Polymer comprising repeating units consisting of a substituted pyrrole ring and products obtained by combining said polymers with carbon allotropes

Abstract

The present invention relates to a polymer comprising repeating units consisting of a substituted pyrrole ring. In particular, the repeating units consist of substituted pyrrole containing polar groups capable of interacting with carbon allotropes such as carbon nanotubes, graphene or nanographites, in order to improve the chemical-physical characteristics of the allotropes mainly by increasing their dispersibility and stability in liquid media and in polymer matrices. The invention also relates to products of addition of these polymers with carbon allotropes in order to obtain easily dispersible macromolecules.

Claims

1. Adduct of a polymer comprising repeating units of formula (I), ##STR00037## wherein if R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, C2-C22 linear or branched alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, C2-C22 linear or branched C2-C22 alkynyl-aryl, heteroaryl; then R is independently selected from the group consisting of: ##STR00038## wherein R5, R6, R7 are selected from the group consisting of: saturated or unsaturated linear or branched C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group with no heteroatoms unsubstituted or substituted by one or more linear or branched C1-C22 hydrocarbon chains, aromatic group containing from 1 to 3 heteroatoms unsubstituted or substituted by one or more saturated or unsaturated linear or branched C1-C22 hydrocarbon chains, or R6 is equal to zero; ##STR00039## wherein R8 is selected from: linear or branched saturated or unsaturated C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group without heteroatoms or substituted by one or more linear or branched saturated or unsaturated C1-C22 hydrocarbon chains, aromatic group containing heteroatoms in number from 1 to 3 unsubstituted or substituted by one or more linear or branched saturated or unsaturated C1-C22 hydrocarbon chains, or compounds of formula ##STR00040## wherein R9, R10, R11, R12 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl or linear or branched C2-C22 alkenyl or alkynyl, aryl, linear or branched C2-C22 alkyl-aryl, linear or branched C2-C22 alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl n is an integer from 1 to 1000; if R is ##STR00041## wherein R13 and R14 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, linear or branched C2-C22 alkenyl or alkynyl, aryl, linear or branched C2-C22 alkyl-aryl, linear or branched C2-C22 alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; or ##STR00042## wherein R15 is independently selected from the group consisting of: a saturated or unsaturated, linear or branched C1-C3 hydrocarbon chain, a carbonyl group; then R1 and R4 are ##STR00043## wherein R16, R17 are independently selected from the group consisting of: hydrogen, C1-C3 alkyl, linear or branched C2-C22 alkenyl or alkynyl, aryl, linear or branched C1-C22 alkyl-aryl, linear or branched C2-C22 alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; m is an integer from 1 to 1000; and a carbon allotrope selected from the group consisting of carbon black, fullerene, single-wall or multiwall carbon nanotube, graphene, graphite with a number of graphene layers from 2 to 10000, graphite oxide, and graphene oxide.

2. Adduct according to claim 1, wherein in said polymer R is: ##STR00044## wherein R5 is selected from the group consisting of: saturated or unsaturated linear or branched C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group with no heteroatoms unsubstituted or substituted by one or more linear or branched C1-C22 hydrocarbon chains, aromatic group containing from 1 to 3 unsubstituted or substituted heteroatoms by one or more linear or branched saturated or unsaturated C1-C22 hydrocarbon chains, and R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; n is an integer from 1 to 1000.

3. Adduct according to claim 1, wherein in said polymer R is ##STR00045## and R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; n is an integer from 1 to 1000.

4. Adduct according to claim 1, wherein in said polymer R is ##STR00046## wherein R7 is selected from the group consisting of: saturated or unsaturated linear or branched C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group without heteroatoms unsubstituted or substituted by one or more linear or branched C1-C22 hydrocarbon chains, aromatic group containing from 1 to 3 unsubstituted or substituted heteroatoms by one or more saturated or unsaturated linear or branched C1-C22 hydrocarbon chains, and R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl, n is an integer from 1 to 1000.

5. Adduct according to claim 1, wherein in said polymer R is ##STR00047## wherein R6 is selected from the group consisting of: saturated or unsaturated linear or branched C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group with no heteroatoms unsubstituted or substituted by one or more linear or branched C1-C22 hydrocarbon chains, aromatic group containing from 1 to 3 unsubstituted or substituted heteroatoms by one or more saturated or unsaturated linear or branched C1-C22 hydrocarbon chains, or R6 is equal to zero, and R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl, n is an integer from 1 to 1000.

