FR1464609A - Dielectrics, as well as the elements and in particular the cables insulated with the aid of this dielectric - Google Patents

Description

Dielectrics, as well as the elements and in particular the isolated cables using this
dielectric.

Synthetic high polymers have der. nally found a growing use, as insulators in different electrical applications
In particular, polymeric olefins, principally polyethylenes and polypropylenes, for example, are generally usable as insulators for electrical wires and cables because of their good mechanical properties and ease of application, together with their excellent properties. electric. For use at high voltages, however, the use of these substances has been possible only within narrow limits, since their degree of theoretical electrical failure has in practice not been reached.

It is also already known that the relative weakness of the insulating qualities of commercially prepared polyolefins is due to the many small defects, and air gaps that have formed during handling and that it is virtually impossible to avoid at the moment. during a commercial manufacturing process. For example, there are always small particles of foreign matter in the parent hydrocarbon
A careful examination of many test failures have shown that these small defects are often the beginning of the development of a lack of insulation, this development of the defect, leading to the rupture, being due to the avalanche of Electrons derived from the current passing through the cable, which produces ionization and subsequent rupture at the defect. A method for reducing the ability of foreign materials to initiate defects, i.e., a method of delaying or preventing the formation of such electron avalanches will naturally result in a significant increase in the degree of electrical failure.

 The object of the present invention is to remedy these drawbacks and concerns for this purpose a dielectric characterized by the fact that it comprises, internally, a polyolefin, in dispersed solid phase and a voltage stabilizing additive, chosen from substituted aromatic hydrocarbon compounds having a recipient group and an electron donor group bonded, in potential hydrogen bond, by a reversible transferable proton, which makes it possible to obtain solid dielectrics with a very high voltage stability and which can be used for the isolation of high-voltage cables voltage.

 According to one characteristic of the radiant invention is present in a soluble proportion sufficient to stabilize the polyolefin eg 0.1 to 10 gb by weight of the polyolefin.

 According to one characteristic of the invention, the additive is chosen from 2,4,6-trinitrotoluene 2,4-dinitrotoluene; 2,6 - dinitrotoluene; 2 nitrodiphenylamine 2,4-dinitrodiphenylamine; o - nitroanisole; o - nitrobiphenyl 2 - nitroaniline anthranilonitrile; 1. fluoro - 2 - nitrobenzene phenyl - alphanaphthylamine; phenyl beta - naphthylamine N, N '- diphenyl - para - phenylene diamine; benzidene; and diparamethoxy diphenylamine; and mixtures of these bodies, mixtures with diphenylamine, and mixtures of diphenylamine with at least one of the following compounds: m dinitrobenzene; m - nitroaniline; p - nitroaniline; m - nitrotoluene; p - nitrotoluene; o - nitrochlorobenzene and p - nitrochlorobenzene.

 The invention also relates to the elements and in particular the cables isolated using the dielectric compliant or similar to the previous one.

According to the invention, it is found that certain chemicals and combinations thereof have a tension-stabilizing effect in polyolefins, and provide a considerable degree of protection against the effects of small imperfections in isolation, when added to them. a polyolefinic insulator, for example polyethylene. These additives are effective because of their ability to absorb energetic electrons, thereby preventing or delaying the formation of electron avalanches that lead to electrical failure of the insulator.
polyolefin. These additives are slowly returning
to their original state, releasing the electrons
absorbs there a lower energy level, and
by dissipating the energy absorbed in the medium
ambient in the form of heat, then being
able, again, to stop or absorb
other energetic electrons and recommen
the cycle of stabilizing action.

It is preferred to use as additives
voltage stabilization, those who avoid the
breaking up to the highest voltages that
are applied. The materials used are
are both effective stabilizers and
products easily found on the market.

