherein:

[0135] R'i represents a branched alkyl radical comprising a number of carbon atoms less than or equal to 6 and

[0136] R'2 represents an alkyl radical, preferably a branched alkyl radical.

[0137] Preferably, in formula (III), R\ represents a branched alkyl radical comprising a number of carbon atoms less than or equal to 6 and R'2 represents a branched alkyl radical.

[0138] Preferably, in formula (III), R\ and R'2 are different.

[0139] According to formula (III), R'i is preferably a C2-C5 branched alkyl radical. Preferably, R'1 is a C3(isopropyl) branched alkyl radical.

[0140] According to formula (III), R'2 is preferably an alkyl radical in CrC 10, preferably in C4-C8. Preferably, R'2 is an alkyl radical in C4 or C5, in particular branched in C5 (tert-amyl) or C6 (tert-hexyl).

[0141] Advantageously, R' i is a C2-C5 branched alkyl radical, and R'2 is a CrCio alkyl radical, in particular a C4-C8 alkyl radical.

[0142] Preferably, the monoperoxycarbonate of formula (III) is chosen from the group consisting of tert-amyl peroxy isopropyl monocarbonate (TAIC), tert-butyl peroxy isopropyl monocarbonate (TBIC), tert-octyl peroxy isopropyl monocarbonate (TOIC) and tert-hexyl peroxy isopropyl monocarbonate (THIC).

[0143] More preferably, the monoperoxycarbonate corresponding to formula (III) is tert-amyl peroxy isopropyl monocarbonate (TAIC).

[0144] Monoperoxycarbonate, different from monoperoxycarbonate of formula (I), may be present in a content ranging from 0.1 to less than 5 parts by weight, preferably from 0.2 to 1.5, more preferably from 0.3 to 1, more preferably from 0.4 to 1, more preferably from 0.4 to 0.7 and even more preferably about 0.5 parts by weight, per 100 parts by weight of the crosslinkable polymer as defined above.

[0145] According to a preferred embodiment, the total amount of organic peroxide in the crosslinkable composition is less than 3 parts by weight per 100 parts by weight of the polyolefin, more preferably less than 1.5 parts by weight per 100 parts by weight of the crosslinkable polymer, preferably of the polyolefin.

[0146] Preferably, the monoperoxycarbonate of formula (I) is present in a content less than or equal to 3 parts by weight per 100 parts by weight, preferably in a content ranging from 0.1 to less than 3 parts by weight of the crosslinkable polymer as defined above.

[0147] According to a preferred embodiment, the crosslinkable composition comprises at least one polyolefin, as defined above, at least one monoperoxycarbonate of formula (I'), (II) or (II'), and at least one monoperoxycarbonate of formula (III).

[0148] Preferably, the crosslinkable composition comprises: - at least one polyolefin, as defined above, - at least one monoperoxycarbonate chosen from the group consisting of the OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octyhnonoperoxyca rbonate (TOOC), - at least one monoperoxycarbonate selected from the group consisting of tert-amyl peroxyisopropyl monocarbonate (TAIC), tert-butyl peroxyisopropyl monocarbonate (TBIC), tert-octyl peroxyisopropyl monocarbonate (TOIC) and tert-hexyl peroxy isopropyl monocarbonate) (THIC).

[0149] More preferably, the crosslinkable composition comprises at least one polyolefin, as defined above, OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), and tert-amyl peroxyisopropyl monocarbonate (TAIC).

[0150] The crosslinkable composition may also include at least one co-agent, which is not an organic peroxide.

[0151] Advantageously, said co-agent comprises at least one carbamate, maleimide, acrylate, methacrylate, or allyl functional group. Allyl carboxylates may be used, which may be selected from the group consisting of allyl, diallyl, and triallyl types.

[0152] Said co-agent may be selected from the group consisting of divinylbenzene, diisopropenylbenzene, alpha-methylstyrene, alpha-methylstyrene dimer, ethylene glycol dimethacrylate, phenylene dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol 200 dimethacrylate, polyethylene glycol 400 dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate, 1,3-glycerol dimethacrylate, diurethane dimethacrylate, trimethylolpropane trimethacrylate, bisphenol A epoxy diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate, ethylene glycol diacrylate, diacrylate of diethylene glycol, triethylene glycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycol ethoxylate diacrylate,butanediol diacrylate, hexanediol diacrylate, aliphatic urethane diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, glycerol propoxylate triacrylate, aliphatic urethane triacrylate, trimethylolpropane triacrylate and dipentaerythritol pentaacrylate, triallyl cyanurate (TAC), triallyl isocyanurate, N,N'-m-phenylenedimaleimide, butadiene, chloroprene and isoprene.

