SYNTHESIS OF FUNCTIONALIZED POLYMERS THROUGH DEVULCANIZATION FROM WASTE CONTAINING ELASTOMERS

Abstract

A method for synthesising polymers through devulcanisation from waste containing elastomers, the method including: —a) contacting the waste containing elastomers with a solvent in the presence of a devulcanisation agent, b) heating the mixture produced in step a), at a temperature of between 20° C. and 250° C. for a period of between 15 minutes and 24 hours in the presence of a devulcanisation agent, the concentration of devulcanisation agent, and the ratio between the concentration of devulcanisation agent, expressed as parts per hundred of elastomer (phr) and a volume of solvent, expressed in ml, is: greater than 0.3 phr/ml of solvent or less than 0.2 phr/ml of solvent when the method is carried out in air, greater than 0.06 phr/ml of solvent when the method is carried out in an inert atmosphere.

Claims

1. A method for synthesizing polymers by devulcanization from waste containing elastomers, said method comprising: a) contacting said waste containing elastomers with a solvent in the presence of an agent for devulcanization of cross-linking points that comprise a sulphur atom bound to another sulphur atom or to a carbon atom; b) heating the mixture obtained in step a) at a temperature comprised between 20° C. and 250° C. for a time comprised between 15 minutes and 24 hours; and said method including: the devulcanizing agent is a compound according to formula (1) ##STR00013## in which R and R′ are identical or different and each represent, independently of one another, a substituent exerting a donor mesomeric effect or an attractor mesomeric effect or a donor inductive effect or an attractor inductive effect, R and R′ are selected independently of one another from the group comprising hydrogen (—H), the halogen atoms selected from iodine, bromine, fluorine and chlorine, the group of (C.sub.1-18)alkyls, primary amines (—NH.sub.2), secondary amines (—NHRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings) or tertiary amines (—NRa.sub.1Ra.sub.2, where Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a (C.sub.1-C.sub.5)alkyl group or an aromatic ring), hydroxyl (—OH), the alcoholates (or a salt) (Ra.sub.1-O.sup.−, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), the (C.sub.1-C.sub.5)alkoxy groups, a thiol (—SH), the thioethers (—SRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), a thiolate (or a salt) (Ra.sub.1—S.sup.−), Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), an aromatic ring, a conjugated base of a carboxylic acid (—COO.sup.−), a carboxyl group (—COOH), the esters (—CO.sub.2 Ra.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and heterocycles), an aldehyde group (—CHO), a carbonyl (—COR), a nitro group (—NO.sub.2), a nitrile group (—CN), a sulphonyl group (—SO.sub.2—), a sulphonate group (salt or acid)(—SO.sub.3), a sulphone (—SO.sub.2R), a phosphate group —O—PO(ORa.sub.1)(ORa.sub.2) where Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a hydrogen or (C.sub.1-C.sub.5)alkyl group or an aromatic ring), a primary amide group (—CONH.sub.2), secondary amide group (—CONHRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings) or tertiary amide group (—CONRa.sub.1Ra.sub.2, Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a (C.sub.1-C.sub.5)alkyl group or an aromatic ring)) and R, R′ or both are different from a hydrogen atom.

2. The method according to claim 1, in which the concentration of devulcanizing agent is such that the ratio of said concentration of devulcanizing agent, expressed in parts per hundred of elastomer (phr), to the volume of solvent, expressed in ml, is: greater than 0.3 phr/ml of solvent or less than 0.2 phr/ml of solvent when the method is carried out under air, greater than 0.06 phr/ml of solvent when the method is carried out under an inert atmosphere.

3. The method according to claim 1, in which the solvent is an organic solvent or an ionic liquid or a deep eutectic solvent or a mixture thereof.

4. The method according to claim 1, characterized in that the heating time of the mixture is comprised between 2 hours and 4 hours when the method is carried out under an inert atmosphere.

5. The method according to claim 1, in which the heating time of the mixture is comprised between 3 hours and 5 hours when the method is carried out under air.

6. The method according to claim 1, characterized in that it comprises, prior to step a), a step of activation of the waste containing elastomers by lyophilization or by swelling.

