Strong Interaction with Carbon Filler of Polymers Obtained by Pyrene Functionalized Hoveyda-Grubbs 2nd Generation Catalyst

Hoveyda-Grubbs 2nd generation catalyst that has the alkylidene functionalized with pyrene (HG2pyrene) was synthesized and characterized. This catalyst can be bound to carbonaceous filler (graphite, graphene or carbon nanotubes) by π-stacking interaction, but, since the catalytic site become poorly accessible to the incoming monomer, its activity in the ROMP (Ring Opening Metathesis Polymerization) is reduced. This is due to the fact that the above interaction also occurs with the aryl groups of NHC ligand of the ruthenium, as demonstrated by nuclear magnetic resonance and by fluorescence analysis of a solution of the catalyst with a molecule that simulated the structure of graphene. Very interesting results were obtained using HG2pyrene as a catalyst in the ROMP of 2-norbornene and 1,5-cyclooctadiene. The activity of this catalyst was the same as that obtained with the classical commercial HG2. Obviously, the polymers obtained with catalyst HG2pyrene have a pyrene as a chain end group. This group can give a strong π-stacking interaction with carbonaceous filler, producing a material that is able to promote the dispersion of other materials such as graphite in the polymer matrix.


Introduction
Polyolefins are widely used materials in many applications such as industrial and food packaging, cling-film and agricultural film, crates, boxes, carrier bags, electrical cable, bottles, pipes, houseware, toys, petrol tanks, carpet fibers, medical appliances, etc., because of their low cost and intrinsic properties of low density, high stiffness, good tensile strength, recyclability, good workability, non-toxicity, and biocompatibility [1]. To enhance these properties and consequently the multi-functionality in advanced applications, it is often necessary to improve the physicochemical and mechanical properties of the polyolefins by introducing fillers into the matrix. In fact, the addition of additives, in particular of nanometric dimensions, has allowed their use for advanced technologies [2][3][4]. Carbon additives such as carbon blacks, carbon nanofiber, carbon nanotubes, and graphene have been largely utilized to improve mechanical properties, thermal stability, flame resistance, and the thermal and electrical conductivities of a pure polyolefin [4][5][6][7][8][9][10][11][12][13][14]. The addition of nanometric filler into polymers enabled important applications in radiation and electromagnetic shielding, antistatic, shrinkage-and corrosion-resistant coatings, light-emitting devices, and batteries [2][3][4][5][6][7][8][9][10][11].
A problem that arises frequently using these fillers is represented by their tendency to form bundles and agglomerates, providing weak interaction within the polymer. Recently, exfoliated the previously mentioned catalytic system, of polymers with a pyrene as a chain terminal. These terminals can provide interaction with the carbon fillers and facilitate the dispersion of the latter in the polymer matrix. The employment of the non-oxidized filler may allow all of the previously mentioned interesting carbonaceous material applications .

Materials
All the reactions were carried out in nitrogen atmosphere using standard Schlenk or glovebox techniques. All the reagents used in this study were of reagent grade quality and sourced from Sigma-Aldrich s.r.l. (Milan, Italy). These reagents were used as received. The solvents were dried and distilled before use. Deuterated solvents were degassed under a nitrogen flow and stored over activated 4 Å molecular sieves. The graphite used (trade names Timrex C-Therm 011/012) from Timcal Graphite & Carbon, Bodio, Switzerland; C is a high surface area graphite (trade name Synthetic Graphite 8427) from Asbury Graphite Mills Inc., with a minimum carbon wt % of 99.8 and a surface area of 330 m 2 /g.

