Optically active photoresponsive multifunctional polymeric materials

In the last year [1], Angiolini and co-workers have synthesized and investigated methacrylic polymers bearing in the side chain the chiral cyclic (S)-3-hydroxypyrrolidine moiety interposed between the main chain and the trans-azoaromatic chromophore, substituted or not in the 4’ position by an electron-withdrawing group. In these materials, the presence of a rigid chiral moiety of one prevailing absolute configuration favours the establishment of a chiral conformation of one prevailing helical handedness, at least within chain segments of the macromolecules, which can be observed by circular dichroism (CD). The simultaneous presence of the azoaromatic and chiral functionalities allows the polymers to display both the properties typical of dissymmetric systems (optical activity, exciton splitting of dichroic absorptions), as well as the features typical of photochromic materials (photorefractivity, photoresponsiveness, NLO properties). The first part of this research was to synthesize analogue homopolymers and copolymers based on bisazoaromatic moiety and compare their properties to those of the above mentioned analogue derivatives bearing only one azoaromatic chromophore in the side chain. We focused also the attention on the effects induced on the thermal and chiroptical behaviours by the insertion of particulars achiral comonomers characterized by different side-chain mobility and grown hindrance (MMA, tert-BMA and TrMA). On the other hand carbazole containing polymers [2] have attracted much attention because of their unique features. The use of these materials in advanced micro- and nanotechnologies spreads in many different applications such as photoconductive and photorefractive polymers, electroluminescent devices, programmable optical interconnections, data storage, chemical photoreceptors, NLO, surface relief gratings, blue emitting materials and holographic memory. The second part of the work was focused on the synthesis and the characterization polymeric derivatives bearing in the side chain carbazole or phenylcarbazole moieties linked to the (S)- 2-hydroxy succinimide or the (S)-3-hydroxy pyrrolidinyl ring as chiral groups covalently linked to the main chain through ester bonds. The last objective of this research was to design, synthesize, and characterize multifunctional methacrylic homopolymers and copolymers bearing three distinct functional groups (i.e. azoaromatic, carbazole and chiral group of one single configuration) directly linked in the side chain. This polymeric derivatives could be of potential interest for several advanced application fields, such as optical storage, waveguides, chiroptical switches, chemical photoreceptors, NLO, surface relief gratings, photoconductive materials, etc.

Morphological transitions in molecular and polymeric materials: patterning, fabrication, devices

This thesis individuates and characterizes irreversible transformations occurring in specific organic and oligomeric/polymeric thin films. These transformations are dewetting in discotic liquid crystals thin films and dewetting and smoothing in oligomeric and polyemeric films. Irreversible transformations are extensively characterized by means of optical and atomic force microscopy. In the case of discotic liquid crystals films the morphological characterization is performed sinchronically with electrical measurements of current during dewetting.

New polymeric materials for vascular surgery

The dramatic impact that vascular diseases have on human life quality and expectancy nowadays is the reason why both medical and scientific communities put great effort in discovering new and effective ways to fight vascular pathologies. Among the many different treatments, endovascular surgery is a minimally-invasive technique that makes use of X-ray fluoroscopy to obtain real-time images of the patient during interventions. In this context radiopaque biomaterials, i.e. materials able to absorb X-ray radiation, play a fundamental role as they are employed both to enhance visibility of devices during interventions and to protect medical staff and patients from X-ray radiations. Organic-inorganic hybrids are materials that combine characteristics of organic polymers with those of inorganic metal oxides. These materials can be synthesized via the sol-gel process and can be easily applied as thin coatings on different kinds of substrates. Good radiopacity of organic-inorganic hybrids has been recently reported suggesting that these materials might find applications in medical fields where X-ray absorption and visibility is required. The present PhD thesis aimed at developing and characterizing new radiopaque organic-inorganic hybrid materials that can find application in the vascular surgery field as coatings for the improvement of medical devices traceability as well as for the production of X-ray shielding objects and garments. Novel organic-inorganic hybrids based on different polyesters (poly-lactic acid and poly-ε-caprolactone) and polycarbonate (poly-trimethylene carbonate) as the polymeric phase and on titanium oxide as the inorganic phase were synthesized. Study of the phase interactions in these materials allowed to demonstrate that Class II hybrids (where covalent bonds exists between the two phases) can be obtained starting from any kind of polyester or polycarbonate, without the need of polymer pre-functionalization, thanks to the occurrence of transesterification reactions operated by inorganic molecules on ester and carbonate moieties. Polyester based hybrids were successfully coated via dip coating on different kinds of textiles. Coated textiles showed improved radiopacity with respect to the plain fabric while remaining soft to the touch. The hybrid was able to coat single fibers of the yarn rather than coating the yarn as a whole. Openings between yarns were maintained and therefore fabric breathability was preserved. Such coatings are promising for the production of light-weight garments for X-ray protection of medical staff during interventional fluoroscopy, which will help preventing pathologies that stem from chronic X-ray exposure. A means to increase the protection capacity of hybrid-coated fabrics was also investigated and implemented in this thesis. By synthesizing the hybrid in the presence of a suspension of radiopaque tantalum nanoparticles, PDMS-titania hybrid materials with tunable radiopacity were developed and were successfully applied as coatings. A solution for enhancing medical device radiopacity was also successfully investigated. High metal radiopacity was associated with good mechanical and protective properties of organic-inorganic hybrids in the form of a double-layer coating. Tantalum was employed as the constituent of the first layer deposited on sample substrates by means of a sputtering technique. The second layer was composed of a hybrid whose constituents are well-known biocompatible organic and inorganic components, such as the two polymers PCL and PDMS, and titanium oxide, respectively. The metallic layer conferred to the substrate good X-ray visibility. A correlation between radiopacity and coating thickness derived during this study allows to tailor radiopacity simply by controlling the metal layer sputtering deposition time. The applied metal deposition technique also permits easy shaping of the radiopaque layer, allowing production of radiopaque markers for medical devices that can be unambiguously identified by surgeons during implantation and in subsequent radiological investigations. Synthesized PCL-titania and PDMS-titania hybrids strongly adhered to substrates and show good biocompatibility as highlighted by cytotoxicity tests. The PDMS-titania hybrid coating was also characterized by high flexibility that allows it to stand large substrate deformations without detaching nor cracking, thus being suitable for application on flexible medical devices.

