Copolymer analysis by mass spectrometry

Polymeric materials have many functions in the modern world. This is due to their tuneable thermal and mechanical properties, the ease at which they can be functionalised, and the scalability of the synthetic methods. Advances in polymer synthetic chemistry have allowed more exact design of these materials for their function, leading to a rise in the complexity of the products and properties available. As the need for more precise synthetic procedures increases as does the need for analysis techniques to characterise their products. Polymers by definition are complex mixtures which makes characterisation challenging. Mass spectrometry is capable of rising to many of the challenges which polymer research presents. Many important features of polymers are capable of being determined by mass spectrometry such as, end groups, molecular weight, composition, and architecture. A commonly used technique for polymer mass spectrometry is matrix assisted laser/desorption time-of-flight mass spectrometry (MALDI-ToF-MS). In this thesis the author presents 3 published works which seek to improve the molecular information which can be gained from polymer mass spectrometry research, with a focus on the determination of monomer sequencing in copolymer samples. The first paper (chapter 2) shows a comparison between 2 commonly used tandem mass spectrometry MALDI-ToF techniques (MALDI-ToF/ToF), and their effect on the fragmentation species examined. These two techniques are post source decay (PSD) and collision-induced dissociation (CID). The methods are used on a variety of homopolymers, to examine the effect of different heteroatoms in the polymer backbone. It is found that PSD produces less fragments than CID in most of the homopolymers. The PSD fragments tend to be generated more often by rearrangements/fragmentation around the heteroatom, whereas CID will provide more fragments in carbon-carbon bonds 5 The second paper (chapter 3) is an investigation of PSD analysis of acrylate homopolymers and copolymers. The paper shows a fragmentation pathway which appears unique to the halide end group polymers. The paper also displays the qualitative differences between a diblock copolymer and a statistical copolymer, displaying the ease at which copolymer microstructure can be determined by tandem mass spectrometry. The diblock copolymer is then examined in more detail, displaying that there is a small amount of mixing discovered at the block boundary, despite the use of controlled radical polymerisation methods. This shows the powerful copolymer sequencing which can be provided by tandem mass spectrometry. The third paper (chapter 4) is centred on the development of a generic algorithm for automatic peak assignment of copolymer MALDI-ToF data. This algorithm allows quick assignment of the monomer composition of each peak present in the spectra, producing a table of these results. This data can then be displayed as a heatmap of the two monomers where the colour is the intensity of the peak. Here qualitative differences can be seen between different copolymer compositions and different copolymer microstructures. This is an examination of the composition distribution, an often-neglected part of a copolymer sample

The photocatalytic degradation of phenolic compounds

Semiconductor photocatalysis degrades phenolic pollutants to carbon dioxide and water, but the mechanisms of this potentially attractive method of environmental remediation remain unclear. This study aimed to elucidate the primary molecular events by HPLC analysis of the initial products of degradation in water or aqueous acetonitrile. The position of substituents relative to the hydroxyl group were found to influence the reaction rate and also primary oxidation steps, and hence the intermediate profile. 2,6- Dialkylated phenols reacted fastest and showed high conversion to dehydrodimeric products as a prelude to degradation. In contrast, 3,5-dialkylated phenols and 4-tert-butylphenol reacted more slowly and appeared to degrade directly to small polar compounds with little accumulation of primary carbocyclic intermediates. The rate of photocatalytic degradation of two isomeric dibromohydroxybenzonitriles was also influenced by substitution pattern. 3,5-Dibromo-2-hydroxybenzonitrile, however, is itself photolabile in daylight giving 3-bromo-2,5-dihydroxybenzonitrile in aqueous solution. The analogous reaction does not occur for 3,5-dibromo-4-hydroxybenzonitrile, the difference in behaviour being attributed to differences in the electronic spectra of the two compounds. The mechanism of photocatalysis appears to be influenced by the orientation of the substrate on the catalyst surface. For the alkyl phenols, particularly those with tert-butyl substitution, minimisation of disturbance to the polar network of the solvent directs the more hydrophobic parts of the molecule towards the oxidising surface of the catalyst. In addition, this effect encourages clustering of molecules with the subsequent formation of aggregated products. While part of the behaviour observed may be attributable to the presence of acetonitrile in the solvent, the hydrophobic profile of a substrate undergoing heterogeneous photocatalytic oxidation in water would seem to be a significant determinant of the molecular pathway selected in the first phase of its degradation