7. The method according to claim 6, in which the devulcanization reaction and the step of activation of the waste containing elastomers are carried out continuously.

8. The method according to claim 1, characterized in that the synthesis of the polymers by devulcanization is carried out starting from waste of highly vulcanized elastomers.

9. A functionalized elastomer according to formula 3 or 3′, ##STR00014## in which x is an integer comprised between 0 and 6, n is an integer comprised between 6 and 600, m is an integer comprised between 6 and 600, Y is a hydrogen atom or a methyl group, and R and R′, which are identical or different for each unit, are selected from the group comprising halogen atoms selected from iodine, bromine, fluorine and chlorine, the group of (C.sub.1-18)alkyls, the primary amines (—NH.sub.2), secondary amines (—NHRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings) or tertiary amines (—NRa.sub.1Ra.sub.2, where Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a (C.sub.1-C.sub.5)alkyl group or an aromatic ring), hydroxyl (—OH), the alcoholates (or a salt) (Ra.sub.1—O.sup.−, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), the (C.sub.1-C.sub.5)alkoxy groups, a thiol (—SH), the thioethers (—SRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), a thiolate (or a salt) (Ra.sub.1—S.sup.−, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings), an aromatic ring, a conjugated base of a carboxylic acid (—COO.sup.−), a carboxyl group (—COOH), the esters (—CO.sub.2 Ra.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and heterocycles), an aldehyde group (—CHO), a carbonyl (—COR), a nitro group (—NO.sub.2), a nitrile group (—CN), a sulphonyl group (—SO.sub.2—), a sulphonate group (salt or acid)(—SO.sub.3), a sulphone (—SO.sub.2R), a phosphate group —O—PO(ORa.sub.1)(ORa.sub.2) where Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a hydrogen or (C.sub.1-C.sub.5)alkyl group or an aromatic ring), a primary amide group (—CONH.sub.2), secondary amide group (—CONHRa.sub.1, Ra.sub.1 being selected from (C.sub.1-C.sub.5)alkyl groups and aromatic rings) or tertiary amide group (—CONRa.sub.1Ra.sub.2, Ra.sub.1 and Ra.sub.2, which are identical or different, may each independently of one another be a (C.sub.1-C.sub.5)alkyl group or an aromatic ring).

10. A polymer composition obtained by the method according to claim 1.

11. A use of the compositions according to claim 10 as additives in mixtures of fresh or new elastomers, as additives or reagents of the type of surfactants, cross-linking agents or chain extenders.

12. A use of functionalized elastomers according to claim 9 as materials, in particular as thermoplastic elastomers or elastomers for biomedical use.

Description

DESCRIPTION OF THE EMBODIMENTS

[0132] According to the embodiments presented, the devulcanization process is carried out starting from granules or crumb rubbers of scrap lorry tyres. The balanced reaction of the process of chemical devulcanization by rupture of the disulphide bridges by means of a devulcanizing agent is presented in reaction schemes 1 and 1′ given below.

##STR00006##

[0133] This devulcanization process therefore constitutes a route for synthesis of polymers starting from scrap tyres. The type of polymer synthesized, in terms of chain length, is mainly governed by the degree of polymerization of the elastomers contained in the waste starting from which the method is carried out. According to the embodiments described, the waste containing elastomers starting from which the method is carried out is derived from scrap lorry tyres. Depending on the parameters used for carrying out the method, synthesis leads to obtaining oligomers or a mixture comprising polymers and oligomers. The polymers obtained according to reaction scheme 1 comprise a number, designated n, of units, each comprising a functional group that was inserted along the polymer chain during devulcanization, which is comprised between 6 and 600, a number of sulphur atoms, designated x, joining the functional group to the polymer chain, which is comprised between 0 and 6, and a number, designated m, of monomers that the polymer comprises, which is comprised between 6 and 600.

[0134] Scrap lorry tyres are known to be highly vulcanized. The devulcanizing agent is introduced at a level of 6 wt % relative to the rubber waste. A person skilled in the art denotes this ratio as “phr”, it being 6 parts of DA per 100 parts of rubber waste by weight, “phr” standing for “per hundred rubber”. The weight of initial waste, when carrying out each of the embodiments presented, is 300 mg.

