WO2024002945A1

WO2024002945A1 - Adduct of a polymer comprising repeating units consisting of a substituted pyrrole ring and an adduct of a carbon allotrope and a pyrrolic compound

Info

Publication number: WO2024002945A1
Application number: PCT/EP2023/067263
Authority: WO
Inventors: Vincenzina BARBERA; Lucia Rita RUBINO; Fatima MARGANI; Maurizio Stefano Galimberti; Peter Zalar
Original assignee: Politecnico Di Milano
Priority date: 2022-06-27
Filing date: 2023-06-26
Publication date: 2024-01-04
Also published as: IT202200013486A1

Abstract

The present invention relates to a screen-printable stretchable conductive carbon ink that comprises pyrrole-functionalized carbon nanoparticles and a specifically designed pyrrole bearing polyurethane binder. In particular, the present invention relates to an adduct comprising a polymer containing repeating units consisting of a substituted pyrrole ring and an adduct between a sp2 carbon allotrope and a pyrrole compound. The adduct comprises a pyrrole ring-substituted polyurethane-based polymer and hydrophilic adducts between a sp2 carbon allotrope and a pyrrole compound.

Description

ADDUCT OF A POLYMER COMPRISING REPEATING UNITS CONSISTING OF A SUBSTITUTED PYRROLE RING AND AN ADDUCT OF A CARBON ALLOTROPE AND A PYRROLIC COMPOUND DESCRIPTION The present invention relates to an adduct comprising a polymer containing repeating units consisting of a substituted pyrrole ring and an adduct between a sp² carbon allotrope and a pyrrole compound. In particular, the invention relates to an adduct comprising a pyrrole ring-substituted polyurethane-based polymer and hydrophilic adducts between a sp² carbon allotrope and a pyrrole compound. Such adduct is preferably used for printed electronics. Printed electronics sets out to revolutionize the way that electronic circuits and components are fabricated by using printing technologies and utilized. This is because printed electronics take advantage of additive manufacturing methods and low- temperature processes. In this regard, this field has already had tremendous success in realizing printed circuit boards and ‘components’ such as transistors, solar cells, and light-emitting diodes on flexible plastic substrates. Futuristic concepts such as those of electronic skins, medical devices, or soft robotics will require materials with excellent flexibility and stretchability to accommodate the extreme mechanical demands placed on them. For example, for some applications related to the human body, strains of up to 50% must be accommodated. This means that constituent materials, such as substrates, conductors, dielectrics, semiconductors, sensors, and encapsulants, must be carefully engineered to perform in challenging conditions. With a toolbox of advanced materials, a mechanically compliant electronic circuit or sensor system can be readily manufactured. Currently, most functional materials used in printed electronics consist of relatively rigid composites, such as those found in conductive wiring (e.g. silver pastes), dielectrics (e.g. clay composites), or sensors (e.g. force sensitive resistors). Other solutions may consist of sintered metallic layers or (doped) conjugated polymers, however the design of materials that embody both the necessary electronic and mechanical performance are limited, necessitating a great deal of rigorous organic synthesis and trial-and-error. To arrive to desired electronic and mechanical properties, the most straightforward approach is to create a composite. Composites are a mixture of two or more materials insoluble in one another, yielding a “new” material with unique physical properties embodying “the best of both worlds”. In this way, one can easily imagine a stretchable conductive material, consisting of a conductive filler (metal nanoparticles, sp² carbon allotropes) and an elastomeric polymer phase (e.g. silicone). While this approach appears simple, various considerations must be made in order to form a homogeneous mix of the two components. Among these considerations are the chemical compatibility of the filler and the polymer phase. In particular, sp² carbon allotropes (graphite, carbon black, carbon nanotubes) represent attractive materials for nanoelectronis thanks to their intrinsic optimal electrical, optical and mechanical properties. However, their use in conductive inks for printed electronics is restricted due to their high aspect ratios resulting in non-covalent attractive interactions (Van der Waals forces), making aggregation difficult to separate and thus preventing a homogeneous dispersion and alignment into the polymer matrix. This degree of attention to surface chemistries and chemical compatibility is rarely taken for the creation of electronic composites for inks in printed electronics. In the present invention, a screen-printable stretchable conductive carbon ink was developed by taking advantage of pyrrole-functionalized carbon nanoparticles and a specifically designed pyrrole bearing polyurethane binder. When compared to an unfunctionalized system, this approach reduces the impact of applied strain on composite resistance while providing performance that is superior to commercially available products. These qualities enable it to be used as the sensing layer in an all-printed force sensing resistor device. It would be highly desirable to have a mixture based on a polymer with adhesive properties on thermoplastic polyurethane supports that can also interact with the conductive component (adduct of formula III), thus generating an interaction between matrix and filler. It would be desirable to have a mixture based on a conductive component (adduct of formula III) that can be dispersed on a polyurethane matrix (formula I) due to the presence of a pyrrole moiety, which can change its solubility parameter. In addition, it would be desirable if the mixture included a polyurethane adhesive, made of repeating units of pyrrole rings, glycerol (as the branching unit), a polyether (flexible unit) and an isocyanate, as well as a conductive part made of conductive carbon black functionalized with 2-(2,5-dimethylpyrrol-1H-yl)-1,3-propanediol, serinol pyrrole, SP. In particular, it would be desirable, that the mixture is composed of a polyurethane adhesive dispersed in 2-butoxyethanol and a conductive carbon black functionalized with 2-(2,5-dimethylpyrrol-1H-yl)-1,3-propanediol dispersed in propylene glycole. The polymer is made up of repeating units consisting of of 2-(2,5-dimethylpyrrol-1H-yl)- 1,3-propanediol, glycerol, a poly(propylene glycol)-block-poly(ethylene glycol)-block- poly(propylene glycol) and hexamethylene diisocyanate. An object of the present invention is to obtain and provide a blend consisting of a polymer with adhesive properties and a conductive part. One object of the present invention is thus to achieve a printable ink made of a polymer with adhesive properties and a conductive part. The mixture should have the following properties: conductivity: 100 kΩ/□ at a thickness of 10 µm; viscosity: 10³ - 10⁴ centipoise at 25 °C; pot life of at least 30 minutes to remain printable; thermal properties: no crosslinking or melting at temperatures up to 110 °C; drying temperature: removal of solvent at a temperatures <120 °C; stretchability: reversible electrical and/or mechanical properties at applied strains of up to 5%. These and other objects of the present invention are achieved by means of an adduct according to claim 1. In particular by means of an adduct of: a polymer comprising repeating units of formula (I),

wherein A, B and D are independently O or S; and wherein at least one of R, R1, R2 or R3 is a substituent of formula (II)

