Polymeric composition and power cable comprising the polymeric composition

Abstract

The invention relates to a crosslinkable and crosslinked polymer composition with improved DC electrical properties and to a cable surrounded by at least one layer comprising the polymer composition.

Description

POLYMERIC COMPOSITION AND POWER CABLE COMPRISING THE POLYMERIC COMPOSITION. FIELD OF THE INVENTION The present invention relates to a polymeric composition suitable for a layer of a power cable, the use of the polymeric composition in a layer of a power cable, a power cable comprising the polymeric composition, and a process for producing the cable. BACKGROUND OF THE INVENTION Polyolefins produced in a high-pressure (HP) process are widely used in demanding polymer applications where the polymers must meet stringent mechanical and / or electrical requirements. For example, in power cable applications, particularly in medium voltage (MV) and especially high voltage (HV) and ultra-high voltage (EHV) cable applications, the electrical properties of the polymer composition are of significant importance. Furthermore, the requirements for electrical properties may differ in different cable applications, as is the case between alternating current (AC) and direct current (DC) cable applications. A typical power cable comprises a conductor surrounded by at least one inner semiconducting layer, one insulating layer, and one outer semiconducting layer, in that order. Space Cargo There is a fundamental difference between AC and DC with respect to the distribution of the electric field in the cable. The electric field in an AC cable is easily calculated, as it depends on a single material property, namely the relative permittivity (the dielectric constant) with a known temperature dependence. The electric field will not influence the dielectric constant. On the other hand, the electric field in a DC cable is much more complex and depends on the conduction, trapping, and accumulation of electric charges, the so-called space charges, within the insulation. The space charges within the insulation will distort the electric field and 2 / 62 can lead to points of very high electrical tension, possibly so high that a dielectric failure will follow. Ideally, there should be no space charges present, as this will make it possible to design the cable easily, since the distribution of the electric field in the insulation will be known. Typically, space charges are located near the electrodes; charges with the same polarity as the nearby electrode are called homocharges, while charges with opposite polarity are called heterocharges. Heterocharges will increase the electric field at this electrode, while homocharges will reduce the electric field. Electrical Conductivity DC electrical conductivity is an important material property, for example, for insulating materials for high-voltage direct current cables. First of all, the strong temperature and electric field dependence of this property will influence the electric field distribution through the accumulation of space charges, as described above. The second issue is the fact that heat will be generated within the insulation by the leakage of electric current circulating between the inner and outer semiconductor layers. This current leakage depends on the electric field and the electrical conductivity of the insulation. High conductivity of the insulating material can even lead to thermal runaway under high voltage / high temperature conditions. The conductivity must therefore be kept sufficiently low to avoid thermal runaway. Compressor Lubricants The high-pressure process is typically operated at high pressures up to 400 MPa (4000 bar). In known high-pressure reactor systems, the starting monomer or monomers need to be compressed (pressurized) before being introduced into the actual high-pressure polymerization reactor. Compressor lubricants are conventionally used in hypercompressors for cylinder lubrication to enable the mechanically demanding compression step of the starting monomers. It is well known that small quantities of the lubricant 3 / 62 normally leak through the reactor seals and mix with the monomers. As a result, the reactive mixture contains traces (up to hundreds of ppm) of compressor lubricant during the actual polymerization step of the monomers. These traces of compressor lubricant can 5 have an effect on the electrical properties of the final polymer. Examples of commercially available compressor lubricants include, for instance, poly(alkylene glycol) (PAG): R - [Cx RyHz-O]n- H, where R can be H or a linear or branched chain hydrocarbyl, ex, y, x, n are independent integers that can vary in a known way, and lubricants based on a mineral oil (a byproduct of petroleum distillation). Compressor lubricants based on mineral oils that meet the requirements established for milky white mineral oil in European Directive 2002 / 72 / EC, Annex V, for plastics used in contact with food are used, for example, to polymerize polymers especially for the food and pharmaceutical industries. Such mineral oil-based lubricants usually contain lubricity additives and may also contain other types of additives, such as antioxidants. Dow company document n2WO 2009 / 012041 describes that in a high-pressure polymerization process, in which compressors are used to pressurize the reactants, i.e., one or more monomers, the compressor lubricant can have an effect on the properties of the polymerized polymer. That document describes the use of a polyether polyol comprising one or no hydroxyl functionality as a compressor lubricant to prevent premature crosslinking, particularly high-pressure silane-modified polyolefins. Dow company document n2WO 2009 / 012092 describes a composition comprising (i) a silane-functionality-free polyolefin, and (ii) a hydrophobic PAG-type polyether polyol, both high-pressure, wherein at least 50% of its molecules comprise no more than a single hydroxyl functionality. Component (ii) appears to originate from a compressor lubricant. The composition is, among other things, for applications 4 / 62 in wires and cables and as stated reduces dielectric losses in medium and high voltage power cables, see page 2, paragraph 0006. In both applications it is stated that the hydrophilic groups (e.g., hydroxyl groups) present in the compressor lubricant can result in greater water uptake by the polymer, which, in turn, can increase electrical losses or, respectively, premature vulcanization, when the polymer is used as a cable layer material. The problems are solved by a specific type of PAG lubricant with a reduced amount of hydroxyl functionalities. There is a continuing need in the field of polymers to discover polymers that are suitable for demanding polymer applications, such as applications in wires and cables with high requirements and strict standards. Objectives of the Invention One of the objectives of the present invention is to provide an alternative polymeric composition with highly advantageous properties for use in a cable layer, preferably in a layer of an alternating current (AC) or direct current (DC) cable, more preferably in a layer of a DC cable. Furthermore, the invention provides an alternative polymeric composition for use in an insulating layer in a power cable, preferably a direct current (DC) power cable. The invention and other objects thereof will be described and defined in detail below. DESCRIPTION OF THE INVENTION The present invention provides a crosslinkable polymer composition comprising a polyolefin, wherein the polymer composition comprises a polyolefin and a crosslinking agent, and wherein the polymer composition has an electrical conductivity of 150 fS / m or less, measured at 30-70 °C and 30 kV / mm average electric field from a non-degassed plate sample 1 mm thick, consisting of a crosslinked polymer composition according to the conductivity method in 5 / 62 CC (1) as described under Methods of Determination. Preferably, the polymeric composition is a crosslinked polymeric composition which, before crosslinking (i.e., before it is crosslinked), comprises a polyolefin and a crosslinking agent, and which has an electrical conductivity of 150 fS / m or less, measured at 70 °C and 30 kV / mm mean electric field from a non-degassed plate sample with a thickness of 1 mm, consisting of a crosslinked polymeric composition according to the DC conductivity method (1), as described in the Determination Methods section. Crosslinkable means that the polymer composition can be crosslinked using one or more crosslinking agents before use in its final application. The crosslinkable polymer composition comprises the polyolefin and the crosslinking agent. Preferably, the polyolefin of the polymer composition is crosslinked. The crosslinking of the polymer composition is conducted at least with the crosslinking agent of the polymer composition of the invention. Furthermore, the crosslinked polymer composition, or respectively, the crosslinked polyolefin, is more preferably crosslinked by means of radical reaction with a free radical generating agent. The crosslinked polymer composition has a typical matrix, among other things, interpolymer crosslinks (bridges), as is known in this technical field.As is evident to those skilled in these techniques, the crosslinked polymer can be and is here defined with characteristics that are present in the polymeric or polyolefin composition before or after crosslinking, as stated or evidenced by the context. For example, the presence of the crosslinking agent in the polymeric composition or the type of composition property, such as melt flow index (MFR), density and / or degree of unsaturation of the polyolefinic component, are defined, unless otherwise indicated, before crosslinking, and the characteristics after crosslinking are, for example, the electrical conductivity or degree of crosslinking, measured from the crosslinked polymeric composition. The preferred crosslinking agent is a free radical generating agent, more preferably one or more peroxides. 6 / 62 Consequently, the present preferred crosslinked polymer composition is obtainable by crosslinking with peroxide, as defined above or below. The terms obtainable by crosslinking, crosslinked with, and crosslinked polymer composition are used interchangeably herein and mean that the crosslinking step provides another technical feature to the polymer composition, as will be explained below. The polymeric composition of the invention is described below considering the preferred embodiment of the cross-linked polymeric composition, which is also referred to herein interchangeably as a polymer composition or polymeric composition. The unexpectedly low electrical conductivity contributed by the polymeric composition is very advantageous for power cables, preferably for direct current (DC) power cables. The invention is particularly advantageous for direct current (DC) power cables. The polymer composition is preferably produced in a high-pressure (HP) process. As is well known, the high-pressure reactor system typically comprises a compression zone for (a) compressing one or more starting monomers in one or more compressors, also known as hypercompressors, a polymerization zone for (b) polymerizing the monomer(s) in one or more polymerization reactors, and a recovery zone for (c) separating unreacted products in one or more separators and recovering the separated polymer. Furthermore, the recovery zone of the high-pressure (HP) reactor system typically comprises a mixing and pelletizing section, such as a pelletizing extruder (after the separator(s)), to recover the separated polymer in pellet form. The process is described in more detail below. It has now been surprisingly discovered that, when in a high-pressure (HP) reactor system for compressing the starting monomer(s), a compressor lubricant comprising a mineral oil is used in compressors for cylinder lubrication, then the resulting polyolefin has highly advantageous electrical properties such as 7 / 62 Reduced electrical conductivity contributes to the excellent electrical properties of the cable. This is unexpected, as mineral oils are conventionally used to produce polymers for the medical and food industries, where health aspects are a concern, not reduced conductivity as required for wire and cable applications. In this descriptive report, the term compressor lubricant refers to a lubricant used in compressors, specifically in high-performance compressors, for cylinder lubrication. The term reduced or low electrical conductivity, as used interchangeably here, means that the value obtained by the direct current conductivity method is low, that is, reduced. Preferably, the polymeric composition comprises a polyolefin and a crosslinking agent, preferably peroxide, and the polyolefin is obtainable by a high-pressure process comprising (a) compressing one or more monomers under pressure in a compressor, using a compressor lubricant for lubrication, (b) polymerizing a monomer optionally together with one or more comonomers in a polymerization zone, (c) separating the polyolefin obtained from the unreacted products and recovering the separated polyolefin in a recovery zone, wherein in step (a) the compressor lubricant comprises a mineral oil. The resulting polymeric composition has the aforementioned advantageous reduced electrical conductivity. The expressions obtainable by the process or produced by the process are used interchangeably here and mean the category product by process, that is, that the product has the technical characteristic that is due to the preparation process. More preferably, the polymer composition has an electrical conductivity of 150 fS / m or less, when measured at 70°C and 30 kV / mm mean electric field from a non-degassed plate sample with a thickness of 1 mm, consisting of a crosslinked polymer composition according to the DC conductivity method (1), co 8 / 62 mo described in the Determination Methods section; and wherein the polyolefin of the polymer composition is obtainable by a high-pressure process comprising (a) compressing one or more monomers under pressure in a compressor, using a compressor lubricant for lubrication, (b) polymerizing a monomer optionally together with one or more comonomers in a polymerization zone, (c) separating the polyolefin obtained from the unreacted products and recovering the separated polyolefin in a recovery zone, wherein in step (a) the compressor lubricant comprises a mineral oil. The low electrical conductivity of the polymer composition is very advantageous for, among other things, use in AC and DC power cables, preferably in direct current (DC) power cables, more preferably in low voltage (LV), medium voltage (MV), high voltage (HV) or ultra-high voltage (EHV) direct current (DC) cables, more preferably in direct current (DC) power cables operating at any voltage, preferably in DC power cables for voltages higher than 36 kV, such as HV or EHV. The invention further relates to a cross-linked power cable, preferably a cross-linked power cable for direct current (DC), comprising a conductor surrounded by one or more layers, wherein at least one of said layers comprises a cross-linked polymeric composition of the invention comprising a cross-linked polyolefin using a cross-linking agent, preferably peroxide. More preferably, the invention relates to a cross-linked power cable, preferably a cross-linked power cable for direct current (DC), more preferably a cross-linked power cable for high voltage (HV) or ultra-high voltage (EHV) DC, comprising a conductor surrounded by at least one inner semiconducting layer, an insulating layer and another outer semiconducting layer, in that order, wherein at least one layer, preferably the insulating layer, comprises a cross-linked polymeric composition of the invention comprising a peroxide-crosslinked polyolefin. 