These effective additives have the following characteristics in common:
An electron-withdrawing group, especially a strongly unsaturated radical, for example a group having a bond, such as -NO2,>CO; -CN, aromatic, pheny. ticks and polyeyclics;
2 An electron donor group, special. a group containing a transferable proton, such as an amino and a lower one, that is to say up to eight carbon atoms, radicals
alkyl, for example -N112 and -CH3;
A potential hydrogen bond between the recipient group and the donor, by a transferable proton, as found when the recipient and donor groups are ortho run with respect to each other, for example on a benzene ring;
The reversibility of proton transfer between the recipient and donor groups, as in the eno-enol isomerization;
5n Structure and links between recipient and donor groups that favor trans
load and energy loads, such as the planar, or nearly planar, structure of
system of links alternately
simple and - double, for example a structure
aromatic cyclic;
6 A dimension and complexity of the sys
conjugate system able to ensure the capture of
trons, and subsequent energy dissipation
without irreversible binding;
70 Solubility of the additive in the matter
insulation, able to ensure the formation of a
number of centers sufficient for the capture of
unacceptable contaminants such as, oxygen
and electrons moving in the field
electric.

Generally speaking, relative affinities
of electrons in the atomic residues are in the order of CI greater than O. O is in turn
bigger than N, which in turn is bigger
The recipient groups have affinities of electrons of the order of -NO2, greater than -CN, which is larger than> CO, in turn larger than phenyl. The relative powers as electron donor of groups such as -N (CH3) 2 are larger than -NH which is larger than -CH5, in turn larger than phenyl. The sigma and sigma plus values represent an approximate measure of the relative receiver and electron donor properties of atoms, and groups.

 Volatile stabilizers include aromatic hydro aromatics, such as 2,4,6 - trinitrotoluene; 2 - nitrodiphenylamine; 2,4 - dinitrodiphenylamine; o - nitroanisols; 2,6 - dinitrotoluene; 2,4 - dinitrotoluene; o-nitrobiphenyl; 2 - nitroaniline; anthranilonitrile; 1-fluoro -2-nitrobenzene; etc., and their mixtures. All of these products produce the desired effect, some to a greater degree than others.

 These additives are particularly effective with polyolefins such as low density polyethylene based compositions which generally have a density in the range of 0.92 to 0.95, and a melt index between 0.2 and 2, 0.

Especially, these polyethylenes are the solid ethylene polymers that are prepared by the high pressure process. The additives are effective, to obtain the desired effect, in polyethylenes - high density (low pressure), and in other polyolefins, for example in polypropylene, although the latter material is generally not usable for risolement cables because of its lack of flexibility. The stabilized polyethylene compositions may naturally contain small amounts of the usual additives, adjuvants and fillers conventionally used in polyethylene compositions, such as carbon black, pigments, antioxidants, heat stabilizers, and the like. stabilizers for resistance to ozone.

Additives are also used to increase the tensile stability of polyethylene compositions for a prolonged period of time, when the polyethylene compositions contain low levels of rubber-like polymers, and olefin copolymers such as isobutylene and isoprene. In addition, the additives are used with polyethylene compositions, which have been substituted by use, for example a peroxide catalyst, dieusylperoxide, 2,5-bis (butylperoxy-tertiary) -2,5-dimethylhexane, 2,5 dimethyl - 2,5 - di (butylperoxy - tertiary) hexyne - 3, etc., or by irradiation, of the order of 10 to 15 megarads, for example with cobalt60 (gamma radiation) or by means of a linear accelerator (beta radiation).

 Since the proportion of additives, i.e., voltage stabilization compounds, necessary for a substantial improvement in the tensile stability of a polyethylene, is generally from about 0.1 to about 10. Go, preferably about 0.2 to 5% by weight, based on the amount of polyethylene, the important criterion limits the possibility of using a particular additive, namely its solubility in polyethylene, which must be 0, 1% by weight and preferably 0.2 g or more. The addition of such stabilization additives to the voltage, in proportion exceeding the soluble proportion, causes their crystallization in the polyethylene with, consequently, a weakening of the entire structure, from the electrical point of view, by creating physical discontinuities; we must therefore avoid it. Addition to polyethylene of 0.5% by weight of additive, based on the amount of polyethylene, provides a particularly effective isolation composition for use in high voltage strength cables.