Advanced polymeric materials for applications in technical equipment for snow sports

The thesis is divided in three chapters, each one covering one topic. Initially, the thermo-mechanical and impact properties of materials used for back protectors have been analysed. Dynamical mechanical analysis (DMTA) has shown that materials used for soft-shell protectors present frequency-sensitive properties. Furthermore, through impact tests, the shock absorbing characteristics of the materials have been investigated proving the differences between soft and hard-shell protectors; moreover it has been demonstrated that the materials used for soft-shell protectors maintain their protective properties after multi-impacts. The second chapter covers the effect of the visco-elastic properties of the thermoplastic polymers on the flexural and rebound behaviours of ski boots. DMTA analysis on the materials and flexural and rebound testing on the boots have been performed. A comparison of the results highlighted a correlation between the visco-elastic properties and the flexural and rebound behaviour of ski boots. The same experimental methods have been used to investigate the influence of the design on the flexural and rebound behaviours. Finally in the third chapter the thermoplastic materials employed for the construction of ski boots soles have been characterized in terms of chemical composition, hardness, crystallinity, surface roughness and coefficient of friction (COF). The results showed a relation between material hardness and grip, in particular softer materials provide more grip with respect to harder materials. On the contrary, the surface roughness has a negative effect on friction because of the decrease in contact area. The measure of grip on inclined wet surfaces showed again a relation between hardness and grip. The performance ranking of the different materials has been the same for the COF and for the slip angle tests, indicating that COF can be used as a parameter for the choice of the optimal material to be used for the soles of ski boots.

Liquid crystal polymers: macromolecular design for enhanced performances

During this work, done mainly in the laboratories of the department of Industrial Chemistry and Materials of the University of Bologna but also in the laboratories of the Carnegie Mellon University in collaboration with prof. K. Matyjaszewski and at the university of Zaragoza in collaboration with prof. J. Barberá, was focused mainly on the synthesis and characterization of new functional polymeric materials. In the past years our group gained a deep knowledge about the photomodulation of azobenzene containing polymers. The aim of this thesis is to push forward the performances of these materials by the synthesis of well defined materials, in which, by a precise control over the macromolecular structures, better or even new functionality can be delivered to the synthesized material. For this purpose, besides the rich photochemistry of azoaromatic polymers that brings to the application, the control offered from the recent techniques of controlled radical polymerization, ATRP over all, gives an enormous range of opportunity for the developing of a new generation of functional materials whose properties are determinate not only by the chemical nature of the functional center (e.g. azoaromatic chromophore) but are tuned and even amplified by a synergy with the whole macromolecular structure. Old materials in new structures. In this contest the work of this thesis was focused mainly on the synthesis and characterization of well defined azoaromatic polymers in order to establish, for the first time, precise structure-properties correlation. In fact a series of well defined different azopolymers, chiral and achiral, with different molecular weight and highly monodisperse were synthesized and their properties were studied, in terms of photoexpansion and photomodulation of chirality. We were then able to study the influence of the macromolecular structure in terms of molecular weight and ramification on the studied properties. The huge amount of possibility offered by the tailoring of the macromolecular structure were exploited for the synthesis of new cholesteric photochromic polymers that can be used as a smart label for the certification of the thermal history of any thermosensitive product. Finally the ATRP synthesis allowed us to synthesize a total new class of material, named molecular brushes: a flat surface covered with an ultra thin layer of polymeric chain covalently bond onto the surface from one end. This new class of materials is of extreme interest as they offer the possibility to tune and manage the interaction of the surface with the environment. In this contest we synthesized both azoaromatic surfaces, growing directly the polymer from the surface, and mixed brushes: surfaces covered with incompatible macromolecules. Both type of surfaces acts as “smart” surfaces: the first it is able to move the orientation of a LC cell by simply photomodulation and, thanks to the robustness of the covalent bond, can be used as a command surface overcoming all the limitation due to the dewetting of the active layer. The second type of surface, functionalized by a grafting-to method, can self assemble the topmost layer responding to changed environmental conditions, exposing different functionality according to different environment.