[0135] According to the invention, on completion of the synthesis process, an additional step for the purpose of recovering the synthesized polymers is carried out: it consists of Soxhlet treatment of the devulcanized waste with acetone for 24 h to recover the functionalized polymers. When the polymers synthesized are in suspension and/or solvated, a person skilled in the art will be able to select the chemical process for separation or extraction that is the most suitable for recovering them.

[0136] The degree of devulcanization, designated DDV hereinafter in the description, obtained after carrying out the method, is determined by the Flory principle through variation of the cross-link density by the method described by Paul J. Flory and John Rehner, The Journal of Chemical Physics, 1943, Vol. 11, p. 521. It therefore allows specific measurement of the ruptures of the disulphide bridges and carbon-sulphur bonds. The value of the DDV will therefore make it possible to evaluate specifically the efficiency of the devulcanization reaction. In the documents of the state of the art, DDV is generally determined from sol-gel measurements, generally by means of a Soxhlet extraction process, and in particular starting from the soluble fraction of the devulcanized polymer. The soluble fraction determined comprises the ruptures of the disulphide bridges and of the carbon-sulphur bonds but also the ruptures of the carbon-carbon bonds of the polymer chain.

[0137] Based on the understanding that rubber is mainly constituted by polyisoprene and that the carbon-carbon double bonds are also sensitive to free radicals, the inventors deduced that the main source of depolymerization is that which is generated by the reaction of the DA on the carbon-carbon double bonds of polyisoprene. Thus, for accurate evaluation of the selectivity of the method according to the invention, the degree of functionalization, designated DOF hereinafter in the description, of the polyisoprene contained in scrap tyres was studied in parallel under conditions identical to those used when carrying out the method. The polyisoprene selected for determining the DOF has a degree of polymerization equivalent to that of the scrap lorry tyres used. The value of the DOF will therefore allow accurate evaluation of the specificity of the devulcanization reaction with respect to disulphide bridges and carbon-sulphur bonds. A process giving a DOF less than 30% will be regarded as having acceptable selectivity. The balance reaction of depolymerization of polyisoprene by reaction of the devulcanizing agent on the carbon-carbon double bonds of polyisoprene or polybutadiene is presented by the following reaction scheme 2.

##STR00007##

[0138] The balance reaction of depolymerization of polyisoprene by reaction of the devulcanizing agent on the carbon-carbon double bonds of polyisoprene or polybutadiene may be supplemented with the following reaction scheme 3.

##STR00008##

[0139] According to a first embodiment, the method for synthesizing oligomers by devulcanization is carried out under air and the DA is benzoyl peroxide of formula 1a, which corresponds to the compound of formula 1 in which R and R′ are hydrogen atoms,

##STR00009##

[0140] The solvent used is xylene.

[0141] Table 1 shows the effect of the temperature on the method according to the first embodiment. It will be noted that moving from a temperature of 80° C. to a temperature of 100° C. causes the DDV to be multiplied by a factor of two but the DOF to be multiplied by a factor of twelve. This demonstrates that the depolymerization reaction is significant beyond 80° C.

TABLE-US-00001 TABLE 1 Volume of Temperature xylene (ml) Time (hours) (° C.) DDV DOF 25 4 80 31.5%  7% 25 4 100 69.3% 83%

[0142] Table 2 shows the effect of time on the method according to the first embodiment. Table 2 shows that the DDV increases, reaching a maximum at a reaction time of 4 hours, and then slowly decreases. For its part, the DOF is relatively stable and low. It changes from 5% for reaction times of two and three hours to 7% for reaction times of four and five hours.

