Silica nanoparticles (SiO2 NPs) were prepared and functionalized with polyethylene (PE@SiO2 NPs) using the surface-initiated polyhomologation (SI polyhomologation) technique. Polyolefin nanocomposites were fabricated later by melt mixing of different ratios of the as-prepared SiO2 NPs and PE@SiO2 NPs with linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) matrices. Firstly, SiO2 NPs were modified with different alkoxysilane ligands, dichloro(divinyl)silane (DCDVS), allyl trimethoxysilane (ATMS), and vinyl triethoxylsilane (VTES). Subsequently, thexylborane, an initiator for SI polyhomologation, was immobilized to the modified surface of SiO2 NPs through hydroboration reactions. Polyhomologation was then allowed to proceed by adding monomer solution to form polyethylene brushes covalently bonded to the surface of the NPs. Physicochemical characterization had confirmed the morphology, chemical structure, and thermal stability for each step of modification reactions. LLDPE and LDPE nanocomposites were prepared by extrusion with SiO2 NPs and PE@SiO2 NPs as nanofillers. Finally, tensile tests and morphological SEM-based analyses are presented to discuss the influence of the grafted PE on both the dispersion of the fillers and the mechanical properties of the filler/matrix interphase.

A systematic study of the surface-initiated polymerisation kinetics of a relatively new type of atom transfer radical polymerisation (ATRP), activators regenerated by electron transfer (ARGET) ATRP, is first demonstrated in this report. Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(methyl methacrylate) (PMMA) were successfully grown from silicon surfaces at room temperature by surface-initiated ARGET ATRP using a "3rd generation" cationic macroinitiator. The polymer films were analysed by ellipsometry, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). With the initial experiment showing that water accelerated conventional ATRP but made it less controlled, the effect of solvent on ARGET ATRP was also evaluated. The living character of ARGET ATRP was demonstrated by successfully reinitiating PHEMA-grafted silicon wafers to grow a second block of PHEMA. Initiator density was shown to have a great effect on the growth rate of PHEMA film thickness on silicon surfaces by comparing the ARGET ATRP growth of PHEMA films using two different initiators, "1st generation" and "3rd generation" cationic macroinitiators, which have different ratios of initiating groups to positive charge. Another type of initiator for ATRP systems, an amide silane, was then investigated as an alternative to polyelectrolyte macroinitiators to avoid degrafting. The effects of solvent, 2, 2′ bipyridyl (bpy) ligand concentration and different types of reducing agent on the growth of PHEMA film from amide-initiator coated silicon wafers by ARGET ATRP were then explored at room temperature. However, it was found that the swings in the uncontrolled laboratory ambient temperature caused inter-sample and inter-experiment variability and so could make the evaluations inaccurate or even wrong. An investigation of temperature on ARGET ATRP showed a dramatic effect on the polymerisation rate. The higher the temperature, the faster the polymerisation proceeded. Therefore, the effects of solvent, ratio of bpy to Cu and reducing agent on the ARGET ATRP growth of PHEMA brushes from amide initiator-coated silicon wafers were re-evaluated at a constant temperature, 30 °C. The development of a polydopamine-based initiator, which was designed to be able to be immobilised on a wide range of surfaces, is then presented in this report. Polydopamine was first shown to be able to deposit on various types of material surfaces by oxidative polymerisation in aqueous solution. Bromoester initiating groups for ATRP systems were incorporated into polydopamine coatings by reacting a fraction of the dopamine monomer with 2-bromoisobutyryl bromide (BIBB) before polymerisation. The modified polydopamine initiator film grew at a comparable rate to unmodified polydopamine, with a 45 nm being grown in 24 hours. Successful incorporation of initiator groups was confirmed by XPS and FTIR, and by the growth of PMMA and PHEMA polymer brushes by ARGET ATRP from the polydopamine initiator coatings. A PMMA brush with a thickness of 239 nm was grown in 72 hours, indicating that the grafting density is sufficiently high to be in the brush regime. This initiator was demonstrated to be able to deposit on a range of substrates, such as metals (steel) and polymers (polystyrene), and successfully initiate polymer growth, demonstrating its broad applicability. The assessment of ARGET ATRP as a simple and effective tool for interfacial shear strength improvement in cellulose-based fibre reinforced thermoplastic composites is finally presented. It was demonstrated by control experiments that grafting polystyrene on glass fibre surfaces via ARGET ATRP greatly improved the interfacial adhesion between glass fibres and a high-impact polystyrene (HIPS) matrix, although a specific value of interfacial strength was not obtained due to failure of the modified glass fibre composite samples in areas other than the interface. It was then demonstrated that PMMA was successfully grown from the surfaces of polydopamine initiator coated cotton fibre and BIBB-modified cotton fibre by ARGET ATRP. Polydopamine initiator was shown to be a better initiator for cotton fibre than BIBB, possibly since the adsorbed water on cotton fibres can react with BIBB. The improvement of interfacial adhesion between cotton fibres and a PMMA matrix by grafting PMMA on the cotton surface was assessed by peel testing of cotton fibres pressed into PMMA sheets. There is a clear trend in the relationship between the peeling force and growth time of PMMA on the cotton fibre by ARGET ATRP, although the inter-sample reproducibility is not good.