6. Adduct according to claim 1, wherein in said polymer R is ##STR00048## wherein R8 is selected from the group consisting of: saturated or unsaturated linear or branched C1-C22 hydrocarbon chain, unsubstituted or substituted C5-C6 cyclic hydrocarbon chain, aromatic group with no heteroatoms unsubstituted or substituted by one or more linear or branched C1-C22 hydrocarbon chains, aromatic group containing from 1 to 3 unsubstituted or substituted heteroatoms by one or more saturated or unsaturated linear or branched C1-C22 hydrocarbon chains, or compounds of formula (II) ##STR00049## wherein R9, R10, R11, R12 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl, and R1, R2, R3, R4 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; n is an integer from 1 to 1000.

7. Adduct according to claim 1, wherein in said polymer R is ##STR00050## wherein R13 and R14 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; or ##STR00051## wherein R15 is independently selected from the group consisting of: saturated or unsaturated linear or branched C1-C3 hydrocarbon chain, carbonyl group; ed R1 e R4 sono ##STR00052## wherein R16, R17 are independently selected from the group consisting of: hydrogen, C1-C22 alkyl, alkenyl or alkynyl, linear or branched C2-C22 alkyl, aryl, C1-C22 alkyl-aryl, alkenyl-aryl, linear or branched C2-C22 alkynyl-aryl, heteroaryl; m is an integer from 1 to 1000.

Description

(1) Characteristics and advantages will be more readily apparent from the description of preferred, but not exclusive, embodiments of the present invention, given as examples in the attached drawings,

(2) wherein:

(3) FIG. 1 is the .sup.1H-NMR 400 MHz in DMSO-d6 spectrum of the polymer as in example 3;

(4) FIG. 2 is the C13-NMR in DMSO-d6 spectrum of the polymer as in example 3;

(5) FIG. 3 is the .sup.1H-NMR 400 MHz in DMSO-d6 spectrum of the polymer as in example 4;

(6) FIG. 4 is the C13-NMR in DMSO-d6 spectrum of the polymer as in example 4.

EXAMPLES

Examples 1-9: Synthesis of the Polymer

Example 1

(7) High T Polyurethane Synthesis

(8) 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.96 mmol) and hexamethylene diisocyanate (0.498 g, 2.96 mmol) are mixed in a 50 mL two-neck flask fitted with a magnetic agitator and kept in a nitrogen atmosphere. The system is brought up to a temperature of 90° C. and agitated for 150 min. After this time has elapsed, the mixture is cooled to 25° C. and immediately solubilized in dichloromethane (3 mL). The polymer is purified by washing with diethyl ether (3×25 mL), filtered through a Buchner funnel and the traces of solvent are removed under a low pressure with the aid of a vacuum pump. 750 mg of polymer are isolated.

Example 2

(9) Low T Polyurethane Synthesis

(10) 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.96 mmol) and hexamethylene diisocyanate (0.498 g, 2.96 mmol) are mixed in a 50 mL two-neck flask fitted with a magnetic agitator and kept in a nitrogen atmosphere. The system is maintained at 45° C. for 150 min. After this time has elapsed, the polymer obtained is solubilized in dichloromethane (3 mL). The polymer is then purified by washing with diethyl ether (3×25 mL), filtered through a Buchner funnel and the traces of solvent are removed under a low pressure with the aid of a vacuum pump. 420 mg of polymer are isolated.

Example 3

(11) Synthesis of Polyurethanes with OH Terminals

(12) Example 3 is conducted in the same way as Example 1, except that the reaction between 0.500 g of 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol and 0.498 g of hexamethylene diisocyanate is conducted for 120 min. After this time has elapsed, another 0.500 g of 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol are added. The system is then agitated for another 60 minutes. 600 mg of polymer are isolated.

(13) The polymer thus obtained was analyzed by nuclear magnetic resonance (NMR) imaging. The one-dimensional spectra .sup.1H- and .sup.13C-NMR at 400 and 100.6 MHz, respectively, were recorded using a Bruker AV 400 equipped with a 5 mm multinuclear probe (reverse detection) (Bruker, Rheinstetten, Germany). The solvents used were deuterated: chloroform, dimethyl sulfur oxides, dimethyl sulfoxide. The temperature of the experiments was 27° C.

(14) FIG. 1 and FIG. 2 respectively show the NMR spectra of the polyurethane, 1H and 13C.