Composite materials design, manufacture and evaluation

Fibre-Reinforced-Plastics are composite materials composed by thin fibres with high mechanical properties, made to work together with a cohesive plastic matrix. The huge advantages of fibre reinforced plastics over traditional materials are their high specific mechanical properties i.e. high stiffness and strength to weight ratios. This kind of composite materials is the most disruptive innovation in the structural materials field seen in recent years and the areas of potential application are still many. However, there are few aspects which limit their growth: on the one hand the information available about their properties and long term behaviour is still scarce, especially if compared with traditional materials for which there has been developed an extended database through years of use and research. On the other hand, the technologies of production are still not as developed as the ones available to form plastics, metals and other traditional materials. A third aspect is that the new properties presented by these materials e.g. their anisotropy, difficult the design of components. This thesis will provide several case-studies with advancements regarding the three limitations mentioned. In particular, the long term mechanical properties have been studied through an experimental analysis of the impact of seawater on GFRP. Regarding production methods, the pre-impregnated cured in autoclave process was considered: a rapid tooling method to produce moulds will be presented, and a study about the production of thick components. Also, two liquid composite moulding methods will be presented, with a case-study regarding a large component with sandwich structure that was produced with the Vacuum-Assisted-Resin-Infusion method, and a case-study regarding a thick con-rod beam that was produced with the Resin-Transfer-Moulding process. The final case-study will analyse the loads acting during the use of a particular sportive component, made with FRP layers and a sandwich structure, practical design rules will be provided.

On Designing Compliant Actuators Based On Dielectric Elastomers

Dielectric Elastomers (DE) are incompressible dielectrics which can experience deviatoric (isochoric) finite deformations in response to applied large electric fields. Thanks to the strong electro-mechanical coupling, DE intrinsically offer great potentialities for conceiving novel solid-state mechatronic devices, in particular linear actuators, which are more integrated, lightweight, economic, silent, resilient and disposable than equivalent devices based on traditional technologies. Such systems may have a huge impact in applications where the traditional technology does not allow coping with the limits of weight or encumbrance, and with problems involving interaction with humans or unknown environments. Fields such as medicine, domotic, entertainment, aerospace and transportation may profit. For actuation usage, DE are typically shaped in thin films coated with compliant electrodes on both sides and piled one on the other to form a multilayered DE. DE-based Linear Actuators (DELA) are entirely constituted by polymeric materials and their overall performance is highly influenced by several interacting factors; firstly by the electromechanical properties of the film, secondly by the mechanical properties and geometry of the polymeric frame designed to support the film, and finally by the driving circuits and activation strategies. In the last decade, much effort has been focused in the devolvement of analytical and numerical models that could explain and predict the hyperelastic behavior of different types of DE materials. Nevertheless, at present, the use of DELA is limited. The main reasons are 1) the lack of quantitative and qualitative models of the actuator as a whole system 2) the lack of a simple and reliable design methodology. In this thesis, a new point of view in the study of DELA is presented which takes into account the interaction between the DE film and the film supporting frame. Hyperelastic models of the DE film are reported which are capable of modeling the DE and the compliant electrodes. The supporting frames are analyzed and designed as compliant mechanisms using pseudo-rigid body models and subsequent finite element analysis. A new design methodology is reported which optimize the actuator performances allowing to specifically choose its inherent stiffness. As a particular case, the methodology focuses on the design of constant force actuators. This class of actuators are an example of how the force control could be highly simplified. Three new DE actuator concepts are proposed which highlight the goodness of the proposed method.