Polymer brushes represent a relatively new class of materials and are referred to an assembly of polymer chains tethered by one of their extremities to a surface by a chemical bond. Different techniques to produce polymer brushes exist but our privileged choice was about the ¡§grafting from¡¨ method due to the better control over the types of grafted polymer, the surface-grafting density, and the chain-lengths. In our project, we focused on polymerizations from self-assembled monolayers of thiol chemisorbed on gold surface, bearing end-group functions as anchoring sites. The main objective of this work is to develop multifunctional polymeric surfaces composed by micro-domains of diverse compounds, which contain opposite features. Poly(ƓÕ-caprolactone) and poly(L,L-lactide)-based brushes both known for their high degree of crystallinity and hydrophobicity, and poly(dimethylamino ethyl methacrylate) (PDMAEMA)-based brushes for their hydrophilicity and external stimuli responsive characteristics were investigated. Moreover, the design of these advanced materials can be achieved with patterning technique such as micro-contact printing, leading to a spatial confinement of the polymer brushes. In order to reach our objective, the thesis was decomposed in different parts. First, the preparation of homogeneous and heterogeneous monolayers derived from thiols on gold surface will be investigated. Secondly, the ¡§grafting from¡¨ synthesis of homo-polymers from thiol end group will be carried out. This part required the development of synthesis conditions for both types of homopolymer brushes. Subsequently, these parameters were applied to the creation of a binary system by the growth of two different macromolecular chains on the same substrate. Finally, upon the ¡§smart¡¨ behavior of PDMAEMA, the potential of the polymer as chemical sensor was evaluated with single walled and multi walled-carbon nanotubes (SW- and MW-CNTs) as interesting conductive (nano)fillers.

<p>This work focused on grafting water-soluble polymers with well-controlled properties such as tuneable polymer chain length and high graft density to improve the biocompatibility of polymer surfaces via surface-initiated atom transfer radical polymerization (s-ATRP); and on gaining improved fundamental understanding of the mechanisms and factors (e.g., graft chain length and surface density of monomer units) in protein resistance of the water-soluble grafts.</p><p>Protein-resistant polyurethane (PU) surfaces were prepared by grafting watersoluble polymers including poly(oligo(ethylene glycol) methacrylate) (poly(OEGMA)) and poly(l-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) via s-ATRP. A typical three-step procedure was used in the ATRP grafting. First, the substrate surface was treated in an oxygen plasma and reactive sites (-OH and -OOH) were formed upon exposure to air. Second, the substrate surface was immersed in 2-bromoisobutyryl bromide (BffiB)-toluene solution to form a layer of ATRP initiator. Finally, target polymer was grafted from the initiator-immobilized surface by s-ATRP with Cu(I)Br/2bpy complex as catalyst. The graft chain length was adjusted by varying the molar ratio of monomer to sacrificial initiator in solution. The modified PU surfaces were characterized by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM).</p><p>Protein adsorption experiments were carried out to evaluate the protein resistance of the surfaces. Adsorption from single and binary protein solutions as well as from plasma decreased significantly after poly(OEGMA) grafting, and decreased with increasing poly(OEGMA) main chain length. Fibrinogen (Fg) adsorption on the most resistant surfaces (chain length 200 units) was in the range of 3-33 ng/cm^2, representing a reduction of more than 96% compared to the control surfaces.