Precise growth of polymer brushes on silica-based nanocomposites via visible-light-regulated controlled radical polymerization

Precise control over molecular variables of grafted polymer brushes is of crucial importance for obtaining polymer nanocomposites with desirable architectures and physicochemical properties, yet it remains a significant synthetic challenge. Recent advances in photoinduced electron/energy transfer reversible addition fragmentation chain transfer (PET-RAFT) polymerization have enabled light-regulated polymer synthesis, in a well-controlled and environmentally friendly manner. However, the utilization of this modern synthetic technique for the precise control of polymer brushes is underdeveloped. Here, PET-RAFT polymerization has been proceeded in a spatiotemporally controlled manner upon light regulation, producing silica nanocomposites coated with well-defined polymer brushes of target molecular weights, narrow dispersities and high grafting densities. The versatility and robustness of this technique have been demonstrated by its extendibility to other monomers and silica-containing nanomaterials. In all examined cases, the resultant high-value polymer nanocomposites possess defined chain sequences and architectures, high uniformity, and can be further expanded to a library of complex nanostructures. This work represents the first demonstration of adopting the PET-RAFT approach for generating precisely controlled polymer brushes on silica-based nanomaterials, and opens a new avenue for developing polymer nanocomposites with sequence-controlled polymer brushes and complex architectures required for a variety of target applications

Analysis Using Size Exclusion Chromatography of poly(N-isopropyl acrylamide) using Methanol as an Eluent

YesSize Exclusion Chromatography is traditionally carried out in either aqueous or non-polar solvents. A system to present molar mass distributions of polymers using methanol as a mobile phase is presented. This is shown to be a suitable system for determining the molar mass distributions poly(N-isopropylacrylamide)s (PNIPAM); a polymer class that is often difficult to analyze by size exclusion chromatography. DOSY NMR was used to provide intrinsic viscosity data that was used in conjunction with a viscometric detector to provide absolute calibration. Then the utility of the system was shown by providing the absolute molar mass distributions of dispersed highly branched PNIPAM with biologically functional end groups.Wellcome Trus

THE DEVELOPMENT OF CONTROLLED POLYMERIZATION PROCESSES AND THEIR APPLICATION TOWARDS THE SYNTHESIS OF TAILOR-MADE MATERIALS

296 pagesOver the last century, synthetic polymers have become highly abundant in everyday life and have therefore drastically changed the way we live. Due to the need for intricate polymer architectures in high-end applications, polymer chemists are posed with the challenge of developing new methods of synthesizing polymers. Specifically, mild polymerization conditions have become increasingly important and the potential to regulate chain growth via external stimuli has recently become a powerful tool for the development of well- defined polymers. Herein, we describe the development of a photocontrolled cationic polymerizations of vinyl ethers (chapter 2 and 5). This method employs unique chain-transfer agents that have the ability to switch between cationic and radical intermediates. We were therefore able to combine our photocontrolled cationic polymerization with photocontrolled radical polymerization in one pot and mediate the two polymerization mechanisms with different light sources to produce vinyl ether-acrylate copolymers (chapter 3). Using a single-electron oxidant rather than photoredox chemistry to mediate cationic polymerization, allowed us to gain absolute control over polymerization mechanism by switching between chemical and photochemical stimuli (chapter 4). Additionally, we describe the development of a novel, organic acid- mediated cationic polymerization, which proceeds under ambient atmosphere while maintaining excellent control. This simple, single-component system enables the polymerization of a large suite of vinyl ethers without the need for rigorous purification or inert atmosphere (chapter 6). Lastly, we take advantage of the living characteristics of anionic polymerization of styrene and create skewed molecular weight distributions (MWD) through temporally-regulated initiation. We demonstrate that the shape of the MWD has a profound influence on material properties by measuring the Young’s Modulus of poly(styrene-block-isoprene) samples with altered polystyrene MWDs (chapter 7)

Das Unternehmen als soziales System: zur Notwendigkeit einer ganzheitlichen Betrachtungsweise

SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel A 205548 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Das Unternehmen Stadt im Wettbewerb: zur Notwendigkeit einer konsistenten City identity am Beispiel der Stadt Vegesack

Available from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel A 205105 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Photocontrolled Radical Polymerization from Hydridic C–H Bonds

Given the ubiquity of C–H bonds in biomolecules and polymer backbones, the development of a photocontrolled polymerization from a C–H bond would represent a powerful strategy for selective polymer conjugation precluding several synthetic steps to introduce complex functionality. We have developed a hydrogen-atom abstraction strategy that allows for a controlled polymerization from a C­–H bond using a benzophenone photocatalyst, a trithiocarbonate-derived disulfide, and visible light. We perform the polymerization from a variety of ethers, alkanes, unactivated C–H bonds, and alcohols as well as showcase the applicability of the method to several monomer classes. Our method lends itself to photocontrol which has important implications for building advanced macromolecular architectures. Finally, we demonstrate that we can graft polymer chains controllably from poly(ethylene glycol) showcasing the potential application of this method for controlled grafting from C–H bonds of commodity polymers.</p

Photocontrolled Interconversion of Cationic and Radical Polymerizations

The ability to combine two polymerization mechanisms in a one-pot setup and switch the monomer selectivity via an external stimulus provides an excellent opportunity to control polymer sequence and structure. We report a strategy that enables monomer incorporation to be determined via the selection of the wavelength of light through selective activation of either cationic or radical processes. This method enables the synthesis of varying polymeric structures under identical solution conditions but with simple modulation of the external stimulus. Additionally, changes in the ratios of the two photocatalysts afford complementary chemical control over these reactions to design elaborated polymeric structures. Our strategy takes advantage of the unique regulation that can be accessed through light

Cationic Polymerization of Vinyl Ethers Controlled by Visible Light

Photoinitiated cationic polymerizations are widely used in industrial processes; however, gaining photocontrol over chain growth would expand the utility of these methods and facilitate the design of novel complex architectures. We report herein a cationic polymerization regulated by visible light. This polymerization proceeds under mild conditions: a combination of a metal-free photocatalyst, a chain-transfer agent, and light irradiation enables the synthesis of various poly­(vinyl ether)­s with good control over molecular weight and dispersity as well as excellent chain-end fidelity. Significantly, photoreversible cation formation in this system enables efficient control over polymer chain growth with light