wherein R4 is selected from the group consisting of: saturated or unsaturated linear or branched C1-C10 hydrocarbon chain; wherein R5 and R6 are independently selected from the group consisting of: hydrogen, saturated or unsaturated linear or branched C1-C10 hydrocarbon chain, R7-R14 are independently selected from the group consisting of: hydrogen, C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, aryl, linear or branched C1-C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl- aryl, heteroaryl; and wherein a is 0 or 1; wherein b is 0 or 1; wherein c is 0 or 1; wherein d is 0 or 1; wherein if a is 1, then c is 1 and b and d are zero; wherein if b is 1 then a, c and d are zero; wherein if d is 1 then a, b and c are zero; wherein e is an integer from 1 to 10; wherein f is 0 or 1; wherein g is an integer from 1 to 10000; wherein i is 0 or 1; wherein h is an integer from 1 to 10; wherein j is an integer from 1 to 100; wherein if f is zero then i is 1 and vice versa, or f and i are both 1; when R1, R2, or R3 are not the substituent of formula (II), they are independently selected from the group consisting of: hydrogen, C1-C3 alkyl, linear or branched C2- C10 alkenyl or alkynyl, aryl, linear or branched C1-C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl and when R is not the substituent of formula (II), it is selected from the group consisting of: amine, hydroxyl, hydrogen, linear or branched C1-C10 alkyl, linear or branched C2- C10 alkenyl or alkynyl, aryl, linear or branched C1-C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl or carboxyl; or R is

wherein E, F and G are independently selected from the group consisting of amine, hydroxyl, hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, or from the group consisting of: _,

wherein R15-R29 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, aryl, linear or branched C1-C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl or carboxyl; R24-R26 are -OCH₂-CH3 or -OCH3; R28 is -CH2-SH or -CH2-CH2-S-CH3, L is Oxygen or Sulfur; if L is sulfur, p is an integer from 1 to 4 if L is oxygen, p is an integer from 1 to 2 l, p, q, r are independently integers from 0 to 12. or R is

, wherein R30 can be hydrogen, alkyl, aryl, benzyl, amine, alkylamine, arylamine, benzylamine, or aminoaryl; R31-R35 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, and 1-(4- aminocyclohexyl) methylene; with an adduct of: a sp² carbon allotrope and/or its derivative and a compound of formula (III)

wherein R36-R39 are independently selected from the group consisting of: hydrogen, C1-C3 alkyl, linear or branched C2-C10 alkenyl or alkynyl, aryl, linear or branched C1- C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl; wherein W is selected from the group consisting of: hydrogen, linear or branched C1- C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, aryl, linear or branched C1- C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl or carboxyl; or W is

wherein M, Q and J are independently selected in a group consisting of amine, hydroxyl, hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, or in a group consisting of: ,

wherein R40-R54 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, aryl, linear or branched C1-C10 alkyl-aryl, linear or branched C2-C10 alkenyl-aryl, linear or branched C2-C10 alkynyl-aryl, heteroaryl or carboxyl; R49-R51 can be -OCH2-CH3, -OCH3; R53 can be -CH2-SH; -CH2-CH2-S-CH3, T is Oxygen or Sulfur; if T is sulfur, p’ is an integer from 1 to 4 if T is oxygen, p’ is an integer from 1 to 2 l’, p’, q’, r’ are independently integers from 0 to 12. or W is

wherein R55 is selected from the group consisting of hydrogen, alkyl, aryl, benzyl, amine, alkylamine, arylamine, benzylamine, or aminoaryl; R56-R60 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, and 1- (4-aminocyclohexyl) methylene. It is therefore possible to obtain a screen-printable stretchable conductive carbon ink by taking advantage of pyrrole-functionalized carbon nanoparticles and a specifically designed pyrrole bearing polyurethane binder. Preferably the sp² carbon allotrope and/or its derivative is selected from the group consisting of: carbon black, fullerene, buckminstefullerenes, carbon nanohorns, carbon nanotubes, single-walled or multi-walled, carbon nanobuds, graphene, bilayer graphene, few-layer graphene, graphenylene, cyclocarbons, graphites with a number of stacked graphene layers from 2 to 10000. Preferably the sp² carbon allotrope derivative contains functional groups selected from the group consisting of: − functional groups containing oxygen, preferably hydroxyls, epoxies; − functional groups containing carbonyls, preferably aldehydes, ketones, carboxylic acids; − functional groups containing nitrogen atoms, preferably amines, amides, nitriles, diazonium salts, imines; - functional groups containing sulfur atoms, preferably sulfides, disulfides, sulfinates, sulfoxides, mercaptans, sulfones, sulfinic, sulfoxylic, and sulfonic groups. Preferably said derivative of the carbon allotrope is graphite oxide. Preferably said derivative of the carbon allotrope is graphene oxide. A further object of the present invention is the use of the adduct as defined above, for the preparation of a conductive ink. Preferably, according to a further aspect of the present invention, the conductive ink provides conductive layers in a resistivity range between 1 × 10² Ω/□ to 1 × 10⁶ Ω/□. Preferably, according to a further aspect of the present invention, the conductive ink provides layers for specific applications such as wiring, antistatic coatings, and mechanical protection of connectors or exposed wriring, with resistance < 500 Ω/□. Even more preferably, according to a further aspect of the present invention, the conductive ink provides layers for specific applications such as resistors in printed circuits (forming RC filters, power control, etc.), force-sensing resistors, and fuses with a resistance of up to 10⁶ Ω/□. One more object of the present invention is to provide a conductive ink comprising the adduct as described above. In a preferred embodiment, the adduct according to the present invention is an adduct of: a polymer comprising repeating units of formula (IV),

wherein at least one of R1, R2 or R3 is a substituent of formula (V)

wherein e is an integer from 1 to 2; wherein g is an integer from 1 to 20; wherein i is 0 or 1; wherein f is 0 or 1; wherein if f is 0 then i is 1 and viceversa, or f and i are both 1; when R1, R2, or R3 are not the substituent of formula (V), they are hydrogen. with an adduct of: a sp² carbon allotrope and/or its derivative and a compound of formula (VI)

The polymers (Formula I) according to the present invention are obtained by means of step-growth polymerization processes between hydroxyl groups of a pyrrole compound bearing hydroxyl groups (i.e., 2-(2,5-dimethylpyrrol-1H-yl)-1,3-propanediol, serinol pyrrole, SP) and other polyfunctionalized molecules. Polymerizations in steps Poly-additions or polycondensations can be obtained by means of the polymerization in steps on hydroxyl groups. The polymerization takes place between molecules possessing at least two reactive functional groups. In general terms, at least two molecules of different type, A and B - i.e. two molecules containing functional groups of different type, A and B, wherein each of these molecules contains at least 2 functional groups - are mixed together. The molecule A contains functional groups that can react with the functional groups of the molecule B. One or more molecules of type A and one or more molecules of type B may be used. For instance, the molecule A may contain at least two isocyanate groups and the molecule B may contain at least two hydroxyl groups. Their reaction will thus form urethane bonds and, since every molecule contains at least 2 functional groups, this will lead to the formation of a poly(urethane). To give another example, the molecule A may contain at least 2 carboxylic acids and the molecule B may contain at least two hydroxyl groups, so that their reaction will form ester bonds and, since every molecule contains at least 2 functional groups, this will lead to the formation of a poly(ester). This type of polymerization can be conducted both in the presence and in the absence of a solvent, both in the presence and in the absence of a catalyst, depending on the types of functional group characterizing the molecules A and B. The polymer according to the present invention is a polyurethane based polimer. Polyurethanes are polymers in which a new functional group, carbamate or urethane, is generated that serves as the hub of the repeating unit of the polymer. The terminals of the polymer will be alcohol (-OH) or isocyanate (-N=C=O), or mixed. One or other terminal is obtained depending on the reaction conditions: in any case, the polymerization is conducted in equimolar quantities and, in this case, a urethane polymer with a mixed terminal will be obtained. If an excess of diol is added in a second stage, the polymer will have alcohol terminals, whereas the isocyanate bis terminal will be obtained with an excess of di-isocyanate. Carbamate is generated by adding an alcoholic function to an isocyanate. The reaction can be seen as the addition of an oxygenated nucleophile to a carbonyl derivative. No secondary products are formed during the synthesis of polyurethanes; they are addition polymerizations. According to the known state of the art, polyurethanes are generally synthesized in the presence of solvents, such as dimethyl formamide, using catalysts, tertiary aliphatic amines such as triethanolamine or diazabicyclo[2.2.2]octane, in conditions in which the temperature ranges from 25 to 110 °C, and under ambient air pressure. The process for the preparation of an adduct comprising a sp² carbon allotrope and/or its derivative and a compound of formula (III) as defined above is now described. The process, in a possible embodiment thereof, comprises the following steps: a) preparing a solution of at least a compound of formula (III)