9 / 62 refers to crosslinked polyolefin cable with a crosslinking agent / peroxide, meaning that the polymer composition prior to crosslinking contains polyolefin and a crosslinking agent, preferably peroxide. It becomes evident to those versed in these techniques that the cable may optionally comprise one or more other layers comprising one or more shielding meshes, one or more sheathing layers, or one or more other protective layers, layers which are conventionally used in the field of wires and cables. The preferred subgroups, properties, and embodiments listed below for the polymer composition before or after crosslinking apply equally and independently to the polymer composition itself, as well as to the crosslinkable cable and the crosslinked cable, as defined above or below. In a preferred embodiment, the polymer composition has an electrical conductivity of 140 fS / m or less, preferably 130 fS / m or less, preferably 120 fS / m or less, preferably 100 fS / m or less, preferably between 0.01 and 90 fS / m, more preferably between 0.05 and 90 fS / m, more preferably between 0.1 and 80 fS / m, more preferably between 0.5 and 75 fS / m, when measured at 70 °C and 30 kV / mm mean electric field from a non-degassed plate sample 1 mm thick, consisting of a crosslinked polymer composition according to the DC conductivity method (1), as described in the Determination Methods section.In this embodiment, the polymer composition also preferably has an electrical conductivity of 140 fS / m or less, preferably 130 fS / m or less, preferably 60 fS / m or less, preferably between 0.01 and 50 fS / m, more preferably between 0.05 and 40 fS / m, more preferably between 0.1 and 30 fS / m, when measured at 70 °C and 30 kV / mm mean electric field from a degassed plate sample 1 mm thick, consisting of a crosslinked polymer composition according to the DC conductivity method (1), as described in the Determination Methods section. The electrical conductivity of the polymer composition is surprisingly low even without removing the volatile byproducts after processing. 10 / 62 crosslinking, that is, without degassing. Consequently, if desired, the degassing step during cable production can be shortened. Furthermore, preferably, the polymer composition has an electrical conductivity of 0.27 fS / m or less, preferably 0.25 f / Sm or less, more preferably between 0.001 and 0.23 fS / m, when measured at 20 °C and 40 kV / mm mean electric field from a degassed plate sample with a thickness of 0.5 mm, consisting of a crosslinked polymer composition according to the DC conductivity method (2), as described in the Determination Methods section. The crosslinking agent is preferably used in an amount less than 10% by weight, more preferably in an amount between 0.2 and 8% by weight, even more preferably in an amount of 0.2 to 3% by weight, relative to the total weight of the composition to be crosslinked. More preferably, the crosslinking agent is a peroxide, and prior to crosslinking, the polymer composition preferably comprises the peroxide in an amount of at least 35 mmol-0.00 / kg of the polymer composition. The unit mmol -OO- / kg of polymer composition in this case means the content (mmol) of peroxide functional groups per kilogram of polymer composition, measured from the polymer composition before crosslinking. For example, 35 mmol -OO- / kg of polymer composition corresponds to 0.95% by weight of the well-known dicumyl peroxide, based on the total amount (100% by weight) of the polymer composition. Even more preferably, the polymer composition prior to crosslinking comprises peroxide in an amount of 36 mmol -OO- / kg of polymer composition or more, preferably between 37 and 90 mmol -OO- / kg of polymer composition, more preferably 37 to 75 mmol -OO- / kg of polymer composition. For example, the concentration range between 37 and 90 mmol of OO- / kg of polymer composition corresponds to 1.0 to 2.4% by weight of dicumyl peroxide (based on the polymer composition) conventionally used to crosslink power cables. The peroxide content depends on the level 11 / 62 of crosslinking is desired. Furthermore, the polyolefin can be unsaturated, in which case the peroxide content may depend on the degree of unsaturation. In a preferred embodiment, the polymer composition is crosslinked using peroxide of at least 35 mmol of -OO- / kg of polymer composition, and has a gel content of at least 30% by weight, preferably peroxide of 36 to 50 mmol of -OO- / kg of polymer composition, and has a gel content of at least 40% by weight, preferably at least 50% by weight, preferably at least 60% by weight, more preferably at least 65% by weight, when measured according to ASTM D 276501, method B, using decalin extraction. Consequently, the electrical properties and degree of polymerization are measured from a polymer composition after crosslinking it using the crosslinking agent present in the composition. The amount of crosslinking agent may vary. Preferably, in these test methods, peroxide is used and the amount of peroxide is at least 35 mmol -OO- / kg of polymer composition, as defined above or in the claims. The preparation of the respective sample of the crosslinked polymer composition is described below in the Determination Methods section. Peroxide is the preferred crosslinking agent. Non-limiting examples include organic peroxides such as di-t-amyl peroxide, 2,5-di(t-butyl-peroxy)-2,5-dimethyl-3-hexyne, 2,5-di(t-butyl-peroxy)-2,5-dimethyl-hexane, t-butyl-cumyl peroxide, di(t-butyl) peroxide, dicumyl peroxide, butyl-4,4-bis(t-butyl) peroxy-valerate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butyl peroxybenzoate, dibenzoyl peroxide, bis(t-butylperoxy-isopropyl)benzene, 2,5-dimethyl-2,5-di(benzoyl-peroxy)hexane, 1,1-di(t-butyl-peroxy)cyclohexane, 1,1-di(t-amyl-peroxy)cyclohexane, or any mixtures thereof. Preferably, the peroxide is selected from 2,5-di(t-butylperoxy)-2,5-dimethylhexane, di(t-butyl-peroxy-isopropyl)benzene, dicumyl peroxide, t-butylcumyl peroxide, di(t-butyl) peroxide, or mixtures thereof. More preferably, the peroxide is dicumyl peroxide. In addition to the crosslinking agent or agents, the polymer composition with advantageous electrical properties may comprise other component(s), such as other polymeric components and / or one or more additives. As additional additives, the polymer composition may contain antioxidants, stabilizers, water-free retarding additives, processing aids, vulcanization retarders, metal deactivators, crosslinking enhancers, flame retardants, acid or ion scavengers, inorganic fillers, voltage stabilizers, or any mixtures thereof. In a preferred embodiment, the polymer composition comprises one or more antioxidants and optionally one or more vulvanization retarders (SR). Examples of antioxidants include, but are not limited to: sterically hindered or semi-hindered phenols, aromatic amines, sterically hindered aliphatic amines, organic phosphites or phosphomites, thiocompounds, and mixtures thereof. Examples of thiocompounds include, for example... 1. Phenolic antioxidants containing sulfur, preferably selected from among thiobisphenols, most preferably 4,4'-thiobis(2-t-butyl-5-methylphenol) (CAS number: 96-69-5), 2,2'-thiobis(6-t-butyl-4-methylphenol), 4,4'-thiobis(220-methyl-6-t-butylphenol), thiodiethylene-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, or 4,6-bis(octylthiomethyl)-o-cresol (CAS: 110553-27-0) or derivatives thereof; or any mixtures thereof, 2. Other thiocompounds such as distearyl thiodipropionate or similar compounds with various carbon chain lengths; or mixtures thereof, 3. or any mixtures of 1) and 2). Group 1) above represents the preferred antioxidants. In this preferred embodiment, the amount of an antioxidant is preferably between 0.005 and 2.5% by weight, based on the weight of the polymer composition. The antioxidants are added, preferably, in an amount of 0.005 to 2.0 by weight, more preferably 0.01 to 1.5% by weight, more preferably 0.03 to 0.8% by weight, even more preferably 13 / 62 0.04 to 0.8% by weight, based on the weight of the polymer composition. In another preferred embodiment, the polymer composition comprises at least one or more antioxidants and one or more vulcanization retarders. Vulcanization retarders (SRs) are a well-known type of additive in this technical field and can, among other things, prevent premature crosslinking. It is also known that vulcanization retarders (SRs) can also contribute to the level of unsaturation of the polymer composition. Examples of vulcanization retarders include allylic compounds such as dimers of alpha-methyl-alkenyl aromatic monomers, preferably 2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituted diphenyl ethylenes, quinone derivatives, hydroquinone derivatives, monofunctional vinyl esters and ethers, monocyclic hydrocarbons with at least two or more double bonds, or mixtures thereof. Preferably, the amount of a vulcanization retarder is within a range of 0.005 to 2.0% by weight, more preferably within a range of 0.005 to 1.5% by weight, based on the weight of the polymer composition.Other preferred ranges are, for example, between 0.01 and 0.8% by weight, 0.03 to 0.75% by weight, 0.03 to 0.70% by weight, or 0.04 to 0.60% by weight, based on the weight of the polymer composition. The preferred vulcanization retarder (SR) of the polymer composition is 2,4-diphenyl-4-methyl-1-pentene (CAS number 6362-80-7). The invention also relates to a process for producing a cross-linked and cross-linked power cable, preferably a cross-linked and cross-linked direct current (DC) power cable, as defined above or below, using the polymer composition of the invention. The other preferred subgroups of the above properties, other properties, and variants and embodiments as defined above or below for the polymer composition or its components apply similarly to the method for reducing electrical conductivity, to the power cord, preferably to the DC power cord, of the invention. 14 / 62 Polyolefin component The following preferred embodiments, properties, and subgroups pertaining to the polyolefin component, suitable for the polymer composition, are generalizable and, as such, may be used in any order or combination to further define the preferred embodiments of the polymer composition. Furthermore, it is evident that the description provided applies to the polyolefin before it is cross-linked. The term polyolefin means a homopolymer of olefin and also a copolymer of an olefin with one or more comonomers. As is generally known, the term comonomer refers to copolymerizable comonomeric units. The polyolefin can be any polyolefin, such as a conventional polyolefin, that is suitable as a polymer in a layer, preferably an insulating layer, of an electrical cable, preferably a power cable. Polyolefin can be, for example, a commercially available polymer or it can be prepared according to or analogously to the known polymerization process described in the chemical literature. More preferably, the polyolefin is a polyethylene (PE) produced in a high-pressure process, more preferably a low-density polyethylene (LDPE) produced in a high-pressure process. The meaning of the LDPE polymer is well known and documented in the literature. Although the term LDPE is an abbreviation for low-density polyethylene, the term should be understood as not limiting the density range, but covering polyethylenes obtained under high pressure (HP) similar to LDPE with low, medium and higher densities. The term LDPE describes and distinguishes only the nature of HP polyethylene with typical characteristics, such as different branching configuration, compared to a PE produced in the presence of an olefin polymerization catalyst. LDPE and the aforementioned polyolefin refer to a low-density ethylene homopolymer (hereinafter referred to as homopolymeric LDPE) or a low-density ethylene copolymer with one or more comonomies. 15 / 62 ros (hereinafter referred to as copolymer LDPE). One or more comonomers of the copolymer LDPE are preferably selected from polar comonomers, nonpolar comonomers, or a mixture of polar and nonpolar comonomers, as defined above or below. Furthermore, said homopolymer LDPE or copolymer LDPE in the quality of said polyolefin may optionally be unsaturated. As polar comonomers for the LDPE copolymer, such as said polyolefin, comonomers containing hydroxyl groups, alkoxy groups, carbonyl groups, carboxyl groups, ether groups, or ester groups, or a mixture thereof, may be used. More preferably, comonomers containing carboxyl and / or ester groups are used as polar comonomers. Even more preferably, the polar comonomers of the LDPE copolymer are selected from the acrylate, methacrylate, or acetate groups, or any mixture thereof. If present in said LDPE copolymer, the polar comonomers are preferably selected from the alkyl acrylate, alkyl methacrylate, or vinyl acetate group, or a mixture thereof. More preferably, said polar comonomers are selected from among CrCe alkyl acrylates, C1-C6 alkyl methacrylates or vinyl acetate.Even more preferably, said polar copolymer LDPE is a copolymer of ethylene with C1-C4 alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate, or vinyl acetate, or any mixture thereof. As nonpolar comonomers for the LDPE copolymer such as the said polyolefin, comonomers other than the polar comonomers defined above may be used. Preferably, the nonpolar comonomers are different from comonomers containing hydroxyl groups, alkoxy groups, carbonyl groups, carboxyl groups, ether groups or ester groups. A preferred group of nonpolar comonomers preferably comprises monounsaturated comonomers (= one double bond), preferably olefins, preferably alpha-olefins, more preferably C3 to C10 alpha-olefins, such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, styrene, 1-octene, 1-nonene; polyunsaturated comonomers (= 16 / 62 more than a double bond); comonomers containing a silane group; or any mixtures thereof. Polyunsaturated comonomers are further described below with respect to unsaturated LDPE copolymers. If the LDPE polymer is a copolymer, it preferably comprises 0.001 to 50% by weight, more preferably 0.05 to 40% by weight, even more preferably less than 35% by weight, even more preferably less than 30% by weight, most preferably less than 25% by weight, of one or more comonomers. The polymer composition, preferably its polyolefin component, more preferably the LDPE polymer, may optionally be unsaturated, that is, the polymer composition, preferably the polyolefin, preferably the LDPE polymer, may comprise carbon-carbon double bonds. The term unsaturated, as used herein, means that the polymer composition, preferably the polyolefin, contains carbon-carbon double bonds per 1,000 carbon atoms in a total amount of at least 0.4 / 1,000 carbon atoms. As is well known, unsaturation can be imparted to the polymer composition, among other things, by means of polyolefin, a compound or compounds of low molecular weight average (Mw), such as crosslinking enhancers or vulcanization retarding additives, or any combination thereof. The total number of double bonds in this case means the double bonds determined from known sources and deliberately added to contribute to the unsaturation. If two or more of the aforementioned double bond sources are chosen to provide the unsaturation, then the total number of double bonds in the composition means the sum of the double bonds present at the double bond sources. It is evident that a characteristic model compound for calibration is used for each chosen source in order to allow quantitative determination by Fourier transform infrared spectroscopy (FTIR). Any measurements of double bonds are conducted before 17 / 62 of the reticulation. If the polymer composition is unsaturated prior to crosslinking, then preferably the unsaturation originates from at least one unsaturated polyolefin component. More preferably, the unsaturated polyolefin is an unsaturated polyethylene, more preferably an unsaturated LDPE polymer, even more preferably an unsaturated homopolymeric LDPE or an unsaturated LDPE copolymer. When polyunsaturated comonomers are present in the LDPE polymer as said unsaturated polyolefin, then the LDPE polymer is an unsaturated LDPE copolymer. In a preferred embodiment, the term total carbon-carbon double bond quantity is defined from the unsaturated polyolefin, and refers, unless otherwise specified, to the combined quantity of double bonds originating from vinyl groups, vinylidene groups, and trans-vinylene groups, if present. Naturally, the polyolefin does not necessarily contain all three types of double bonds mentioned above. However, any of the three types, when present, is calculated in relation to the total carbon-carbon double bond quantity. The