[0153] More preferably, the co-agent is chosen from the group consisting of: triallyl cyanurate, triallyl isocyanurate, N,N'-m-phenylenedimide, triallyl trimellitate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, preferably is chosen from the group consisting of: triallyl cyanurate (TAC), triallyl isocyanurate, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane trimethacrylate (TMPTMA) and even more preferably is triallyl isocyanurate.

[0154] Said co-agent may be present from 0.05% to 30%, preferably from 0.1% to 10% by weight relative to the total weight of the composition.

[0155] The crosslinkable composition may further comprise one or more additives such as coupling agents, UV stabilizers, UV absorbers, fillers, plasticizers, flame retardants, antioxidants, colorants, organic or mineral pigments, and mixtures thereof. Examples of coupling agents are monoalkyl titanates, (vinyl)trichlorosilanes, and (vinyl)trikoxysilanes, particularly 3-methacryloxypropyltrimethoxysiloxane. They may represent from 0.01 to 5% by weight relative to the weight of the ethylene polymer.

[0156] UV stabilizers can be selected from masked amine optical stabilizers (HALS), while UV absorbers can be selected, for example, from benzophenones, triazines, and benzotriazoles. These compounds can represent from 0.01 to 3% by weight relative to the weight of ethylene polymer.

[0157] Inorganic fillers such as silicon dioxide, alumina, talc, calcium carbonate can be added to increase mechanical strength, although nanometric clays are preferred because of the transparency they confer.

[0158] Organic or mineral pigments may also be added to color the crosslinkable composition. Titanium dioxide, in particular, can be used to obtain a white color, which is especially useful when the composition is used to manufacture a film for the backing of photovoltaic panels.

[0159] Examples of plasticizers are paraffinic or aromatic mineral oils, phthalates, azelates, adipates and the like.

[0160] The antioxidants may be phenolic, phosphate, or sulfur antioxidants. Alternatively, quinolines such as 1,2-dihydro-2,2,4-trimethylquinoline may be used as an antioxidant.

[0161] According to a preferred embodiment, the crosslinkable composition of this invention does not comprise any aromatic peroxide such as dicumyl peroxide.

[0162] Process for preparing the crosslinkable composition

[0163] The present invention also relates to a method for preparing the crosslinkable composition as defined above, comprising at least one step of mixing at least one crosslinkable polymer, preferably at least one polyolefin, as described above, and at least one monoperoxycarbonate of formula (I) as described above, and optionally at least one monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), preferably corresponding to formula (III) as described above.

[0164] Advantageously, the mixing step can be implemented in conventional devices such as continuous mixers and mixer-extruders, preferably at a temperature below the degradation temperature of the monoperoxycarbonates of the invention. crosslinking process

[0165] Another aspect of the present invention lies in a crosslinking process of a composition comprising at least one crosslinkable polymer, preferably at least one polyolefin, as defined above, comprising at least one crosslinking step of said polymer with at least one monoperoxycarbonate corresponding to formula (I) as defined above, preferably at least one monoperoxycarbonate corresponding to formula (I'), (II) or (II').

[0166] The crosslinking step is preferably carried out at a temperature ranging from 130 to 180°C, more preferably ranging from 140 to 165°C.

[0167] Preferably, said crosslinking step is carried out for a period of 8 to 30 minutes, more preferably from 12 to 25 minutes. Crosslinked polymer

[0168] Furthermore, the present invention also relates to a polymer, preferably a polyolefin, as defined above, crosslinked with at least one monoperoxycarbonate of formula (I) as defined above, preferably at least one monoperoxycarbonate of formula (I'), (II) or (II').

[0169] In other words, the invention relates to a crosslinked polymer, preferably a crosslinked polyolefin, which can be obtained by a crosslinking process using at least one monoperoxycarbonate corresponding to formula (I), as defined above, preferably at least one monoperoxycarbonate of formula (I'), (II) or (II'), and possibly at least one monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), preferably corresponding to formula (III) as described above.