Measurements
NMR spectra were recorded on Bruker Avance 400 spectrometer ( 1 H, 400 MHz; 13 C, 100 MHz, Rheinstetten, Germany) operating at 298 K. The samples were prepared by dissolving 10 mg of product in 0.5 mL of deuterated solvent (CDCl 3 or CD 2 Cl 2 ). Tetramethylsilane (TMS) was used as internal chemical shift reference. Spectra are reported as follows: chemical shift (ppm), multiplicity and integration. Multiplicities are abbreviated: singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m) and broad (br). Elemental analysis for C, H, N was recorded on a Thermo-Finnigan flash EA 1112 and were performed according to standard micro-analytical procedures. FT-IR spectra was obtained at a resolution of 2.0 cm −1 with a FT-IR (BRUKER Vertex70) spectrometer equipped with deuterated triglycine sulfate (DTGS) detector and a KBr beam splitter, using KBr pellets. The frequency scale was internally calibrated to 0.01 cm −1 using a He-Ne laser. 32 Scans were signal averaged to reduce the noise. Thermogravimetric analyses (TGA) were carried out on a TG 209 F1, manufactured by Netzsch Geraetebau, Selb, Germany, at a heating rate of 10 • C min −1 , under air flow. Fluorescence measurements of the samples were recorded by a Varian Cary Eclipse spectrophotometer. The morphological features were investigated by means of Field Emission Scanning Electron Microscopy (FESEM) analysis. The FESEM characterization was performed with a field emission scanning electron microscope (mod. LEO 1525, Carl ZeissSMTAG, Oberkochen, Germany).

First
Step: Synthesis of 4-(1-pyrenyl)-butyryl Chloride (2) 4-(1-pyrenyl)-butyryl chloride (2), as shown in Scheme 1, was synthesized by treatment of 4-(1-pyrenyl) butyric acid (1) (2.0 g, 6.94 mmol) with oxalyl chloride (2.1 mL, 21 mmol) in 225 mL of CH 2 Cl 2 and two drops of dimethylformamide. The reaction mixture was stirred for 5 h at room temperature. The volume of the solution was reduced under vacuum and to the resulting light brown solid was added diethyl ether (22 mL) and hexane (45 mL Trimethylamine (450 μL, 3.23 mmol) and a crystal of 4-dimethylaminopyridine (DMAP) was added to a stirred solution of 200 μL of 2-norbornene-5-yl-methanol (1.63 mmol) in 50 mL of diethyl ether under nitrogen atmosphere at 0 °C. A solution of 500 mg of 4-(1-pyrenyl)-butyryl chloride (2) (1.63 mmol) in 25 mL of diethyl ether was added dropwise. The reaction was carried at room temperature and stirred for 8 h. Deionized water was added at the reaction mixture and the organic layer was dried over anhydrous Na2SO4, filtered, concentrated, and the residual yellow oil was purified by chromatographic column on silica gel (eluent: hexane/ethyl acetate 5:1). The mixture eluent was removed, and the residue was dried in a vacuum oven. The pure product was isolated in a mixture of endo-and exo-isomers. Yield: 59%. 1

Third
Step: Synthesis of Pyrene-Ru-Catalyst (HG2pyrene) (4) The product (3) (188 mg, 4.94 × 10 −1 mmol) and Hoveyda-Grubbs catalyst 2nd generation (HG2) (309 mg, 4.94 × 10 −1 mmol) at 130 mL of dry CH2Cl2 were added in a reaction flask. The mixture of reaction was stirred at room temperature for 18 h. After the reaction was completed, the suspension was filtered, and the residue was washed with diethyl ether (3x20 mL). The solvent was removed, and the residue was dried in a vacuum oven. Yield: 48%. 1

Functionalization of Graphite with HG2pyrene Catalyst
In an oven-dried Schlenk reaction flask of 100 mL, 200 mg of HG2pyrene (1.63 × 10 −1 mmol), graphite (1.06 g) and dry CH2Cl2 (50 mL) were introduced. The mixture was stirred for 2 h at room temperature, then it was filtered and washed with dry CH2Cl2 (40 mL). The product was recovered and dried in vacuo overnight. Yields 1.09 g.  (2) (1.63 mmol) in 25 mL of diethyl ether was added dropwise. The reaction was carried at room temperature and stirred for 8 h. Deionized water was added at the reaction mixture and the organic layer was dried over anhydrous Na 2 SO 4 , filtered, concentrated, and the residual yellow oil was purified by chromatographic column on silica gel (eluent: hexane/ethyl acetate 5:1). The mixture eluent was removed, and the residue was dried in a vacuum oven. The pure product was isolated in a mixture of endoand exo-isomers. Yield: 59%. 1