 The additives are preferably selected such that they can be incorporated into the polyethylene without occurring, decomposing the polyethylene, or volatilizing the stabilizing additive to the voltage. Since temperatures of 150.degree. C. to 200.degree. C. are used to satisfactorily mix polyethylenes with other materials, the voltage stabilizing additives are preferably liquid and have a low vapor pressure within this temperature range. . Accordingly, the stabilizers preferably have a melting point of less than 360 OC and a higher boiling point at about 150 OC.

The process of the invention is represented by way of nonlimiting example in the accompanying drawings in which
Figures 1 to 3 illustrate the development process in the additive, during the capture of an electron, in the case of ortho-nitrotoluene (1-methyl-2-nitrobenzene);
Figures 4 to 8 illustrate additional resonant forms of orthonitrotoluene after the capture of the electron.

In the embodiment shown in FIG. 1, the electron recipient of the orthonitrotoluene is the nitro group, -NO 2, and the electron donor is the methyl group -CH 3, which is in the ortho position with respect to the nitro group. All solid straight lines in FIG. 1, as in the other figures, represent sigma (r) bonds of electron pairs. The links Pi (s) are represented by a pair of points under the r. Unconnected electron pairs are represented by a single pair of dots or a dash. The values of the angles are approximate values. All the atoms forming cycles, indicated by A and B, are placed on the same plane and the cycles themselves are situated in nearly the same plane. Atoms
H a and H ss alone are not in this plane.

 The donor and the recipient are in such a position that they can form a hydrogen bond, indicated by a dashed line between the proton of hydrogen on the methyl group and the bonded oxygen atom of the nitro group. .

This proton is potentially transferable and the transfer is reversible. The length of the hydrogen bond is approximately twice that of the sigma (r) bond between the carbon and hydrogen atoms. The structure between the acceptor and donor groups is approximately flat, and the atoms in the ring A, between the atom N of the recipient group, and the atom
O with potential hydrogen bonding of the donor group, including the C atoms, which are on the path, are joined together by a sys. alternatively single and double bonds. The ring A is further connected to the conjugate ring and is part thereof, the latter consisting of the benzene ring B which provides a size and complexity suitable for the capture of an electron and the dissipation of energy without rupture. irreversible link.

An electron arriving at any point in the structure shown in FIG. 1 is easily transferred by the conjugate system.
B, at the point of the molecule which has the greatest affinity for the electron, that is to say the nitro group and in particular, at the oxygen atony of the nitro group connected by a hydrogen to the methyl group, link indicated by the dashed line.

 Figure 2 shows the skeleton of the structural formula of orthonitrotoluene, in one of its resonance forms, after the capture (reception) of electron x, which has migrated to the atom having the highest affinity for tron, which in this case is the r-bonded oxygen atom in the strongest group receiving the eletron, the nitro -NO2 group. The captured electron then causes the proton to be transferred from the hydrogen bond to the oxygen atonia (see Fig. 3). This in turn triggers a redistribution of the electrons, between the donor and recipient groups, through the benzene ring system B, in which the pair of electrons, which originally held the proton on the methyl group, is detached, for form a bond between the carbon atoms of the preceding methyl group and the carbon latome of the benzene ring to which this methyl group is bonded. The original distribution of the electrons in the nitro group and the benzene nucleus is thus replaced by only sigma bonds, between the nitrogene and oxygen atoms of the nitro group, a pair without an electron bond on the nitrogen atom, and a pair of electrons without bond on the carbon atom of the benzene ring connected to the nitrogen atom.