[0170] Said polyolefin is as defined above, in particular is chosen from the group consisting of ethylene vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE) and mixtures thereof, preferably ethylene vinyl acetate (EVA) copolymers or elastomeric polyolefins (POE).

[0171] Preferably, the crosslinking process is as defined above.

[0172] Method for manufacturing a material from the crosslinkable composition

[0173] The invention also relates to a method for manufacturing a material comprising (a) at least one crosslinking (or hardening) step of a crosslinkable composition as defined above.

[0174] The material is in particular selected from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible hoses (including pipes for automobile radiators, drinking water and underfloor heating, for example), roller coatings, rotary moldings, honeycomb articles, and shoe soles.

[0175] Advantageously, the material is a solar cell encapsulation material.

[0176] Preferably, the crosslinking (or hardening) step consists of a rolling step.

[0177] Preferably, the crosslinking step (a) is carried out at a temperature ranging from 130 to 180°C, more preferably ranging from 140 to 165°C.

[0178] Preferably, said crosslinking step (a) is carried out for a period of 8 to 30 minutes, more preferably from 12 to 25 minutes.

[0179] Preferably, said process includes a step preceding and / or concurrent (a') with the crosslinking step (a) selected from the group consisting of molding, extrusion, and injection of the composition as defined above. When the material is a solar cell encapsulation material, said step is preferably an extrusion step.

[0180] Step (a') can be conducted so as to obtain a sheet having a thickness of 50 to 2000 pm, preferably 100 to 1000 pm, for example.

[0181] Said step (a') can be carried out with a T-die extruder or alternatively a twin-screw extruder coupled to a twin-roll mill.

[0182] Preferably, step (a') is conducted at a temperature ranging from 80 to 150 °C, more preferably ranging from 90 to 120 °C.

[0183] Preferably, no crosslinking is obtained during step (a').

[0184] In a particular embodiment, steps (a') and (a) are carried out in one only one step. Manufacturing process for a photovoltaic module

[0185] According to one embodiment, the present invention relates to a method for manufacturing a photovoltaic module comprising:

[0186] (i) at least one rolling step of an assembly comprising successively: • a first transparent layer forming the front face of a photovoltaic module, • a layer obtained from the crosslinkable composition according to the invention, • a plurality of solar cells arranged side by side and electrically connected to each other, • a layer obtained from the crosslinkable composition according to the invention, • a second layer or a multilayer assembly forming the back face (or support) of the module

[0187] (ii) optionally, at least one step of pressing the laminated layers together during step (i).

[0188] The pressing step can be carried out using conventional techniques, under heating and / or vacuum, for example at a temperature of 130 to 180 °C, more preferably 140 to 165 °C under vacuum, for a curing time that can vary in the range of 8 to 30 minutes, for example from 8 to 25 minutes. The composition of the invention can be crosslinked during this pressing step or subsequently.

[0189] Preferably, the process comprises a single simultaneous pressing and hardening (or crosslinking) step. Polyolefin-based material

[0190] Similarly, another object of the invention relates to a material comprising at least one crosslinked polymer, preferably a crosslinked polyolefin, with at least one monoperoxycarbonate corresponding to formula (I) as defined above, preferably at least one monoperoxycarbonate of formula (T), (II) or (II'), in particular selected from the group consisting of OO-tert-butyl-O-octyhnonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), and mixtures thereof.

[0191] In other words, an object of the invention is a material comprising at least one crosslinked polymer, preferably a crosslinked polyolefin, capable of being obtained by a crosslinking process using at least one monoperoxycarbonate of formula (I) as defined above, preferably at least one monoperoxycarbonate of formula (I'), (II) or (II'), in particular selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), and mixtures thereof.

[0192] The material obtained is preferably chosen from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible hoses (including pipes for automobile radiators, drinking water and underfloor heating, for example), roller coatings, rotary moldings, honeycomb articles and shoe soles.

[0193] Advantageously, the material is an encapsulation material, and even more preferably a solar cell encapsulation material.

[0194] More advantageously, the encapsulation material is a transparent film disposed between the solar cells and the glass panel forming the front face of a photovoltaic module (upper glass panel), or a transparent or tinted film disposed between the glass panel forming the rear face of the module (lower glass panel) and the solar cells in the case of bi-glass processes.