quantity of each type of double bond is measured as indicated in the Determination Methods section. If a homopolymeric LDPE is unsaturated, then the unsaturation can be provided, for example, by a chain transfer agent (CTA), such as propylene, and / or by the polymerization conditions. If a copolymeric LDPE is unsaturated, then the unsaturation can be provided by one or more of the following means: by a chain transfer agent (CTA), by one or more polyunsaturated comonomers, or by polymerization conditions. It is well known that the selected polymerization conditions, such as peak temperatures and pressure, can influence the level of unsaturation. In the case of an unsaturated LDPE copolymer, it is preferably an unsaturated ethylene LDPE copolymer with at least one polyunsaturated comonomer, and optionally with other comonomers, such as polar comonomers that 18 / 62 are preferably selected from acrylate or acetate comonomers. More preferably, an unsaturated LDPE copolymer is an unsaturated LDPE copolymer of ethylene with at least one polyunsaturated comonomer. Suitable polyunsaturated comonomers for unsaturated polyolefin preferably consist of a linear carbon chain with at least 8 carbon atoms and at least 4 carbons between non-conjugated double bonds, of which at least one is terminal; more preferably, said polyunsaturated comonomer is a diene, preferably a diene comprising at least eight carbon atoms, the first double bond being terminal and the second carbon-carbon double bond being non-conjugated to the first. Preferred dienes are selected from non-conjugated C8 to C14 dienes or mixtures thereof, more preferably selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or mixtures thereof. Even more preferably, the diene is selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any mixture thereof, however, without limitation to the dienes above. It is well known that, for example, propylene can be used as a comonomer or as a chain transfer agent (CTA), or both, whereby it can contribute to the total amount of C-C double bonds, preferably to the total amount of vinyl groups. In this case, when a compound that can also act as a comonomer, such as propylene, is used as a CTA to provide double bonds, then the said copolymerizable comonomer is not calculated for the comonomer content. If the polyolefin, more preferably the LDPE polymer, is unsaturated, then it preferably has a total number of carbon-carbon double bonds, originating from vinyl groups, vinylidene groups, and trans-vinylene groups, if present, of more than 0.5 / 1,000 carbon atoms. The upper limit on the number of carbon-carbon double bonds present in the polyolefin is not limited and may preferably be... 19 / 62 less than 5.0 / 1000 carbon atoms, preferably less than 3.0 / 1000 carbon atoms. In some embodiments, when, for example, a higher level of crosslinking of the final crosslinked insulating layer is desired, the total quantity of carbon-carbon double bonds originating from vinyl groups, vinylidene groups and trans-vinylene groups, if present, in the unsaturated LDPE, is preferably higher than 0.50 / 1,000 carbon atoms, preferably higher than 0.60 / 1,000 carbon atoms. If desired, the higher content of double bonds combined with the presence of a crosslinking agent, preferably peroxide, gives the polymer composition an advantageous balance between electrical and mechanical properties, preferably combined with good resistance to heat and deformation. Consequently, the polyolefin is preferably unsaturated and contains at least 15 vinyl groups, and the total amount of vinyl groups is preferably higher than 0.05 / 1,000 carbon atoms, even more preferably higher than 0.08 / 1,000 carbon atoms, and most preferably higher than 0.11 / 1,000 carbon atoms. Preferably, the total amount of vinyl groups is less than 4.0 / 1,000 carbon atoms. More preferably, the polyolefin, before crosslinking, contains vinyl groups in a total amount of more than 0.20 / 1,000 carbon atoms, even more preferably more than 0.30 / 1,000 carbon atoms, and most preferably more than 0.40 / 1,000 carbon atoms.In certain demanding applications, preferably in power cables, more preferably in DC power cables, at least one layer, preferably the insulating layer, comprises an LDPE polymer, preferably an LDPE copolymer, containing vinyl groups in a total amount of more than 0.50 / 1,000 carbon atoms. The preferred polyolefin for use in the polymer composition is a saturated homopolymer LDPE or a saturated copolymer LDPE of ethylene with one or more comonomers; or an unsaturated LDPE polymer, which is selected from an unsaturated homopolymer LDPE or a copolymer LDPE. 20 / 62 unsaturated ethylene limeric polymer with one or more comonomers, even more preferably an unsaturated homopolymeric LDPE or an unsaturated copolymer LDPE of ethylene with one or more comonomers, which is preferably at least one polyunsaturated comonomer, preferably a diene as defined above, and optionally with one or more comonomers, and has the total amount of carbon-carbon double bonds, which originate from vinyl groups, vinylidene groups and trans-vinylene groups, if present, as defined above, preferably has the total amount of vinyl groups as defined above. Said unsaturated LDPE polymer is highly usable for an insulating layer of a power cable, preferably a DC power cable, of the invention. Typically, and preferably, in wire and cable applications, the density of the polyolefin, preferably the LDPE polymer, is higher than 860 kg / m3. Preferably, the density of the polyolefin, preferably the LDPE polymer, the ethylene homopolymer or copolymer is not higher than 960 kg / m3, and preferably is between 900 and 945 kg / m3. The MFR2 (2.16 kg, 190 °C) of the polyolefin, preferably the LDPE polymer, is preferably between 0.01 and 50 g / 10min, more preferably between 0.1 and 20 g / 10min, and most preferably between 0.2 and 10 g / 10min. Compressor Lubricant The compressor lubricant, used in the polymerization process to produce the preferred polyolefin of the polymer composition, comprises mineral oil, which is a known petroleum product. Mineral oils have a well-known meaning and are used, among other things, for lubrication in commercial lubricants. The terms compressor lubricant comprising a mineral oil and mineral oil-based compressor lubricants are used interchangeably herein. Mineral oil can be either synthetic mineral oil, which is produced synthetically, or mineral oil obtainable from crude oil refining processes. Typically, mineral oil, also known as petroleum. Liquid 21 / 62 is a byproduct of petroleum distillation to produce gasoline and other petroleum-based products from crude oil. The mineral oil of the compressor lubricant of the invention is preferably a paraffinic oil. Such paraffinic oil is derived from petroleum-based hydrocarbon feedstocks. Mineral oil is preferably the base oil of the compressor lubricant. The compressor lubricant may comprise other components, such as lubricity additives, viscosity modifiers, antioxidants, other additives, or any mixture thereof, as is well known in these techniques. More preferably, the compressor lubricant comprises a mineral oil that is conventionally used as a compressor lubricant for producing plastics, for example, LDPE, for the food or medical industry; more preferably, the compressor lubricant comprises a mineral oil that is a milky white oil. Even more preferably, the compressor lubricant comprises milky white oil like the mineral oil and is suitable for the production of polymers for the food or medical industry. Milky white oil has a well-known significance. Furthermore, such a milky white oil-based lubricant for compressors is well-known and available on the market. Even more preferably, the milky white oil meets the requirements for a milky white oil for food or medicine. As is known, mineral oil, preferably the milky white mineral oil of the preferred compressor lubricant, contains paraffinic hydrocarbons. Even more preferably, the compressor lubricant meets one or more of the following criteria: - In a preferred embodiment, the mineral oil, preferably milky white mineral oil, of the compressor lubricant has a viscosity of at least 8.5 x 10-6 m2 / s at 100 °C; - In a second preferred embodiment, the mineral oil, preferably milky white mineral oil, of the compressor lubricant contains 5% in 22 / 62 by weight (% by weight) or less of hydrocarbons with fewer than 25 carbon atoms; - In a third preferred embodiment, the hydrocarbons of the mineral oil, preferably the milky white mineral oil, of the compressor lubricant have a weight-average molecular weight (Mw) of 480 or more. The terms hydrocarbon quantity, viscosity and Mw above are preferably in accordance with European Directive 2002 / 72 / EC of 6 August 2002. It is preferred that the compressor lubricant conforms to each of the three modalities 1-3 above. The most preferred compressor lubricant of the invention meets the requirements set out for milky white mineral oil in European Directive 2002 / 72 / EC of 6 August 2002, Annex V, for plastics used for food contact. This directive is published, for example, in L 220 / 18 EN Official Journal of the European Communities 15.8.2002. Consequently, the mineral oil, and most preferably a milky white mineral oil, meets the said European Directive 2002 / 72 / EC of 6 August 2002, Annex V. Furthermore, it is preferred that the compressor lubricant meets the said European Directive 2002 / 72 / EC of 6 August 2002. The compressor lubricant of the invention may be a commercially available compressor lubricant, produced by conventional means, and is preferably an industrial lubricant used in high-pressure polymerization processes to produce plastics for medical or food applications. Non-limiting examples of commercially available compressor lubricants are, for example, Exxcolub Series R, a compressor lubricant for the production of polyethylene used in contact with food, supplied, among others, by ExxonMobil, Shell Corena for producing polyethylene for pharmaceutical use and supplied by Shell, or CL-1000-SONO-EU, supplied by Sonneborn. The compressor lubricant preferably does not contain any components based on polyalkylene glycols. 23 / 62 It is preferred that any mineral oil present in the polymer composition of the invention originates from compressor lubricants used in process equipment during the polyolefin polymerization process. Consequently, it is preferred that no mineral oil be added to the polymer composition or to the polyolefin after its polymerization. Traces of mineral oil originating from the compressor lubricant and present, if any, in the produced polyolefin would typically correspond to a maximum quantity of up to 0.4% by weight based on the amount of polyolefin. The limit provided is the absolute maximum based on the calculation of the worst-case scenario in which all the lost compressor lubricant (average leakage) would contaminate the final polyolefin. This worst-case scenario has the unlikely and normal consequence that the resulting polyolefin will clearly contain a lower level of mineral oil. The compressor lubricant of the invention is used in a conventional manner and well known to those skilled in compressor lubrication techniques in the compression stage (a) of the invention. Process The high-pressure (HP) process is the preferred process for producing polyolefin from the polymer composition, preferably a low-density polyethylene (LDPE) polymer selected from homopolymeric LDPE or ethylene copolymer LDPE with one or more comonomers. The invention further provides a process for polymerizing a polyolefin in a high-pressure process comprising the steps of: (a) compressing one or more monomers under pressure in a compressor, wherein a compressor lubricant is used for lubrication, (b) polymerizing a monomer optionally together with one or more comonomers in one or more polymerization zones, (c) separating the polyolefin obtained from the unreacted products and recovering the separated polyolefin in a recovery zone, wherein in step (a) a compressor lubricant comprises a mineral oil including its preferred embodiments. 24 / 62 Consequently, the polyolefin of the invention is preferably produced at high pressure by free radical-initiated polymerization (referred to as high-pressure radical polymerization). The preferred polyolefin is homopolymeric LDPE or copolymeric LDPE of ethylene with one or more comonomers, as defined above. The LDPE polymer obtainable by the process of the invention preferably exhibits the advantageous electrical properties defined above or below. High-pressure (HP) polymerization and the adjustment of process conditions to further individualize the other properties of the polyolefin depending on the desired end application are well known and described in the literature, and can be easily used by those skilled in these techniques. Compression Step (a) of the Invention Process: The monomer, preferably ethylene, with one or more optional comonomers, is fed into one or more compressors in the compression zone to compress the monomer(s) to a desired polymerization pressure, and to allow the handling of large quantities of monomer(s) at a controlled temperature. Typical compressors, i.e., hypercompressors, for the process can be piston compressors or diaphragm compressors. The compression zone usually comprises one or more compressors, i.e., hypercompressors, which can operate in series or in parallel. The compressor lubricant of the invention is used for cylinder lubrication in at least one, preferably in all, hypercompressors present in the compression zone. The compression stage (a) usually comprises 2-7 compression stages, often with intermediate cooling zones. The temperature is typically low, usually in the range of less than 200 °C, preferably less than 100 °C.Any recycled monomer, preferably ethylene, and optional comonomers, can be added at feasible points depending on the pressure. Polymerization Step (b) of the Process: High-pressure polymerization is preferred and carried out in a polymerization zone comprising one or more polymerization reactors. 