FIG. 3 represents the skeleton of the structure of orthonitrotoluene, in one of its resonance forms, after capture of the electron x, the subsequent passage of the proton from the methyl group to the oxygen atom of the nitro group, and the redistribution of the electrons s and the detached pair of electrons previously bound in the sigma bond, between the carbon atom and the transferred proton. The primitive methyl group has now become a group plan = C1i2 and the nitro group has become the strong acid group

The residual negative charge is located on the nitrogen or oxygen atoms. An equivalent form is one where the electrons s between the carbon and nitrogen atoms separate, giving an unseparated pair of electrons on the nitrogen atom, and an unpaired electron on the adjacent carbon atom where it is paired with one of the two unpaired electrons, and any molecule of oxygen.

 The negative charge continues to remain, to a large extent, on the oxygen atoms, and the electrons without bond on the carbon and nitrogen atoms, bonded together, can take part in the bonds, or bind with the molar oxygen cuIaire. The eventual release of the captured electron and the energy it has communicated to the system will allow the restoration of the entire system, in its original state.

 The structure and electronic distribution described above is only one of many forms of resonance. Figures 4 to 9 show other forms of resonance of the redistributed orthonitrotoluene negative ions.

Unpaired electrons are indicated by the symbol.

The same general step occurs in a combination of molecules, where the recipient and donor groups, forming ring A in Figs. 1-3, are on adjacent but separate and possibly different molecules. Examples of possible combinations can be found

<tb> For <SEP> to be <SEP> used <SEP> only <SEP> or <SEP> On <SEP> I <SEP> For <SEP> to be <SEP> used <SEP> only
<tb><SEP> combination, <SEP> with <SEP> example <SEP> in <SEP> combination <SEP> with <SEP> of <SEP>
<tb><SEP> with <SEP> of <SEP><SEP> diphenylamine <SEP> diphenylamine, <SEP> by <SEP> example
<tb><SEP> o-nitroaniline <SEP> m-dinitrobenzene
<tb><SEP> o <SEP> -nitrotoluene <SEP> m-nitroassine <SEP>
<tb><SEP> 2,4-dinitroaniline <SEP> p <SEP> p-nitroaniline <SEP>
<tb><SEP> m-nitrotolnene <SEP>
<tb><SEP> p-nitrotoluene <SEP>
<tb><SEP> o-Nitrochlorobenzene <SEP>
<tb><SEP> i <SEP> p-nitroehlorbenzene <SEP>
<Tb>
The compounds indicated for use only in combination, do not fulfill the general conditions indicated above, which conditions must present the additives, and are in themselves mediator stabilizers voltage. In combination, the recipient and donor groups of adjacent molecules bind together and form effective stabilizers. The proportion of additives used in combination is variable; however, equimolar amounts are preferably employed to allow the recipient and electron donor groups on the different additives to match each other, so that the bond can occur between adjacent but separate molecules, particularly when the The recipient and donor groups on the individual molecules are not such as to allow hydrogen bonding.

 Other materials accept an electron in a manner similar to what o - nitrotoluene does.

If we consider as an example the 2, 4 dini trotoluene, the nitro group in position 2 can capture an electron that moves in its vicinity, under the influence of the electric field in the insulator, under the electric tension.

This situation is stabilized by exchanging a proton from the adjacent methyl group of the toluene molecule. Then when the electron is released (at low energy), the proton returns to the methyl group, and the dinitrotoluene resumes its original state and can continue to act in the same way. Based on this hypothesis, 2,6 - dinitrotoluene is found to be better stahilizer than 2,4 - dinitrotoluene, since the former has two nitro groups adjacent to the methyl group, while the second only one in this position.