in a protic or aprotic polar solvent selected from the group consisting of: water, alcohols, carbonyl solvents such as acetone, esters such as ethylene acetate, dimethyl sulfoxide, acetonitrile, ethers; b) preparing a suspension of the carbon allotrope in the protic or aprotic polar solvent used to prepare the solution of the compound of formula (III); c) mixing the solution of the compound of formula (III) and the suspension of the carbon allotrope, using a mechanical or magnetic stirring system, or by means of sonication with sonication equipment, for example using an ultrasonic bath; d) removing the solvent from the mixture obtained. With the procedure described in points a) – c) it is possible to obtain a relatively homogeneous dispersion of the filler and of at least one pyrrole derivative and therefore to obtain a homogeneous dispersion on the carbon filler of the pyrrole compound. The solvents are removed before the successive actions aimed at transferring energy to the adduct between the carbon nanofiller and at least one pyrrole derivative. The term "solvent" is used with reference to a chemical species able to solubilize a molecule containing a pyrrole ring of formula (III) and evidently not to the carbon allotrope, for which the solvent only acts as dispersion medium. The solvent must preferably be environmentally friendly. Hereinafter in the present description, the terms “carbon allotrope” and “carbon filler” are used interchangeably. Generally, due to the chemical nature of carbon, dispersion of carbon fillers in liquid matrices is somewhat difficult. The use of ultrasound allows dispersion in reduced times and improves the homogeneity of the dispersion of carbon filler (even a few seconds). Moreover, the use of sonication allows separation, to different extents, of the carbon nanofillers in the elementary units. The carbon nanotubes can be separated into individual tubes from the mass in which they are interwoven with other tubes. The use of low power sonicators, such as classic ultrasonic baths, is advisable. With suitable solvents it is also possible to obtain at least partial exfoliation of a graphite having a different starting number of stacked layers. Graphites with a low number of stacked layers have nanometric dimensions and are called nano-graphites. Therefore, it is preferable for the nanofiller to be preliminarily contacted with a liquid, in order to obtain, through sonication and according to the nanofiller, either unraveling of the carbon nanotubes or an exfoliation, to a greater or lesser extent, of the graphite or nano graphite. This procedure causes an improvement in the contact between the nanofiller and the pyrrole derivative, also causing an increase in the exposed area of the nanofiller. According to the present invention, the term “sonochemistry” indicates the physical- chemical discipline that studies chemical reactions that occur in a solution irradiated by ultrasound. This irradiation gives rise, for an intensity of the range above a given threshold, to a phenomenon of cavitation in the solution. The gaseous microcavities (bubbles) present in the solution, subjected to subsequent expansions and contractions induced by the oscillating sound pressure field, expand and then implode, producing areas of very high temperature and pressure. In these extreme conditions, chemical reactions of considerable interest can occur in the field of synthesis of organic substances, of polymerization processes, and of degradation of toxic and harmful substances. With the application of sonication techniques, it is also possible to obtain amorphous materials that, outside the extreme conditions typical of sonication, would naturally tend to crystallize. The procedure to remove the solvent, pursuant to point d), from the mixture obtained, can take place using any suitable method for removing solvent, such as vacuum evaporation, spray drying, etc. The mixture obtained after removing the solvent from the mixture containing the compound of formula (III) and the carbon allotrope, can be subjected to a further step e), in which energy is transferred to the composition. The addition reaction, which leads to the formation of the adduct, is obtained with transfer of energy to the system formed by the molecule containing the pyrrole ring bound to a diol and by the carbon allotrope. The transfer of energy occurs in order to improve interaction between the molecule containing the pyrrole ring bound to a diol and the carbon allotrope. If there is no transfer of energy, a weaker interaction between the pyrrole ring bound to the diol and the carbon allotrope is obtained. A weaker interaction causes partial release from the carbon allotrope of the molecule containing the pyrrole ring bound to a diol, especially if the adduct is in a polar environment. The forms of energy that can be transferred to the composition to allow its formation are: - mechanical energy - thermal energy - photons Mechanical energy The mixture obtained between the nanofiller and at least one pyrrole derivative, obtained through the process described above in steps a-c, ii treated using a mechanical process. The mechanical treatment consists of placing the powder obtained (nanofiller/PyC) in a jar equipped with stainless steel balls. After closing the jar, it is placed in a planetary mixer and left to rotate at a speed from 200 to 500 rpm for times from 1 to 360 minutes. The powder is decanted immediately afterwards. The mechanical treatment referred to is used both to induce disorder (exfoliation in the case of graphite) in order to obtain improved PyC distribution on the nanofiller, and to induce a much more stable interaction. This is possible considering that the possibility of inducing chemical reactions in dry mixtures by subjecting them to mechanical forces is known in chemistry. Mechanochemistry is a branch of chemistry that is not very well known, but which arouses great interest, given its environmentally friendly nature. A mechanochemical process can be triggered simply by using a mortar and pestle or bulkier systems that simply operate such as ball mills, used both in the pharmaceutical and food industry. Planetary ball mills contain cylindrical reactors, jars, held in vertical position on a rotating platform. In mills with jars containing balls, the collision between balls, which are typically between 5 and 50 in number, is exploited. The efficiency with which a given mill operates in relation to a given mechanochemical transformation is intimately linked to the frequency of collisions between the balls and the inner wall of the jar and to the mechanical energy transferred. These quantities in turn depend on the dynamics of the balls, on their number and size, on the oscillating, or working, frequency of the mill, and on the total amount of powder inside the reactor. Thermal energy The mixture obtained between the nanofiller and at least one pyrrole derivative obtained through the process described above in steps a-c, is treated by means of a thermal process. The thermal treatment consists of placing the powder obtained (nanofiller/PyC) in a reaction flask provided with refrigerant or in a sealed vial. After positioning the reactor on a heating plate, the reaction is conducted at a temperature from 130 to 180°C. Heating is maintained for a minimum of 2 up to 12 hours. The heat treatment induces the formation of stable interactions. Photons The mixture obtained between the nanofiller and at least one pyrrole derivative (or pyrrole compounds, PyC), obtained through the process described above in steps a-c, is treated by means of an irradiation process using a lamp with a suitable wavelength. The photon treatment consists of placing the powder obtained (nanofiller/PyC) in a laboratory crystallizer forming a thin layer or placing the powder in a sealed quartz vial. After positioning the reactor inside a dark room equipped with a 254 nm low pressure mercury lamp (or using a Rayonet^R reactor equipped with the same type of lamp), the mixture is irradiated for times variable from 30 to 180 minutes. After this time, the mixture is decanted and analyzed. With an adduct according to the present invention it is possible to obtain suspensions of carbon nanofillers stable both in aqueous media and in other substrates, such as polymer compounds or rubbers, thus obtaining homogeneous products that have the specific properties of carbon nanofillers, such as high mechanical properties, high electrical conductivity, resistance to high temperatures, flame-retardant properties. With an adduct according to the present invention, it is also possible to obtain uniform and continuous layers of black fillers on different substrates, in order to obtain highly conductive surfaces. The adducts according to the present invention were prepared by mixing the polymer of formula (I) with the adduct of formula (III) and following one of these mixing procedures: i. In the presence of a solvent, polymer and functionalized carbon allotrope are mixed. ii. In the absence of a solvent, mixing of polymer and functionalized carbon allotrope. iii. In situ mixing of polymer and functionalized carbon allotrope (one-pot). In one aspect of the present invention, an ink is a mixture of a polymer, a humectant (i.e. propylene glycol), and a functionalized carbon allotrope, both dispersed in a solvent. The adopted procedure (1) consists of a first mixture of the polymer and the humectant. Secondarily, the functionalized carbon allotrope was added to the previous mixture. A non-volatile protic solvent (i.e., 2-buthoxyethanol) could be added (1) or not added (2) at the end of the mixing. The polymer, the functionalized carbon allotrope and humectant could be mixed in a one-pot procedure (3). Also in this case, the solvent could be added (3) or not added (2) at the end of the mixing. Results reported in the present invention show that the presence of a high boiling protic solvent influence several aspects of the final product. The chosen solvent affects the drying properties, the viscosity, the tension surface of the ink. Furthermore, the presence of a solvent facilitates to avoid clogging of the nozzle during the printing phase and improves the compatibility of the carbon allotrope and the polymer. 