TABLE-US-00002 TABLE 2 Volume of Temperature xylene (ml) Time (hours) (° C.) DDV DOF 25 2 80 17.4% 5% 25 3 80 .sup. 26% 5% 25 4 80 31.5% 7% 25 5 80 30.5% 7%

[0143] Table 3 shows the effect of the concentration of DA on the method according to the first embodiment. For a concentration of 0.24 phr per millilitre of solvent, i.e. a quantity of 6 wt % of DA in a volume of solvent of 25 ml, the DDV is relatively low and the DOF is 5%. For a concentration of DA of 0.6 phr/ml of solvent, i.e. a quantity of 6 wt % of DA in a volume of solvent of 10 ml, regarded as a high concentration, the DDV is 61.3% and the DOF is 82%. For a concentration of DA of 0.06 phr/ml of solvent, i.e. a quantity of 6 wt % of DA in a volume of solvent of 100 ml, regarded as a low concentration, the DDV is 61.2% and the DOF is 18%. Surprisingly, for one and the same time for which the method is carried out, the DDV obtained for a high concentration of DA is similar to that obtained for a low concentration of DA. The high value of the DOF observed when carrying out the method with a high concentration of DA confirms the presence of a secondary depolymerization reaction. It should be noted that even if selectivity is low when using a high concentration of DA, the DDV obtained for highly vulcanized waste such as scrap lorry tyres, having a cross-link density of 13.5×104 mol/ml, is at least equal to, or even greater than, that obtained for rubbers having much lower cross-link densities, typically 2.6×104 mol/ml. It can be seen that for low concentrations of DA, the method makes it possible to obtain good DDV values and has very good selectivity, 18% of DOF.

TABLE-US-00003 TABLE 3 Volume of xylene Time Temperature (ml) (hours) (° C.) DDV DOF 25 4 80 31.5%  5% 10 4 80 61.3% 82% 100 4 80 61.2% 18%

[0144] According to a second embodiment, the method is carried out under an inert atmosphere, under argon, the DA is benzoyl peroxide of formula 1a and the solvent used is xylene

##STR00010##

[0145] Table 4 shows the effect of the inert atmosphere on the DDV according to the second embodiment. The DDV is multiplied by a factor of two compared to the method carried out under the same conditions under air. However, the DOF is also multiplied by a factor of two but still has a low value. Thus, when optimum selectivity is required, carrying out the method under air is to be preferred, whereas when an optimum efficiency of devulcanization is required, carrying out the method under argon is to be given preference.

TABLE-US-00004 TABLE 4 Volume of xylene Time Temperature Atmosphere (ml) (hours) (° C.) DDV DOF Under air 25 4 80 31.5%  5% Under 25 4 80 67.3% 14% argon

[0146] Table 5 shows the effect of time on the method according to the second embodiment. Table 5 shows that the DDV increases, reaching a maximum at a reaction time of 3 hours, and then quickly decreases. For its part, the DOF increases with time. It changes from 100/for reaction times of two and three hours to 140/and then 160/for reaction times of four and five hours.

TABLE-US-00005 TABLE 5 Volume of Temperature xylene (ml) Time (hours) (° C.) DDV DOF 25 2 80 60% 10% 25 3 80 70% 10% 25 4 80 67.3%.sup.  14% 25 5 80 55% 16%

[0147] Table 6 shows the effect of the concentration of DA on the method according to the second embodiment. It can be seen that a decrease in the concentration of DA leads to a decrease in the DDV and an increase in the DOF. Thus, in contrast to carrying out the method under air, values of the concentration of DA greater than 0.06 phr/ml of solvent are to be preferred when the method is carried out under argon. This indicates that when the method is carried out under argon, in addition to the reactions of devulcanization and of radical depolymerization, an additional reaction appears. It may for example be cross-linking of sulphur-containing radicals on disulphide bridges and/or double bonds of the polymer chain.

[0148] It can also be seen that carrying out the method according to the second embodiment for values of concentration of DA greater than 0.06 phr/ml of solvent gives rise to values of DDV and of DOF that are equivalent to, or even slightly better than, those obtained when the method is carried out according to the first embodiment for values of concentration of DA less than 0.2 phr/ml of solvent.

TABLE-US-00006 TABLE 6 Volume of xylene Time Temperature Atmosphere (ml) (hours) (° C.) DDV DOF Under argon 25 4 80 67.3% 14% Under argon 100 4 80 59.3% 20% Under air 100 4 80 61.2% 18%

[0149] According to a particular embodiment of the method according to the invention, a step of activation of the granules of scrap tyres is carried out prior to the devulcanization reaction.