</p><p>OEGMA monomers with three different molecular weights (MW 300, 475, 1100 g/mol) were used to achieve different side chain lengths of poly(OEGMA). Fibrinogen (Fg) and lysozyme (Lys) were used as model proteins in adsorption experiments. The effects of side chain length as well as main chain length were then investigated. It was found that adsorption to the poly(OEGMA)-grafted PU (PU/PO) surfaces was protein size dependent. Resistance was greater for the larger protein. For grafts of a given side chain length, the adsorption of both proteins decreased with increasing polymer main chain length. For a given main chain length, the adsorption of Fg, the larger protein, was independent of side chain length. Surprisingly, however, Lys (the smaller protein) adsorption increased with increasing side chain length. A reasonable explanation is that graft main chain density decreased as monomer size and footprint on the surface increased. Protein size-based discrimination suggests that the chain density was lower than required to form layers in the "brush" regime in which protein size is expected to have little effect on protein adsorption.</p><p>In order to achieve high surface densities of ethylene oxide (EO) units, we used a sequential double grafting approach whereby the surface was grafted first with poly(2-hydroxyethyl methacrylate) (HEMA) by s-ATRP. OEGMA grafts were then grown from the hydroxyl groups on HEMA chains by a second ATRP. The effect of EO density on protein-resistant properties was then investigated. Protein adsorption on the sequentiallygrafted poly(HEMA)-poly(OEGMA) surfaces (PU/PH/PO) was not only significantly lower than on the unmodified PU as expected, but also much lower than on the PU/PO surfaces with the same poly(OEGMA) chain length. Moreover, protein adsorption decreased with increasing EO density for these grafts. On the PU/PH/PO surface with a poly(OEGMA) chain length of 100, the adsorption of Ls and Fg were reduced by ~98% and >99%, respectively, compared to the unmodified PU. Binary protein adsorption experiments showed that suppression of protein adsorption on the PU/PH/PO surfaces was essentially independent of protein size. The double-grafted OEG layers resisted both proteins equally.</p><p>The general applicability of this approach which combines oxygen plasma treatment and ATRP grafting was also studied. Various kinds of polymers such as PU, silicone hydrogel, and polydimethylsiloxane (PDMS) were chosen as substrates. Poly(MPC) grafts with different chain lengths were achieved by the three-step ATRPgrafting procedure. It was found that protein adsorption levels on the poly(MPC) grafts were significantly lower than on the respective unmodified surfaces. Protein adsorption decreased with increasing poly(MPC) chain length. Among the surfaces investigated, PU/MPC showed the highest protein resistance for a given chain length.</p> / Thesis / Doctor of Philosophy (PhD)

Thesis advisor: Jeffery A. Byers / Thesis advisor: Petter Zhang / This thesis discusses the development of a surface-initiated N-carboxyanhydride (NCA) polymerization system from a redox-switchable catalyst for polyamide synthesis and further efforts towards the synthesis of polypeptide-based materials through the integration of NCA synthesis and its polymerization. In Chapter one, the most used methods to obtain polypeptide-based materials as well as their significant limitations are introduced. A new strategy is presented to access the polypeptide-based materials based on the integrated catalysis under spatial and temporal control. In Chapter two, a strategy to allow the attachment of a redox-switchable NCA polymerization catalyst on surface of titania for the synthesis of polyamide brushes will be demonstrated. Investigations about the kinetics of this surface-initiated ring-opening polymerization will be presented by carrying out the reaction in batch and under flow. Chapter three will discuss efforts towards achieving the integration of NCA synthesis and NCA polymerization, which includes an additional anchoring method to support polymerization catalyst and compatibility tests between the two separate reactions. / Thesis (MS) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