[0195] Thus the material is preferentially used in a manufacturing process for a photovoltaic module, in particular in a bi-glass process.

[0196] More preferably, the material comprising a polyolefin, as defined above, is a film, in particular an ethylene polymer film, in particular of homogeneously linear and branched ethylene and alpha-olefin copolymers.

[0197] The material according to the invention exhibits improved crosslinking density and a marked reduction, or even the absence, of gridding problems. This allows for the production of films free from surface defects and with good resistivity. Photovoltaic module

[0198] The invention also relates to a photovoltaic module comprising at least one solar cell encapsulation material as described above.

[0199] In particular, the photovoltaic module according to the invention comprises at least: • a first transparent layer forming the front face of the photovoltaic module and designed to receive a luminous flux, • an encapsulating material, as described above, for a plurality of solar cells arranged side by side and electrically connected to each other, • a second layer or a multilayer assembly forming the back face (or support) of the photovoltaic module;

[0200] the material encapsulating the plurality of solar cells being located between the first layer and the second layer or the multilayer assembly.

[0201] The following examples serve to illustrate the invention without, however, being limiting in nature. EXAMPLES

[0202] L Example of alkyl chloroformate synthesis

[0203] Synthesis of n-octyl chloroformate (according to the process described in document CN112441923)

[0204] 325 parts by weight of n-octanol are introduced into a reactor and then cooled to a temperature of -15°C. Phosgene is then introduced while the temperature is gradually raised to around -5°C / -2°C. The mixture is then heated to a temperature of around 20°C-25°C and allowed to react for up to 2 hours.

[0205] Gaseous nitrogen is then introduced at a temperature of 15°C in order to remove excess phosgene and hydrochloric acid to obtain n-octyl chloroformate. 2. Examples of monoperoxycarbonate synthesis

[0206] Synthesis of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC)

[0207] 45.3g of a 30% wt. potassium hydroxide solution in water is loaded into a reactor. Then 28.4g of a 70% wt. tert-butyl hydroperoxide (TBHP) commercial solution in water is gradually poured in.

[0208] Next, 35g of n-octyl chloroformate is introduced while maintaining the reactor at 0°C. After the introduction of the chloroformate, the temperature of the reactor is raised to 5° / 10°C and the reaction is allowed to continue for 120 min.

[0209] After stopping the stirring and allowing the sediment to settle, the organic phase is recovered and washed with sodium hydroxide, then with water. After washing, 41.5 g of organic phase are recovered, containing 99% by weight of TBOC.

[0210] Synthesis of OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC)

[0211] The procedure is the same as in the example above but replacing the TBHP with a commercial solution of TAHP at 85% by weight in water.

[0212] 69g of a 30% wt. potassium hydroxide solution in water is loaded into the reactor. Then 40.1g of an 85% wt. TAHP solution in water is gradually added.

[0213] Next, 53.5g of n-octyl chloroformate is introduced while maintaining the reactor at 0°C. After the introduction of the chloroformate, the temperature of the reactor is raised to 5° / 10°C and the reaction is allowed to continue for 120 minutes.

[0214] After decantation and washing, 67.7g of an organic solution containing TAOC is obtained.

[0215] Synthesis of OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC)

[0216] 73.7 g of 30% potassium hydroxide are charged into water. Then 52.3 g of 92% TOHP are introduced. Then 32.8 g of n-heptane are added.

[0217] The reactor temperature is reduced to 0°C and n-octyl chloroformate 57.6 g is added gradually.

[0218] After the introduction of chloroformate, the temperature is raised to 10°C and the reaction is allowed to continue for 120 minutes. After decantation and washing, the n-heptane solvent is removed by evaporation under vacuum.

[0219] 85.5 g of product containing TOOC is obtained. 3. Ingredients used

[0220] In the following examples, the following ingredients were used:

[0221] TBOC: OO-tert-butyl-O-octyhnonoperoxycarbonate (prepared in accordance with the preceding section),

[0222] Luperox® TBEC: OO-tert-butyl-(2-ethylhexyl) monoperoxycarbonate (sold by Arkema)

[0223] TAIC: crosslinking co-agent (sold by Sigma Aldrich)

[0224] Evatane® 28-25: Ethylene-vinyl acetate (EVA) copolymer with 28% by weight of vinyl acetate and having a melt flow index (MFI) of 25 g / 10 minutes, measured at 190°C, according to ASTM 1238.