Third
Step: Synthesis of Pyrene-Ru-Catalyst (HG2 pyrene ) (4) The product (3) (188 mg, 4.94 × 10 −1 mmol) and Hoveyda-Grubbs catalyst 2nd generation (HG2) (309 mg, 4.94 × 10 −1 mmol) at 130 mL of dry CH 2 Cl 2 were added in a reaction flask. The mixture of reaction was stirred at room temperature for 18 h. After the reaction was completed, the suspension was filtered, and the residue was washed with diethyl ether (3 × 20 mL). The solvent was removed, and the residue was dried in a vacuum oven. Yield: 48%. 1

Functionalization of Graphite with HG2 pyrene Catalyst
In an oven-dried Schlenk reaction flask of 100 mL, 200 mg of HG2 pyrene (1.63 × 10 −1 mmol), graphite (1.06 g) and dry CH 2 Cl 2 (50 mL) were introduced. The mixture was stirred for 2 h at room temperature, then it was filtered and washed with dry CH 2 Cl 2 (40 mL). The product was recovered and dried in vacuo overnight. Yields 1.09 g. The amount of Ru linked to graphite was evaluated by (TGA). The analysis was performed in air flow to allow the Ru to oxidize in the form of ruthenium oxide (RuO 2 ). From the residue at 1000 • C, it was possible to calculate the amount of supported catalyst: 6.01 × 10 −8 mol/mg. 2.3.6. ROMP of the 2-Norbornene and 1,5-Cyclooctadiene In a typical experiment, a solution of initiator (HG2 pyrene or HG2) or suspension of graphite-HG2 pyrene (see Table 1) in tetrahydrofuran (1 mL) was mixed with a stirred solution of monomer (2-norbornene or 1,5-cyclooctadiene) in tetrahydrofuran (99 mL). The mixture was kept at room temperature for the times shown in Table 1. The polymerization was stopped with the addition of some drops of ethyl vinyl ether and polymer was coagulated in ethanol. The polymer product was dried under vacuum.
2.3.7. Hydrogenation of Pyrene-Polybutadiene 300 mg of pyrene-polybutadiene (run 5, Table 1) was dissolved in 30 mL of hot-xylene, followed by the addition of 1.50 g of p-toluenesulfonylhydrazide. The mixture was stirred at 140 • C for 6 h, filtered, and the hot filtrate poured into methanol (30 mL). The precipitated polymer was recovered by filtration, washed several times with hexane and dried under vacuum to yield the hydrogenated polymer (225 mg).

Interaction of Graphite with Polymers
The polymer was dissolved in chloroform, for 100 mg of polymer were used 20 mL of solvent, the ratio between graphite and polymer was 1:1 by weight. Once the polymer was completely dissolved, the graphite was added, and the solution was stirred for 16 h. The solvent was removed in vacuo.