We reported a non-crosslinking approach to synthesize nitroxide radical polymer brushes for thin-film electrodes via surface-initiated atom transfer radical polymeization (SI-ATRP), which was effective to yield the organic radical polymer brushes with high grafting density and to attain a uniform surface. As mentioned above, the covalent bonding of nitroxide polymer brushes to the conducting substrate not only prevented the polymer dissolution into organic electrolyte solution but improved the cycle life performance of batteries. Moreover, they can be the potential application in microbatteries by using microcontact printing to produce the patterned nitroxide polymer brushes on a conducting substrate. Even though the organic radical polymer brushes provided a new approach to syn-thesize thin-film electrodes, they still existed many problems that needed to study and to figure out. We discussed the morphology and electrochemical performance about ni-troxide radical polymer in the thesis. In the measurement of surface properties, we used the contact angle, electron spectroscopy for chemical analysis (ESCA) and atomic force microscopic (AFM) to proceed. Another, in the measurement of electrochemical analysis, we used the cyclic voltammetry(CV), alternating current (AC) impedance and charge-discharge to understand the regarding mechanism in this polymer layer during the electrochemical reaction. In chapter 4, we discussed the oxidative problem in the polymer brushes. It should be well controlled during the oxidation reaction, because the oxidation level may affect the diffusion of electron that resulted the capacity better or not. In chapter5, we controlled the density of polymer brushes to construct the possible mechanism during the electro-chemical reaction, and found out the possible factors that affected the electrochemistry. In chapter 6, we applied the better results from the front chapter to the organic radical battery, and compared their electrical performance.

Diese Arbeit gibt neue Einblicke in die kinetischen und mechanistischen Aspekte der konventionellen radikalischen und der Reversible-Addition–Fragmentation-chain-Transfer- (RAFT-)Polymerisation von der Oberfläche von Silica-Nanopartikeln. Die Terminierungskinetik der oberflächeninitiierten Polymerisation von n-Butylmethacrylat (n-BMA) wurde mit Hilfe der Single-pulse–pulsed-laser-Polymerisation (SP–PLP) in Kombination mit der Elektronenspinresonanzspektroskopie (ESR-Spektroskopie) analysiert. Die Polymerisation wurde dabei durch den neu entwickelten oberflächengebundenen Photoinitiator 2,2-Dimethoxy-2-phenyl-1-(2-(2-(trimethoxysilyl)-ethyl)phenyl)-1-on (DMPTS) initiiert. Die erhaltenen Geschwindigkeitskoeffizienten der Terminierung kt, die ausschließlich der Terminierungsreaktion zwischen zwei oberflächengebundenen Radikalen zugeordnet werden konnten, waren signifikant kleiner als die Literaturwerte für das entsprechende homogene Polymerisationssystem. Erstaunlicherweise konnte außerdem keine Kettenlängenabhängigkeit von kt gefunden werden. Dies zusammen mit der Tatsache, dass bei temperaturabhängigen Untersuchungen eine Aktivierungsenergie für kt gefunden wurde, die in exzellenter Übereinstimmung mit der des Propagationsgeschwindigkeitskoeffizienten von n-BMA ist, lässt das Bild einer reaktionsdiffusionskontrollierten Terminierung oberflächengebundener Makroradikale entstehen. Die Entwicklung des oberflächengebundenen Photoinitiators DMPTS