Example 4

(15) Synthesis of Polyurethanes with —NCO Terminals

(16) Example 4 is conducted in the same way as Example 3, with the difference that, after the first 120 min of reaction, 0.500 g of hexamethylene diisocyanate are added instead of 0.550 g of diol. After adding the second aliquot of isocyanate, the system is agitated for another 60 minutes. 670 mg of polymer are isolated.

(17) The polymer thus obtained was analyzed by (NMR) imaging. The one-dimensional spectra .sup.1H- and .sup.13C-NMR, at 400 and 100.6 MHz, respectively, were recorded using a Bruker AV 400 equipped with a 5 mm multinuclear probe (reverse detection) (Bruker, Rheinstetten, Germany). The solvents used were deuterated: chloroform, dimethyl sulfoxide. The temperature of the experiments was 27° C.

(18) FIG. 3 and FIG. 4 show the NMR spectra of the polyurethanes 1H and 13C, respectively.

Example 5

(19) Polyether Synthesis (Method A)

(20) 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.95 mmol) and anhydrous potassium hydroxide (0.500 g, 5.90 mmol) are added one after the other to a 25 mL single-neck flask at room temperature. After 30 min, 1,6-dibromohexane (0.545 mL) is added and the mixture is first sonicated for 30 min, then heated to 130° C. for 60 min. After this time has elapsed, the mixture is first cooled to room temperature, then water (10 mL) is added and then extracted with ethical acetate three times. The organic phases are pooled together and anhydrified on sodium sulfate, then dried under a low pressure. The residue is resolubilized in dichloromethane (2 mL) and added in an excess of hexane. 510 mg of polymer are isolated.

Example 6

(21) Polyether Synthesis (Method B)

(22) 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.95 mmol) is solubilized in isopropanol (10 mL) in a 25 mL flask and anhydrous potassium hydroxide (0.500 g, 5.90 mmol) is added at room temperature. After 30 min, 1,6-dibromohexane (0.545 mL) is added and the mixture is first sonicated for 30 min, then heated to 90° C. for 60 min. After this time has elapsed, the solvent is removed under a low pressure with the aid of a rotary evaporator. The residue is resolubilized in dichloromethane (10 mL), washed with a saturated solution of magnesium chloride (15 mL), anhydrified on sodium sulfate and dried. 500 mg of polymer are isolated.

Example 7

(23) Polyether Synthesis (Method C)

(24) 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.95 mmol) and anhydrous potassium hydroxide (0.500 g, 5.90 mmol) are added one after the other to a 25 mL single-neck flask at room temperature. After 30 min, 1,6-dibromoesano (0.545 mL) is added and the mixture is irradiated with microwaves for 30 min at 130° C. After this time has elapsed, water (10 mL) is added and the mixture is extracted three times with ethyl acetate. The organic phases are pooled together, anhydrified on sodium sulfate, and dried under a low pressure. The residue is resolubilized in dichloromethane (2 mL) and added in an excess of hexane. 600 mg of polymer are isolated.

Example 8

(25) Polyester Synthesis

(26) A solution of 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (0.500 g, 2.95 mmol) in chloromethane (10 mL) is placed in a 25 mL single-neck flask and the following are added one after the other: first adipoyle chloride (0.540 g, 2.95 mmol), then triethylamine (0.820 mL) at 0° C., in an inert atmosphere. After 20 min, the mixture is warmed to room temperature and agitated for 5 hours. After this time has elapsed, distilled water (5 mL) is slowly added and the mixture is dried under a low pressure. The residue is resolubilized in dichloromethane (10 mL), repeatedly washed with a saturated solution of NaCl (3×15 mL), anhydrified on sodium sulfate and concentrated under a low pressure. 570 mg of polymer are isolated.

Example 9

(27) Polycarbonate Synthesis

(28) The following are placed one after the other in a 100 mL flask fitted with a Claisen condenser and a thermometer, and maintained in a nitrogen atmosphere: 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediolo (0.500 g, 2.95 mmol), diethyl carbonate (0.349 g, 2.95 mmol) and 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (2 mg, 0.5% mol). The mixture is agitated for 60 min at 80° C. After this time has elapsed, the system is connected to a vacuum pomp and left at 90° C. for 3 hours. The reaction mixture is cooled to room temperature, then water (10 mL) is added. The water is extracted by means of three successive washes performed with 10 mL of ethyl acetate. The organic phases are pooled together, anhydrified on sodium sulfate and dried under a low pressure.

Example 10

(29) Monomer Synthesis for Polypyrrole

(30) The monomer used is 2-(1H-pyrrol-1-yl)-1,3-diethyl propan diether.