[0150] According to a first variant, activation comprises a step of swelling of the granules. Table 7 shows the effect of the type of solvent on the degree of swelling of the granules and on the proportion of the granules solubilized by the solvent. This swelling step consists of putting a given quantity of granules from scrap tyres in a solvent for a given time and recovering the proportion of the scrap tyres that has been solubilized by the solvent. The experiments were each carried out three times, and the calculated average is reported in Table 7. Table 7 shows that the polar solvents, acetone (dipole moment μ=2.86 debye), are not effective, the solubilized proportion of the waste is very low and the degree of swelling is also very low. The non-polar solvents, pentane (dipole moment μ=0.2 D), are not very effective. However, the solvents of low polarity, dichloromethane (DCM) (dipole moment μ=1.55 D) and tetrahydrofuran (THF) (dipole moment μ=1.75 D), show a very good efficiency of dissolution of the waste and swelling of the waste. This is in particular the case when the experiment is carried out using an extractor of the Soxhlet type. Generally, it is considered that a non-polar solvent has a polar moment less than 0.5 D and that a polar solvent has a dipole moment greater than 2D or even 2.5 D. Regarding the protic or aprotic aspect of the solvent, it would appear that the protic solvents have the lowest efficiency. In fact, when a comparison is made, ethanol (μ=1.74 D), which has a dipole moment equal to that of THF and lower than that of acetone, produces the lowest degree of swelling and the lowest dissolution of the waste.

TABLE-US-00007 TABLE 7 Degree of Soluble Solvent Time Conditions swelling fraction DCM 2.5 h 20 ml 128% 6.4% DCM 2.5 h Soxhlet 131% 8.4% DCM 24 h 20 ml 131% 9.8% THF 24 h 20 ml 126% 10.7%  Acetone 2.5 h 20 ml  12% 4.9% Ethanol 2.5 h 20 ml  5% 2.3% Pentane 2.5 h 20 ml  49% 7.7%

[0151] According to a second variant, activation comprises a step of lyophilization of the granules. The granules are swollen in DCM for 24 h by the method described in the first variant. Then, a DCM-ethanol and then ethanol-water solvent exchange is carried out. The water-swollen granules are then frozen and lyophilized for 48 h.

[0152] Table 8 shows the effect of activation by lyophilization on the devulcanization of granules from scrap tyres.

[0153] When the method is carried out under air starting from lyophilized granules, the DDV is markedly greater than that obtained with granules that have not undergone activation. The DOF remains unchanged, and low.

[0154] When the method is carried out under argon starting from lyophilized granules, the DDV decreases significantly whereas the DOF remains constant. This indicates that the radical cross-linking that appears when the method is carried out under argon is exacerbated when the scrap tyres are lyophilized. Moreover, when the concentration of DA decreases, from 0.24 phr/ml of solvent to 0.06 phr/ml of solvent, the DDV decreases and the DOF increases. This again confirms the above results and those presented in Table 6, according to which radical cross-linking is amplified when the concentration of DA decreases.

TABLE-US-00008 TABLE 8 Volume of Type of xylene Time Temperature waste Atmosphere (ml) (hours) (° C.) DDV DOF Granules Under air 25 4 80 31.5%  7% Lyophilized Under air 25 4 80 53.1%  7% granules Granules Under argon 25 4 80 67.3% 14% Lyophilized Under argon 25 4 80 55.8% 14% granules Lyophilized Under argon 100 4 80 .sup. 48% 20% granules Granules Under argon 100 4 80 59.3% 20%

[0155] According to a third variant, activation comprises a step of swelling of the granules in an ionic liquid, trihexyltetradecylphosphonium chloride, known by the trade name “Cyphos 101” for 12 hours.

[0156] Table 9 shows the effect of carrying out the method under air starting from granules that have undergone a step of swelling in ionic liquid. Compared to the DDV and DOF obtained in the absence of activation, an increase of the DDV by a factor of two and a clear increase in the DOF is observed. Compared to the DDV and DOF obtained during activation by lyophilization, an appreciable increase in the DDV and a clear increase in the DOF is observed.