erlaubte weiterhin neue Einblicke in die Propagationskinetik – insbesondere deren Temperaturabhängigkeit betreffend – oberflächengebundener Makroradikale. Mittels der PLP von n-BMA in Kombination mit der Größenausschlusschromatographie (engl. size-exclusion chromatography, SEC) wurden Werte für den Geschwindigkeitskoeffizienten der Propagation kp und die entsprechende Aktivierungsenergie ermittelt, die exzellent mit den Daten der International Union of Pure and Applied Chemistry (IUPAC) für die Polymerisation von n-BMA in homogenem Reaktionsmedium übereinstimmen, sodass kein Einfluss der Oberflächenverankerung der Makroradikale auf die Propagationskinetik ersichtlich ist. Weiterhin wurde die Kinetik der RAFT-Polymerisation von n-Butylacrylat (BA) von Oberflächen bei –40 °C mit Hilfe verschiedener ESR-spektroskopischer Methoden für den R- und den Z-Gruppen-Ansatz unter Verwendung oberflächengebundener Trithiocarbonate als RAFT-Agenzien untersucht. Die kinetischen Analysen des R-Gruppen-Ansatzes mittels stationärer ESR-Experimente lieferten Gleichgewichtskonstanten Keq, die um eine Größenordnung kleiner sind als die Literaturwerte für entsprechende homogene Polymerisationssysteme, was darauf hindeutet, dass die Oberflächenverankerung des RAFT-Agens einen signifikanten Einfluss auf die Kinetik der RAFT-Polymerisation hat. Durch die Aufnahme zeitlicher Konzentrationsverläufe der Intermediatspezies und der propagierenden Radikale nach Einzelpulsinitiierung mittels der hochaufgelösten zeitabhängigen ESR-Spektroskopie (SP–PLP–ESR–RAFT) in Kombination mit PREDICI®-Simulationen wurden diese Ergebnisse bestätigt, da eine Abnahme des Geschwindigkeitskoeffizienten der Addition eines Makroradikals an die RAFT-Gruppe mit zunehmender Anzahl beteiligter oberflächengebundener Makromoleküle gefunden wurde. Dieser Befund ist im Einklang mit der Vorstellung, dass die Additionsreaktion bei Beteiligung verankerter Makromoleküle diffusionskontrolliert abläuft, was auf die unterdrückte Translations- und die eingeschränkte Segmentdiffusion oberflächengebundener Polymerketten zurückzuführen ist. Ein noch kleinerer Wert von Keq wurde für den Z-Gruppen-Ansatz gefunden und kann darauf zurückgeführt werden, dass die in Lösung wachsenden Ketten für die Additionsreaktion mit der RAFT-Gruppe, die sich über den gesamten Verlauf der Polymerisation in unmittelbarer Nähe zur Partikeloberfläche befindet, durch die Polymerschicht auf der Oberfläche diffundieren müssen. Die Wahrscheinlichkeit dafür, dass eine Additionsreaktion stattfindet, nimmt mit zunehmender Polymerschichtdicke ab, was durch einen kleineren Wert von Keq bei Verwendung von einem RAFT-Agens, das über die Z-Gruppe verankert war und über eine makromolekulare anstatt einer niedermolekularen R-Gruppe verfügte, gezeigt werden konnte. Die vorgestellten Ergebnisse geben einen umfangreichen Überblick über den Einfluss der Oberflächenverankerung von Komponenten, die am Prozess der radikalischen Polymerisation beteiligt sind, auf die Kinetik der oberflächeninitiierten radikalischen Polymerisation und ebnen den Weg für detaillierte, systematische Untersuchungen der Zusammenhänge zwischen der Kinetik von radikalischen Polymerisationen an Oberflächen und der molekularen Struktur der erhaltenen oberflächengebundenen Polymere.

Self-assembled microsphere monolayers (SMMs) hold significant promise for micro- and nanopatterning. Here we exploit, for the first time, SMMs as stamps for microcontact printing (μCP) and demonstrate this to fabricate patterned initiator templates that can subsequently be amplified into polymer brushes by surface initiated atom transfer radical polymerization (SI-ATRP). SMM stamps avoid the need for expensive and sophisticated instrumentation in pattern generation, and provide a broad range of accessible surface chemistries and pitch size control.