[0225] POE Engage® PV 8669: Ethylene / l-octene copolymer (POE) having a melt flow index (MFI) of 14 g / 10 minutes, measured at 190°C, according to ASTM D 1238 (sold by Dow Chemicals).

[0226] KH570: 3-methacryloxy-propyltrimethoxysiloxane (sold by Sigma) Aldrich) 4. Composition Formulations

[0227] 4.1 Tested compositions

[0228] The compositions (A1) and (A2) according to the invention and the comparative compositions (B1) and (B2) were prepared from the ingredients indicated in Table 1 below.

[0229] In Table 1, the quantities of the ingredients are indicated in parts per hundred parts of the polyolefin used (phr).

[0230] [Tables 1] Al Bl A2 B2 POE 100 100 - - EVA - - 100 100 TBOC 0.6 0.6 - TBEC - 0.6 - 0.6 TAIC 0.5 0.5 0.5 0.5 KH570 0.3 0.3 0.3 0.3

[0231] 4.2 Protocol

[0232] The polyolefin (POE or EVA) is introduced into a mixer (Rheomix 600 from ThermoScientific equipped with two Banbury type rotors) in operation (50 revolutions / minute temperature at 40°C) and plasticized for approximately 4 minutes.

[0233] Monoperoxycarbonate and additives are then added and mixing continues for 6 minutes. The final internal temperature of the mixer is between 50°C and 65°C.

[0234] Each recovered mixture is then passed through a calender (Comerico Ercole equipped with two cylinders) to obtain a film with a thickness of approximately 2 millimeters.

[0235] This gives four films with a thickness of approximately 2 millimeters.

[0236] Comparative measurements using the RPA Rheometer at a temperature of 145°C, under the conditions indicated in Table 2, were carried out on each film following ASTM D5289 A.

[0237] [Tables2] Measuring instrument Units of measurement Rheometer RPA Temperature °C 145 Time minutes 30 Frequency Hz 1.667 Strain Degrees 1 Strain % 13.96

[0238] For the four films resulting from compositions (A1), (A2), (B1) and (B2), the following parameters are measured: - MH-ML (units in Dn.m) corresponding to the crosslinking density, - T90 (units in minutes) corresponding to the crosslinking time for reach 90% of the MH-ML value - TS1 (units in minutes) corresponding to the toasting time (premature crosslinking)

[0239] Measurements of these parameters were carried out 24 hours and 40 days after the films were made. 5. Results

[0240] 5.1 Results - 24 hours after obtaining the films

[0241] Measurements were taken three times for each parameter evaluated. Table 3 shows the average obtained over the three measurements for each of the parameters tested.

[0242] [Tables3] Al Bl A2 B2 MH-ML (dN.m) 3.9 4.0 7.6 7.4 T90 (min) 21.7 20.2 14.6 14.6 TS1 (min) 8.10 6.87 3.85 4.01

[0243] 5.2 Results - 40 days after obtaining the films

[0244] The films obtained in section 3 were left exposed in the open air under the same conditions.

[0245] Measurements were taken twice for each parameter evaluated. Table 4 shows the average obtained for the MH-ML parameter.

[0246] [Tables4] Al B1 A2 B2 MH-ML (dN.m) 3.57 3.12 7.48 7.25

[0247] With regard to the samples with crosslinked polyolefin elastomer (POE), it is observed that the crosslinking density decreases significantly with TBEC between the results obtained in Table 3 and Table 4.

[0248] In particular, it is observed that the crosslinking density decreases more with TBEC (composition A2 - film with crosslinked POE) than with TBOC (composition Al - crosslinked POE film).

[0249] With regard to the samples with crosslinked EVA, it is observed that the crosslinking density is better with TBOC than with TBEC both after 24 hours and after 40 days. 6. Yellowing Index (YI) Measurements

[0250] After the RPA rheometer measurements, the yellowing indices (YI) are measured using a spectrophotometer (X-Rite Model SP60) for POE films.

[0251] The results are grouped in the following table 5:

[0252] [Tables5] Al B1 YI 6.8 7.5

[0253] In the POE-based sample, it is observed that TBOC leads to less yellowing than TBEC. General Conclusion

[0254] It is observed that Luperox® TBOC is a crosslinking agent which limits yellowing and is as effective as Luperox® TBEC with a more stable crosslinking density while having a bio-based origin.