(31) ##STR00036##

(32) This monomer is a yellow oil.

(33) 1.4534 g of 2-(1H-pyrrol-1-yl)-1,3-propanediol (0.0103 mol) and 2.7128 g of finely-powdered KOH (0.0484 mol) are mixed in a single-neck flask fitted with a magnetic agitator, then 4 ml of ethyl iodide (7.8 g, 0.0500 mol) and 2 ml of THF are added to the reaction mixture. The reaction mixture is agitated for a weekend at room temperature. After this time has elapsed, the crude reaction product is a white precipitate and a yellow solution. In TLC, using AcOEt/hexane 7:3 as the eluent, the starting product is completely converted into the end product. The solution containing the bisubstituted product is separated from the solid by filtering and dried. The derivative obtained is isolated as a yellow oil with an 85% yield.

(34) Polypyrrole Synthesis

(35) 0.6 ml of H.sub.2O, 0.0600 g of 2-(1H-pyrrol-1-yl)-1.3-diethyl propan diether (0.000304 mol), 0.0090 g of AgNO.sub.3 (0.000053 mol) and 0.1154 g of K.sub.2S.sub.2O.sub.8 (0.000679 mol) are mixed in the above order in a single-neck flask fitted with a magnetic agitator at room temperature. The resulting biphasic solution is agitated overnight, after which it reveals a yellow supernatant and a black, viscous precipitate. After the stated time has elapsed, the two phases of the reaction mixture are separated by decanting. The dark tarry precipitate is dried with a mechanical pump for 3 hours at room temperature. In TLC, using an AcOEt/MeOH, 95:5 eluent mixture, the precipitate reveals the disappearance of the starting compound Rf=0.55 (not detectable on UV-vis spectroscopy) and the presence of a stain with Rf=0 (UV-vis, λ=254 nm and 366 nm).

Examples 11-13: Preparation of the Polymer and Carbon Allotrope Adduct 1

Example 11

(36) Adduct consisting of polyurethane and carbon nanotube (CNT). Single-walled or multiwalled carbon nanotubes are used. The multiwalled carbon nanotubes (MWCNT) used are the NC7000 series by NANOCYL™ Inc. They are used as received from the supplier. The multiwalled carbon nanotubes (MWCNT) have a mean diameter from 3 to 20 nm, they are between 20 nm and 10 micron long, and the number of walls varies between 2 and 20. The carbon nanotubes are sonicated in acetone (1 mg/mL) in an ultrasound bath (2 L, power 260 W) for 15 min. Before any separation occurs, a solution of the polyurethane obtained in Example 1 in acetone is added to the unstable suspension. The resulting suspension is further sonicated for another 15 min and a stable suspension is obtained. The stability of the suspension was tested by checking for the absence of separation after centrifugation (5000 rpm, 5 minutes), using an ALC-Centrifugette 4206, and after storing the suspension at room temperature with no further agitation for 7 months. The suspensions were stored in glass laboratory vials with a capacity of 5 mL at a concentration of 1 mg/mL; 3 mg of CNT/PU were placed in a vial and 3 mL of solvent were added.

Example 12

(37) Adduct consisting of polyether and carbon nanotubes (CNT). Single-walled or multiwalled carbon nanotubes are used. The multiwalled carbon nanotubes (MWCNT) used are the NC7000 series by NANOCYL™ Inc. They are used as received from the supplier. The multiwalled carbon nanotubes (MWCNT) have a mean diameter from 3 to 20 nm, they are between 20 nm and 10 micron long, and the number of walls varies between 2 and 20.

(38) The carbon nanotubes are sonicated in ethyl acetate (1 mg/mL) in an ultrasound for 15 minutes. Before any separation occurs, a solution of the polyurethane obtained in Example 5 in ethyl acetate is added to the unstable suspension. The resulting suspension is further sonicated for another 15 min and a stable suspension is obtained. The stability of the suspension was tested by checking for the absence of separation after centrifugation (5000 rpm, 5 minutes), using an ALC-Centrifugette 4206, and after storing the suspension at room temperature with no further agitation for 3 months. The suspensions were stored in glass laboratory vials with a capacity of 5 mL at a concentration of 1 mg/mL; 3 mg of CNT/PU were placed in a vial and 3 mL of solvent were added.

Example 13

(39) Adduct Consisting of Polyether and nanoG.