The performance and life time of organic solar cells are critically dependent on the properties of active layer materials and device interfaces. In this manuscript, we developed new organic-inorganic hybrid materials to create intimate contact between donor and acceptor phases and facilitate the interfacial electronic charge transfer through the device. First, the synthesis of versatile triethoxysilane-terminated poly(3-hexylthiophene) P3HT for direct anchoring (grafting-onto) in one step procedure to various metallic oxides was reported. Electro-optical analysis showed an efficient charge transfer from the polymer to nanoparticles; suggesting that these materials are suitable candidates for photovoltaic application. In the second part, we demonstrate for the first time the elaboration of low band gap polymer brushes on metallic oxide surfaces via surface initiated step growth polymerization (grafting-through). In both cases, a higher grafting density, better packing of polymer chains and enhanced optical properties were observed due to the grafting methodology and polymer characteristics. Finally, P3HT brushes were elaborated on indium tin oxide surface (ITO) as hole transporting layer of organic solar cells. Photovoltaic performances showed that P3HT self-assembled monolayer (SAMs) could be promising alternatives to PEDOT:PSS. / Les performances et la durée de vie des cellules solaires organiques sont fortement dépendantes de la qualité des matériaux de la couche active et des interfaces dans le dispositif. Dans ce manuscrit, nous avons développé des nouveaux matériaux hybrides organiques-inorganiques pour favoriser le contact entre les matériaux donneur/accepteur d’électrons et ainsi faciliter le transfert de charges à travers le dispositif. Tout d'abord, la synthèse de poly(3-hexylthiophène) P3HT fonctionnalisé par le triéthoxysilane a permis le greffage direct (« grafting-onto ») sur des oxydes métalliques. L’analyse des propriétés électro-optiques montre un transfert de charge efficace du polymère aux nanoparticules; ce qui suggère que ces matériaux sont des candidats potentiels pour l'application photovoltaïque. Dans la deuxième partie, nous avons montré pour la première fois, l’élaboration de brosses de polymères dits à faible bande interdite sur des surfaces d’oxydes métalliques par la technique « grafting-through ». Une densité de greffage élevée, un meilleur empilement des chaines de polymères et des propriétés optiques améliorées ont été obtenus grâce à la technique de greffage et aux caractéristiques du polymère greffé. Enfin, des brosses de P3HT ont été élaborées sur la surface d’oxyde d'indium et d’étain (ITO) en tant que couche de transport de trous de cellules solaires organiques. Les performances photovoltaïques ont montré que les monocouches auto-assemblées de P3HT (SAM) peuvent être une alternative au PEDOT: PSS.

Self-assembled monolayers and surface-initiated polymer, or polymer brushes, have attracted attention as they form dense layers with much higher structural order than bulk or solution polymers. Another field of research which has emerged over the last two decades is the field of organic and polymer electronics. In this field molecular order and surface modification are of major influence on the device performance, hence that both self-assembled monolayers as polymer brushes have been investigated to find applications in organic electronic devices. After an introduction into the field self-assembled monolayers, polymer brushes and organic electronics, the first part of this thesis focusses on three applications of surface modification techniques for applications in devices. Alignment of the active material is crucial for high mobilities in organic electronics. Chapter 2 discusses the synthesis of a liquid crystalline surface-initiated polymer and its application to induce strong homeotropic alignment. The alignment is homogeneous over large areas and can be patterned by combining the polymerization with soft lithographic techniques. Mobilities of organic electronic materials can also be strongly influenced by dopants in the material. In field-effect transistors the positioning of the dopant is thought to be crucial, as the conductance predominantly takes place in only a small channel near the dielectric interface. In chapter 3 dopant functionalized monolayers and polymer brushes are presented which enable the localized deposition of dopants in the channel of organic transistors. It is shown that the mobility of charges and hence the device performance is affected by the introduction of this dopant layer. Polymer brushes have been suggested for the fabrication of highly ordered semiconducting polymers. In chapter 4 the use of a thiophene functionalized polymer brush is shown, that can be used as a template for the subsequent growth of highly conjugated surface grafted polythiophene layers. Thick polythiophene layers are obtained, that are low in roughness and show photoluminescence and polychromism upon doping. The second part (chapter 5 and 6) of this thesis presents new techniques for surface polymerizations. It is attractive to investigate reduction of reactor volume for polymer brush growth. Chapter 5 discusses a method to achieve volume reduction by back-filling the superfluous volume with beads. It is found that this influences the polymerization kinetics significantly. The combined advantages of less volume and enhanced reaction speeds enable reduction of the total amount of monomer needed by up to 90%. Chapter 6 presents a controlled way to convert initiators for atom transfer radical polymerization into initiators for nitroxide mediated polymerization. In this way mixed polymer brushes and block co-polymer brushes become accessible. This combination makes it an attractive tool to fabricate complex polymer architectures. The technologies used in this thesis show that the synthesis of polymer brushes enable the fabrication of complex architectures without the wastes normally associated with surface-initiated polymers. Combined with several functionalized polymer brushes with properties that enhance order, influence mobility or serve as template for the growth of surface attached conjugated polymers this shows the high potential for the application of surface-initiated polymers in organic electronics.