Magnetic and electrostatic effects on the polymerization of water-soluble monomers

Free radical polymerization is the most frequently used technique to produce synthetic polymers. They represent more than 25% of the total volume of materials made by the mankind. 3% thereof correspond to water soluble polymers with annual growth rates estimated as 8%. Therefore, everything contributing to progress of the radical polymerization of water soluble monomers may be evaluated as signicant. This thesis was devoted to identify the influence of magnetic (MF) and electrostatic interactions on the kinetics and mechanism of the radical polymerization of water soluble monomers. Acrylamide (AM), acrylic acid (AA), its ionized species, acrylate (A-), and diallyldimethylammonium chloride (DADMAC) were selected for homo and copolymerization case studies. Thermal and photochemically initiated polymerizations were performed varying the MF intensity, pH, ionic strength, monomer and initiator concentration, conversion degree, viscosity and temperature of the polymerization medium. The thesis reports the experiments, results, and conclusions thereof, increasing gradually the complexity of the polymerization system. It was demonstrated that an hybrid mechanism rules the persulfate initiated polymerization of AM also at 0.05

Interactive Surfaces Based on Polymer Brushes

Dusko Paripovic

While the bulk structure of a material determines its mechanical properties, its surface plays a key role when interactions with the environment are important. Nowadays materials in bio- and nanotechnology are required to possess very complex functionalities and to interact specifically to the stimuli they receive from their surroundings. Thus, their surface modifications are becoming very demanding. In recent years surface initiated controlled radical polymerization techniques have emerged as very versatile strategies that provide a powerful toolbox to tackle the challenges that are set to material scientists. The attractiveness of these methods lies in the possibility to create well defined surface arrangements of polymer chains, which we refer to as polymer brushes, with precise control over thickness, composition and architecture. In addition, these techniques can be applied to very challenging substrates with respect to the chemical composition and geometry, which also includes porous materials. This Thesis, therefore, exploits the possibilities that surface-initiated controlled radical polymerization techniques offer to finely tune interfacial properties of materials and render them capable to interact with chemical and biological species in a desired way. Its paramount aim is to demonstrate how the functionalities and geometry of a polymer brush matrix can be employed to influence inorganic film deposition using synthetic, biomimetic and purely biological mechanism or enhance polymer brushed stability in aqueous media. This Thesis is divided into five distinct chapters, which will be briefly summarized in following paragraphs. Chapter 1 describes the preparation of polymer brushes and strategies that are used to control their chemical composition and architecture. Additionally, it will give an overview on the use of brushes as cell adhesive surfaces as well as templates for the production of nanoparticles and thin inorganic films. Chapter 2 explores a new strategy to guide the chemical solution deposition of thin, microstructured metal films. The proposed strategy is based on the use of poly(2-(methacryloyloxy)ethyl ammonium chloride) (PMETAC) brushes grown via surface-initiated atom transfer radical polymerization as a template. Thin films are prepared by first loading the PMETAC brushes with an appropriate precursor, followed by its reduction by NaBH4 and finally an oxygen plasma treatment to remove the stabilizing polymer brush matrix and generate the desired thin metallic film. Of particular interest is the question whether the thickness and lateral dimensions of the deposited metallic films can be controlled by micropatterning the polymer brush template and varying the brush thickness. In addition, this concept will be extended to the preparation of bimetallic (gold/palladium) films using a single polymer brush matrix. A similar strategy is explored in Chapter 3 to control the deposition of thin calcium carbonate films using a biomimetic process. The process is characterized by the stabilization of amorphous calcium carbonate, the geometry and localication of which can be controlled by the poly(methacrylic acid) brush template. A special focus of this Chapter is to examine the influence of the polymer brush thickness on the mineral deposition and to determine to which extent is the mineral phase is integrated into the polymer brush film. The aim of Chapter 4 is to develop a general approach for the modification of implantable materials with a polymer brush based coating that promotes bone formation. The proposed coatings are prepared via surface-initiated copolymerization of 2-hydoxyethyl methacrylate and 2-(methacryloyl)ethyl phosphate, which results in a thin hydrogel layer that mimics the negatively charged matrix macromolecules involved in natural bone formation. To further emulate the properties of the natural bone extracellular matrix, the coatings will be functionalized with the cell adhesive GGGRGDS peptide. The ability of the proposed coatings to induce bone formation is investigated in in vitro experiments on MC3T3-E1 pre-osteoblasts and evaluated using an ALP and alizarin red assays. Finally, Chapter 5 focuses on studying the parameters that could prevent the hydrolytic cleavage of Si-O bond, which tethers the polymer brushes grafted from SiOx in aqueous media. In the first part of the study, the length of the organosilane initiator's alkyl spacer will be varied, in order to evaluate to which extent it can insulate the site that anchors the hydrophilic polymer brush to the substrate. In the second part, a short, hydrophobic block will be introduced between the silicon oxide substrate and the hydrophilic polymer in order to more efficiently protect the underlying Si-O bond from the surrounding aqueous media and prevent the chain detachment.