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, wherein: - Figure 1 is the ¹H-NMR 400 MHz spectrum in DMSO-d₆ of Polyurethane (PU-SP) obtained as reported in example 1. - Figure 2 is the FT-IR spectra of Polyurethane (PU-SP) obtained as reported in example 1. - Figure 3 is the TGA thermogram of Polyurethane (PU-SP) obtained as reported in example 1. - Figure 4 is the ¹H-NMR 400 MHz spectrum in DMSO-d₆ of Polyurethane (PU) obtained as reported in example 2. - Figure 5 is the FT-IR spectra of Polyurethane (PU) obtained as reported in example 2. - Figure 6 is the TGA thermogram of Polyurethane (PU) obtained as reported in example 2. - Figure 7 is the TGA thermogram of CBc-SP (CBc-SP 1%) obtained as reported in example 3. - Figure 8 is the WAXD pattern of pristine CBc (a), CBc-SP 1% (b) and CBc-SP 5% adducts (c). - Figure 9 is the TGA thermogram of CBc-SP (CBc-SP 5%) obtained as reported in example 4. - Figures 10 and 11 are the FT-IR spectra of pristine CBc (a) and CBc-SP 5% (b) in transmission mode in Diamond Anvil Cell (DAC). Figure 10 (Panel (I)): 700–3900 cm⁻¹ region; Figure 11 (Panel (II)): fingerprint region 700–1800 cm⁻¹ after baseline correction. - Figures 12 a-d are the TEM and HRTEM micrographs of commercial INK (Dupont PE671/PE773) (a,b), and Ink1 (c,d), at low (a,c) and higher magnification (b,d). - Figures 13 e-h are the TEM and HRTEM micrographs of Ink 2 (e,f) and Ink 3 (g,h), at low (e,g) and higher magnification (f,h). - Figures 14 A-E are the contact angle measures on the TPU substrate (A), commercial ink (B); Ink 1 (C), Ink 2 (D) and Ink 3 (E). - Figures 15 Aa-Ee are the SEM micrographs of (Aa) the TPU substrate, commercial ink (Bb); Ink 1 (Cc), Ink 2 (Dd) and Ink 3 (Ee), cross-sections (A-E) and plane views (a-e). - Figure 16 is the tensile tests showing the change in sensor resistance as a function of time for printed substrates of example 12. - Figure 17 are the Resistance-Strain dependence of the developed INKs in comparison to a commercial ink: printed substrate of example 12. - Figure 18 is the tensile tests showing the change in sensor resistance as a function of time for printed substrates of example 13. - Figure 19 is the Resistance-Strain dependence of the developed INKs in comparison to a commercial ink: printed substrate of example 13. - Figure 20 is the tensile tests showing the change in sensor resistance as a function of time for printed substrates of example 14. - Figure 21 is the Resistance-Strain dependence of the developed INKs in comparison to a commercial ink: printed substrate of example 14. - Figure 22 is the tensile tests showing the change in sensor resistance as a function of time for printed substrates of example 15. - Figure 23 is the Resistance-Strain dependence of the developed INKs in comparison to a commercial ink: printed substrate of example 15. EXAMPLES Experimental part Materials Reagents and solvents are commercially available and were used without any further purification. Conductive Carbon Black fillers, named CBc, were ENSACO 360G from Imerys (30 nm as mean diameter of spherical primary particles, BET surface area 780 m²/g and volume resistivity 19 Ohm x cm) and PRINTEX XE2 from Orion (30 nm as mean diameter of spherical primary particles, BET surface area 1000 m²/g and electrical resistivity 43 Ohm x cm). The powders were characterized by means of Thermogravimetric analysis (TGA), Infrared spectroscopy, X-ray diffraction, High- resolution transmission electron microscopy (HRTEM). Propylene glycol, 2- butoxyethanol, Poly(propylene glycol)-block-poly(ethylene glycol)-block- poly(propylene glycol) (PPG-PEG-PPG, Mn ∼ 2.000), 1,4-butanediol, glycerol and 1,6- Hexamethylene diisocyanate (HDI) were purchased from Sigma-Aldrich. 2-(2,5- dimethyl-1H-pyrrol-1-yl)propan-1,3-diol (Serinol pyrrole, SP) was prepared as reported Barbera et al [US10329253 B2; EP3154939 B1]. Commercial Ink A commercially available ink has been selected as comparison in order to check the performances of innovative INKs: a stretchable carbon conductor paste for printed low- voltage circuitry on elastic film and textile substrates (DUPONT™ INTEXAR™ PE671). The commercial ink is made up of two components: the carbon conductor (Dupont PE671) and the adhesive stretchable (Dupont PE773). Printing substrate The substrate selected for the final printing is a stretchable bilayer thermoplastic polyurethane (TPU) film (thickness = 90 µm, DuPont™ Intexar™ TE-11C). Characterizations Nuclear Magnetic Resonance Spectroscopy (NMR) ¹H-NMR and ¹³C-NMR spectra were recorded on a Bruker 400 MHz (100 MHz ¹³C) instrument at 298 K. Chemical shifts were reported in ppm with the solvent residual peak as internal standard (DMSO-d₆: δ_H= 2.50 ppm, CDCl₃: δ_H= 7.26 ppm). Powder X-Ray Diffraction Wide-angle X-Ray diffraction (WAXD) patterns were obtained in reflection, with an automatic Bruker D8 Advance diffractometer, with nickel filtered Cu–K_α radiation. Patterns were recorded in 10° – 90° as the 2θ range, being 2θ the peak diffraction angle. Distance between crystallographic planes was calculated from the Bragg law. The Dhkℓ correlation length, in the direction perpendicular to the hkl crystal graphitic planes, was determined applying the Scherrer equation D_hkℓ = K θ / (β_hkℓ cos θ_hkℓ) (Eq.15.1) where: K is the Scherrer constant, λ is the wavelength of the irradiating beam (1.5419 Å, Cu- Kα), β_hkℓ is the width at half height, and θ_hkℓ is the diffraction angle. The instrumental broadening, b, was determined by obtaining a WAXD pattern of a standard silicon powder 325 mesh (99%), under the same experimental conditions. The width at half height, β_hkℓ = (B_hkℓ – b) was corrected, for each observed reflection with β_hkℓ < 1°, by subtracting the instrumental broadening of the closest silicon reflection from the experimental width at half height, B_hkℓ. Thermogravimetric analysis (TGA) TGA tests under flowing N₂ (60 mL/min) were performed with a Perkin Elmer STA 6000 instrument according to the standard method ISO9924-1. Method used for adducts with CBc: samples (5-10 mg) were heated from 30 to 300 °C at 10°C/min, kept at 300 °C for 10 min, and then heated up to 550 °C at 20°C/min. After being maintained at 550 °C for 15 min, they were further heated up to 900 °C with a heating rate of 10 °C/min and kept at 900 °C for 3 min, then kept at 900 °C for 30 min under flowing air (60 mL/min). Method used for polyurethanes: samples (5-10 mg) were heated from 30 to 600 °C at 10°C/min, kept at 600 °C for 1 min, and then kept at 600 °C for 10 minutes under flowing air (60 mL/min). Fourier Transform Infrared spectroscopy (FT-IR) The IR spectra were recorded in transmission mode (128 scan and 4 cm^-1 resolution) in a diamond anvil cell (DAC) using a ThermoElectron FT-IR Continuµm IR microscope. Attenuated total reflectance (ATR) The FTIR-ATR spectra were recorded by using a Varian 640-IR FT-ATR spectrometer. Sonication 2 L ultrasonic bath (power 260 W) Soltec Sonica Ultrasonic Cleaner. High-resolution transmission electron microscopy (HRTEM) HRTEM investigations on CBc samples taken from the sonicated suspensions, were carried out with a Philips CM 200 field emission gun microscope operating at an accelerating voltage of 200 kV. Few drops of the suspensions were deposited on 200 mesh lacey carbon-coated copper grid and air-dried for several hours before analysis. During acquisition of HRTEM images, the samples did not undergo structural transformation. Low beam current densities and short acquisition times were adopted. Contact angle The contact angle instrument was a Data Physics OCA 150 and the software was SCA20 version 2.3.9. build 46. The contact angles were measured directly on the printed ink surface, putting above water droplets of 2µl Screen printing of inks The inks were screen-printed on TPU films using a Dek Horizon 03i screen printer or by using a bar coater. Each layer was ~ 6 – 12 µm thick and was cured in oven at 110 °C for 30 minutes. Mechanical and electrical properties of screen-printed inks Tensile tests on screen-printed inks have been performed using a Mark-10 tensile tester. The samples had a line width of 2000 µm with a conductive trace length of 76 mm. The 4-wire resistivity of the printed lines on TPU substrates was measured at varying forces. The bars have been pulled with the method reported in Table 1. The sensors were pulled 6 times to 2%, 5%, and 10% successively. Table 1. Tensile test method for screen-printed inks.