Trasporto di materia in membrane polimeriche e nanocomposite per la separazione di gas

Membrane-based separation processes are acquiring, in the last years, an increasing importance because of their intrinsic energetic and environmental sustainability: some types of polymeric materials, showing adequate perm-selectivity features, appear rather suitable for these applications, because of their relatively low cost and easy processability. In this work have been studied two different types of polymeric membranes, in view of possible applications to the gas separation processes, i.e. Mixed Matrix Membranes (MMMs) and high free volume glassy polymers. Since the early 90’s, it has been understood that the performances of polymeric materials in the field of gas separations show an upper bound in terms of permeability and selectivity: in particular, an increase of permeability is often accompanied by a decrease of selectivity and vice-versa, while several inorganic materials, like zeolites or silica derivates, can overcome this limitation. As a consequence, it has been developed the idea of dispersing inorganic particles in polymeric matrices, in order to obtain membranes with improved perm-selectivity features. In particular, dispersing fumed silica nanoparticles in high free volume glassy polymers improves in all the cases gases and vapours permeability, while the selectivity may either increase or decrease, depending upon material and gas mixture: that effect is due to the capacity of nanoparticles to disrupt the local chain packing, increasing the dimensions of excess free volume elements trapped in the polymer matrix. In this work different kinds of MMMs were fabricated using amorphous Teflon® AF or PTMSP and fumed silica: in all the cases, a considerable increase of solubility, diffusivity and permeability of gases and vapours (n-alkanes, CO2, methanol) was observed, while the selectivity shows a non-monotonous trend with filler fraction. Moreover, the classical models for composites are not able to capture the increase of transport properties due to the silica addition, so it has been necessary to develop and validate an appropriate thermodynamic model that allows to predict correctly the mass transport features of MMMs. In this work, another material, called poly-trimethylsilyl-norbornene (PTMSN) was examined: it is a new generation high free volume glassy polymer that, like PTMSP, shows unusual high permeability and selectivity levels to the more condensable vapours. These two polymer differ each other because PTMSN shows a more pronounced chemical stability, due to its structure double-bond free. For this polymer, a set of Lattice Fluid parameters was estimated, making possible a comparison between experimental and theoretical solubility isotherms for hydrocarbons and alcoholic vapours: the successfully modelling task, based on application of NELF model, offers a reliable alternative to direct sorption measurement, which is extremely time-consuming due to the relevant relaxation phenomena showed by each sorption step. For this material also dilation experiments were performed, in order to quantify its dimensional stability in presence of large size, swelling vapours.

Analisi sperimentale dell'influenza dei parametri di processo sulla resistenza di contatto tra polimero e stampo durante la formatura

Con gli strumenti informatici disponibili oggi per le industrie, in particolar modo coi software CAE, le possibile simulare in maniera più che soddisfacente i fenomeni fisici presenti in natura. Anche il raffreddamento di un manufatto in polimero può venire simulato, a patto che si conoscano tutti i dati dei materiali e delle condizioni al contorno. Per quanto riguarda i dati dei materiali, i produttori di polimeri sono molto spesso in grado di fornirli, mentre le condizioni al contorno devono essere padroneggiate dal detentore della tecnologia. Nella pratica, tale conoscenza è al più incompleta, quindi si fanno ipotesi per colmare le lacune. Una tra le ipotesi più forti fatte è quella di una perfetta conduzione all'interfaccia tra due corpi. Questo è un vincolo troppo forte, se paragonato alla precisione di tutti gli altri dati necessari alla simulazione, e quindi si è deciso di eseguire una campagna sperimentale per stimare la resistenza al passaggio flusso termico all'interfaccia polimero-stampo ovvero determinare la conduttanza termica di contatto. L'attività svolta in questa tesi di dottorato ha come scopo quello di fornire un contributo significativo allo sviluppo e al miglioramento dell'efficienza termica degli stampi di formatura dei polimeri termoplastici con tecnologia a compressione.