EPFL2011

Continuous Polyol Synthesis of Metal and Metal Oxide Nanoparticles Using a Segmented Flow Tubular Reactor (SFTR)

Paul Bowen, Frank Pilger, Jose Enrico Quijano Quinsaat, Christoph Stähli, Andrea Testino

Over the last years a new type of tubular plug flow reactor, the segmented flow tubular reactor (SFTR), has proven its versatility and robustness through the water-based synthesis of precipitates as varied as CaCO3, BaTiO3, Mn((1-x))Ni(x)C(2)O(4)2H(2)O, YBa oxalates, copper oxalate, ZnS, ZnO, iron oxides, and TiO2 produced with a high powder quality (phase composition, particle size, and shape) and high reproducibility. The SFTR has been developed to overcome the classical problems of powder production scale-up from batch processes, which are mainly linked with mass and heat transfer. Recently, the SFTR concept has been further developed and applied for the synthesis of metals, metal oxides, and salts in form of nano- or micro-particles in organic solvents. This has been done by increasing the working temperature and modifying the particle carrying solvent. In this paper we summarize the experimental results for four materials prepared according to the polyol synthesis route combined with the SFTR. CeO2, Ni, Ag, and Ca-3(PO4)(2) nanoparticles (NPs) can be obtained with a production rate of about 1-10 g per h. The production was carried out for several hours with constant product quality. These findings further corroborate the reliability and versatility of the SFTR for high throughput powder production.

Molecular Diversity Preservation International2015

Photoredox-Catalyzed Decarboxylation for the Transfer of Alkynes and Nitriles Using Hypervalent Iodine Reagents

Franck Le Vaillant

Aliphatic alkynes and nitriles are privileged motifs in organic chemistry. Therefore, alkynes and nitriles have played a central role for the exploration and development of novel strategies to forge C-C bonds in efficient manner. They are broadly used as versatile building blocks for applications in every fields of chemistry, from pharmaceuticals to material sciences. Alkynes are also of paramount importance in chemical biology for labelling experiments due to their bio orthogonality. In this context, radical chemistry provides endless alternatives to nucleophilic and electrophilic alkynylation and cyanation reactions. For decades, organic chemists have designed and improved the structure of alkynylating reagents in order to enhance the efficiency of group transfer process. Methods enabling alkynylation and cyanation of alkyl radicals have emerged and while providing useful tools, they set the basis for further improvements. Notably, the formation of alkyl radicals is limited to harsh conditions using peroxides, elevated temperature and radical initiators. To overcome these major limitations, photoredox catalysis has emerged as a powerful tool for the generation of alkyl radicals under ambient conditions. The combination of photocatalysts and alkynylating reagents allowed the photoredox-catalyzed alkynylation of organoboron trifluoroborates salt and N-phtalimide esters. In this regard, the goal of my PhD was first to extend the photoredox catalyzed alkynylation to carboxylic acids. Indeed, carboxylic acids are broadly available from biomass, and widely occurring in drugs and fine chemicals, thus making them attractive starting materials. Their conversion to alkynes would provide efficient disconnections for the construction of Csp3-Csp, and find useful applications in chemical biology. Ethynyl Benziodoxolone (EBX) reagents, CsOBz and iridium photocatalysts were identified as a promising combination for the development of this novel transformation, in which silyl, aryl and alkyl substituted alkynes were transferred. ï¡ïamino, ï¡ïoxy and non-heteroatom stabilized radicals could be alkynylated in good to excellent yields upon visible light irradiation. This strategy was next applied to the decarboxylative cyanation of carboxylic acids. In that regard, Cyano Benziodoxolone CBX was introduced for the first time in photoredox-catalyzed cyanation. The combination of CBX, CsOBz and the same iridium photocatalyst allowed the smooth conversion of amino and oxy acids to their corresponding nitriles, and this novel method was applied to the synthesis of important intermediates in the synthesis of APIs. During scope investigations, hydantoins were isolated as side products. This background reaction was further optimized as a novel and efficient synthesis of chiral hydantoins starting from amino acids and CBX. Finally, investigations of the reaction mechanisms of the photoredox-catalyzed decarboxylations revealed that the cyanation followed a divergent mechanism compared to alkynylation. A additional redox step between CBX and ï¡-amino radical allows the generation of cyanide and iminium, which upon recombination affords the nitrile product. Then, the second goal of my PhD was to implement the photoredox mediated alkynylation and cyanation to other starting materials. In this regard, the use of carboxylic acids as starting materials to initiate photoredox catalyzed radical fragmentations was an appealing strategy.