Examples 1-2: preparation of polyurethane adhesives with 2-(2,5-dimethyl-1H-pyrrol-1- yl)propan-1,3-diol (serinol pyrrole, SP) or 1,4-butanediol as chain extender. Example 1: synthesis of polyurethane adhesive with 2-(2,5-dimethyl-1H-pyrrol-1- yl)propan-1,3-diol (serinol pyrrole, SP) as chain extender (PU-SP). In a 500 mL becker were added in sequence PPG-PEG-PPG (90 g, 0.045 mol), glycerol (4.14 g, 0.045 mol) and 2-(2,5-dimethyl-1H-pyrrol-1-yl)propan-1,3-diol (serinol pyrrole, SP, 30.42 g, 0.18 mol). The mixture was magnetically stirred at room temperature for 2 minutes. Then, hexamethylene diisocyanate (HDI, 45.4 g, 41.6 mL, 0.27 mol) was added. The mixture was left stirring at room temperature overnight. After this time, an excess of HDI (22.7 g, 20.8 mL, 0.135 mol) was added and the reaction was quenched with 2-butoxyethanol (20 mL). The ratio between the polyol, glycerol and SP was 1:1:4, respectively. About 200 g of polymer were obtained. The product was characterized by means of ¹H NMR (Figure 1) and FT-ATR spectroscopies (Figure 2) and TGA analysis (Figure 3). In the ¹H NMR spectrum (Figure 1), the signal at 7.10 ppm, assigned to the carbamate N-H, is typical of urethane linkage. The characteristic signals of the heterocyclic unit are detected at 5.59 ppm, the pyrrole hydrogens in the β-position, and at 2.17 ppm the methyl group in α-position. The signals due to the polyether unit are visible at 1.00 ppm (-CH₃ of the PPG chain) and 3.2-3-5 ppm (-CH₂ of the PEG and PPG chains, –CH of the PPG chain). In the IR spectrum (Figure 2), the absorption region at 3200-3300 cm^-1 is attributed to the N-H stretching vibration whereas the absorption region near 1700 cm^-1 is attributed to the hydrogen-bonded C=O stretching vibration. Other main peaks in the spectrum are near 2800-2900 cm^-1, assigned to the symmetric and asymmetric stretching vibrations of CH₂ groups. The broad and weak absorptions in the region at 3100 – 3000 cm⁻¹ are assigned to aromatic CH stretching. The peak at 1537 cm⁻¹ is due to urethane N-H bending and C-N stretching vibrations. The peak at 1261 cm^-1 is attributed to C-O stretching. The strong peak near 1100 cm^-1 is assigned to the ether C- O-C stretching. In the TGA thermogram (Figure 3), the typical mass losses of polyurethanes can be observed, usually starting from 150-200°C to about 400°C and depending on the nature of substituents on the polyol and isocyanate. The first mass loss is due to the degradation of hard segments since urethane groups have low thermal stability. The second mass loss is associated to the soft segments decomposition. Oxidation of the residues occurs in air at 600°C. Example 2: synthesis of polyurethane adhesive with 1,4-butanediol as chain extender (PU). (comparison) Example 2 was conducted with the procedure described in example 1, except that instead of SP, 1,4-butanediol was used as a chain extender. In a 500 mL becker were added in sequence PPG-PEG-PPG (90 g, 0.045 mol), glycerol (4.14 g, 0.045 mol) and 1,4-butanediol (16.22 g, 0.18 mol). The mixture was magnetically stirred at room temperature for 2 minutes. Then, hexamethylene diisocyanate (HDI, 45.4 g, 41.6 mL, 0.27 mol) was added. The mixture was left stirring at room temperature overnight. After this time, an excess of HDI (22.7 g, 20.8 mL, 0.135 mol) was added and the reaction was quenched with 2-butoxyethanol (20 mL). About 200 g of polymer were obtained. The product was characterized by means of NMR (Figure 4) and FT-ATR spectroscopies (Figure 5) and TGA analysis (Figure 6). In the ¹H NMR spectrum (Figure 4), the signal at 7.0 ppm, assigned to the carbamate N- H, is typical of urethane linkage. Methylene protons of 1,4-butanediol unit are visible at 3.9 ppm (-CH₂ protons adjacent to oxygen) and 1.56 ppm (-CH₂ protons of the aliphatic chain). The signals due to the polyether unit are visible at 1.00 ppm (-CH₃ of the PPG chain) and 3.2-3-5 ppm (-CH₂ of the PEG and PPG chains, –CH of the PPG chain). In the IR spectrum (Figure 5), the absorption region at 3200-3300 cm^-1 is attributed to the N-H stretching vibration whereas the absorption region near 1700 cm^-1 is attributed to the hydrogen-bonded C=O stretching vibration. Other main peaks in the spectrum are near 2800 cm^-1, assigned to the symmetric and asymmetric stretching vibrations of CH₂ groups. The peak at 1539 cm⁻¹ is due to urethane N-H bending and C-N stretching vibrations. The peak at 1257 cm^-1 is attributed to C-O stretching. The strong peak near 1100 cm^-1 is assigned to the ether C-O-C stretching. In the TGA thermogram (Figure 6), the typical mass losses of polyurethanes can be observed, usually starting from 150- 200°C to about 400°C and depending on the nature of substituents on the polyol and isocyanate. The first mass loss is due to the degradation of hard segments since urethane groups have low thermal stability. The second mass loss is associated to the soft segments decomposition. Oxidation of the residues occurs in air at 600°C. Examples 3-4: preparation of adducts between conductive carbon black (CBc) and 2- (2,5-dimethyl-1H-pyrrol-1-yl)propan-1,3-diol (serinol pyrrole, SP). CBc-SP Example 3: adduct between conductive carbon black (CBc) and 2-(2,5-dimethyl-1H- pyrrol-1-yl)propan-1,3-diol (SP). CBc-SP 1%. 10 g of CBc were weighed in a 250 mL round bottom flask, and then 200 mL of acetone were added in order to submerge the carbon allotrope powder completely. The suspension was sonicated for 20 minutes, using a 2 L ultrasonic bath. Then, 0.1 g of SP was dissolved in acetone and added to the flask containing the suspension of CBc. The suspension was sonicated for other 20 minutes, using a 2 L ultrasonic bath. After this time, the solvent was removed under reduced pressure using a rotary evaporator. The 250 mL round bottom flask was then equipped with a magnetic stirrer and a condenser and heated up to 180 °C in an oil bath; it was then left under stirring (300 rpm) for 2 hours. The reaction was therefore carried out neat, with no solvents or catalysts. Once the functionalization was completed, the mixture was thoroughly washed with acetone leaving it stirring at room temperature overnight then placed in a Büchner funnel with a sintered glass disc, recovered and dried in oven. The powder was characterized by means of TGA (Figure 7) and WAXD (Figure 8). The decomposition profile (Figure 7) is characterized by four main steps, in the following temperature ranges: below 150°C, from 150°C to 400°C, from 400°C to 900°C and above 900°C. For pristine CBc was found a carbon content of 93.6% by mass, in line with what is reported on the technical data sheet. For all the sample the weight loss below 900 °C indicate the presence of minor amounts of functional groups and alkenyl pendant groups that can undergo degradation below the typical temperature for the degradation of CA. Low molar mass substances, mainly water, could be responsible for the mass loss at T < 150 °C. Also, decomposition of alkyl or alkenylic groups, possibly present as defects in the allotrope, should be in this temperature range. Decomposition of the organic part, arising from functionalization with SP, should occur in the temperature range from 150 °C to 400 °C for the oxygenated moieties and from 400 °C to 900 °C for the ring moiety. Combustion of carbonaceous structure of the allotrope occurs with oxygen at T > 900 °C. Mass loss values in the range 150 – 400 °C were exploited to determine the degree of functionalization of each adduct, defined as the percent value of the difference between the weight loss of the CBc-SP adduct and that of the pristine CBc in the temperature