Claims

Demands

1. Use of at least one monoperoxycarbonate corresponding to the following formula (I): [Chem.1] R^—-0—0 —C —O—R „ II ° (I) Formula (I) in which: Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, R2 represents a branched alkyl radical; for the crosslinking of at least one crosslinkable polymer.

2. Use according to claim 1, characterized in that the crosslinkable polymer(s) is or are polyolefins, preferably selected from the group consisting of elastomeric polyolefins (POE), ethylene-vinyl acetate (EVA) copolymers and mixtures thereof, more preferably selected from the group consisting of elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers.

3. Use according to claim 1 or 2, characterized in that, in formula (I), R2 represents a C3-Cio branched alkyl radical, preferably a C4-C8 branched alkyl radical, more preferably a C4, C5 or C8 branched alkyl radical, better branched at C4.

4. Use according to any one of the preceding claims, characterized in that, in formula (I), Ri represents a linear alkyl radical in Ci-Cio, preferably a linear alkyl radical in C2-Cio, more preferably a linear alkyl radical in C4-Ci0, better a linear alkyl radical in C6-Ci0.

5. Use according to any one of the preceding claims, characterized in that the monoperoxycarbonate(s) correspond(s) to the following formula (!'): [Chem. 3] q 0 il rX xo (F) Formula (F) in which: R2 represents a branched alkyl radical, preferably a C3-Ci0 branched alkyl radical, more preferably a C4-C8 branched alkyl radical.

6. Use according to any one of the preceding claims, characterized in that the monoperoxycarbonate(s) is or are selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), preferably OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC).

7. Monoperoxycarbonate of the following formula (II): [Chem.2] O ........... O SArt, WWW « Zà $ •: 1 o (II) Formula (II) wherein: Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, as defined according to claim 1 or 4, R2a represents a branched alkyl radical comprising a number of carbon atoms strictly greater than 4, preferably a C5-C10 branched alkyl radical, preferably a C5-C8 branched alkyl radical, better a C5 or C8 branched alkyl radical.

8. Crosslinkable composition comprising: - at least one crosslinkable polymer, as defined according to claim 1 or 2, - at least one monoperoxycarbonate of formula (I), as defined according to any one of claims 1, 3 to 6, or of formula (II) as defined in claim 7.

9. Crosslinkable composition according to the preceding claim, characterized in that the monoperoxycarbonate of formula (I) is present in a content less than or equal to 3 parts by weight per 100 parts by weight, preferably in a content ranging from 0.1 to less than 3 parts by weight of the crosslinkable polymer as defined according to claim 1 or 2.

10. Crosslinkable composition according to claim 8 or 9, characterized in that it further comprises at least one additional organic peroxide different from the monoperoxycarbonate corresponding to formula (I), preferably a monoperoxycarbonate corresponding to the following formula (III): [Chem. 8] ​​R.':—g O—c—a—Ri II O (III) Formula (III) in which: R' i represents a branched alkyl radical comprising a number of carbon atoms less than or equal to 6, and R'2 represents an alkyl radical, preferably a branched alkyl radical.

11. Crosslinkable composition according to the preceding claim, characterized in that the additional organic peroxide is selected from the group consisting of tert-amyl peroxy isopropyl monocarbonate (TAIC), tert-butyl peroxy isopropyl monocarbonate (TBIC), tert-octyl peroxy isopropyl monocarbonate (TOIC) and tert-hexyl peroxy isopropyl monocarbonate (THIC).

12. A method for preparing a crosslinkable composition, as defined according to any one of claims 8 to 11, comprising at least one step of mixing at least one crosslinkable polymer, as defined according to claim 1 or 2, and at least one monoperoxycarbonate of formula (I) as defined according to any one of claims 1, 3 to 7, and optionally at least one organic peroxide as defined according to claim 10 or 11.

13. A method for manufacturing a material comprising (a) at least one crosslinking step of a crosslinkable composition such as defined according to any one of claims 8 to 11, the material is preferably chosen from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible tubing, roller coatings, rotary moldings, honeycomb articles, and shoe soles.

14. Material comprising at least one crosslinked polyolefin capable of being obtained by a crosslinking process employing at least one monoperoxycarbonate corresponding to formula (I), as defined according to any one of claims 1 and 3 to 6, or of formula (II) as defined in claim 7.