25 / 62 tion, preferably at least one tubular reactor or an autoclave reactor, preferably a tubular reactor. The polymerization reactor(s), preferably a tubular reactor, may comprise one or more reactor zones where different polymerization conditions may occur and / or may be adjusted, as is known in the high-pressure field. One or more reactor zones are arranged in a known manner with means for feeding the monomer and optional comonomers, as well as with means for adding initiators and / or other components, such as chain transfer agents (CTAs). Additionally, the polymerization zone may comprise a preheating section that precedes or is integrated into the polymerization reactor.In a preferred high-pressure process, the monomer, preferably ethylene, optionally along with one or more comonomers, is polymerized in a preferably tubular reactor, preferably in the presence of one or more chain transfer agents. Tubular Reactor: The reaction mixture is fed into the tubular reactor. The tubular reactor can be operated as a single-feed system (also known as front-feed), where the total monomer flow from the compression zone is fed into the inlet of the first reaction zone of the reactor. Alternatively, the tubular reactor can be a multi-feed system, where, for example, the monomer(s), optional comonomers, or other components (such as CTA(s)) from the compression zone, separately or in any combination, are split into two or more streams, and the split feeds are introduced into the tubular reactor to different reaction zones along the reactor. For example, 10-90% of the total amount of monomer is fed into the first reaction zone, and the other 90-10% of the remaining amount of monomer is optionally further split, with each split injected at different locations along the reactor.Furthermore, the primer feed can be split into two or more streams. Additionally, in a system with multiple feeds, the split streams of monomer (or comonomer) and / or other optional components, such as... 26 / 62 CTA, and, respectively, the split streams of initiators, may have components or concentrations that are the same or different from the components, or both. The system with a single feed for the monomer and optional comonomers is preferred in the tubular reactor for producing the polyolefin of the invention. The first part of the tubular reactor is for adjusting the temperature of the monomer feed, preferably ethylene, and optional comonomers; the usual temperature is below 200 °C, such as 100-200 °C. Then, the radical initiator is added. As a radical initiator, any compound or mixture thereof that decomposes into radicals at an elevated temperature can be used. Usable radical initiators, such as peroxides, are commercially available. The polymerization reaction is exothermic. There may be several injection points for the radical initiator, for example, 1-5 points, along the reactor, usually equipped with separate injection pumps.As already mentioned, the monomer, preferably ethylene, and optional comonomers, is also added upfront, and optionally the monomer feed(s) can be split for the addition of the monomer and / or optional comonomers at any time during the process, in any zone of the tubular reactor, and from one or more injection points, for example, 1-5 points, with or without separate compressors. Furthermore, one or more CTAs are preferably used in the polyolefin polymerization process. The preferred CTAs may be selected from one or more non-agnostic CTAs and one or more polar CTAs, or any mixture thereof. If the supporting CTA is present, it is preferably selected from: i) one or more compounds that do not contain a polar group selected from among nitrile (CN), sulfide, hydroxyl, alkoxy, aldehyde (HC=O), carbonyl, carboxyl, ether or ester groups, or mixtures thereof. The CTA support is preferably selected from one or more non-aromatic hydrocarbyls with 27 / 62 linear, branched or cyclic chain, optionally containing a heteroatom such as O, N, S, Si or P. More preferably, the supporting CTA is selected from one or more cyclic alpha-olefins with 5 to 12 carbons or one or more alpha-olefins with a linear or branched chain having 3 to 12 carbon atoms, more preferably from one or more alpha-olefins with a linear or branched chain having 3 to 6 carbon atoms. The preferred supporting CTA is propylene. The polar CTA, if present, is preferably selected from: i) one or more compounds comprising one or more polar groups selected from nitrile (CN), sulfide, hydroxyl, alkoxy, aldehyde (HC=O), carbonyl, carboxyl, ether or ester groups, or mixtures thereof; ii) one or more aromatic organic compounds, or iii) any mixture thereof. Preferably, any of these polar CTAs has up to 12 carbon atoms, for example, up to 10 carbon atoms, preferably up to 8 carbon atoms. A preferred option includes one or more straight-chain or branched-chain alkanes having up to 12 carbon atoms (for example, up to 8 carbon atoms) and having at least one nitrile (CN), sulfide, hydroxyl, alkoxy, aldehyde (HC=O), carbonyl, carboxyl, or ester group. More preferably, the polar CTA, if present, is selected from (i) one or more compounds containing one or more hydroxyl, alkoxy, HC=O, carbonyl, carboxyl and ester groups, or a mixture thereof, more preferably from one or more alcohol, aldehyde and / or ketone compounds. Preferred polar CTAs, if present, are straight-chain or branched-chain alcohols, aldehydes or ketones having up to 12 carbon atoms, preferably up to 8 carbon atoms, especially up to 6 carbon atoms, and most preferably isopropanol (IPA), methyl ethyl ketone (MEK) and / or propionaldehyde (PA). The quantity of the preferred CTA(s) is not limited and can be individualized by those skilled in these techniques within the limits of the invention depending on the desired final properties of the final polymer. Consequently, the preferred chain transfer agent(s) 28 / 62 components can be added to the polymer mixture at any injection point in the reactor. The addition of one or more CTAs can be carried out from one or more injection points at any time during polymerization. If the polymerization of the polyolefin is carried out in the presence of a mixture of CTAs, comprising one or more polar CTAs, as defined above, and one or more non-polar CTAs, as defined above, then the feed ratio in % by weight of polar CTA to non-polar CTA is preferably: for 99% by weight of polar CTA, and for 99% by weight of supporting CTA, based on the combined amount of polar CTA and supporting CTA within the reactor. The addition of optional monomer, comonomer(s) and CTA(s) may include, and typically does include, fresh and recycled feeds. The reactor is cooled continuously, for example, by water or steam. The highest temperature is called the peak temperature, and the temperature at which the reaction begins is called the initiation temperature. The appropriate temperatures are in the range up to 400 °C, preferably between 80 and 350 °C, and the pressure is from 70 MPa (700 bar), preferably 100 to 400 MPa (1,000 to 4,000 bar), more preferably between 100 and 350 MPa (1,000 and 3,500 bar). The pressure can be measured at least after the compression stage and / or after the tubular reactor. The temperature can be measured at various points during all stages. High temperature and high pressure generally increase the production volume. Using various temperature profiles selected by those skilled in these techniques will allow control of the polymer chain structure, i.e., long-chain and / or short-chain branching, density, degree of branching, comonomer distribution, melt flow index (MFR), viscosity, molecular weight distribution, etc. The reactor conventionally ends with a valve, a so-called production control valve. The valve regulates the reactor pressure and depressurizes the reactive mixture from the reaction pressure to the separation pressure. 29 / 62 Recovery Stage (c) of the Process: Separation: The pressure is typically reduced to approximately 10 to 45 MPa (100 to 450 bar) and the reactive mixture is fed to a separator vessel, where most of the unreacted products, often gaseous, are removed from the polymer stream. The unreacted products comprise, for example, monomer or the optional comonomer or comonomers, and most of the unreacted components are recovered. The polymer stream is optionally further separated at a lower pressure, typically less than 0.1 MPa (1 bar), in a second separator vessel, where further quantities of unreacted products are recovered. Typically, low molecular weight compounds, i.e., wax, are removed from the gas. The gas is usually cooled and cleaned before recycling. Recovery of Separated Polymer: After separation, the resulting polymer is typically in the form of a molten polymer that is normally mixed and pelletized in a pelletizing section, such as a pelletizing extruder, arranged in connection with the high-pressure (HP) reactor system. Optionally, additive(s), such as antioxidant(s), may be added to this mixer in a known manner to result in the polymer composition. Further details on the production of ethylene (co)polymers by high-pressure radical polymerization can be found, among other documents, in the Encyclopedia of Polymer Science and Engineering, Volume 6 (1986), pages 383-410, and Encyclopedia of Materials: Science and Technology, 2001 Elsevier Science Ltd.: Polyethylene: High-pressure, R.Klimesch, D.Littmann and F.-O. Mähling, pages 7181-7184. Regarding the polymer properties, for example, melt flow index (MFR), of the polymerized polymer, preferably LDPE polymer, the properties can be adjusted using, for example, a chain transfer agent during polymerization, or by adjusting the temperature. 30 / 62 or reaction pressure (which also has, to a certain degree, an influence on the level of unsaturation). When an ethylene-unsaturated LDPE copolymer is prepared, the content of CC double bonds can be adjusted by polymerizing the ethylene, for example, in the presence of one or more polyunsaturated comonomers, one or more chain transfer agents, process conditions, or any combination thereof, for example, using the desired feed ratio between the monomer, preferably ethylene, and the polyunsaturated comonomer and / or chain transfer agent, depending on the nature and quantity of CC double bonds desired for the LDPE copolymer. Among others, document n2WO 9308222 describes a high-pressure radical polymerization of ethylene with polyunsaturated monomers, such as α,ω-alkadienes, to increase the unsaturation of an ethylene copolymer.Unreacted double bonds thus generate, among other things, pendant vinyl groups in the polymer chain formed at the site where the polyunsaturated comonomer was incorporated by polymerization. As a result, the unsaturation can be uniformly distributed along the polymer chain in a random manner during copolymerization. Furthermore, for example, document n2WO 9635732 describes a radical polymerization of ethylene under high pressure and a certain type of polyunsaturated α,ω-divinyl-siloxanes. Additionally, as is known, propylene, for example, can be used as a chain transfer agent to produce said double bonds. Polymer Composition Prior to crosslinking, the polymer composition comprises at least one crosslinking agent, preferably at least one peroxide containing at least one -OO- linkage. Naturally, if two or more different peroxide products are used in the polymer composition, then the preferred amount (in mmol) of -OO- / kg of polymer composition, as defined above, below or in the claims, is the sum of the amounts of -OO- / kg of polymer composition of each peroxide product. The polymer composition of the invention typically comprises 31 / 62 at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 75% by weight, more preferably between 80 and 100% by weight, and most preferably between 85 and 100% by weight, of polyolefin based on the total weight of the polymer components present in the polymer composition. The preferred polymer composition consists of polyolefin as the sole polymer component. This statement means that the polymer composition does not contain other polymer components, but only polyolefin as the sole polymer component. However, it should be understood in this case that the polymer composition may comprise other components besides the polymer components, such as additives that may optionally be added to a mixture with a polymer formulation, i.e., so-called master mixture. The polymer composition preferably comprises additives conventionally used for applications in wires and cables, such as one or more antioxidants and optionally one or more vulcanization retarders, preferably at least one or more antioxidants. The quantities of additives used are conventional and well known to those skilled in these techniques, for example, as already described above in the Description of the Invention section. The polymer composition preferably consists of polyolefin, preferably polyethylene, more preferably homopolymeric or copolymeric LDPE of the invention, which may optionally be unsaturated, as the sole component of the polymer. The most preferred polyolefin in the polymer composition is an unsaturated homopolymeric or copolymeric LDPE. End Uses and End Applications of the Invention As mentioned above, the new polymer composition is highly useful in a wide range of applications in wires and cables, most preferably in one or more layers of a power cable. A power cable is defined as being capable of transmitting power while operating at any voltage, typically operating at voltages 32 / 62 higher than 1 kV. The voltage applied to the power cable can be alternating current (AC), direct current (DC), or momentary current (in pulses). The polymeric composition of the invention is very suitable for power cables, especially for power cables operating at voltages higher than 6 kV to 36 kV (medium voltage (MV) cables) and at voltages higher than 36 kV, known as high voltage (HV) cables and ultra-high voltage (EHV) cables, EHV cables which, as is well known, operate at very high voltages. The terms have well-known meanings and indicate the operational level of these cables. In the case of high voltage (HV) and ultra-high voltage (EHV) direct current (DC) power cables, the operating voltage is defined here as the electrical voltage between the grounding and the conductor of the high voltage cable.High-voltage direct current (HVDC) and ultra-high-voltage direct current (UHVDC) power cables can operate, for example, at voltages of 40 kV or higher, even at voltages of 50 kV or higher. Ultra-high-voltage (EHV) direct current power cables operate in very high voltage ranges, for example, as high as 800 kV, however, without being limited to them. The polymer composition with advantageous direct current conductivity properties is also highly suitable for direct current (DC) power cables operating at any voltage, preferably at voltages higher than 36 kV, such as high-voltage or ultra-high-voltage direct current power cables, as defined above. In addition to reduced electrical conductivity, the polymer composition also preferably has very good space-load properties, which are advantageous for power cables, especially DC power cables. The invention further provides for the use of the polyolefin of the invention, which is obtainable by the high-pressure process of the invention, to produce an insulating layer for a power cable, preferably a DC power cable. A cross-linked power cable, preferably a cross-linked direct current (DC) power cable, is provided, comprising a con 33 / 62 conductor surrounded by one or more layers, preferably at least one insulating layer, more preferably at least one inner semiconducting layer, an insulating layer and an outer semiconducting layer, in this order, wherein at least one of said layers, preferably the insulating layer, comprises a polymeric composition of the invention, comprising a crosslinkable polyolefin and a crosslinking agent, preferably a peroxide, which is preferably present in an amount of at least 35 mmol of -OO- / kg of the polymeric composition, preferably at least 36 mmol of -OO- / kg of the polymeric composition, 37 mmol of -OO- / kg of the polymeric composition or more, preferably between 37 and 90 mmol of -OO- / kg of the polymeric composition, more preferably 37 to 75 mmol of -OO- / kg of the polymeric composition.The insulating layer of the power cable, preferably of the direct current (DC) power cable, preferably comprises said crosslinkable unsaturated LDPE copolymer, as defined above. The term conductor in this descriptive report above and below means that the conductor comprises one or more wires. Furthermore, the cable may comprise one or more such conductors. Preferably, the conductor is an electrical conductor and comprises one or more metallic wires. The invention also provides a process for producing a power cable, preferably a cross-linked power cable, more preferably a cross-linked DC power cable, more preferably a cross-linked DC power cable for high voltage or ultra-high voltage, as defined above or in the claims, comprising a conductor surrounded by one or more layers, preferably at least one insulating layer, more preferably at least one inner semiconductor layer, an insulating layer and an outer semiconductor layer, in this order, wherein the process comprises the steps of applying one or more layers onto a conductor wherein at least one layer, preferably the insulating layer, comprises a cross-linked polymeric composition of the invention comprising a polyolefin and a cross-linking agent, preferably a peroxide, preferably in an amount of at least 34 / 62 in the 35 mmol of -OO- / kg of the polymer composition, preferably at least 36 mmol of -OO- / kg of the polymer composition, 37 mmol of -OO- / kg of the polymer composition or more, preferably between 37 and 90 mmol of -OO- / kg of the polymer composition, more preferably 37 to 75 mmol of -OO- / kg of the polymer composition. In the preferred embodiment of the power cable production process of the invention, a crosslinkable power cable is produced by (a) making available and mixing, preferably by melt mixing in an extruder, said crosslinkable polymer composition of the invention as defined above or below in the claims, (b) applying said melt mixture of the polymer composition obtained in step (a), preferably by (co)extrusion, onto a conductor to form one or more layers, preferably at least one insulating layer, and (c) optionally crosslinking at least the polymer composition in said at least one layer, preferably in the insulating layer. More preferably, a cross-linked