TABLE-US-00009 TABLE 9 Volume of Time Temperature Type of waste xylene (ml) (hours) (° C.) DDV DOF Granules swollen 25 4 80 55.8% 30%  in ionic liquid Granules 25 4 80 31.5% 7% Lyophilized 25 4 80 53.1% 7% granules

[0157] According to a fourth variant, activation comprises a step of swelling of the granules by treatment with supercritical CO.sub.2 (ScCO.sub.2). The activation step consists of treating the granules by swelling in ethanol or acetone, and then carrying out a solvent exchange between ethanol, or acetone, and ScCO.sub.2 in a dehydrator. The results of the synthesis of polymers by devulcanization carried out starting from granules swollen by treatment with ScCO.sub.2 are presented in Table 10.

TABLE-US-00010 TABLE 10 Volume of Time Temperature Type of waste xylene (ml) (hours) (° C.) DDV DOF Granules 25 4 80 27% 7% swollen by treatment with ScCO.sub.2

[0158] According to another embodiment of the method according to the invention, the devulcanizing agent used corresponds to formula 1 in which R and R′ are different from a hydrogen atom. These DAs are therefore derivatives of benzoyl peroxide (BPO). The use of said derivatives makes it possible to synthesize functionalized oligomers according to formula 3 and/or 3′ by devulcanization of rubber waste. Besides the fact that the synthesized oligomers are derived from rubber waste, the fact that they are functionalized constitutes an additional advantage with a view to their subsequent use. In fact, as the functional group may comprise a wide choice of substituents R, R′ such as proposed according to the invention, subsequent use is facilitated thereby and the technical fields of potential applications are broadened. Advantageously, the derivatives of PBO used are those corresponding to formula 1 in which R and R′ are identical and are in the para position relative to the peroxide group. In a more preferred embodiment, the derivatives correspond to formulae 1b, 1c and 1d. The compound of formula 1b comprises two fluorine atoms as substituent R and R′, which exert an effect of the attractor inductive type on the aromatic ring to which they are bound. The compound of formula 1c comprises two methoxy groups (—OCH.sub.3) as substituent R and R′, which exert an effect of the donor mesomeric type on the aromatic ring to which they are bound. The compound of formula 1d comprises acetoxy groups (—C(═O)OCH.sub.3) as substituent R and R′, which exert an effect of the attractor mesomeric type on the aromatic ring to which they are bound.

##STR00011##

[0159] The method was carried out under air starting from granules from scrap lorry tyres that had not undergone activation. The effect of the various substituents R and R′ is shown in Table 11. Each of the derivatives of BPO (1b, 1c and 1d) gives rise to a clear improvement of the DDV. Compounds 1b and 1d give rise to an improvement of the DDV by a factor of two. Compounds 1b and 1c also produce a notable increase in the DOF, but it remains less than 30%. Compound 1d, however, produces a decrease in the DOF to 2% and consequently makes the method highly selective. Surprisingly, whether the electron density of the aromatic ring is increased by the effect of the substituents exerting a donor effect or whether its electron density is depleted by the effect of the substituents exerting an attractor effect, the DDV remains markedly increased with the substituted derivatives of BPO comprising donor or attractor substituents R and R′.

[0160] This therefore makes it possible to envisage the synthesis of a great variety of functionalized oligomers. The results obtained when compound 1d is used when carrying out the method are particularly interesting in terms of selectivity and DDV.

TABLE-US-00011 TABLE 11 Volume Devulcanizing of xylene Time Temperature agent (ml) (hours) (° C.) DDV DOF 1a 25 4 80 31.5%  7% 1b 25 4 80 57.9% 27% 1c 25 4 80 50.2% 27% 1d 25 4 80 60.4%  2%

[0161] According to this embodiment, other derivatives of benzoyl peroxide (BPO) were used as DAs. These compounds are designated 1e, 1f, 1g and 1 h. Compound 1e comprises two methyl groups (—CH.sub.3) as substituent R and R′ which exert an effect of the donor inductive type on the aromatic ring to which they are bound. Compound if comprises two nitro groups (—NO.sub.2) as substituent R and R′ which exert an effect of the attractor mesomeric type on the aromatic ring to which they are bound. Compound 1g comprises two chlorine atoms in the ortho position as substituent R and R′ which exert an effect of the attractor inductive type on the aromatic ring to which they are bound. Compound 1h comprises two bromine atoms as substituent R and R′ which exert an effect of the attractor inductive type on the aromatic ring to which they are bound.