Synthesis of Ruthenium-Based Metathesis Catalyst Having the Alkylidene Functionalized with a Pyrene
The modified Hoveyda-Grubbs second-generation ruthenium catalyst (HG2 pyrene ) was obtained using the synthetic strategy reported in Scheme 1, by reacting the suitable pyrene derivative with the classic second-generation Hoveyda-Grubbs catalyst [43,44]. The first synthetic step consists in the reaction of 4-(1-pyrenyl)-butyric acid with oxalyl chloride in order to obtain the 4-(1-pyrenyl)-butyryl chloride (2). This compound was esterificated by reaction with 2-norbornen-5-yl-methanol to give 4-pyren-1-yl-butyric acid bicyclo[2.2.1]-hept-5-en-2-yl-methyl ester (3). The product (3) was characterized by FT-IR, 1 H and 13 C NMR analysis and elemental analysis. FT-IR signal at 1731 cm −1 attributable to the stretching of the ester group confirms that the reaction occurred. Since, the 5-norbornene-2-methanol used as reagent was in eso/endo mixture both 1 H and 13 C NMR appear rather complex. However, in the 1 H-NMR at about 6 ppm, the signals of the protons on the double bond of the norbornene are identified, and in the 13 C NMR it was possible to observe the signals at about 68.79 and 68.11 ppm of the O-CH 2 and the signal at 173.68 ppm attributable to carboxylic carbon. The synthesis of Hoveyda-Grubbs catalyst 2nd generation having the alkylidene functionalized with a pyrene was carried out by metathesis reaction of dichloro-[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinyl-idene][(2-isopropoxyphenyl-methylene)ruthenium(II)] (HG2) with product 3, obtaining HG2 pyrene , (see Scheme 1) a stable compound, characterized by NMR analysis. Among the distinctive signals in the 1 H NMR we should highlight the singlet at 16.57 ppm, which is characteristic of the H-alkylidenic bonded to Ru of the Hoveyda Grubbs catalyst, while in the 13 C NMR spectrum the signals at 211.29 ppm and at 68.53 ppm of the NCN carbene and of the OCH 2 , respectively. Furthermore, in the 1 H-NMR spectrum the signals between 5.99 and 6.21 ppm present in the spectrum of compound 3, attributed to protons on unsaturated carbons of norbornene ring disappear, confirming the metathesis reaction of norbornene ring with HG2. It is worth noting that in Scheme 1, only the complex with a cis double bond between cyclopentane and phenyl ring is shown. Obviously, the ring-opening metathesis of norbornene produces also a trans double bond between these rings, as it results from multiplet signal at 6.85 ppm. Thus, through few synthetic steps, it is possible to functionalize the HG2 with the pyrene (HG2 pyrene ). The pyrene group can give a π-stacking interaction with the graphitic plane through solubilization of the catalyst in a suitable solvent, i.e., CH 2 Cl 2 , and then adding the carbonaceous nanofiller at the solution. The mixture is stirred for few hours, then filtered obtaining a catalyst supported on the nanofiller. The occurred formation of the supported catalyst (graphite-HG2 pyrene ) is confirmed by the fact that in the methylene chloride the ruthenium complex is no longer present. The amount of Ru supported on graphite plane was evaluated by thermogravimetric analysis like in previously published papers where Ru-based catalysts were covalently linked to graphene oxide [45,46]. Graphite-HG2 pyrene was tested in the ring-opening polymerization of 2-norbornene (  1, run 3). The conversion obtained in run 1 was 84.8%, only slightly lower than obtained by HG2 in run 3, while in run 2 was only 2.63%. A similar decrease in activity was observed by Gomez et al. using a first-generation Grubbs catalyst functionalized with pyrene and making it interact with single-walled carbon nanotubes [47]. It is likely that the π-stacking interaction between the pyrene group and the graphitic plane was very strong and the monomer had difficulty in reaching the catalytic site, thus the activity was drastically reduced. It should be emphasized that, in our catalytic system, the π-π interaction can also occur between the aromatic rings of the NHC nitrogen substituents and the graphitic plane, and this would certainly make the catalytic site difficult to access. To verify this last hypothesis and the identity of the interaction established between the catalyst and the nanofiller, an investigation by 1 H NMR and fluorescence analysis with the catalyst HG2 and molecules that simulate the behavior of the nanofiller was carried out. Since the carbon nanofiller is insoluble, we choose the pyrene itself as a molecule which can try to be like the graphitic plane. The pyrene is a fluorophore, in fact, after absorbing photons of a certain wavelength exhibits fluorescence, emitting the absorbed radiation to a different wavelength than the incident radiation. The sample was irradiated at λ ex 338 nm, the excitation frequency of the pyrene. The pyrene, in chloroform solution, shows an intense absorbance at λ 478 nm (red profile in Figure 1) while the catalyst HG2 doesn't show absorbance (black profile in Figure 1).
The mixture of pyrene/HG2 at molar ratio 1:1 in CHCl 3 leads to the shift and the decrease of the absorbance of the pyrene at λ 499 nm (blue profile in Figure 1). It is important to note that when an isolated aromatic group form a dimer via the π-stacking interaction, the bathochromic shift is usual. In fact, the excited level of the chromophore isolated, after the dimerization, is divided into a lower and a higher energy level [48]. Furthermore, the interaction can create more non-radiative decay channels and therefore decrease the quantum yield. These two effects evidently indicate that the catalyst establishes a strong interaction with the aromatic network. Probably, this fact makes it difficult for the monomer to reach the catalytic site justifying the low activity of the system [43]. The mixture of pyrene/HG2 at molar ratio 1:1 in CHCl3 leads to the shift and the decrease of the absorbance of the pyrene at λ 499 nm (blue profile in Figure 1). It is important to note that when an isolated aromatic group form a dimer via the π-stacking interaction, the bathochromic shift is usual. In fact, the excited level of the chromophore isolated, after the dimerization, is divided into a lower and a higher energy level [48]. Furthermore, the interaction can create more non-radiative decay channels and therefore decrease the quantum yield. These two effects evidently indicate that the catalyst establishes a strong interaction with the aromatic network. Probably, this fact makes it difficult for the monomer to reach the catalytic site justifying the low activity of the system [43].
As further confirmation of the interaction π-stacking between the pyrene and the catalyst was obtained by 1 H NMR analysis. The commercial HG2 catalyst was solubilized in a suitable solvent (CDCl3) and introduced into an NMR tube, then pyrene at various concentrations was added (from 1:1 at a 1:4 HG2:pyrene molar ratio).
