Metathesis reactions catalyzed by ruthenium complexes for the self-healing of aeronautical materials

2015 - 2016In this PhD thesis work, Ruthenium catalysts were covalently and non-covalently linked to carbon-based nanomaterials, in order to give self-repairing ability to the aeronautical materials. These supported catalysts have been characterized and their activity has been evaluated in metathesis reactions. The 1st and 2nd generation Grubbs and Hoveyda-Grubbs catalysts were covalently bonded to graphite oxide and tested in the ring-opening metathesis polymerization reaction of tensed monomers, and subsequently their catalytic activity was verified in the aeronautical composites. To optimize the performance of such supported catalysts, catalytic sites have been protected from the highly reactive environment by a polymeric globular shell. These catalysts have been further supported on multi-walled carbon nanotubes and graphite by an alternative covalent synthetic approach that allows to preserve the chemical and physical properties of the carbon nanotubes employed, avoiding the initial oxidation step. For non-covalent functionalization, the same catalysts were first linked to pyrene molecules and then, by π-stacking, anchored on graphite. Their activity was determined in metathesis reactions and their conductivity was estimated within aeronautical composites. Such complex pyrene-catalyst, highly versatile, have been used to synthesize polymers having a terminal pyrene capable of improving the dispersion of the same carbon nanotubes used in aeronautical materials in order to improve their performance. Lastly, was evaluated the possibility of self-repairing the aeronautical material through radical polymerization of monomers such as styrene, using Copper catalysts.[edited by author]XXIX n.s

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

Protection of graphene supported ROMP catalyst through polymeric globular shell in self-healing materials

Protected Ru-catalyst, immobilized on graphene sheets, was prepared and used for Ring Opening Metathesis Polymerization (ROMP) in strongly reactive environments based on epoxy resins. The protection mechanism, proposed in this paper, is based on the formation of a micrometric globular shell that partially englobed the catalytic site, causing hindrances for the deactivation of the catalyst due to an equimolecular reaction between the catalyst complex and the oxirane ring. The catalytic performance evaluated in reactive self-healing systems showed the overcoming of several critical drawbacks. The proposed system allows curing temperatures typical of structural materials and, in addition to preventing the agglomeration of the catalyst particles, a remarkable reduction from 5% to 0.3% by wt of expensive catalyst in the self-healing composite material

Trame di parole. Studi in memoria di Clara Borrelli.

l volume miscellaneo Trame di parole. Studi in memoria di Clara Borrelli raccoglie circa trenta contributi, da parte di colleghi, amici e allievi, su temi e autori della letteratura italiana a lei cari, soprattutto dell’Otto-Novecento (Manzoni, Leopardi, Ungaretti, Quasimodo, Elsa Morante, Pirandello, Primo Levi, Ginzburg, Eduardo De Filippo). Vi si annoverano anche saggi su Petrarca e Boccaccio, sulla letteratura del Cinquecento e del Seicento, sul rapporto tra letteratura e cinema, letteratura e teatro, mentre in generale il volume presenta ampi interessi linguistici e comparatistici, in specifico relativi all’area romena e soprattutto spagnola.Tre saggi sono in lingua spagnola. Il presente volume vuole essere un segno di amicizia e di continuità nel ricordo di una cara docente, amica, collega e maestra

Use of graphene oxide functionalized with Grubbs and Hoveyda Grubbs catalyst to activate metathesis reaction in epoxy mixtures

In this paper we discuss the possibility to use graphite oxide functionalized with Grubbs and Hoveyda Grubbs catalysts to activate metathesis reactions in epoxy mixtures

Synthesis of ruthenium catalysts functionalized graphene oxide for self-healing applications

Graphene Oxide (GO) was prepared by chemical oxidation of high surface area graphite (G). GO was used to support ruthenium catalysts with the aim to activate self-healing reactions in multifunctional materials able to integrate simultaneously the healing reactions with the very interesting properties of graphene-based materials.Grubbs catalysts 1st (G1) and 2nd generation modified (G2 o-tol), Hoveyda-Grubbs catalysts 1st (HG1) and 2nd generation (HG2) were covalently bonded to GO preserving the same catalytic activity of the catalysts not bonded to the graphene sheets. GO-G2 o-tol and GO-G1deactivate during the process of preparation of the self-healing epoxy mixtures at 90°C. Evidence of the self-healing activity of the various catalytic complexes was investigated for both uncured and cured samples. Results show that GO-HG1 and GO-HG2 are not deactivated and hence they are able to trigger self-healing reaction based on the ROMP of 5-ethylidene-2-norbornene (ENB). This behavior is most likely due to the formation of 16 electron Ru-complexes that are more stable than the 14 electron complexes of GO-G1 and GO-G2 catalyst