DC power cable, preferably a cross-linked DC power cable for high voltage or ultra-high voltage, is produced, comprising a conductor surrounded by an inner semiconductor layer, an insulating layer, and an outer semiconductor layer, in that order, wherein the process comprises the steps of (a) - to provide and mix, preferably by melt mixing in an extruder, a first crosslinkable semiconductor composition comprising a polymer, a carbon black and optionally other components for the inner semiconductor layer, - to provide and mix, preferably by melt mixing in an extruder, a crosslinkable polymeric composition of the invention for the insulating layer, - to provide and mix, preferably by melt mixing in an extruder, a second semiconductor composition that is preferably crosslinkable and comprises a polymer, a carbon black and optionally other 35 / 62 components for the outer semiconductor layer, (b) apply onto a conductor, preferably by coextrusion, - a molten mixture of the first semiconductor composition obtained in step (a) to form the inner semiconductor layer, - a molten mixture of the polymeric composition of the invention obtained in step (a) to form the insulating layer, and - a deep mixture of the second semiconductor composition obtained in step (a) to form the outer semiconductor layer, and (c) optionally crosslinking under crosslinking conditions one or more between the polymeric composition of the insulating layer, the semiconductor composition of the inner semiconductor layer and the conductive composition of the outer semiconductor layer, of the cable obtained, preferably at least the polymeric composition of the insulating layer, more preferably the polymeric composition of the insulating layer and at least one, preferably both, between the semiconductor composition of the inner semiconductor layer and the semiconductor composition of the outer semiconductor layer. The polymer of the first and second semiconductor compositions is preferably selected independently from a polyolefin, for example, as described with respect to the polymeric composition of the invention. The carbon black can be any conventional carbon black used in the semiconductor layers of a power cable, preferably in the semiconductor layer of a direct current (DC) power cable. Examples of carbon blacks are conductive carbon blacks, such as the well-known furnace carbon black and acetylene carbon black. Furthermore, the first and second semiconductor compositions may be different or identical, preferably identical. The term melt mixing means mixing above the melting point of at least the major component or components of the resulting mixture and is typically conducted at a temperature at least 101 °C above the melting or softening point of the polymer component or components. The term coextrusion in this descriptive report means that, in 36 / 62 In the case of two or more layers, said layers may be extruded in separate stages, or at least two or all said layers may be co-extruded in the same extrusion stage, as is well known in these techniques. The term (co)extrusion here means that all or part of the layers are formed simultaneously using one or more extrusion heads. For example, a triple extrusion may be used to form three layers of the cable. As is well known, the polymeric composition of the invention and the optional and preferred compositions of the first and second semiconductor compositions can be produced before or during the cable production process. Furthermore, the polymeric composition of the invention and the optional and preferred compositions of the first and second semiconductor compositions can each independently comprise part or all of their components before being introduced into the melt mixing step (a) of the cable production process. Preferably, said part or all of the polymer composition, preferably at least the polyolefin, is in the form of powder, granules or pellets when fed into the cable production process. The pellets can be of any size and shape, and can be produced by any conventional pelletizing device, such as a pelletizing extruder. According to one embodiment, the polymer composition comprises said other optional components. In this embodiment, some or all of said other components may, for example, be added. 1) mixing the polyolefin in a molten state, which may be in the form obtained from a polymerization process, and then the resulting molten mixture is pelletized, and / or 2) mixing with polyolefin pellets, which pellets may already contain some of the said other components. In this option (2), some or all of the other components may be mixed by fusion together with the pellets and then the resulting molten mixture is pelletized; and / or some or all of the 37 / 62 other components can be impregnated into the solid pellets. In a second alternative embodiment, the polymer composition can be prepared in connection with the cable production line, for example, by feeding the polyolefin, preferably in the form of pellets which may optionally comprise some of the other components, and combined with all or the remainder of the other components in the mixing step (a) to produce a molten mixture for step (b) of the process of the invention. If the polyolefin pellets contain some of the other components, then the pellets can be prepared as described in the first embodiment above. The other components are preferably selected from at least one or more additives, preferably from free radical scavenging agents, more preferably from peroxides, optionally, and preferably from antioxidants and optionally from vulcanization retarders, as mentioned above. The mixing step (a) of the provided polymer composition and the preferred first and second semiconductor compositions is preferably carried out in the cable extruder. Step (a) may optionally comprise a separate mixing step, for example, in a mixer upstream of the cable extruder. Mixing in the separate upstream mixer may be carried out with or without external heating (heating with an external source) of the components. Any other components of the polymer composition or of the preferred first and second semiconductor compositions, if present and added during the cable production process, may be added at any stage and at any point in the cable extruder, or to the optional separate mixer preceding the cable extruder.Additives can be added simultaneously or separately as is, preferably in liquid form, or in a well-known master mix formulation, and at any stage during the mixing step (a). Preferably, the molten mixture of the polymer composition obtained in the melt mixing step (a) consists of the polyolefin of the invention. 38 / 62 as the sole component of the polymer. Optional and preferred additives may be added to the polymer composition as is or as a mixture with a polymer formulation, i.e., in the form of a so-called master mixture. More preferably, the mixture of the polymeric composition of the invention and the mixture of each of the first and second optional semiconductor compositions obtained in step (a) is a melt mixture produced at least in an extruder. In the preferred embodiment, the polymeric composition of the invention is fed into the cable production process in the form of prefabricated pellets. In a preferred embodiment of the cable production process, a crosslinkable power cable is produced, preferably a crosslinkable direct current (DC) power cable, more preferably a crosslinkable high voltage (HV) or ultra-high voltage (EHV) DC power cable, wherein the insulating layer comprises the polymeric composition of the invention comprising a crosslinkable polyolefin, preferably an unsaturated LDPE homopolymer or copolymer, and a crosslinking agent, preferably peroxide, in an amount provided above or below, and then the crosslinkable polyolefin in the insulating layer of the cable obtained is crosslinked in step (c) under crosslinking conditions.More preferably, in this embodiment, a cross-linked power cable is produced, preferably a cross-linked direct current (DC) power cable, more preferably a high-voltage (HV) or ultra-high-voltage (EHV) direct current power cable, comprising a conductor surrounded by an inner semiconductor layer comprising, preferably consisting of a first semiconductor composition, an insulating layer comprising, preferably consisting of a crosslinkable polymeric composition of the invention comprising a polyolefin and a crosslinking agent, preferably peroxide, as defined above, and optionally, and preferably, an outer semiconductor layer comprising, preferably consisting of a second semiconductor composition. 39 / 62 wherein the polymeric composition of the insulating layer is crosslinked under crosslinking conditions in step (c) in the presence of a crosslinking agent, preferably peroxide, preferably in an amount defined above or in the claims, and wherein the first semiconductor composition of the inner semiconductor layer, and optionally, and preferably, the second semiconductor composition of the outer semiconductor layer are crosslinked under crosslinking conditions in step (c) in the presence of one or more crosslinking agents, preferably in the presence of one or more free radical generating agents, which are preferably peroxides. The crosslinking agent or agents may already be present in the first and second optional semiconductor compositions before being introduced in the crosslinking step (c) or introduced during the crosslinking step (c). A peroxide is the preferred crosslinking agent for said first and second semiconductor compositions and is preferably included in the pellets of the semiconductor composition before the composition is used in the cable production process as described above. Crosslinking can be carried out at an increased temperature, which, as is well known, is chosen depending on the type of crosslinking agent. For example, temperatures above 150 °C are typical, although they are not limited to this. The invention further provides a cross-linked power cable, preferably a cross-linked direct current (DC) power cable, comprising a conductor surrounded by one or more layers, preferably at least one insulating layer, more preferably at least one inner semiconductor layer, an insulating layer and an outer semiconductor layer, in that order, wherein at least the insulating layer comprises the cross-linked polymeric composition or any of the preferred subgroups or embodiments thereof, as defined above or in the claims. More preferably, the inner semiconductor composition and the optional and preferred outer semiconductor composition are also cross-linked. Naturally, the polymeric composition of the invention, used in at least one layer of the cable, preferably in an insulating layer, 40 / 62 of the cable of the invention has, when cross-linked, the advantageous electrical properties defined above or in the claims. The use of the polymer composition, or any of its preferred subgroups or embodiments, as defined above or in the claims, in at least one of the layers, preferably at least in an insulating layer, of a cross-linked power cable, preferably a cross-linked direct current (DC) power cable, preferably a high-voltage (HV) or ultra-high-voltage (EHV) DC power cable, comprising a conductor surrounded by at least one layer, preferably at least one inner semiconducting layer, an insulating layer and an outer semiconducting layer, in this order, and optionally surrounded by one or more other layers, such as shielding braids, one or more sheathing layers, or one or more other protective layers, as is well known in these techniques. The thickness of the insulation layer of the power cable, preferably of the direct current (DC) power cable, more preferably the high voltage (HV) or ultra-high voltage (EHV) direct current (DC) power cable, is typically 2 mm or more, preferably at least 3 mm, preferably at least 3 to 100 mm, measured in the cross-section of the cable's insulation layer. The invention further provides for the use of the polymeric composition of the invention in an insulating layer of a cross-linked DC power cable, preferably a high-voltage (HV) or ultra-high-voltage (EHV) DC power cable, comprising a conductor surrounded by at least one layer, preferably at least one inner semiconductor layer, an insulating layer and an outer semiconductor layer, in that order, to reduce the DC electrical conductivity of said cable. Determination Methods Unless otherwise noted in the descriptive report or experimental section, the following methods were used to determine the properties. Wt%: % by weight 41 / 62 Melt Flow Index The melt flow index (MFR) is determined according to the ISO 1133 method and is indicated in g / 10 min. The MFR is an indication of the flowability, and therefore, an indication of the processability of the polymer. The higher the melt flow index, the lower the viscosity of the polymer. The MFR is determined at 190 °C for polyethylenes and can be determined at different loads, such as 2.16 kg (MFR2) or 21.6 kg (MFR21). Density Density was measured according to the ISO 1183-2 method. Sample preparation was performed according to the ISO 1872-2 Table 3 Q method (compression molding). Molecular weight Mz, Mw, Mn, and MWD were measured by Gel Permeation Chromatography (GPC) for low molecular weight polymers, as is known in this technical field. Comonomer Content a) Quantification of alpha-olefin content in linear low-density polyethylenes and low-density polyethylenes by NMR spectroscopy: The comonomer content was determined by quantitative 13C nuclear magnetic resonance (NMR) spectroscopy after basic designation (J. Randall, JMS - Rev. Macromol. Chem. Phys., C29(2&3), 201-317 (1989)). The experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task. Specifically, solution-state NMR spectroscopy was employed using a Bruker Avancelll 400 spectrometer. Homogeneous samples were prepared by dissolving approximately 0.200 g of polymer in 2.5 mL of deuterated tetrachloroethylene in 10 mm test tubes using a heating block and rotary tubular oven at 140 °C. Single-pulse, proton-dissociated NMR spectra with NOE (powergated) were recorded using the following acquisition parameters: a 90-degree tilt angle, 4 simulated scans, 42 / 62 4096 transients, an acquisition time of 1.6 s, a spectral amplitude of 20 kHz, a temperature of 125 °C, a two-level proton dissociation scheme, and an attenuation delay of 3.0 s. The resulting free induction decay (FID) was processed using the following parameters: zero-padding up to 32k data points and apodization using a Gaussian window function; automatic zero-order and first-order phase correction; and automatic baseline correction using a fifth-order polynomial restricted to the region of interest. The quantities were calculated using simple corrected ratios of the sign integrals of representative sites, based on well-known methods in these techniques. b) Polar comonomer content in low-density polyethylene (1) Polymers containing > 6% by weight of polar comonomer units The comonomer content (% by weight) was determined using a known method based on Fourier transform infrared spectroscopy (FTIR) calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. The determination of the polar comonomer content of ethylene / ethyl acrylate, ethylene / butyl acrylate, and ethylene / methyl acrylate is exemplified below. Film samples of the polymers were prepared for FTIR measurement: a thickness of 0.5–0.7 mm was used for ethylene / butyl acrylate and ethylene / ethyl acrylate, and a film thickness of 0.10 mm for ethylene / methyl acrylate in an amount >6% by weight. The films were pressed using a Specac film press at approximately 150 °C for 5 t, 1–2 minutes, and then cooled with ice water in an uncontrolled manner. The precise thickness of the obtained film samples was measured. After FTIR analysis, baselines in absorbance mode were drawn for the peaks to be analyzed. The absorbance peak for the comonomer was normalized with the absorbance peak of polyethylene (e.g., the peak height for butyl acrylate or acrylate). 