As is shown in Figure 2, almost all the signals undergo a shift that increases with the increase in the concentration of pyrene, e.g. the signal related to the alkylidene proton of HG2 (~16.5 ppm), as well as those of methyls of mesityles (~2.5 ppm) move to lower fields, whereas the signals of methylenes (~4.1 ppm) of the backbone shift to higher fields. As further confirmation of the interaction π-stacking between the pyrene and the catalyst was obtained by 1 H NMR analysis. The commercial HG2 catalyst was solubilized in a suitable solvent (CDCl 3 ) and introduced into an NMR tube, then pyrene at various concentrations was added (from 1:1 at a 1:4 HG2:pyrene molar ratio).
As is shown in Figure 2, almost all the signals undergo a shift that increases with the increase in the concentration of pyrene, e.g., the signal related to the alkylidene proton of HG2 (~16.5 ppm), as well as those of methyls of mesityles (~2.5 ppm) move to lower fields, whereas the signals of methylenes (~4.1 ppm) of the backbone shift to higher fields. Thus, the HG2pyrene system is deactivated when placed together with the graphite, but this does not limit its use as it is. In fact, with this catalytic system two monomers (i.e.,: norbornene and 1,5-cyclooctadiene) were polymerized (run 4 and 5 of Table 1). The polymers obtained have a pyrene as chains end (see Figure 3), so by adding graphite to the polymers dissolved in a suitable solvent, a strong π-stacking interaction between the carbon nanofiller and the polymers was obtained. Thus, the HG2 pyrene system is deactivated when placed together with the graphite, but this does not limit its use as it is. In fact, with this catalytic system two monomers (i.e.,: norbornene and 1,5-cyclooctadiene) were polymerized (run 4 and 5 of Table 1). The polymers obtained have a pyrene as chains end (see Figure 3), so by adding graphite to the polymers dissolved in a suitable solvent, a strong π-stacking interaction between the carbon nanofiller and the polymers was obtained. Thus, the HG2pyrene system is deactivated when placed together with the graphite, but this does not limit its use as it is. In fact, with this catalytic system two monomers (i.e.,: norbornene and 1,5-cyclooctadiene) were polymerized (run 4 and 5 of Table 1). The polymers obtained have a pyrene as chains end (see Figure 3), so by adding graphite to the polymers dissolved in a suitable solvent, a strong π-stacking interaction between the carbon nanofiller and the polymers was obtained. Polymerizations were carried out using a monomer/HG2pyrene ratio of 100, in order to obtain short polymer chains, and to maximize the interaction with carbon-filler. The product obtained after polymerizing the 1,5-cyclooctadiene is a polybutadiene with a pyrene terminal. 1 H NMR analysis shows signals between 8.27 and 7.83, at 5.41 and at 2.03 ppm attributable to hydrogens of pyrene, protons of unsaturated carbons and protons of saturated carbons of the polymer chain, respectively. A fraction of this polymer was hydrogenated to give a pyrene-bonded polyethylene.
The polymers reported in Figure 3 were dissolved in a suitable solvent, then the graphite was added in a 1:1 ratio in mass to allow the formation of the non-covalent interactions. It is interesting to note that, when the graphite is added to the solution, it remains well dispersed even in the absence of agitation. Instead, it tends to deposit on the bottom of the vial either when it is placed alone in the same solvent and when it is mixed with a polymer that does not have the terminal pyrene.
In order to better understand what was observed, field emission scanning electron microscopy analysis was performed. Figure 4 shows the FESEM images of graphite (a), of a sample consisting of graphite and of polybutadiene with a terminal pyrene (b) and of a sample consisting of polybutadiene (without terminal pyrene) and graphite (c). Polymerizations were carried out using a monomer/HG2 pyrene ratio of 100, in order to obtain short polymer chains, and to maximize the interaction with carbon-filler. The product obtained after polymerizing the 1,5-cyclooctadiene is a polybutadiene with a pyrene terminal. 1 H NMR analysis shows signals between 8.27 and 7.83, at 5.41 and at 2.03 ppm attributable to hydrogens of pyrene, protons of unsaturated carbons and protons of saturated carbons of the polymer chain, respectively. A fraction of this polymer was hydrogenated to give a pyrene-bonded polyethylene.
The polymers reported in Figure 3 were dissolved in a suitable solvent, then the graphite was added in a 1:1 ratio in mass to allow the formation of the non-covalent interactions. It is interesting to note that, when the graphite is added to the solution, it remains well dispersed even in the absence of agitation. Instead, it tends to deposit on the bottom of the vial either when it is placed alone in the same solvent and when it is mixed with a polymer that does not have the terminal pyrene.
In order to better understand what was observed, field emission scanning electron microscopy analysis was performed. Figure 4 shows the FESEM images of graphite (a), of a sample consisting of graphite and of polybutadiene with a terminal pyrene (b) and of a sample consisting of polybutadiene (without terminal pyrene) and graphite (c).  From the comparison of the images in Figure 4, it can be seen how in sample b), the polymer is perfectly adhered to the surface of the graphite, which appears to have a very similar aspect to that of the graphite in a). In sample c), there is poor adhesion between the polymer and the graphitic surface, while the interactions between the polymer chains themselves, which then go to form clearly visible separate strands, prevail. From the comparison of the images in Figure 4, it can be seen how in sample b), the polymer is perfectly adhered to the surface of the graphite, which appears to have a very similar aspect to that of the graphite in a). In sample c), there is poor adhesion between the polymer and the graphitic surface, while the interactions between the polymer chains themselves, which then go to form clearly visible separate strands, prevail.
The X-ray profile in Figure 5 of graphite shows the characteristic reflection 002 due to the interlayer distance between the graphitic planes, which is d 002 = 0.34 nm, and a correlation length d 002 = 6 nm [49]. The in-plane periodicities (d 100 and d 110 ) is well-defined. These parameters do not change by the interaction of the graphite with pyrene-polymer, showing that there is no exfoliation of the graphite. Clearly, the addition of pyrene-polymer determines only a separation between the agglomerated microcrystals. Moreover, it should be noted that the integrity of the graphite layers is preserved even after the non-covalent interactions, in fact, the layer reflexes 100 and 110 remain clear and clearly visible in the diffraction profiles. The graphite-pyrene-polybutadiene product has been subjected to exhaustive extractions in two different solvents: toluene and xylene. No soluble fraction was recovered for both extractions, indicating that the interaction between the pyrene and the graphitic plane is particularly strong, so it is obviously not necessary to form covalent bonds between the polymer and the carbonaceous nanofiller layer (graphene, carbon nanotubes or exfoliated graphite) to have strong adherence between polymers and these fillers.