Control of Corrosion on SS316L Using Surface Initiated Polymers

Pitting corrosion is arguably one of the most destructive and dangerous forms of corrosion, resulting in damage to structures, the environment, and public health. In addition, damage caused to structures such as bridges, pipelines, and boats, corrosion also has a profound effect on the biomedical community. Implanted metallic devices (i.e., vascular stents and artificial joints) are prone to pitting corrosion caused by aggressive ions present in extracellular fluid. To provide a corrosion-resistant surface on SS316L, films of poly(styrene), poly(methyl acrylate), and poly(methyl methacrylate) were formed using surface-initiated atom transfer radical polymerization (SI-ATRP). The resulting hydrophobic polymer films had a fractional coverage of up to 99% and protection efficiencies of up to 99.6%, indicating that the modifications had excellent coverage of the surface and were capable of resisting corrosion, respectively. Additionally, films of poly(oligo(ethylene glycol)acrylate) and poly(oligo(ethylene glycol)methacrylate) were formed on SS316L in an attempt to create a surface modification that was both cell and corrosion-resistant. However, PEGylated SI-polymers were not capable of inhibiting corrosion to a high degree. To improve the corrosion resistance of the polymer films, an films of poly(styrene) were formed using SI-ATRP, then chain extended with PEGylated acrylate and methacrylate. The SI polymerization of epoxides provides an attractive opportunity to impart both antifouling and corrosion-resistant properties to a surface. Films of poly(propylene oxide) were synthesized using anionic ROP methodology; however, the result was not able to be replicated

Design, Synthesis, Stability, and Photocatalytic Studies of Sustainable Metal-Organic Frameworks

The presented dissertation focuses on the design, synthesis, and characterization of metal-organic frameworks (MOFs) composed of earth-abundant elements the exhibit photoredox activity and studied their application as heterogeneous photocatalysts in organic synthesis and in solar-to-chemical energy conversion. In particular, the structure-property relationships of titanium-based MOFs relating the structure of the organic building unit and the photophysical and photochemical activity of the solid material is studied. The first novel family of seven MOFs isoreticular to MIL-125-NH2, includes functionalized with N-alkyl groups with increasing chain length (methyl to heptyl) and with varying connectivity (primary or secondary). The functionalized materials displayed reduced optical bandgaps correlated with the increased inductive donor ability of the alkyl substituents, enhanced excited-state lifetimes, mechanistic information towards visible light CO2 reduction, and improved water stability. The second family of titanium MOFs was prepared with a new secondary building unit and organic links of varying lengths, for which Their crystal structure was solved utilizing powder X-ray diffraction crystallography. This work provides guidelines for the next generation of photocatalyst for the conversion of solar-to-chemical energy and other organic transformations

Scanning Probe Studies of Quasi-Two-Dimensional Organic Networks

Organic based polymer materials have an abundance of potential applications due to the ability to tailor their molecular components and network topology. The experimental work featured in this thesis focuses on a small selection of quasi-two-dimensional materials within two subclasses of these polymers, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Both are porous networks of organic molecules linked together by metal ions (MOFs) or covalent bonds (COFs). In layered 3D variants, this porosity grants the material an impressive internal surface area available for catalysis, gas storage, and molecular separation. In 2D, the organic molecular network produces a variety of electronic properties, with pi-bonding molecular orbitals predicted to create both Dirac bands and flat bands. This work presents studies of the atomic and electronic structures of these materials by ultrahigh vacuum (UHV) scanning probe microscopy (SPM).Ph.D

Functional molecular materials: supramolecular networks and coordination polymers with optical and/or magnetic properties