(40) The graphite used is Synthetic Graphite 8427, purchased from Asbury Graphite Mills Inc., with a minimum carbon content of 99.8% by weight and a surface area of 330 m.sup.2/g. It is characterized by approximately 35 overlapping layers of crystalline aggregate, as reported in “Chemically Reduced Graphite Oxide with Improved Shape Anisotropy” J. Phys. Chem. C 116 (2012) 24809-24813. It has nanometric dimensions and is known as nanographite (nanoG).

(41) nanoG is sonicated in ethyl acetate (1 mg/mL) in an ultrasound bath for 30 min. A solution of the polyether prepared in Example 5 in ethyl acetate is added to the unstable suspension thus prepared before any separation occurs. The resulting suspension is further sonicated for 30 min and a stable suspension is obtained. The stability of the suspension was tested by checking for the absence of separation after centrifugation (5000 rpm, 5 minutes), using an ALC-Centrifugette 4206, and after storing the suspension at room temperature with no further agitation for 2 months. The suspensions were stored in glass laboratory vials with a capacity of 5 mL at a concentration of 1 mg/mL; 3 mg of NanoG/polyether were placed in each vial and 3 mL of solvent were added.

Examples 14-15: Stability Assessment on the Compound According to the Invention, and Example for Comparison

Example 14

(42) The suspension of Example 10 is dried, obtaining the CNT/polyurethane compound (Compound 14.A).

(43) The powdered CNT/polyurethane compound (100 mg) is placed in a 50 mL round-bottom flask fitted with a magnetic agitator. Then ethyl acetate (25 mL) is added. The resulting mixture is agitated overnight at room temperature. After this time has elapsed, the mixture is centrifuged at 5000 rpm for 30 min. The supernatant solvent is removed. The residual powder is dried under a low pressure, obtaining the Compound 14.B. The Compound A and the Compound B undergo thermogravimetric analysis, conducted with a Mettler TGA SDTA/851 according to the standard method in ISO 9924-1. The samples are heated under a flow of N.sub.2 (at a flow rate of 60 ml/min) from 30° C. to 300° C. at a rate of 10° C. per minute, then maintained at 300° C. for 10 min, then heated from 300° C. to 550° C. at a rate of 20° C. per minute and maintained at 550° C. for 15 min. Then they are heated from 550° C. to 650° C. at a rate of 30° C. per minute and maintained at 650° C. for 20 min. Then they are maintained at <650° C. for a further 20 min in a flow of air (flow rate 60 ml/min): a 1% reduction is found in the weight of the compound attributable to the polyurethane.

Example 15

(44) Example for Comparison

(45) 2,2-dimethylpropanediol (0.403 g, 3.87 mmol) and hexamethylene diisocyanate (0.650 g, 3.87 mmol) are mixed in a 50 mL two-neck flask fitted with a magnetic agitator and kept in a nitrogen atmosphere. The system is brought up to a temperature of 50° C. and agitated for 150 min. After this time has elapsed, another 0.403 g of 2,2-dimethylpropanediol are added. The system is then agitated for a further 60 min. 500 mg of polymer are isolated.

(46) The CNT/polyurethane adduct is generated with the polyurethane thus obtained: the carbon nanotubes are sonicated in acetone (1 mg/mL) by means of an ultrasound bath for 15 min. Before any separation occurs, a solution of the polyurethane obtained in acetone is added to the unstable suspension. The resulting suspension is further sonicated for 15 min. An unstable suspension is obtained from which the solvent is removed under a low pressure, obtaining a powder that constitutes Compound 15A.

(47) This Compound 15A (100 mg) is placed in a round bottom flask (50 mL) fitted with a magnetic agitator. Then ethyl acetate (25 mL) is added. The resulting mixture is agitated overnight at room temperature. After this time has elapsed, the mixture is centrifuged at 5000 rpm for 30 min. The supernatant solvent is removed. The residual powder is dried under low pressure, obtaining the Compound 15B. The Compound A and the Compound B undergo thermogravimetric analysis, conducted with a Mettler TGA SDTA/851 according to the standard method in ISO 9924-1. The samples are heated under a flow of N.sub.2 (at a flow rate of 60 ml/min) from 30° C. to 300° C. at a rate of 10° C. per minute, then maintained at 300° C. for 10 min, then heated from 300° C. to 550° C. at a rate of 20° C. per minute and maintained at 550° C. for 15 min. Then they are heated from 550° C. to 650° C. at a rate of 30° C. per minute and maintained at 650° C. for 20 min. Then they are maintained at <650° C. for a further 20 min in a flow of air (flow rate 60 ml/min): a 23% reduction is found in the weight of the compound attributable to the polyurethane.