43 / 62 ethyl at 3,450 cm⁻¹ was divided by the height of the polyethylene peak at 2,020 cm⁻¹). The NMR spectroscopy calibration procedure was performed in the conventional manner that is well documented in the literature, explained below. To determine the methyl acrylate content, a 0.10 mm thick film sample was prepared. After analysis, the maximum absorbance for the methyl acrylate peak at 3455 cm⁻¹ was subtracted from the absorbance value for the baseline at 2475 cm⁻¹ (A2660-A2475). Then, the maximum absorbance for the polyethylene peak at 2660 cm⁻¹ was subtracted from the absorbance value for the baseline at 2475 cm⁻¹ (A2660-A2475). The ratio between (A2660-A2475) and (A2660-A2475) was then calculated in the conventional manner that is well documented in the literature. Weight percentage can be converted to mole percentage by calculation. This is well documented in the literature. Quantification of Copolymer Content in Polymers by NMR Spectroscopy The comonomer content was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic designation (e.g., NMR Spectra of Polymers and Polymer Additives, AJ Brandolini and DD Hills, 2000, Marcel Dekker, Inc., New York). The experimental parameters were adjusted to ensure the measurement of quantitative spectra for this specific task (e.g., 200 and More NMR Experiments: A Practical Course, S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). The quantities were calculated using simple corrected ratios of the signal integrals from representative sites in a manner known in these techniques. (2) Polymers Containing 6% or Less by Weight of Polar Comonomeric Units The comonomer content (% by weight) was determined in a known manner, based on Fourier transform infrared (FTIR) spectroscopy calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. The determination is exemplified below. 44 / 62 nation of the polar comonomer content of ethylene / butyl acrylate and ethylene / methyl acrylate. For the FT-IR measurement, film samples with a thickness of 0.05 to 0.12 mm were prepared as described above in method (1). The precise thickness of the film samples obtained was measured. After FT-IR analysis, baselines were drawn for the peaks to be analyzed. The maximum absorbance for the comonomer peak (e.g., for methyl acrylate at 1164 cm⁻¹ and butyl acrylate at 1165 cm⁻¹) was subtracted from the baseline absorbance value at 1850 cm⁻¹ (A comonomer peak - A1850). Then, the maximum absorbance peak for the polyethylene peak at 2660 cm⁻¹ was subtracted from the baseline absorbance value at 1850 cm⁻¹ (A2660 - A1850). The ratio between (A comonomer - A1850) and (A2660 - A1850) was then calculated. The NMR spectroscopy calibration procedure was performed in the conventional manner that is well documented in the literature, as described above in method (1). Weight percentage can be converted to mole percentage by calculation. This is well documented in the literature. Gel Content The gel content is measured in accordance with ASTM D 2765-01, method B, using decalin extraction. However, there were three minor deviations from this norm: 1) An additional extraction for 1 hour with more decalin was performed to ensure that all soluble compounds had been extracted. 2) Only 0.05% of antioxidant (Irganox 1076, octadecyl 3,5-di-(t)-butyl-4-hydroxyhydrocinnamate, CAS: 2082-79-3) was added to the decalin instead of 1% as specified in the standard. 3) The cut cable strips are 0.2 mm thick, not 0.4 mm as specified in the standard. The sample was obtained from the insulating layer, manufactured from a polymer composition as close as possible to the inner semiconductor layer of a 20 kV cable. This three-layer cable core was produced using a 1+2 construction on a pilot-scale continuous catenary vulcanization (CCV) line. The conductor was made of... The 45 / 62 aluminum core had an area of ​​50 mm². The inner semiconductor layer was 0.9 mm thick, the insulating layer was 5.5 mm thick, and the outer semiconductor layer was 0.8 mm thick. The line speed used for manufacturing the cable cores was 2 m / min. This CCV line has two heating zones for dry curing, each 3 m long, and the temperatures used in these two zones were 450 and 400 °C respectively. The cooling section was 12.8 m long; the cable was cooled with water maintained at a temperature of approximately 25-30 °C. Methods for Determining Conductivity in Direct Current (DC) DC Conductivity Method 1: Electrical conductivity measured at 70 °C and 30 kV / mm average electric field from a 1 mm thick non-degassed or degassed plate sample consisting of a cross-linked polymeric composition. Plate Sample Preparation: The plates are compression-molded from pellets of polymeric composition under testing. The final plates have a thickness of 1 mm and a diameter of 330 mm. The plates are molded in a press at 130 °C for 12 min while the pressure is gradually increased from 2 to 20 MPa. After that, the temperature is increased and reaches 180 °C after 5 min. The temperature is then maintained at 180 °C for 15 min, during which time the plate becomes completely cross-linked by the peroxide present in the polymeric composition under test. Finally, the temperature is decreased using a cooling rate of 15 °C / min until it reaches room temperature, at which point the pressure is relieved. The plates are wrapped in metal foil immediately after pressure relief to prevent loss of volatile substances (used for non-degassed determination). If the plate is to be degassed, it is placed in a vacuum oven at a pressure of less than 10 Pa and degassed for 24 hours at 70°C. After that, the plate is rewrapped in metal foil to... 46 / 62 prevent further exchange of volatile substances between the plate and its surroundings. Measurement Procedure: A high-voltage source is connected to the upper electrode to apply voltage to the sample under test. The resulting current through the sample is measured with an electrometer. The measuring cell is a three-electrode system with brass electrodes. The brass electrodes are equipped with heating tubes connected to a heating circulator to facilitate measurements at high temperatures and provide uniform temperature of the sample under test. The diameter of the measuring electrode is 100 mm. Silicone rubber skirts are placed between the edges of the brass electrodes and the sample under test to prevent spark discharges from the rounded edges of the electrodes. The applied voltage was 30 kV DC, meaning an average electric field of 30 kV / mm. The temperature was 70 °C. The current through the plate was recorded throughout the entire experiment, which lasted 24 hours. The current after 24 hours was used to calculate the conductivity of the insulation. This method and a schematic diagram of the measurement setup for conductivity measurements was described extensively in a paper presented at the Nordic Insulation Symposium 2009 (Nord-IS 09), Gothenburg, Sweden, June 15-17, 2009, pages 55-58: Olsson et al, Experimental determination of DC conductivity for XLPE insulation. DC Conductivity Method 2: Electrical conductivity at 20 °C and 40 kV / mm average electric field from a plate sample consisting of a cross-linked polymeric composition. Preparation of Plate Samples: Polymer composite pellets were compression molded under the following conditions: first, the pellets were melted at 120 °C for 1 min at 2 MPa (20 bar). Then, the temperature was increased to 180 °C while simultaneously increasing the pressure to 20 MPa (200 bar). The plates then become completely cross-linked by 47 / 62 medium of the peroxide present in the polymer composition. The total crosslinking time was 12 min including the time to increase the temperature from 120 to 180 °C. After completing the crosslinking, the plates were cooled to room temperature at a cooling rate of 15 °C / min while still under pressure. After removal from the press, the cooled plates were degassed in an oven at 70 °C for 72 hours at 1 atm. The final thickness of the plates was 0.5 mm. Measuring the conduction current: The conduction current measurement is performed using a three-terminal cell under nitrogen at a pressure of 0.3 MPa (3 bar) and a temperature of 20°C. Specimens are tested with gold-coated electrodes obtained by cold cracking. The low-voltage electrode has a diameter of 25 mm (the measurement area is thus 490 mm²). A guard electrode is situated around, but separate from, the low-voltage electrode. The high-voltage electrode has a diameter of 50 mm, the same dimension as the outer diameter of the guard electrode. A DC voltage (U) equal to the average target voltage (E) x measured insulation thickness (d) is applied across the high-voltage electrode. The average target voltage E is in this case 40 kV / mm. The current through the tape between the high-voltage and low-voltage electrodes is measured with an electrometer. Measurements are terminated when the current reaches an equilibrium level, typically after 24-48 hours. The reported conductivity σ is calculated from the equilibrium current (I) using the equation σ = l*d / (A*U) where A is the measurement area, in this case 490 mm². DC Conductivity Method 3: Electrical conductivity measured at 70 °C and 30 kV / mm average electric field from a 1 mm thick non-degassed or degassed plate sample consisting of a cross-linked polymeric composition. The plates are compression-molded from pellets of the polymer composition under test. The final plates have a thickness of 48 / 62 ±10% mm and 195 x 195 mm2. The thickness is measured at 5 different locations on the plates. The plates are molded in a press at 130°C by 600 sec and 2 MPa (20 bar). After that, the temperature is increased and reaches 180°C after 170 sec, and the pressure is simultaneously increased to 20 MPa (200 bar). The temperature is then maintained constant at 180°C for 1000 sec, during which time the plate becomes completely cross-linked by the peroxide present in the polymer composition under test. Finally, the temperature is decreased using a cooling rate of 15°C / min until it reaches room temperature, at which point the pressure is relieved. The thickness of the plate is determined immediately after compression molding and then placed in the test cell described below for conductivity measurement. A high-voltage source is connected to the upper electrode to apply voltage to the test sample. The resulting current through the sample is measured with an electrometer. The measuring cell is a three-electrode system with brass electrodes. The cell is installed in a heating oven to facilitate measurements at high temperatures and to provide a uniform temperature for the test sample. The diameter of the measuring electrode is 100 mm. Silicone rubber skirts are placed between the edges of the brass electrodes and the test sample to prevent spark discharges from the rounded edges of the electrodes. The applied high voltage direct current (HVDC) was regulated according to the measured thickness of the plate to achieve an average electric field of 30 kV / mm. The temperature was 70°C. The current through the plate was recorded during the entire experiments, which lasted 24 hours. The current after 24 hours was used to calculate the conductivity of the insulation. DC Conductivity Method 4: The electrical conductivity of a 1.5 mm thick sample plate of the cross-linked polymer composition as an insulating layer and the cross-linked semiconductor composition of the test as a semiconductor layer was measured at 70°C and a 30 kV / mm average electric field. Cable Preparation Template: 49 / 62 Three-layer cable cores were produced using a 1+2 construction on a pilot-scale continuous catenary vulcanization (CCV) line. The conductor was made of copper and had an area of ​​1.5 mm². The inner and outer semiconductor layers consisted of the same test semiconductor composition, comprising a crosslinking agent, which in the experimental part below was peroxide. The inner semiconductor layer had a thickness of 0.7 mm, the insulating layer a thickness of 1.5 mm, and the outer semiconductor layer a thickness of 0.5 mm. The cable cores were produced in two stages. In stage 1, the cable cores were extruded using a line speed of 8 m / min without passing through a vulcanization tube. In stage 2, the cable cores only passed through the vulcanization tube at a line speed of 5 m / min.The tube has two heating zones for dry curing (crosslinking under nitrogen), each 3 m long, and the temperatures used in these two zones were 400 and 380 °C respectively. This resulted in fully crosslinked cables due to the peroxide present in the insulating and semiconductor materials. The cooling section was 12.8 m long; the cable was cooled with water maintained at a temperature of approximately 25-30 °C. The cables were not degassed prior to the conduction current measurements. To prevent unwanted degassing, the cables were covered with aluminum foil until the measurements were conducted. The cables were then cut into 3-meter-long samples with an active length of 100 cm (measurement zone) in the middle where the outer semiconductor layer is present. The outer semiconductor layer at the 100 cm ends of the sample was removed using a stripping tool. A schematic view of the three-layer model cables with 1.5 mm insulation thickness used in method 5 is illustrated in Figure 1. Conduction Current Measurements: The conduction current measurements are performed using a three-terminal cell where the conductor acts as the high-voltage electrode. 50 / 62 are. The low-voltage electrode is an aluminum foil covering the outer semiconductor on the active side. Guard electrodes are inserted through the aluminum foil covering the insulation on both sides of the measuring zone. The distances between the low-voltage electrode and the guard electrodes are 5 cm. The applied voltage is 45 kV DC (30 kV / mm average electric field) and the temperature is 70°C. Measurements are terminated after 24 hours, and conductivity is measured as the average between 23-24 hours. The current in the equilibrium state (leakage current) is used in the calculations. The conductivity s (S / m) was calculated using the formula A In(-) σ =-— 2nLR and R = U / I = Applied voltage (V) Leakage current (A). Table. Data used for conductivity calculation from model cable specimens. Parameter Value L Cable length (m) 1 d Inner diameter of insulation (mm) 2.8 D Outer diameter of insulation (mm) 5.8 U Applied voltage (kV) 45 Method for determining the number of double bonds in the polymer composition or in the polymer. A) Quantification of carbon-carbon double bonds by IR spectroscopy Quantitative infrared (IR) spectroscopy was used to quantify the amount of carbon-carbon (C=C) double bonds. Calibration was performed prior to determining the molar extinction coefficient of C=C functional groups in representative low molecular weight model compounds with known structure. The quantity of each of these groups (N) was determined as the number of carbon-carbon double bonds per thousand total carbon atoms (C=C / 1000C) by means of: 51 / 62 N = (Aχ 14) / (Ex Lx D) where A is the maximum absorbance defined as the peak height, E is the molar extinction coefficient of the group in question (l-mor^mm'1), L is the film thickness (mm) and D is the density of the material (gcnrí1). The total number of C=C bonds per thousand total carbon atoms can be calculated by summing N for the individual components that contain C=C. In the case of polyethylene samples, solid-state infrared spectra were recorded using an FTIR spectrometer (Perkin Elmer 2000) on compression-molded thin films (0.5-1.0 mm) at a resolution of 4 cm⁻¹ and analyzed in absorption mode. 1) Polymer compositions comprising homopolymers and copolymers of polyethylene, except polyethylene copolymers with > 0.4% by weight of polar comonomer. In the case of polyethylenes, three types of C=C-containing functional groups were quantified, each with a characteristic absorption and each calibrated to a different model compound, resulting in individual extinction coefficients: • vinyl (R-CH=CH2) via 910 cm⁻¹ based on 1-decene [dec-1-ene] giving E = 13.13 l mol⁻¹ mm⁻¹ • vinylidene (RR'C=CH2) via 888 cm⁻¹ based on 2-methyl-1-heptene [2-methylhept-1-ene] giving E = 18.24 l mol⁻¹ mm⁻¹ • trans-vinylene (R-CH=CH-R') via 965 cm⁻¹ based on trans-4-decene [(E)dec-4-ene] giving E = 15.14 l mol⁻¹ mm⁻¹ In the case of polyethylene homopolymers or copolymers with < 0.4% by weight of polar comonomer, a linear baseline correction was applied between approximately 980 and 840 cm⁻¹. 2) Polymer Compositions Comprising Polyethylene Copolymers with > 0.4% by weight of Polar Comonomer In the case of