range 150 – 400 °C. The degree of functionalization for this sample was 1.1%. WAXD analysis (Figure 8) was performed on pristine and functionalized CBc. In each pattern a (002) reflection at a 2theta of 24.6 degrees is visible, corresponding to an interlayer distance of 0.361 nm and a (004) reflection is detectable at 54.3 degrees. The interlayer distance can be calculated by applying Bragg’s Law as explained in the experimental section. The out of plane correlation lengths were found to be about 1.6 nm for both pristine carbon and adducts. This value was determined by applying the Scherrer equation. The corresponding number of staked layers in the crystalline domain is therefore around 5 for both CBc and CBc-adducts. The superimposition of the patterns presents a rather curious situation, anomalous for carbon blacks. It is indeed interesting to underline how it seems that there is a decrease in the amorphous component typical of carbon blacks as regards the 002 reflection. Functionalization seems to slightly increase the crystalline degree of the system. Example 4: adduct between conductive carbon black (CBc) and 2-(2,5-dimethyl-1H- pyrrol-1-yl)propan-1,3-diol (SP). CBc-SP 5%. Example 4 was conducted with the procedure described in example 3, except that instead of 1% of SP was used 10% of pyrrole.10 g of CBc were weighed in a 250 mL round bottom flask, and then 200 mL of acetone were added in order to submerge the carbon allotrope powder completely. The suspension was sonicated for 20 minutes, using a 2 L ultrasonic bath. Then, 1 g of SP was dissolved in acetone and added to the flask containing the suspension of CBc. The suspension was sonicated for other 20 minutes, using a 2 L ultrasonic bath. After this time, the solvent was removed under reduced pressure using a rotary evaporator. The 250 mL round bottom flask was then equipped with a magnetic stirrer and a condenser and heated up to 180 °C in an oil bath; it was then left under stirring (300 rpm) for 2 hours. The reaction was therefore carried out neat, with no solvents or catalysts. Once the functionalization was completed, the mixture was thoroughly washed with acetone leaving it stirring at room temperature overnight then placed in a Büchner funnel with a sintered glass disc, recovered and dried in oven. The powder was characterized by means of TGA (Figure 9), FT-IR (Figures 10 and 11), WAXD (Figure 8). The FT-IR spectra of pristine and functionalized CBc (Figures 10 and 11) are characterized by an increasing background toward high wavenumbers due to diffusion/reflection phenomena of the IR light by the particles of the sample. Spurious signals due to CO₂ and diamond absorptions are identified in the region 1900 cm^-1 – 2500 cm^-1. The spectrum of pristine CBc is characterized by the band at 1570 cm^-1 which is the peak typical of graphite and graphene related materials, assigned to E_1u IR active mode of collective C=C stretching vibration. Indeed, spectra of graphitic samples (recorded with DAC) show this peculiar band shape, due to the interplay of specular reflection superimposed to the absorption feature of graphitic particles. In the spectrum of CBc-SP 5 % adduct the C=C peak at 1570 cm^-1 is still observed along with new bands. The features ascribed to the pyrrole ring, between about 1550 cm⁻¹ and 1000 cm⁻¹ can be hardly detected. Two new absorption bands absent in pristine CBc spectrum can be observed at 1706 cm^-1and 1752 cm^-1. They can be attributed to the oxidized methyl groups in the α positions of the pyrrole ring, in particular to carboxylic and aldehydic groups, respectively. The typical features of the pyrrole ring between about 1550 cm⁻¹ and 1000 cm⁻¹ and the strong C–H out-of-plane bending at 760 cm⁻¹ can not to be recognized in the spectrum of the CBc-SP adduct. These findings suggest that the aromatic pyrrole ring mostly undergoes a chemical modification as a consequence of the reaction with CBc. Examples 5-11: preparation of Inks composed of conductive carbon black (CBc), pristine or functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propan-1,3-diol (serinol pyrrole, SP), and polyurethane adhesives. Example 5: preparation of Ink 1 (Entry 1 of Table 2) (Invention). In a 250 mL becker were added in sequence 0.74 g of CBc, 1.48 g of propylene glycol and 13 mL of 2-butoxyethanol (see Entry 1 of Table 2). The mixture was magnetically stirred at room temperature for 1 hour to obtain a homogeneous mixture. After this time, 20 g of PU-SP was added and the mixture was mixed in planetary mixer at 2000 rpm for 2 minutes to obtain INK1. The INK was characterized by means of HRTEM (Figure 12). Micrographs of the commercial Ink (Dupont PE671/PE773) and of the Inks prepared show that between the carbon material and the polymeric part of the final inks the interaction seems intimate (Figure 12). The presence of polymeric material adhering to the carbonaceous structures is indicated by arrows. Example 6: preparation of Ink 2 (Entry 2 of Table 2) (Invention). Example 6 was conducted with the procedure described in example 5, except that instead of pristine CBc, CBc-SP 1% was used to obtain INK2 (see Entry 2 of Table 2). In a 250 mL Becker were added in sequence 0.74 g of CBc-SP 1%, 1.48 g of propylene glycol and 13 mL of 2-butoxyethanol. The mixture was magnetically stirred at room temperature for 1 hour to obtain a homogeneous mixture. After this time, 20 g of PU-SP was added and the mixture was mixed in planetary mixer at 2000 rpm for 2 minutes to obtain INK2. The INK was characterized by means of HRTEM (Figure 13). Example 7: preparation of Ink 3 (Entry 3 of Table 2) (Invention). Example 7 was conducted with the procedure described in example 6, except that instead of CBc-SP 1%, CBc-SP 5 % was used, to obtain INK3 (see Entry 3 of Table 2). In a 250 mL becker were added in sequence 0.74 g of CBc-SP 5 %, 1.48 g of propylene glycol and 13 mL of 2-butoxyethanol. The mixture was magnetically stirred at room temperature for 1 hour to obtain a homogeneous mixture. After this time, 20 g of PU-SP was added and the mixture was mixed in planetary mixer at 2000 rpm for 2 minutes to obtain INK3. The INK was characterized by means of HRTEM (Figure 13). Example 8: preparation of Ink 4 (Entry 4 of Table 2) (comparison). Example 8 was conducted with the procedure described in example 5, except that instead of PU-SP, the pyrrole-free PU of example 2 was used. However, the preparation of this INK was not possible because the 1,4-butanediol-based polymer rapidly lost its solubility in common ink solvents. Example 9: preparation of Ink 5 (Entry 5 of Table 2) (comparison). Example 9 was conducted with the procedure described in example 8, except that instead of pristine CBc, CBc-SP 1% was used. However, the preparation of this INK was not possible because the 1,4-butanediol-based polymer rapidly lost its solubility in common ink solvents. Example 10: preparation of Ink 6 (Entry 6 of Table 2) (comparison). Example 10 was conducted with the procedure described in example 8, except that instead of pristine CBc, CBc-SP 5 % was used. However, the preparation of this INK was not possible because the 1,4-butanediol-based polymer rapidly lost its solubility in common ink solvents. Example 11: preparation of Commercial INK (comparison). Example 11 was conducted to compare INK1, INK2 and INK3 of examples 5, 6 and 7 respectively with a commercially available ink. In a 50 mL becker, 1 g of carbon conductor (Dupont PE671) was mixed with 1 g of the adhesive stretchable (Dupont PE773) for few minutes to obtain the commercial ink. Table 2. Recipes for the preparation of INKs