El camp dels materials moleculars atrau l’atenció de molts científics degut al gran potencial de la química molecular en el disseny de materials amb un ajust precís de les seues propietats. Els dos projectes tractats en aquesta tesi representen dos temes que destaquen en aquesta àrea, materials de transició d’espín i polímers de coordinació amb propietats òptiques i/o magnètiques, gràcies al seu significant progrés i ràpid desenvolupament en els últims anys. La primera part d’aquesta tesi es basa en l’ús d’enllaços d’hidrogen en el disseny de xarxes multifuncionals de ferro(II) amb transicions d’espín abruptes. El capítol 1 és una introducció a aquest tema des de la perspectiva dels complexos [Fe(bpp)2]2+ (bpp = 2,6-bis(pirazol-3-il)piridina). El capítol 2 mostra un anàlisi comparatiu de les sals [Fe(bpp)2]2+ construïdes amb l’anió flexible adipat o l’anió rígid tereftalat com acceptors d’enllaç d’hidrogen. Aquest estudi mostra la rellevància de la rigidesa dels anions en les propietats magnètiques de les xarxes resultants. A més a més, dos materials anhidres amb diferents comportaments magnètics i grau de cristal·linitat han sigut obtinguts per al derivat basat en l’anió adipat en funció del tractament tèrmic emprat. El capítol 3 descriu la incorporació d’anions acèntrics mononegatius, la qual cosa permet l’optimització de la connectivitat dels enllaços d’hidrogen. Concretament, l’ús de l’anió isonicotinat ha permés la construcció d’una xarxa cristal·lina acèntrica de tipus diamant en base a un senzill disseny per sintetitzar xarxes acèntriques. La fase anhidra d’aquest material exhibeix una transició de fase entre dos estructures ferroelèctriques en el mateix rang de temperatura en el que s’observa la transició d’espín. L’ús de l’anió isonicotinat N-òxid ha donat lloc a l’aïllament de dos sals que presenten transicions d’espín abruptes i que desencadenen noves redistribucions estructurals en resposta a l’aplicació de llum o a un canvi de temperatura: una isomerització d’un enllaç d’hidrogen que involucra a un carboxilat i un desplaçament de protó entre dos anions que formen un enllaç d’hidrogen molt fort. Experiments isotòpics i dades de difracció de neutrons revelen una gran influència dels enllaços d’hidrogen sobre les propietats de transició d’espín. Específicament, els enllaços d’hidrogen presents en la segona esfera de coordinació del ferro són més curts en l’estat de baix espín en comparació a aquelles distàncies mesurades en l’estat d’alt espín. La segona part d’aquesta tesi se centra en la síntesi i caracterització de polímers de coordinació basats en una nova família de lligands politòpics segmentats per triples enllaços. L’objectiu d’aquest treball és millorar l’estabilitat en aigua i a valors de pH extrems dels compostos de coordinació actuals mitjançant l’ús del grup funcional quelant picolinat. El capítol 4 conté un breu resum sobre les aproximacions sintètiques i aplicacions d’aquest tipus de materials. El capítol 5 descriu la síntesi (reaccions d’acoblament tipus Sonogashira) i caracterització de la nova família de lligands. La metodologia sintètica, propietats magnètiques, tèrmiques, estructurals i luminescents dels compostos cristal·lins construïts a partir d’aquests lligands i ions divalents es descriuen en el capítol 6. En canvi, el capítol 7 descriu el progrés assolit amb ions lantànids trivalents. Els experiments de detecció revelen que els derivats de Zn i Eu poden ser selectivament emprats com a sondes luminescents en medi aquós per tal de detectar ions Fe3+ i nitrobenzè gràcies a un descens dramàtic en la seua senyal luminescent. Finalment, el capítol 8 conté les conclusions generals d’aquesta tesi doctoral.The field of molecular materials attracts the interest of many scientists due to the huge potential of molecular chemistry in materials design and fine tuning of materials properties. The two different projects addressed in this thesis represent two topics that stand out in this area, spin crossover (SCO) compounds and coordination polymers with optical and/or magnetic properties, due to their significant progress and rapid development in the last years. The first part of this thesis is based on the use of hydrogen bonds in the design of multifunctional iron(II) supramolecular networks with abrupt spin transitions. Chapter 1 is an introduction to this topic from the perspective of [Fe(bpp)2]2+ complexes (bpp = 2,6-bis(pyrazol-3-yl)pyridine). Chapter 2 shows a comparative analysis of [Fe(bpp)2]2+ salts with the flexible adipate or the rigid terephthalate as hydrogen bond acceptors. This study shows the relevance of the rigidity of the anions in defining the magnetic properties. Moreover, two anhydrous materials with distinct magnetic behaviour and degree of crystallinity were obtained for the adipate derivative depending on the thermal treatment used. Chapter 3 describes the incorporation of acentric mononegative anions which enables the optimisation of the hydrogen bond connectivity. In particular, the use of the isonicotinate linker has allowed the construction of an acentric diamond-like crystal lattice, following a basic design for acentric networks. The anhydrous phase of this material exhibits a phase transition between two ferroelectric structures in the same temperature range in which the spin crossover is observed. The employment of the isonicotinate N-oxide anion has led to the isolation of two salts that present abrupt spin transitions triggering novel structural rearrangements that respond towards light irradiation or temperature change: a supramolecular linkage (H-bond) isomerisation involving a carboxylate moiety and a proton displacement between two anions that form a short strong hydrogen bond. Isotopic experiments and neutron diffraction data reveal that hydrogen bonding influences the spin crossover properties. Specifically, hydrogen bonds in the 2nd iron coordination sphere are found to be shorter for the low-spin species in comparison to those in the high-spin state. The second part of this thesis relies on the synthesis and characterisation of coordination polymers based on a novel family of ethynyl-bridged polytopic ligands. The aim of this work is to improve the stability in water and at extreme pH values of current coordination compounds through the use of the chelating picolinate functional group. Chapter 4 contains a brief summary about synthetic approaches and applications of these materials. Chapter 5 describes the synthesis (Sonogashira-type cross-coupling reactions) and characterisation of the novel family of ligands. The synthetic methodology, thermal, structural, luminescent and magnetic properties of crystalline compounds constructed from these ligands and divalent ions are described in Chapter 6. Instead, Chapter 7 gathers the progress achieved with trivalent lanthanide ions. Sensing experiments reveal that Zn and Eu derivatives can be selectively used as luminescent probes in aqueous medium towards Fe3+ and nitrobenzene detection through luminescent quenching. All these polymers are remarkably robust in water within a wide pH range. Finally, Chapter 8 compiles the general conclusions of the present dissertation