Experience results show that this is so. Similarly, anthranilonitrile is consistent with the general description of the present invention with the cyano group acting as an electron acceptor, and the amino group as a proton donor. The general description of the present invention is further supported by a comparison of 2,6 - dinitroaniline with 3,5 - dinitroaniline and 2 - nitroaniline with 3 - nitroaniline, where in both cases the amino group acts as a donor of proton. Here again, the maximum of stabilizing activity occurs when the nitro groups are adjacent to the proton donor on the ring structure. Based on the description of the present invention, it is evident that substitution of a nitro group on diphenyl. amine in a position ortho to the amino group, in fact, a particularly effective additive, and that the result is exactly in line with expectations. Again, the total reaction is reversible, after the absorption of an energetic electron, and after thus helping to avoid the formation of an avalanche of electrons, the stabilizer molecule releases electron and resumes its ability to capture electrons .

The process of the invention is described in the non-limiting examples below.
Example 1 - A number of tests, summarized in Table 1, confirm the long-term voltage stability, at different voltages, with solid dielectric compositions of polyethylene, using a density polyethylene 0.92, melt index 0.3, and containing a trace of an antioxidant eommereial. A series of eight essays is examined for each composition. The first series of samples examined consist of polyethylene, with no voltage stabilization additive. The other compositions examined contain polyethylene and 0.5% by weight of a voltage stabilizing additive (except as indicated).

All samples containing additives are prepared by mixing, on a hot mill, at temperatures between 160 C and 200 C and are identical in shape and size.

 Each sample is subjected to uniform AC voltage at ambient temperature, and the occurrence of high-voltage failure is examined from a single-needle test which is an accelerated selection for insulators. , for high voltage polyethylene.

 For this test, a standard defect is used to determine the relative dielectric quality, and to indicate the probable live life of the polyethylene insulation by checking for the presence of trees that are generally accepted as being the first stage of the test. dielectric breakdown. The standard defect is to push a needle into a polyethylene sample under controlled conditions. The blocks are then mounted in such a way that the tips of the needle are always at the same distance from a flat, base electrode (101.6 mm) and then the sample is put under stress, by applying a voltage, between the needle and the base for one hour. The sample is then examined under a 25x microscope to search for detectable trees to reveal electrical failure.

Visible deterioration is considered a break. The voltage at which 4 out of 8 samples examined in duplicate, reveal trees in one hour is the characteristic voltage of one hour.

The needle test appeared to correspond with the results of examinations of life at the tension on wire. This is true for polyethylenes with tension stabilizers, as well as for conventional polyethylene compositions.