^apolyurethane was prepared as reported in example 1; ^bpolyurethane was prepared as reported in example 2; ^c CBc-SP 1% was prepared as reported in example 3; ^d CBc-SP 5% was prepared as reported in example 4 Examples 12-14: printing of inks Example 12: printing of the Ink prepared as reported in example 5 (Invention). Example 12 refers to the printing of the ink prepared as reported in example 5 (INK1) on a TPU support by using a bar coater or by using a Dek Horizon 03i screen printer. Each layer was ~ 6 – 12 µm thick and was cured in oven at 110 °C for 30 minutes. The printed layer was then characterized by means of contact angle (Figure 14) and SEM (Figure 15). Mechanical and electrical properties were evaluated (Figures 16 and 17). The results in Figure 14 show that the TPU substrate, the commercial ink and Ink 1 are strongly hydrophobic while Ink 2 and Ink 3 are hydrophilic. The presence of hydroxyl groups on the carbon black after the functionalization with SP seems to be fundamental for the hydrophilic properties of the deposited finale layer. The chemical nature of the surface after screen-printing seems positively tunable thanks to the functionalization. As showed in Figure 16, the sensors are pulled 6 times to 2%, 5%, and 10% successively. The behavior of the commercial ink (Figure 22) is much different than the ink developed in this invention. As the functionalization level of the ink is increased, the resistance change with strain and the stability at the top of the strain is decreased sequentially. Additionally, the resistance remains more stable (flat) when the strain is held at the peak target value. For a stretchable printed trace, minimal resistance changes with strain are desirable. It is also evident that the commercial ink has a very strange behavior – exhibiting peak resistance values when the peak strain was not applied. This is why the commercial ink trace does not overlap with the other samples. The resistance-strain behavior can better be visualized in Figure 17. The strange behavior of the commercial ink is even more clear (Figure 23). Increased carbon functionalization leads to a subsequent decrease in the hysteresis and magnitude of the resistance change with strain. The commercial ink shows many peaks even though the strain is bimodal (up/down). The inks of this invention show excellent behavior if compared with the commercial one. The baseline of the inks extends because the residual strain has extended, so when the strain is 0, the line still behaves as if it is being strained. This is due to the mechanical behavior of the substrate and can be influenced by the way the substrate is manufactured or pre-treated prior to use. The residual strain of the substrate is calculated to be ~4%. Example 13: printing of the Ink prepared as reported in example 6 (Invention). Example 13 was conducted with the procedure described in example 12, except that instead of the ink reported in example 5 (INK1), the ink reported in example 6 (INK2) was used. The ink prepared as reported in the example 6 (INK2) has been printed on a TPU support by using a bar coater or by using a Dek Horizon 03i screen printer. Each layer was ~ 6 – 12 µm thick and was cured in oven at 110 °C for 30 minutes. The printed layer was then characterized by means of contact angle (Figure 14) and SEM (Figure 15). Mechanical and electrical properties were evaluated (Figures 18 and 19). The results in Figure 14 show that the TPU substrate, the commercial ink and Ink 1 are strongly hydrophobic while Ink 2 and Ink 3 hydrophilic. The presence of hydroxyl groups on the carbon black after the functionalization with SP seems to be fundamental for the hydrophilic properties of the deposited finale layer. The chemical nature of the surface after screen-printing seems positively tunable thanks to the functionalization. As showed in Figure 18, the sensors are pulled 6 times to 2%, 5%, and 10% successively. The behavior of the commercial ink (Figure 22) is much different than the ink developed in this invention. As the functionalization level of the ink is increased, the resistance change with strain and the stability at the top of the strain is decreased sequentially. Additionally, the resistance remains more stable (flat) when the strain is held at the peak target value. For a stretchable printed trace, minimal resistance changes with strain are desirable. It is also evident that the commercial ink has a very strange behavior – exhibiting peak resistance values when the peak strain was not applied. This is why the commercial ink trace does not overlap with the other samples. The resistance-strain behavior can better be visualized in Figure 19. The strange behavior of the commercial ink is even more clear (Figure 23). Increased carbon functionalization leads to a subsequent decrease in the hysteresis and magnitude of the resistance change with strain. The commercial ink shows many peaks even though the strain is bimodal (up/down). The inks of this invention show excellent behavior if compared with the commercial one. The baseline of the inks extends because the residual strain has extended, so when the strain is 0, the line still behaves as if it is being strained. This is due to the mechanical behavior of the substrate and can be influenced by the way the substrate is manufactured or pre-treated prior to use. The residual strain of the substrate is calculated to be ~4%. Example 14: printing of the Ink prepared as reported in example 7 (Invention). Example 14 was conducted with the procedure described in example 13, except that instead of the ink reported in example 6 (INK2), the ink reported in example 7 (INK3) was used. The ink prepared as reported in the example 7 (INK3) has been printed on a TPU support by using a bar coater or by using a Dek Horizon 03i screen printer. Each layer was ~ 6 – 12 µm thick and was cured in oven at 110 °C for 30 minutes. The printed layer was then characterized by means of contact angle (Figure 14) and SEM (Figure 15). Mechanical and electrical properties were evaluated (Figures 20 and 21). The results in Figure 14 show that the TPU substrate, the commercial ink and Ink 1 are strongly hydrophobic while Ink 2 and Ink 3 are hydrophilic. The presence of hydroxyl groups on the carbon black after the functionalization with SP seems to be fundamental for the hydrophilic properties of the deposited finale layer. The chemical nature of the surface after screen-printing seems positively tunable thanks to the functionalization. As showed in Figure 20, the sensors are pulled 6 times to 2%, 5%, and 10% successively. The behavior of the commercial ink (Figure 22) is much different than the ink developed in this invention. As the functionalization level of the ink is increased, the resistance change with strain and the stability at the top of the strain is decreased sequentially. Additionally, the resistance remains more stable (flat) when the strain is held at the peak target value. For a stretchable printed trace, minimal resistance changes with strain are desirable. It is also evident that the commercial ink has a very strange behavior – exhibiting peak resistance values when the peak strain was not applied. This is why the commercial ink trace does not overlap with the other samples. The resistance-strain behavior can better be visualized in Figure 21. The strange behavior of the commercial ink is even more clear (Figure 23). Increased carbon functionalization leads to a subsequent decrease in the hysteresis and magnitude of the resistance change with strain. The commercial ink shows many peaks even though the strain is bimodal (up/down). The inks of this invention show excellent behavior if compared with the commercial one. The baseline of the inks extends because the residual strain has extended, so when the strain is 0, the line still behaves as if it is being strained. This is due to the mechanical behavior of the substrate and can be influenced by the way the substrate is manufactured or pre-treated prior to use. The residual strain of the substrate is calculated to be ~4%. Example 15: printing of the commercial Ink prepared as reported in example 11. Example 15 refers to the printing of the commercial ink prepared as reported in example 11 on a TPU support by using a bar coater or by using a Dek Horizon 03i screen printer. Each layer was ~ 6 – 12 µm thick and was cured in oven at 110 °C for 30 minutes. The printed layer was then characterized by means of contact angle (Figure 14) and SEM (Figure 15). Mechanical and electrical properties were evaluated (Figures 22 and 23). As showed in Figure 22, the sensors are pulled 6 times to 2%, 5%, and 10% successively. The behavior of the commercial ink is much different than the ink developed in this invention. As the functionalization level of the ink is increased, the resistance change with strain and the stability at the top of the strain is decreased sequentially. Additionally, the resistance remains more stable (flat) when the strain is held at the peak target value. For a stretchable printed trace, minimal resistance changes with strain are desirable. It is also evident that the commercial ink has a very strange behavior – exhibiting peak resistance values when the peak strain was not applied. This is why the commercial ink trace does not overlap with the other samples. The resistance-strain behavior can better be visualized in Figure 23. The strange behavior of the commercial ink is even more clear. Increased carbon functionalization leads to a subsequent decrease in the hysteresis and magnitude of the resistance change with strain. The commercial ink shows many peaks even though the strain is bimodal (up/down). The inks of this invention show excellent behavior if compared with the commercial one. The baseline of the inks extends because the residual strain has extended, so when the strain is 0, the line is still behaving as if it is being strained. This is due to the mechanical behavior of the substrate and can be influenced by the way the substrate is manufactured or pre-treated prior to use. The residual strain of the substrate is calculated to be ~4%.