New materials for electrochemiluminescence

The study of electrochemiluminescence (ECL) involves photophysical and electrochemical aspects. Excited states are populated by an electrical stimulus. The most important applications are in the diagnostic field where a number of different biologically-relevant molecules (e.g. proteins and nucleic acids) can be recognized and quantified with a sensitivity and specificity previously not reachable. As a matter of fact the electrochemistry, differently to the classic techniques as fluorescence and chemiluminescence, allows to control the excited state generation spatially and temporally. The two research visits into A. J. Bard electrochemistry laboratories were priceless. Dr. Bard has been one of ECL pioneers, the first to introduce the technique and the one who discovered in 1972 the surprising emission of Ru(bpy)3 2+. I consider necessary to thank by now my supervisors Massimo and Francesco for their help and for giving me the great opportunity to know this unique science man that made me feel enthusiastic. I will never be grateful enough… Considering that the experimental techniques of ECL did not changed significantly in these last years the most convenient research direction has been the developing of materials with new or improved properties. In Chapter I the basics concepts and mechanisms of ECL are introduced so that the successive experiments can be easily understood. In the final paragraph the scopes of the thesis are briefly described. In Chapter II by starting from ECL experimental apparatus of Dr. Bard’s laboratories the design, assembly and preliminary tests of the new Bologna instrument are carefully described. The instrument assembly required to work hard but resulted in the introduction of the new technique in our labs by allowing the continuation of the ECL studies began in Texas. In Chapter III are described the results of electrochemical and ECL studies performed on new synthesized Ru(II) complexes containing tetrazolate based ligands. ECL emission has been investigated in solution and in solid thin films. The effect of the chemical protonation of the tetrazolate ring on ECL emission has been also investigated evidencing the possibility of a catalytic effect (generation of molecular hydrogen) of one of the complexes in organic media. Finally, after a series of preliminary studies on ECL emission in acqueous buffers, the direct interaction with calf thymus DNA of some complexes has been tested by ECL and photoluminescence (PL) titration. In Chapter IV different Ir(III) complexes have been characterized electrochemically and photophysically (ECL and PL). Some complexes were already well-known in literature for their high quantum efficiency whereas the remaining were new synthesized compounds containing tetrazolate based ligands analogous to those investigated in Chapt. III. During the tests on a halogenated complex was unexpectedly evidenced the possibility to follow the kinetics of an electro-induced chemical reaction by using ECL signal. In the last chapter (V) the possibility to use mono-use silicon chips electrodes as ECL analitycal devices is under investigation. The chapter begins by describing the chip structure and materials then a signal reproducibility study and geometry optimization is carried on by using two different complexes. In the following paragraphs is reported in detail the synthesis of an ECL label based on Ru(bpy)3 2+ and the chip functionalization by using a lipoic acid SAM and the same label. After some preliminary characterizations (mass spectroscopy TOF) has been demonstrated that by mean of a simple and fast ECL measurement it’s possible to confirm the presence of the coupling product SAM-label into the chip with a very high sensitivity. No signal was detected from the same system by using photoluminescence.

Application of FTIR microscopy to cultural heritage materials

Research in art conservation has been developed from the early 1950s, giving a significant contribution to the conservation-restoration of cultural heritage artefacts. In fact, only through a profound knowledge about the nature and conditions of constituent materials, suitable decisions on the conservation and restoration measures can thus be adopted and preservation practices enhanced. The study of ancient artworks is particularly challenging as they can be considered as heterogeneous and multilayered systems where numerous interactions between the different components as well as degradation and ageing phenomena take place. However, difficulties to physically separate the different layers due to their thickness (1-200 µm) can result in the inaccurate attribution of the identified compounds to a specific layer. Therefore, details can only be analysed when the sample preparation method leaves the layer structure intact, as for example the preparation of embedding cross sections in synthetic resins. Hence, spatially resolved analytical techniques are required not only to exactly characterize the nature of the compounds but also to obtain precise chemical and physical information about ongoing changes. This thesis focuses on the application of FTIR microspectroscopic techniques for cultural heritage materials. The first section is aimed at introducing the use of FTIR microscopy in conservation science with a particular attention to the sampling criteria and sample preparation methods. The second section is aimed at evaluating and validating the use of different FTIR microscopic analytical methods applied to the study of different art conservation issues which may be encountered dealing with cultural heritage artefacts: the characterisation of the artistic execution technique (chapter II-1), the studies on degradation phenomena (chapter II-2) and finally the evaluation of protective treatments (chapter II-3). The third and last section is divided into three chapters which underline recent developments in FTIR spectroscopy for the characterisation of paint cross sections and in particular thin organic layers: a newly developed preparation method with embedding systems in infrared transparent salts (chapter III-1), the new opportunities offered by macro-ATR imaging spectroscopy (chapter III-2) and the possibilities achieved with the different FTIR microspectroscopic techniques nowadays available (chapter III-3). In chapter II-1, FTIR microspectroscopy as molecular analysis, is presented in an integrated approach with other analytical techniques. The proposed sequence is optimized in function of the limited quantity of sample available and this methodology permits to identify the painting materials and characterise the adopted execution technique and state of conservation. Chapter II-2 describes the characterisation of the degradation products with FTIR microscopy since the investigation on the ageing processes encountered in old artefacts represents one of the most important issues in conservation research. Metal carboxylates resulting from the interaction between pigments and binding media are characterized using synthesised metal palmitates and their production is detected on copper-, zinc-, manganese- and lead- (associated with lead carbonate) based pigments dispersed either in oil or egg tempera. Moreover, significant effects seem to be obtained with iron and cobalt (acceleration of the triglycerides hydrolysis). For the first time on sienna and umber paints, manganese carboxylates are also observed. Finally in chapter II-3, FTIR microscopy is combined with further elemental analyses to characterise and estimate the performances and stability of newly developed treatments, which should better fit conservation-restoration problems. In the second part, in chapter III-1, an innovative embedding system in potassium bromide is reported focusing on the characterisation and localisation of organic substances in cross sections. Not only the identification but also the distribution of proteinaceous, lipidic or resinaceous materials, are evidenced directly on different paint cross sections, especially in thin layers of the order of 10 µm. Chapter III-2 describes the use of a conventional diamond ATR accessory coupled with a focal plane array to obtain chemical images of multi-layered paint cross sections. A rapid and simple identification of the different compounds is achieved without the use of any infrared microscope objectives. Finally, the latest FTIR techniques available are highlighted in chapter III-3 in a comparative study for the characterisation of paint cross sections. Results in terms of spatial resolution, data quality and chemical information obtained are presented and in particular, a new FTIR microscope equipped with a linear array detector, which permits reducing the spatial resolution limit to approximately 5 µm, provides very promising results and may represent a good alternative to either mapping or imaging systems.