polyethylene copolymers with > 0.4% by weight of polar comonomer, two types of C=C-containing functional groups were quantified, each with a characteristic absorption and each calibrating 52 / 62 for a different model compound, resulting in individual extinction coefficients: • vinyl (R-CH=CH2) via 910 cm⁻¹ based on 1-decene [dec-1-ene] giving E = 13.13 l mol⁻¹ mm⁻¹ • vinylidene (RR'C=CH2) via 888 cm⁻¹ based on 2-methyl-1-heptene [2-methylhept-1-ene] giving E = 18.24 l mol⁻¹ mm⁻¹ EBA: In the case of systems with poly(ethylene-butyl coacrylate) (EBA), a linear baseline correction was applied between approximately 920 and 870 cm⁻¹. EMA: In the case of systems with poly(ethylene-methyl coacrylate) (EMA), a linear baseline correction was applied between approximately 930 and 870 cm⁻¹. 3) Polymeric Compositions Comprising Low Molecular Weight Unsaturated Molecules In the case of systems containing low molecular weight species that contain C=C, a direct calibration was performed using the molar extinction coefficient of C=C absorption in the low molecular weight species themselves. B) Quantification of Molar Extinction Coefficients by Infrared Spectroscopy Molar extinction coefficients were determined according to the procedure provided in ASTM standards D3124-98 and ASTM D624898. Infrared spectra in the solution state were recorded using an FTIR spectrometer (Perkin Elmer 2000) equipped with a liquid cell with a path length of 0.1 mm at a resolution of 4 cm⁻¹. The molar extinction coefficient (E) was determined as 1 mol·1mm⁻¹ by means of: E = A / (C x L) where A is the maximum absorbance defined as peak height, C is the concentration 53 / 62 traction (molT1) and L is the cell thickness (mm). At least three 0.18 mol-L⁻¹ carbon disulfide (CS₂) solutions were used, and the average extinction coefficient value was determined. Experimental Part Preparation of Polyolefins from the Examples of the Present Invention and from the Reference Examples The polyolefins were low-density polyethylenes produced in a high-pressure reactor. The production of the polymers of the invention and reference polymers is described below. Regarding the feeds of chain transfer agents (CTA), for example, the PA content can be given as liter-hour or kg / h converted into other units using a PA density of 0.807 kg / liter for recalculation. Examples of Invention 1: Ethylene with recycled CTA was compressed in a 5-stage pre-compressor and a 2-stage hypercompressor with intercooling to achieve an initial reaction pressure of approximately 257.6 MPa (2,576 bar). The total compressor capacity was approximately 30 t / hour. In the compressor area, approximately 4.9 liters / hour of propionic aldehyde (CAS number: 123-38-6) were added along with approximately 119 kg / hour of propylene as chain transfer agents to maintain a melt flow rate (MFR) of 2.1 g / 10 min. The compressed mixture was heated to 166 °C in a preheating section of a three-zone tubular reactor with front feed, having an internal diameter of approximately 40 mm and a total length of 1,200 meters.A mixture of commercially available free radical initiator peroxides dissolved in isododecane was injected immediately after the preheater in a quantity sufficient for the exothermic polymerization reaction to reach peak temperatures of approximately 276 °C, after which it was cooled to approximately 221 °C. The subsequent reaction temperatures of the 2nd and 3rd peaks were 271 °C and 261 °C, respectively, with a cooling between them to 225 °C. The reactive mixture was depressurized by a relief valve, res. 54 / 62 chilled, and the polymer was separated from the unreacted gas. Example of Invention 2: Ethylene with recycled CTA was compressed in a 5-stage pre-compressor and a 2-stage hypercompressor with intercooling to achieve an initial reaction pressure of approximately 252.3 MPa (2,523 bar). The total compressor capacity was approximately 30 t / hour. In the compressor area, approximately 4.5 liters / hour of propionic aldehyde were added along with approximately 118 kg / hour of propylene as chain transfer agents to maintain a melt flow rate (MFR) of 2.0 g / 10 min. In this case, 1,7-octadiene was also added to the reactor at a rate of 23 kg / h. The compressed mixture was heated to 160 °C in a preheating section of a three-zone tubular reactor with front feed, having an internal diameter of approximately 40 mm and a total length of 1,200 meters.A commercially available mixture of radical-initiating peroxides, dissolved in isododecane, was injected immediately after the preheater in sufficient quantity to cause the exothermic polymerization reaction to reach peak temperatures of approximately 272 °C, after which it was cooled to approximately 205 °C. The subsequent reaction temperatures of the 2- and 3-peaks were 270 °C and 253 °C, respectively, with a cooling between them to 218 °C. The reactive mixture was depressurized by a relief valve, cooled, and the polymer was separated from the unreacted gas. Example of Invention 3: Ethylene with recycled CTA was compressed in a 5-stage pre-compressor and a 2-stage hypercompressor with intercooling to achieve an initial reaction pressure of approximately 259.2 MPa (2,592 bar). The total compressor capacity was approximately 30 t / hour. In the compressor area, approximately 4.9 liters / hour of propionic aldehyde were added along with approximately 77 kg / hour of propylene as chain transfer agents to maintain a melt flow rate (MFR) of 1.9 g / 10 min. The compressed mixture was heated to 163 °C in a preheating section of a three-zone tubular reactor. A 55 / 62 front-feed submersible, having an internal diameter of 40 mm and a total length of 1,200 meters, was used. A commercially available mixture of radical-initiating peroxides, dissolved in isododecane, was injected just before the preheater in sufficient quantity to cause the exothermic polymerization reaction to reach peak temperatures of approximately 281 °C, after which it was cooled to approximately 208 °C. Subsequent peak reaction temperatures were 282 °C and 262 °C, respectively, with a cooling period between them to 217 °C. The reactive mixture was depressurized by a relief valve, cooled, and the polymer was separated from the unreacted gas. Example of Invention 4: Ethylene with recycled CTA was compressed in a 5-stage pre-compressor and a 2-stage hypercompressor with intercooling to achieve an initial reaction pressure of approximately 277.1 MPa (2,771 bar). The total compressor capacity was approximately 30 t / hour. In the compressor area, approximately 5.3 liters / hour of propionic aldehyde were added along with approximately 86 kg / hour of propylene as chain transfer agents to maintain a melt flow rate (MFR) of 0.7 g / 10 min. The compressed mixture was heated to 171 °C in a preheating section of a three-zone tubular reactor with front feed, having an internal diameter of 40 mm and a total length of 1,200 meters.A mixture of commercially available radical-initiating peroxides, dissolved in isododecane, was injected just before the preheater in sufficient quantity to cause the exothermic polymerization reaction to reach peak temperatures of approximately 281 °C, after which it was cooled to approximately 203 °C. The subsequent reaction temperatures of the 2- and 3-peaks were 273 °C and 265 °C, respectively, with a cooling between them to 226 °C. The reactive mixture was depressurized by a relief valve, cooled, and the polymer was separated from the unreacted gas. Reference Example 1: Purified ethylene was liquefied by compression and cooling. 56 / 62 up to a pressure of 9 MPa (90 bar) and a temperature of -30 °C, and divided into two equal streams of approximately 14 t / hour each. CTA (methyl ethyl ketone, MEK), air, and a commercially available radical initiator peroxide dissolved in a solvent were added to the two liquid ethylene streams in individual quantities. In this case, 1,7-octadiene was also added to the reactor at a rate of 24 kg / h. The two mixtures were pumped separately through an array of 4 intensifiers to achieve pressures of 220-230 MPa (2,200-2,300 bar) and outlet temperatures of about 40 °C. These two streams were fed, respectively, to the front (zone 1) (50%) and side (zone 2) (50%) of a two-zone split-feed tubular reactor. The internal diameters and lengths of the two zones of the reactor were 32 mm and 200 m for zone 1, and 38 mm and 400 m for zone 2.MEK was added at a rate of 205 kg / h to the front feed stream to maintain an MFR2 around 2 g / 10 min. The front feed stream was passed through a heating section to reach a temperature sufficient for the exothermic polymerization reaction to initiate. The peak reaction temperatures reached were 253 °C and 290 °C in the first and second zones, respectively. The side feed stream cooled the reaction to a second zone initiation temperature of 168 °C. Air and peroxide solution were added to both streams in sufficient quantities to reach the desired peak temperatures. The reactive mixture was depressurized through the product valve, cooled, and the polymer was separated from the unreacted gas. Reference Example 2: Purified ethylene was liquefied by compression and cooling to a pressure of 9 MPa (90 bar) and a temperature of -30 °C, and divided into two equal streams of approximately 14 t / hour each. CTA (methyl ethyl ketone, MEK), air, and a commercially available radical-initiating peroxide dissolved in a solvent were added to the two liquid ethylene streams in individual quantities. The two mixtures were pumped separately through an array of 4 intensifiers to 57 / 62 achieve pressures of 210-230 MPa (2,100-2,300 bar) and outlet temperatures of approximately 40 °C. These two streams were fed, respectively, to the front (zone 1) (50%) and the side (zone 2) (50%) of a split-feed two-zone tubular reactor. The internal diameters and lengths of the two reactor zones were 32 mm and 200 m for zone 1, and 38 mm and 400 m for zone 2. MEK was added in amounts of approximately 216 kg / h to the front stream to maintain an MFR2 around 2 g / 10 min. The front feed stream was passed through a heating section to reach a temperature sufficient for the exothermic polymerization reaction to begin. The peak reaction temperatures reached were 250 °C and 318 °C in the first and second zones, respectively. The side feed stream cooled the reaction to a second zone initiation temperature of 165–170 °C.Air and peroxide solution were added to both streams in sufficient quantities to achieve the desired peak temperatures. The reactive mixture was depressurized through the product valve, cooled, and the polymer was separated from the unreacted gas. Reference Example 3: Purified ethylene was liquefied by compression and cooling to a pressure of 9 MPa (90 bar) and a temperature of -30 °C, and split into two equal streams of approximately 14 t / hour each. CTA (methyl ethyl ketone, MEK), air, and a commercially available radical initiator peroxide dissolved in a solvent were added to the two liquid ethylene streams in individual amounts. The two mixtures were pumped separately through an array of 4 intensifiers to achieve pressures of 210–230 MPa (2,100–2,300 bar) and outlet temperatures of about 40 °C. These two streams were fed, respectively, to the front (zone 1) (50%) and side (zone 2) (50%) of a split-feed two-zone tubular reactor. The internal diameters and lengths of the two zones of the reactor were 32 mm and 200 m for zone 1, and 38 mm and 400 m for zone 2.MEK was added at a rate of approximately 201 kg / h to the front stream to maintain an MFR2 around 0.75 g / 10. 58 / 62 min. The front feed stream was passed through a heating section to reach a temperature sufficient for the exothermic polymerization reaction to begin. The peak reaction temperatures reached were 251 °C and 316 °C in the first and second zones, respectively. The side feed stream cooled the reaction to a second zone initiation temperature of 185-190 °C. Air and peroxide solution were added to both streams in sufficient quantities to reach the desired peak temperatures. The reactive mixture was depressurized by the product valve, cooled, and the polymer was separated from the unreacted gas. Semiconductor compositions for semiconductor layers of sample model cables Semiconductor 2: LE0550, commercial grade from Borealis with acetylene carbon black, density 1,100 kg / cm3, DC yolumetric resistivity at 23 °C less than 100 Ωcm and at 90 °C less than 1,000 Ωcm (ISO3915), Hot Elongation Test (200 °C, 0.20 MPa, IEC 60811-21): Elongation under load 25%, Permanent Deformation 0%. Elastography Apparatus Göttfert 1.2 Nm. Experimental Results: Mineral oil = Examples of the invention 1-3: mineral oil-based lubricant, Shell Corena E150, supplier Shell; Example of the invention 4: mineral oil-based lubricant, M-RARUS PE KPL 201, supplier ExxonMobil PAG = References: polyalkylene glycol-based lubricant, Syntheso D201N, supplier Klueber. PA = propionaldehyde (CAS number: 123-38-6) MEK = methyl ethyl ketone. 59 / 62 Table 1. Summary and Components of AO Polymer Compositions: 4,4'-thiobis-(2-t-butyl-5-methylphenol) (CAS n- 96-69-5) ADD (% by weight) 0.35 i 1 1 0.29 0.26 Peroxide mmol -OO- / kg of polymer composition, (% by weight) 49.9 (1.35) 77.7(2.10) 70.2(1.9) 66.6(1.80) 42.5(1.15) 74.0 (2.0) 48.8(1.32) AO (% by weight) 00 oo 0.19 0.19 0.19 oo oo” 0.19 0.07 Comonomer 1,7-octadiene No comonomer No comonomer No comonomer 1,7-octadiene No comonomer No comonomer Compressor lubricant used in the polymerization process PAG PAG PAG Mineral oil Mineral oil Mineral oil Mineral oil, Polymer composition, Reference example 1, Reference example 2, Reference example 3, Example of the invention 1, Example of the invention 2, Example of the invention 3, Example of the invention 4 Peroxide: Dicumyl peroxide (CAS n- 80-43-3) Additive (ADD): 2,4-Diphenyl-4-methyl-1-pentene (CAS 6362-80-7) 60 / 62 Table 2. Properties of the polyolefin components of the polymer composition. Properties of the Base Resin Ex. Inv.1 Ex. Inv.2 Ex. Inv. 3 Ex. Inv. 4 Ex. Ref.1 Ex. Ref. 2 Ex. Ref. 3 MFR 2.16kg, 190°C [g / 10min] 2.1 2.0 1.9 0.7 2.0 2.0 0.75 Density [kg / m³] 922 920 921 922 922 922 922 Vinyl [C=C / 1000°C] 0.37 0.56 0.25 0.26 0.25 0.11 0.11 Vinylidene [C=C / 1000°C] 0.17 0.19 0.20 0.16 0.26 0.22 0.22 Trans-vinylene [C=C / 1000C] 0.04 0.07 0.04 0.04 0.06 0.05 0.04 Table 3. Conductivity (fS / m) of 1 mm thick press-molded insulated polymer composite boards, measured at 70 °C and 530 kV / mm average electric field (DC conductivity Method 1)__________ Byproducts in the sample Reference example 1 Example of the invention 2 No degassing 166 (fS / m) 67 (fS / m) Degassed 77 (fS / m) 14 (fS / m) Table 4. Conductivity of 0.5 mm press-molded plates of cross-linked polymer composition insulation, measured at 20 °C and 40 kV / mm (DC Conductivity Method 2)___________________________ Compressor Lubricant Polymer Composition Code Comonomer Conductivity (fS / m) Reference Example 1 PAG 1,7-octadiene 0.30 Example of the invention 1 Mineral oil No comonomer 0.20 Example of the invention 2 Mineral oil 1,7-octadiene 0.10 The gel content of example 2 was 78.2% by weight and the gel content of comparative example 1 was 77.9% by weight, measured according to the gel content method defined above in the Determination Methods section. 61 / 62 Table 5. Conductivity (fS / m) of 1 mm press-molded plates of cross-linked polymer composition insulation, measured at 70 °C and 30 kV / mm average electric field (DC Conductivity Method 3) Byproducts in sample Reference example 3 (fS / m) Example of the invention 4 (fS / m) No degassing 160.1 (fS / m) 65.6 (fS / m) 62 / 62 Table 6. Cable compositions and test results for 1.5 mm gauge cables, measured at 70°C and 30 kV / mm average electric field (DC Conductivity Method 4)______________________________________________________________________ Conductivity measured from a sample of model cable (fS / m) 450.1 72.6 Semiconductor composition of the inner and outer semiconductor layers of the model cable sample Semiconductor 2: Acetylene carbon black (LE0550) Semiconductor 2: Compressor lubricant used in the polymerization process of the polymeric composition of the insulating layer of the model cable sample PAG Mineral oil Polymer composition of the insulating layer of the model cable sample Reference example 3 Example of the invention 4