##STR00012##

[0162] The method was carried out under air starting from granules from scrap lorry tyres that had not undergone activation. The effect of the various substituents R and R′ is shown in Table 12. All the derivatives of BPO presented produce a clear improvement of the DDV. Compounds 1e, 1g and 1 h produce an improvement of the DDV greater than a factor of two. Compound if also produces a notable increase in the DOF, but it remains less than 30%. Compounds if and 1 h also produce a decrease in the DOF of 6% and 3% respectively and consequently make the method highly selective. Once again, whether the electron density of the aromatic ring is increased by the effect of the substituents exerting a donor effect or whether its electron density is depleted by the effect of the substituents exerting an attractor effect, the DDV remains markedly increased with the substituted derivatives of BPO comprising donor or attractor substituents R and R′.

[0163] Regarding compound 1g, it is to be noted that to obtain DDV levels equivalent to the other compounds presented (1b, 1c, 1d, 1e, 1f and 1 h), a reaction time of three hours was selected. A reaction time of 4 h leads to a DDV equivalent to that obtained with compound 1a and to a substantial increase in the DOF.

[0164] These results confirm the possibility of envisaging the synthesis of a great variety of functionalized oligomers. The results obtained when compounds 1f and 1 h are used when carrying out the method are particularly interesting in terms of selectivity and DDV. The results obtained when compounds 1e and 1 h are used when carrying out the method are particularly interesting in terms of DDV. Compounds 1d and 1 h seem quite particularly interesting in view of the high DDV that they make it possible to obtain and the low DOF (selective reaction, i.e. little depolymerization).

TABLE-US-00012 TABLE 12 Volume Devulcanizing of xylene Time Temperature agent (ml) (hours) (° C.) DDV DOF 1e 25 4 80 65.2% 12%  1f 25 4 80 52.1% 6% 1g 25 3 80 60.6% 14.8%   1h 25 4 80 62.2% 3%

[0165] According to a third embodiment, the solvent used when carrying out the method is trihexyltetradecylphosphonium chloride, an ionic liquid marketed under the name “Cyphos 101”, the DA used is benzoyl peroxide of formula 1a, and the method is carried out under air or under an inert atmosphere. The use of an ionic liquid as solvent gives rise automatically to swelling of the waste, concomitantly with devulcanization. This makes it possible to increase the DDV, as discussed above. Furthermore, the use of an ionic liquid as solvent actually gives rise to precipitation of the synthesized functionalized oligomers. Accordingly, the method can be carried out continuously and no longer requires an extraction step subsequent to the carrying out of devulcanization.

[0166] According to the third embodiment, additional experiments were carried out to illustrate the effect of the solvent. The DDV and the DOF were measured after the method was carried out in a eutectic solvent, choline chloride/urea, designated 2a, and in ionic liquids, respectively in “Cyphos 101”, designated 2b, and in dioctylimidazolium bromide ([DOIM][BR]), designated 2c. The method was carried out under air starting from granules from scrap lorry tyres that had not undergone prior activation. BPO was used as DA. The results are reported in Table 13.

[0167] In the case of “Cyphos 101”, the extraction of the products of the devulcanization reaction was not sufficient for determining the DOF. On comparing these results with those obtained with compound 1a (BPO) in Table 11, it can be seen that the DDV is increased considerably when ionic liquids or eutectic solvents are used. Conversely, a slight increase in the DOF is observed when a eutectic solvent is used and a sizeable increase when an ionic liquid is used.

TABLE-US-00013 TABLE 13 Volume of solvent Time Temperature Solvent (ml) (hours) (° C.) DDV DOF 2a 25 4 80 54.2% 10% 2b 25 4 80 45.6% — 2c 25 4 80 53.7% 21%

[0168] The results presented above demonstrate that the method for synthesizing polymers by devulcanization according to the invention makes it possible, among other things, to obtain functionalized polymers that may contain a large number of different substituents, degrees of depolymerization lower than those obtained by the methods usually used and degrees of devulcanization higher than those obtained by the methods usually used.