Conclusion
Synthesis of Hoveyda-Grubbs catalyst 2nd generation that has the alkylidene functionalized with a pyrene (HG2pyrene) was obtained through few synthetic steps. The products were characterized by FT-IR, 1 H and 13 C NMR and calorimetric analysis. The pyrene group can give a strong π-stacking interaction with carbonaceous filler and mixing HG2pyrene with graphite in CH2Cl2, a catalyst supported on nanofiller (graphite-HG2pyrene), was obtained. HG2pyrene and graphite-HG2pyrene were tested in ROMP of 2-norbornene and 1,5-cyclooctadiene. The catalytic activity in the ROMP of system graphite-HG2pyrene was very low because the π-stacking interaction between pyrene group and the graphitic plane was strong and it prevents the coordination of the incoming monomer. The strong interaction between pyrene group and the graphitic plane was demonstrated by NMR and fluorescence analysis.
The catalyst having the alkylidene functionalized with a pyrene (HG2pyrene) was, instead, very active in catalysing the ROMP of 2-norbornene and 1,5-cyclooctadiene. The polymers were synthesized have a pyrene as chain end group, which was able to give a strong π-stacking interaction with carbonaceous filler, thus producing a material able to favourite the dispersion of graphite in the polymer matrix. The graphite-pyrene-polybutadiene product has been subjected to exhaustive extractions in two different solvents: toluene and xylene. No soluble fraction was recovered for both extractions, indicating that the interaction between the pyrene and the graphitic plane is particularly strong, so it is obviously not necessary to form covalent bonds between the polymer and the carbonaceous nanofiller layer (graphene, carbon nanotubes or exfoliated graphite) to have strong adherence between polymers and these fillers.