<SEP> Number <SEP> of <SEP> breaks <SEP> in <SEP> 1 <SEP> time <SEP> on <SEP> 8 <SEP> samples
<tb> Additives
<tb><SEP> Test Tension <SEP><SEP> kV
<tb><SEP> 18 <SEP> 20 <SEP> 23 <SEP> 30 <SEP> 40 <SEP> 50 <SEP> 60
<tb><SEP> Without ........................................... ........... <SEP> 4
<tb><SEP> 2 <SEP>% <SEP> 2,4,6-trinitrotoluene ............................. .... <SEP> 0 <SEP> 3 <SEP> 5
<tb><SEP> Orthomethylanisol ......................................... <SEP > 5
<tb><SEP> 2-nitro <SEP> diphenylamine <SEP> ................. <SEP> O <SEP> O <SEP> O <SEP>
<tb><SEP> 2,4-dinitroanisol ....................................... .. <SEP> 0 <SEP> 6
<tb><SEP> 2-methoxy-4-nitroaniline .................................. <SEP> 0 <SEP> 8
<tb><SEP> 4-methoxy-2-nitroainiline ................................. <SEP> 0 <SEP> 8
<tb><SEP> 2,4-dinitrodiphenylamine <SEP>. <SEP><SEP>.<SEP>.<SEP> i <SEP>
<tb><SEP> Ortho <SEP> nitroanisol <SEP> ................................... <SEP> 0 <SEP> 0 <SEP> 2
<tb><SEP> Chloranil <SEP>. <SEP>. <SEP>. <SEP><SEP> 3
<tb><SEP> 2,6-dinitrotoluene ....................................... . <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 3
<tb><SEP> 2,4-dinitrotoluene <SEP> (techn.) ............................... <SEP> 0 <SEP> 0 <SEP> 5 <SEP> 8
<tb><SEP> 2,4-dinitrotoluene <SEP> (teehn. <SEP> @ <SEP> frenouvele ') <SEP>. <SEP>. <SEP> 0 <SEP> 3 <SEP> 7
<tb><SEP> orthonitrodiphenyl ........................................ <SEP> 0 <SEP> 0 <SEP> 3
<tb><SEP> 2,4-dinitrochlorbenzene .................................... <SEP> 4 <SEP> 7 <SEP> 7
<tb><SEP> Diphenylamine ........................................... .. <SEP> 0 <SEP> 0 <SEP> 2
<tb><SEP> 2-nitroaniline ......................................... ... <SEP> 0 <SEP> 5
<tb><SEP> 3-nitroaniline ......................................... ... <SEP> 2
<tb><SEP> Antbranilonitrile <SEP>. <SEP><SEP> O <SEP>. <SEP> i <SEP>
<tb><SEP> 3,5-dinitroaniline <SEP> .................................... ... <SEP> 1 <SEP><SEP> T <SEP>
<tb><SEQ> 2.6.dinitroaniline <SEP> I <SEP> 1 <SEP>
<tb><SEP> 1-fluoro-dinitrobenzene .................................. <SEP> 0 <SEP> 0 <SEP> 3
<Tb>
The improvements in dielectric strength obtained by incorporating small amounts of stabilization additives into the voltage shown above are transposed into large scale samples in an industrial plant.

We do a lot of testing lots, giving great lengths
of 15 kV polyethylene insulated cable
lene, using polyethylene containing
additives of the type described. The obtained results
in the tests, made on samples of these
production lots, are uniformly superior
the results obtained in similar tests carried out on insulated cables, with the poly

Claims (7)