Structural changes and dynamic behaviour of vanadium oxide-based catalysts for gas-phase selective oxidations

Selective oxidation is one of the simplest functionalization methods and essentially all monomers used in manufacturing artificial fibers and plastics are obtained by catalytic oxidation processes. Formally, oxidation is considered as an increase in the oxidation number of the carbon atoms, then reactions such as dehydrogenation, ammoxidation, cyclization or chlorination are all oxidation reactions. In this field, most of processes for the synthesis of important chemicals used vanadium oxide-based catalysts. These catalytic systems are used either in the form of multicomponent mixed oxides and oxysalts, e.g., in the oxidation of n-butane (V/P/O) and of benzene (supported V/Mo/O) to maleic anhydride, or in the form of supported metal oxide, e.g., in the manufacture of phthalic anhydride by o-xylene oxidation, of sulphuric acid by oxidation of SO2, in the reduction of NOx with ammonia and in the ammoxidation of alkyl aromatics. In addition, supported vanadia catalysts have also been investigated for the oxidative dehydrogenation of alkanes to olefins , oxidation of pentane to maleic anhydride and the selective oxidation of methanol to formaldehyde or methyl formate [1]. During my PhD I focused my work on two gas phase selective oxidation reactions. The work was done at the Department of Industrial Chemistry and Materials (University of Bologna) in collaboration with Polynt SpA. Polynt is a leader company in the development, production and marketing of catalysts for gas-phase oxidation. In particular, I studied the catalytic system for n-butane oxidation to maleic anhydride (fluid bed technology) and for o-xylene oxidation to phthalic anhydride. Both reactions are catalyzed by systems based on vanadium, but catalysts are completely different. Part A is dedicated to the study of V/P/O catalyst for n-butane selective oxidation, while in the Part B the results of an investigation on TiO2-supported V2O5, catalyst for o-xylene oxidation are showed. In Part A, a general introduction about the importance of maleic anhydride, its uses, the industrial processes and the catalytic system are reported. The reaction is the only industrial direct oxidation of paraffins to a chemical intermediate. It is produced by n-butane oxidation either using fixed bed and fluid bed technology; in both cases the catalyst is the vanadyl pyrophosphate (VPP). Notwithstanding the good performances, the yield value didn’t exceed 60% and the system is continuously studied to improve activity and selectivity. The main open problem is the understanding of the real active phase working under reaction conditions. Several articles deal with the role of different crystalline and/or amorphous vanadium/phosphorous (VPO) compounds. In all cases, bulk VPP is assumed to constitute the core of the active phase, while two different hypotheses have been formulated concerning the catalytic surface. In one case the development of surface amorphous layers that play a direct role in the reaction is described, in the second case specific planes of crystalline VPP are assumed to contribute to the reaction pattern, and the redox process occurs reversibly between VPP and VOPO4. Both hypotheses are supported also by in-situ characterization techniques, but the experiments were performed with different catalysts and probably under slightly different working conditions. Due to complexity of the system, these differences could be the cause of the contradictions present in literature. Supposing that a key role could be played by P/V ratio, I prepared, characterized and tested two samples with different P/V ratio. Transformation occurring on catalytic surfaces under different conditions of temperature and gas-phase composition were studied by means of in-situ Raman spectroscopy, trying to investigate the changes that VPP undergoes during reaction. The goal is to understand which kind of compound constituting the catalyst surface is the most active and selective for butane oxidation reaction, and also which features the catalyst should possess to ensure the development of this surface (e.g. catalyst composition). On the basis of results from this study, it could be possible to project a new catalyst more active and selective with respect to the present ones. In fact, the second topic investigated is the possibility to reproduce the surface active layer of VPP onto a support. In general, supportation is a way to improve mechanical features of the catalysts and to overcome problems such as possible development of local hot spot temperatures, which could cause a decrease of selectivity at high conversion, and high costs of catalyst. In literature it is possible to find different works dealing with the development of supported catalysts, but in general intrinsic characteristics of VPP are worsened due to the chemical interaction between active phase and support. Moreover all these works deal with the supportation of VPP; on the contrary, my work is an attempt to build-up a V/P/O active layer on the surface of a zirconia support by thermal treatment of a precursor obtained by impregnation of a V5+ salt and of H3PO4. In-situ Raman analysis during the thermal treatment, as well as reactivity tests are used to investigate the parameters that may influence the generation of the active phase. Part B is devoted to the study of o-xylene oxidation of phthalic anhydride; industrially, the reaction is carried out in gas-phase using as catalysts a supported system formed by V2O5 on TiO2. The V/Ti/O system is quite complex; different vanadium species could be present on the titania surface, as a function of the vanadium content and of the titania surface area: (i) V species which is chemically bound to the support via oxo bridges (isolated V in octahedral or tetrahedral coordination, depending on the hydration degree), (ii) a polymeric species spread over titania, and (iii) bulk vanadium oxide, either amorphous or crystalline. The different species could have different catalytic properties therefore changing the relative amount of V species can be a way to optimize the catalytic performances of the system. For this reason, samples containing increasing amount of vanadium were prepared and tested in the oxidation of o-xylene, with the aim of find a correlations between V/Ti/O catalytic activity and the amount of the different vanadium species. The second part deals with the role of a gas-phase promoter. Catalytic surface can change under working conditions; the high temperatures and a different gas-phase composition could have an effect also on the formation of different V species. Furthermore, in the industrial practice, the vanadium oxide-based catalysts need the addition of gas-phase promoters in the feed stream, that although do not have a direct role in the reaction stoichiometry, when present leads to considerable improvement of catalytic performance. Starting point of my investigation is the possibility that steam, a component always present in oxidation reactions environment, could cause changes in the nature of catalytic surface under reaction conditions. For this reason, the dynamic phenomena occurring at the surface of a 7wt% V2O5 on TiO2 catalyst in the presence of steam is investigated by means of Raman spectroscopy. Moreover a correlation between the amount of the different vanadium species and catalytic performances have been searched. Finally, the role of dopants has been studied. The industrial V/Ti/O system contains several dopants; the nature and the relative amount of promoters may vary depending on catalyst supplier and on the technology employed for the process, either a single-bed or a multi-layer catalytic fixed-bed. Promoters have a quite remarkable effect on both activity and selectivity to phthalic anhydride. Their role is crucial, and the proper control of the relative amount of each component is fundamental for the process performance. Furthermore, it can not be excluded that the same promoter may play different role depending on reaction conditions (T, composition of gas phase..). The reaction network of phthalic anhydride formation is very complex and includes several parallel and consecutive reactions; for this reason a proper understanding of the role of each dopant cannot be separated from the analysis of the reaction scheme. One of the most important promoters at industrial level, which is always present in the catalytic formulations is Cs. It is known that Cs plays an important role on selectivity to phthalic anhydride, but the reasons of this phenomenon are not really clear. Therefore the effect of Cs on the reaction scheme has been investigated at two different temperature with the aim of evidencing in which step of the reaction network this promoter plays its role.