Conclusions
Synthesis of Hoveyda-Grubbs catalyst 2nd generation that has the alkylidene functionalized with a pyrene (HG2 pyrene ) was obtained through few synthetic steps. The products were characterized by FT-IR, 1 H and 13 C NMR and calorimetric analysis. The pyrene group can give a strong π-stacking interaction with carbonaceous filler and mixing HG2 pyrene with graphite in CH 2 Cl 2 , a catalyst supported on nanofiller (graphite-HG2 pyrene ), was obtained. HG2 pyrene and graphite-HG2 pyrene were tested in ROMP of 2-norbornene and 1,5-cyclooctadiene. The catalytic activity in the ROMP of system graphite-HG2 pyrene was very low because the π-stacking interaction between pyrene group and the graphitic plane was strong and it prevents the coordination of the incoming monomer. The strong interaction between pyrene group and the graphitic plane was demonstrated by NMR and fluorescence analysis.
The catalyst having the alkylidene functionalized with a pyrene (HG2 pyrene ) was, instead, very active in catalysing the ROMP of 2-norbornene and 1,5-cyclooctadiene. The polymers were synthesized have a pyrene as chain end group, which was able to give a strong π-stacking interaction with carbonaceous filler, thus producing a material able to favourite the dispersion of graphite in the polymer matrix. Therefore, the functionalization by pyrene of the 2nd generation Hoveyda-Grubbs catalyst yields a system capable of producing any polymer obtainable by ROMP with a terminal which makes them capable of binding to carbon fillers, thereby favouring their compatibility.