Claims

CLAIMS 1. Adduct of: a polymer comprising repeating units of formula (I),

wherein E, F and G are independently selected from the group consisting of amine, hydroxyl, hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, or from the group consisting of:

wherein R30 can be hydrogen, alkyl, aryl, benzyl, amine, alkylamine, arylamine, benzylamine, or aminoaryl; R31-R35 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, and 1-(4- aminocyclohexyl) methylene; with an adduct of: a sp² carbon allotrope and/or its derivative and a compound of formula (III)

wherein M, Q and J are independently selected in a group consisting of amine, hydroxyl, hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, or in a group consisting of: _,

, , wherein R55 is selected from the group consisting of hydrogen, alkyl, aryl, benzyl, amine, alkylamine, arylamine, benzylamine, or aminoaryl; R56-R60 are independently selected from the group consisting of: hydrogen, linear or branched C1-C10 alkyl, linear or branched C2-C10 alkenyl or alkynyl, and 1- (4- aminocyclohexyl) methylene. 2. Adduct according to claim 1, characterized in that said sp² carbon allotrope and/or its derivative is selected from the group consisting of: carbon black, fullerene, buckminstefullerenes, carbon nanohorns, carbon nanotubes, single-walled or multi- walled, carbon nanobuds, graphene, bilayer graphene, few-layer graphene, graphenylene, ciclocarbons, graphites with a number of stacked graphene layers from 2 to 10000. 3. Adduct according to one or more of the preceding claims characterized in that said sp² carbon allotrope derivative contains functional groups selected from the group consisting of: − functional groups containing oxygen, preferably hydroxyls, epoxies; − functional groups containing carbonyls, preferably aldehydes, ketones, carboxylic acids; − functional groups containing nitrogen atoms, preferably amines, amides, nitriles, diazonium salts, imines; − functional groups containing sulfur atoms, preferably sulfides, disulfides, sulfinates, sulfoxides, mercaptans, sulfones, sulfinic, sulfoxylic, and sulfonic groups. 4. Adduct according to one or more of the preceding claims, characterized in that said derivative of said carbon allotrope is graphite oxide. 5. Adduct according to one or more of the preceding claims, characterized in that said derivative of said carbon allotrope is graphene oxide. 6. Use of the adduct according to one or more of the preceding claims, for the preparation of a conductive ink. 7. Conductive ink comprising the adduct according to one or more of claims 1 to 5.