Search results for "polymerization"
showing 10 items of 1689 documents
Amphiphilic Polyethers of Controlled Chain Architecture
2003
The amphiphilic polymers, polymers which contain in their macromolecules both hydrophilic and hydrophobic units1, are the base for valuable materials due to their diversified interaction with liquids. So they may act as emulsifiers, compatibilizers, “smart” materials (responding to external stimuli)2 and many others. In order to control their properties, the hydrophilic — hydrophobic balance in the macromolecules has to be controlled. This balance depends not only upon the constitution of the chain repeating units, but also upon the art of their distribution in the chains (copolymers of controlled unit sequences), the chain topology, the size of the chains and many others. So a careful engi…
Kinetics and Mechanisms in the Anionic Polymerization of Methacrylic Esters
1987
Under appropriate conditions the anionic polymerization of methacrylates proceeds in an ideal manner leading to polymers with narrow molecular weight distributions. From the kinetics of polymerization and from the microstructure of the polymers the existence of different active species is concluded, the most important one being a peripherally solvated contact ion pair. Depending on polymerization conditions two different modes of monomer addition can occur. Homo- and copolymerization experiments show that the influence of the ester group is mainly given by electronic effects. In non- polar solvents the polymerization of tert.-butyl methacrylate (in contrast to methyl methacrylate) leads to …
Pressure-Induced Polymerization of Polycyclic Arene-Perfluoroarene Cocrystals: Single Crystal X-ray Diffraction Studies, Reaction Kinetics, and Desig…
2020
Pressure-induced polymerization of aromatic compounds leads to novel materials containing sp3 carbon-bonded networks. The choice of the molecular species and the control of their arrangement in the crystal structures via intermolecular interactions, such as the arene–perfluoroarene interaction, can enable the design of target polymers. We have investigated the crystal structure compression and pressure-induced polymerization reaction kinetics of two polycyclic 1:1 arene–perfluoroarene cocrystals, naphthalene/octafluoronaphthalene (NOFN) and anthracene/octafluoronaphthalene (AOFN), up to 25 and 30 GPa, respectively, using single-crystal synchrotron X-ray diffraction, infrared spectroscopy, a…
Oxygen atom transfer catalysis by dioxidomolybdenum(VI) complexes of pyridyl aminophenolate ligands
2021
Abstract A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in the 4-position of the phenolate ring, viz. Cl, Br and NO2, respectively, whereas the ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative of 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures of complexes 2, 3 and 5 reveal that they have a distorted octahedral geometry with the bonding parameters around the metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties of 5 with…
Transfer of Some Alkyl Substituted Ferrocenes from Water to Cationic Surfactant Micelles Studied by Kinetic Method
1994
Abstract Binding of ferrocene and its 1,1′-dimethyl and n -butyl derivatives to dodecyl and tetradecyltrimethylammonium nitrate micellar aggregates has been studied at 20.0°C and ionic strength 0.02 tool dm -3 by examining the micellar retarding effects on the rates of iron(III) oxidation of these substrates. Solubilization of the ferrocenes in the cationic micellar phase increases as the substrate hydrophobic character increases and, to a lesser extent, as the surfactant hydrocarbon chain length becomes longer. The critical micelle concentrations of the surfactants used and the incremental free energy of transfer of methylene groups of both the substrate and the surfactant from the aqueous…
Temperature-responsive inclusion complex of cationic PNIPAAM diblock copolymer and γ-cyclodextrin
2012
Aqueous mixtures of γ-cyclodextrin (γ-CD) and the thermosensitive cationic diblock copolymer poly(N-isopropylacrylamide)-b-poly(3-acrylamidopropyl)trimethylammonium chloride (PNIPAAM24-b-PAMPTAM(+)9) or the PNIPAAM homopolymer PNIPAAM47 have been investigated using various experimental methods. Solid γ-CD–polymer inclusion complexes (pseudopolyrotaxanes) form at ambient temperatures in fairly concentrated CD solutions. The NMR measurements showed that the stoichiometry of the inclusion complexes is close to two NIPAAM units per CD molecule. The cationic block of the copolymer is not incorporated into the CD cavity. Synchrotron radiation X-ray diffraction spectra of the solid inclusion compl…
Polymerization of Mono- and Bi-functional Diacetylene Derivatives in Monolayers at the Gas-Water Interface
1979
The spreading and polymerization behaviour of long chain acids and phospholipid analogues containing diacetylene groups is described. Especially the polymerization in monolayers is followed spectroscopically with a new device used in connection with a commercial UV spectrometer. The polymerization is topochemically controlled. Sonification of the phospholipid analogues in water results in the formation of liposomes with multilayered membranes. Polymerization of the liposomes in water forms aqueous solutions of polymer vesicles.
Kinetic studies of the interaction between DNA and polycations based on polyasparthylhydrazide
2008
Abstract In the present paper, a systematic kinetic study on the interaction between interpolyelectrolytes such as positive-charged polymers and DNA was carried out. In particular, a qualitative–quantitative kinetic investigation on the interaction between copolymers of the α,β-poly(aspartylhydrazide) and DNA calf thymus filaments was performed. This study gives a new model starting from a well known “pseudo-phase model”, and permits to give a qualitative explanation about the trends of experimentally observed kinetic constants by varying the concentration of one of the two poly-electrolytes. Moreover, this study permits to verify the dependence of the binding constants KPAHy–CPTA and KDNA …
Langmuir-Blodgett films of biocompatible poly(HPMA)-block-poly(lauryl methacrylate) and poly(HPMA)-random-poly(lauryl methacrylate): influence of pol…
2010
Membranes based on functional biocompatible polymers can be regarded as a useful model system to study biological interactions, e.g. antibody-antigen interactions or protein polymer interactions. These model systems may give a better insight into these processes and may help to find suitable polymeric structures offering biocompatibility as well as reduced polymer protein interaction. In this respect, Langmuir-Blodgett (LB) layer formation at the air/water (A/W) interface is studied in respect to polymer architecture in this article. For this purpose, narrowly distributed N-(2-hydroxypropyl)-methacrylamide (HPMA) random and block copolymers have been prepared by the RAFT polymerization meth…
Helix–Coil Transition in Cylindrical Brush Polymers with Poly-l-lysine Side Chains
2012
Cylindrical brush polymers with poly-l-lysine side chains were prepared by grafting lysine NCA from a macroinitiator via living ring-opening polymerization. The main chain degree of polymerization of the methacrylate main chain was Pw = 870, the side chains consisted of 25 and 55 lysine repeat units, respectively. Upon deprotection, the cylindrical brush polymers in 0.005 M NaBr exhibited an almost rodlike conformation with a Kuhn statistical segment length of several hundred nanometers. Cryo-TEM as well as AFM in aqueous solution clearly demonstrated pronounced undulations along the main chain at low ionic strength which could not be detected at higher salt concentrations. With increasing …