conventional ethylene that does not contain voltage stabilization additives. These remarks are particularly applicable to the voltage test and are most striking in the case of tests of very long duration, such as the test of life sounds voltage in which a sample of cable is subjected to the voltage, for 2 times 1/2 the duration of the normal service, and is maintained under this tension until the rupture occurs. As a result of the live testing, polyethylene containing voltage stabilizing additives has a greater duration than unstabilized polyethylene in the ratio of 5 or more. EXAMPLE II The additives of Example I give, in polypropylene and polyisobutylene, tensile stability characteristics when mixed therein in proportions of about 1/2 to 20% by weight, based on when polyolefin used. Example III. To illustrate the stabilizing effect on the tension of a combination of additives, the test is carried out, according to the test of the single needle of the polyethylene, similar to that of Example I, and containing 1/2 g of a mixture of equal parts of 2,4 - dinitrotoluene and diphenylamine. There is no break in the test voltages of 50 kV and 60 kV. Example IV. - Additional additives giving a similar voltage stability in polyethylene, if mixed in equimolar proportions with diphenylamine, to form a product which is incorporated in the polyethylene in the proportion of 1/2% by weight based on the amount of polyethylene: <tb> o-nitroaniline <SEP> m-dinitrobenzene <tb> o-nitrotolnene <SEP> m-nitroaliine <SEP> <tb> 2,4-dinitroanine <SEP> p-mtroanillin <SEP> <tb> <SEP> m-nitrotoInene <tb> <SEP> p-nitrotoluene <tb> <SEP> o-nitrochlorbenzene <tb> <SEP> p-nitrochlorbenzene <tb> The following table shows examples of other additives used in accordance with this invention as tension stabilizers. In each example, the additive compound is mixed with a polyethylene whose density is 0.92, and the melt index of 0.3, containing a trace of commercial antioxidant. The mixture, as indicated above, is carried out in a hot mill between 160 ° C. and 205 ° C. (See column table opposite). The polyethylene compositions described in the table above, and in each of the other examples, are used as dielectric compositions, for example, in conventional extrusion. In addition, <tb> <SEP> Part <SEP> <tb> <SEP> at <SEP> Weight <tb> Example <SEP> Additive <SEP> Additive <SEP> <tb> <SEP> n <SEP > for <SEP> 100 <tb> <SEP> parts <SEP> of <tb> <SEP> polyethylene <tb> <SEP> V <SEP> Phenyl-alpha-naphthyl <SEP> amine <SEP> - <SEP> - <SEP> <SEP> 2 <tb> <SEP> VI <SEP> - <SEP> Diphenylamine <SEP> ............ <SEP> 0.1 <SEP> <tb> <SEP> VII <SEP> Phenylbeta-naphthylamine .......... <SEP> 5 <tb> <SEP> VIII <SEP> N, N'-diphenyl-para-phenylene <SEP> di <tb > <SEP> amine <SEP> 5 <tb> <SEP> IX <SEP> Benzidine <SEP>. <SEP> <SEP> ... <SEP> 10 <tb> <SEP> X <SEP> Diparamethoxy-diphenylamine .... <SEP> 2 <tb> The polyethylene compositions also contain substitution catalysts, such as the extruded product is a substituted polyethylene. Optionally the extruded product is transformed by irradiation. In addition, the compositions additionally contain carbon black, in small proportions, for use as cladding compositions for insulated sheathed cables, and contain carbon black, in large proportion, such that the polyethylene composition can be used as a semiconductor product. Of course the invention is not limited to the embodiments described above and shown from which we can provide other variants, without departing from the scope of rinvention. SUMMARY The invention extends in particular to the following characteristics and their various possible combinations.  A dielectric characterized in that it comprises internally a dispersed solid phase polyolefin and a voltage stabilizing additive, selected from substituted aromatic hydrocarbon compounds having a recipient group and a bonded electron donor group, in potential hydrogen bond, by a reversible transferable proton, which allows to obtain solid dielectrics with a very high voltage stability and used for the insulation of high voltage cables.  The additive is present in a soluble proportion sufficient to stabilize the polyolefin, for example 0.1 to 10% by weight of the polyolefin.  3D The electron donor group and the electron acceptor group are in the ortho position.  The recipient and electron donor groups are on different aromatic hydrocarbon compounds, but dispersed near each other.  The electron donor group is  an amino radical;  b. A lower allyl radical having 1 to 8 carbon atoms.  60 The electron receiver group is  at. A strongly unsaturated radical;  b. An aromatic group selected from phenyl and polycyclic aromatics.  The addition has a melting point of less than 260 ° C, a boiling point above 150 ° C and a solubility in the polymer of at least 0.1% by weight.  The additive is selected from 2,4,6-trinitrotoluene 2,4-dinitrotoluene; 2,6-dinitroto luene; 2 - nitrodiphenylamine; 2,4 - dinitrodiphenylamine; o - nitroanisole; o-nitrobiphenyl 2-nitroaniline anthranilonitrile; 1 - fluoro 2 - nitrobenzene phenyl - alphanaphthylamine; phenyl - beta - naphthylamine N, N '- diphenyl paraphenylene diamine; benzidene; and diparamethoxy diphenylamine; and mixtures of these corpora; mixtures with diphenylamine, and mixtures of diphenylamine with at least one of the following compounds: m-dinitrobenzene; nitroaniline; p - nitroaniline; m - nitrotoluene; p - nitrotoluene; o - nitrochlorobenzene and p nitrochlorobenzene.  9 "The polymer is  at. Polyethylene;  b. Polypropylene;  c. Polyisobutylene.  The additive is incorporated in the polymer in the proportion of 0.2 to 5% by weight.  11 "Elements and in particular the cables insulated with the dielectric compliant or similar to the previous.