Porous Polymeric Bioresorbable Scaffolds for Tissue Engineering

Tissue engineering is a discipline that aims at regenerating damaged biological tissues by using a cell-construct engineered in vitro made of cells grown into a porous 3D scaffold. The role of the scaffold is to guide cell growth and differentiation by acting as a bioresorbable temporary substrate that will be eventually replaced by new tissue produced by cells. As a matter or fact, the obtainment of a successful engineered tissue requires a multidisciplinary approach that must integrate the basic principles of biology, engineering and material science. The present Ph.D. thesis aimed at developing and characterizing innovative polymeric bioresorbable scaffolds made of hydrolysable polyesters. The potentialities of both commercial polyesters (i.e. poly-e-caprolactone, polylactide and some lactide copolymers) and of non-commercial polyesters (i.e. poly-w-pentadecalactone and some of its copolymers) were explored and discussed. Two techniques were employed to fabricate scaffolds: supercritical carbon dioxide (scCO2) foaming and electrospinning (ES). The former is a powerful technology that enables to produce 3D microporous foams by avoiding the use of solvents that can be toxic to mammalian cells. The scCO2 process, which is commonly applied to amorphous polymers, was successfully modified to foam a highly crystalline poly(w-pentadecalactone-co-e-caprolactone) copolymer and the effect of process parameters on scaffold morphology and thermo-mechanical properties was investigated. In the course of the present research activity, sub-micrometric fibrous non-woven meshes were produced using ES technology. Electrospun materials are considered highly promising scaffolds because they resemble the 3D organization of native extra cellular matrix. A careful control of process parameters allowed to fabricate defect-free fibres with diameters ranging from hundreds of nanometers to several microns, having either smooth or porous surface. Moreover, versatility of ES technology enabled to produce electrospun scaffolds from different polyesters as well as “composite” non-woven meshes by concomitantly electrospinning different fibres in terms of both fibre morphology and polymer material. The 3D-architecture of the electrospun scaffolds fabricated in this research was controlled in terms of mutual fibre orientation by properly modifying the instrumental apparatus. This aspect is particularly interesting since the micro/nano-architecture of the scaffold is known to affect cell behaviour. Since last generation scaffolds are expected to induce specific cell response, the present research activity also explored the possibility to produce electrospun scaffolds bioactive towards cells. Bio-functionalized substrates were obtained by loading polymer fibres with growth factors (i.e. biomolecules that elicit specific cell behaviour) and it was demonstrated that, despite the high voltages applied during electrospinning, the growth factor retains its biological activity once released from the fibres upon contact with cell culture medium. A second fuctionalization approach aiming, at a final stage, at controlling cell adhesion on electrospun scaffolds, consisted in covering fibre surface with highly hydrophilic polymer brushes of glycerol monomethacrylate synthesized by Atom Transfer Radical Polymerization. Future investigations are going to exploit the hydroxyl groups of the polymer brushes for functionalizing the fibre surface with desired biomolecules. Electrospun scaffolds were employed in cell culture experiments performed in collaboration with biochemical laboratories aimed at evaluating the biocompatibility of new electrospun polymers and at investigating the effect of fibre orientation on cell behaviour. Moreover, at a preliminary stage, electrospun scaffolds were also cultured with tumour mammalian cells for developing in vitro tumour models aimed at better understanding the role of natural ECM on tumour malignity in vivo.