Claims

1. A crosslinkable polymeric composition, characterized in that it comprises a polyolefin and a crosslinking agent, and wherein the polymeric composition has an electrical conductivity of 150 fS / m or less, measured at 70 °C and 30 kV / mm mean electric field from a non-degassed 1 mm thick plate sample, consisting of a crosslinked polymeric composition, according to DC conductivity method (1), as described in the Determination Methods section;and wherein the polyolefin is an unsaturated LDPE copolymer of ethylene with one or more nonpolar comonomer(s), and wherein the unsaturated LDPE copolymer comprises a total amount of carbon-carbon double bonds / 1000 carbon atoms of more than 0.4 / 1000 carbon atoms, and contains vinyl groups and the total amount of vinyl groups present in the unsaturated LDPE copolymer is greater than 0.05 / 1000 carbon atoms, and wherein the polymer composition is free of polyethylene glycol-based components and wherein the polymer composition comprises mineral oil and up to 0.4% by weight of mineral oil based on the total polyolefin.

2. Polymer composition according to claim 1, characterized in that the mineral oil is a white mineral oil that meets the requirements set out for white mineral oil in European Directive 2002 / 72 / EC of 6 August 2002, Annex V, for plastics used in contact with food.

3. Polymer composition according to claim 1 or 2, characterized in that it has an electrical conductivity of 0.27 fS / m or less, when measured at 20°C and 40 kV / mm average electric field of a 0.5 mm thick degassed plate sample consisting of a crosslinked polymer composition according to the DC conductivity method (2), as described in Determination Methods.

4. Polymer composition according to any one of claims 1 to 3, characterized in that, prior to crosslinking, the polymer composition comprises peroxide, and the amount of peroxide is at least 35 mmol of -OO- / kg of polymer composition.

5. Polymeric composition, according to any one of claims 1 to 4, characterized in that it further comprises antioxidant(s) selected from sterically hindered or semi-hindered phenols, aromatic amines, sterically hindered aliphatic amines, organic phosphites or phosphonites, thiocompounds, and mixtures thereof, and optionally further comprises vulcanization retarder(s) selected from allylic compounds, substituted or unsubstituted diphenylethylenes, quinone derivatives, hydroquinone derivatives, esters and ethers containing monofunctional vinyl, monocyclic hydrocarbons having at least two or more double bonds, or mixtures thereof.

6. Polymer composition, according to any one of claims 1 to 5, characterized in that the total amount of vinyl groups present in the unsaturated LDPE is greater than 0.08 / 1000 carbon atoms.

7. Polymer composition, according to any one of claims 1 to 6, characterized in that the unsaturated LDPE copolymer is an unsaturated LDPE copolymer of ethylene with at least one polyunsaturated comonomer and optionally with one or more other comonomer(s).

8. Polymer composition, according to claim 7, characterized in that the polyunsaturated comonomer consists of a linear carbon chain with at least 8 carbon atoms and at least 4 carbons between the non-conjugated double bonds, of which at least one is terminal.

9. Polymer composition, according to any one of claims 1 to 8, characterized in that the polyolefin contains vinyl groups in a total amount of more than 0.20 / 1,000 carbon atoms.

10. Polymer composition, according to any of the claims 1 to 9, characterized by the fact that it has been crosslinked.

11. Polymeric composition, according to any one of claims 1 to 10, characterized in that the polyolefin is crosslinked with the peroxide.