Materiali Politiofenici Otticamente Attivi

Much effort has been devoted in the recent years to the investigation of optically active polythiophenes characterized by the presence of a chiral moiety linked to the 3-position of the aromatic ring. In addition to their potential technological applications as materials for enantioselective electrodes and membranes, chiral poly(thiophene)s offer the possibility of studying the structural changes accompanying the transition from the disordered state by following the variation of their chiroptical properties by circular dichroism (CD). In solution of a good solvent, that kind of polythiophenes doesn’t display any optical activity arising from the presence of dissymmetric conformation of the backbone, as shown by circular dichroism (CD) spectra. When the macromolecules begin to aggregate, as it occurs e.g. by addition of a poor solvent, or lowering the solution temperature, or when the macromolecules are assembled in the solid state as thin films obtained by solution casting or spin coating, significant CD bands are observed in the spectral region related to the electronic absorptions of the aromatic polythiophene chromophore. These CD bands are indicative of a chiral macromolecule arrangement of one prevailing chirality. The synthesis of -substituted polythiophenes can be carried out starting from the corresponding -substituted mono- or oligomeric thiophenic monomers under regioselective or regiospecific conditions in order to minimize or avoid the formation of head-to-head dyads unfavourably affecting the presence of coplanar conformations of thiophene rings as a consequence of steric interactions between the side-chain substituents, both in solution and in the solid state. To this regard, non-symmetrically substituted monomers require therefore to perform the polymerization in the presence of highly demanding catalysts and reaction condition, whereas with symmetrically substituted oligothiophenic monomers containing the -substituents located far apart from the reacting sites, it is instead possible to obtain regioregular macromolecules by adopting more simple and economic polymerization methods, such as, e. g., the chemical oxidative polymerization with iron (III) trichloride. In order to verify how the polymer structure affects its optical activity, further poly-3-alkylthiophenes, substituted by an enantiomerically pure chiral alkyl group, namely poli[3,3”-di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’:5’,2”-terthiophene] (PDMBOETT), poli[3,3’di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’-bitiofene] (PDMBOEBT), poli[3,3””-didodecyl-4’,3”’-di(S)-(+)-2-methylbutyl-2,2’:5’,2”:5”,2”’:5”’,2””-quinquethiophene (PDDDMBQT) have been synthesized and characterized by instrumental techniques. The spectroscopic behaviour of thin films of poly(DDDMBQT) has been investigated in the solid state under different sample preparation procedures. It was also compared with the behaviour of polymers previously made. The experimental results are interpreted in terms of influence of the side-chain substituents on the extent of planarity of the polymeric chains and the formation of optically active chiral aggregates. In recent years conjugated block copolymers have received considerable attention. It is well known that conjugated block copolymers composed of two electronically different blocks can have morphologic and optical properties, that differ from those of their homopolymers. A recent study has also shown that the electronic properties and the supramolecular organization of one conjugated block can also be influenced by the other block. In order to study better this behavior, a new conjugated block copolymers, composed of a regioregular hydrophylic block and a regioregular hydrophobic block namely poli[3[2-(2-metossietossi)etossi]metiltiofene]-co- poli[3(1-octilossi)tiofene], has been synthesized and characterized.