Search results for "cationic polymerization"
showing 10 items of 441 documents
Redox-Responsive Host–Guest Chemistry of a Flexible Cage with Naphthalene Walls
2020
"Naphthocage", a naphthalene-based organic cage, reveals very strong binding (up to 1010 M-1) to aromatic (di)cationic guests, i.e., the tetrathiafulvalene mono- and dication and methyl viologen. Intercalation of the guests between two naphthalene walls is mediated by C-H···O, C-H···π, and cation···π interactions. The guests can be switched into and out of the cage by redox processes with high binding selectivity. Oxidation of the flexible cage itself in the absence of a guest leads to a stable radical cation with the oxidized naphthalene intercalated between and stabilized by the other two. Encapsulated guest cations are released from the cavity upon cage oxidation, paving the way to futur…
Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes
2012
We report new bis-cyclometalated cationic indium(III) complexes [((CN)-N-boolean AND)(2)Ir(CN-tert-Bu)(2)](CF3SO3) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluoropheny1)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or 5-trifluoromethyl) as (CN)-N-boolean AND ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or bluegreen phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-…
Synthesis of Linear and Star-Shaped Block Copolymers of Isobutylene and Methacrylates by Combination of Living Cationic and Anionic Polymerizations
1998
A new synthetic route for the preparation of polyisobutylene (PIB)-based linear and star-shaped block copolymers was developed by combining living carbocationic and anionic polymerizations. Living PIB chains were quantitatively endcapped with 1,1-diphenylethylene, leading to 1,1-diphenyl-1-methoxy (DPOMe) or 2,2-diphenylvinyl (DPV) termini, or both. Both the DPOMe- and DPV-terminated PIBs, and the mixtures of both endgroups were quantitatively metalated with K/Na alloy, Cs metal, or Li dispersion in THF at room temperature. The resulting stable macrocarbanion obtained by metalation with K/Na alloy was used to initiate living anionic polymerization of tert-butyl methacrylate (tBMA) yielding …
Synthesis of linear and three-arm star tert-chlorine-telechelic polyisobutylenes by a two-step conventional laboratory process
1997
A two-step conventional laboratory process was developed for the synthesis of mono- and difunctional linear and three-arm star tert-chlorine-telechelic polyisobutylenes (PIB) with desired molecular weights (MW) and narrow molecular weight distribution (MWD) by living carbocationic polymerization (LCCP). This polymerization method applies easy to handle operations and chemicals. LCCP of isobutylene (IB), was carried out in CH2Cl2 as solvent and with BCl3 as coinitiator in the first step to obtain soluble low MW PIB prepolymer with narrow MWD. This was followed by addition of hexane, TiCl4 and additional monomer in the second step to prepare PIBs with desired MW and narrow MWD in practically …
Endfunctional Polymers by Functionalization of Living Cationic Chain Ends with 1,1-Diphenylethylene
1995
Abstract A new functionalization method has been developed for the synthesis of 2,2-diphenylvinyl(DPV)-telechelic polyisobutylene (PIB). First, living carbocationic polymerization (LCCP) of isobutylene (IB) is quantitatively end-quenched with a nonpolymerizable olefin, 1,1-diphenylethylene (DPE). This process yields a mixture of diphenyl substituted vinyl and tertiary chlorine endgroups. Treatment of the resulting polymer with potassium-tert-butoxide (tBuOK) leads to the quantitative formation of DPV-telechelic PIB which is a potential macroinitiator precursor for living anionic polymerizations.
Non-ionic photo-acid generators for applications in two-photon lithography
2009
Non-ionic photoacid generators (PAGs) have been designed and synthesized for use in two-photon lithography (TPL). The chromophores in these new PAGs are covalently linked to the photocleavable group by a flexible joint. Their thermal stability, solubility and efficiency to produce acid under both one- and two-photon excitation were characterized. The potential of these PAGs for TPL was tested in two negative-tone resist systems relying on different mechanisms: free-radical/cationic polymerization or a cationically initiated cross-linking reaction. These PAGs needed lower threshold power for polymerization compared to a commercially available photoinitiator, isopropylthioxanthone, and a phot…
Relation between structural and release properties in a polysaccharide gel system.
2007
Abstract The potential utility of κ-carrageenan gels for preparing drug release devices is here shown. Structural properties of κ-carrageenan gels prepared with different salt composition and containing Ketoprofen sodium salt, as model drug, have been evaluated with static light scattering and rheological measurements. These properties have been correlated with release profiles in vitro at pH 5.5. Release properties from gelled matrices have been compared with those obtained by two commercial products containing the same drug. Results show that: i) in this system it is possible to easily control the gel texture by using different cationic concentration; ii) the kinetics of drug release by κ…
Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain-length dependence of the rate and equilibrium constants
1986
The rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α-lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain-length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain-length. This is discussed in terms of intramolecular coordination…
Initiatoren für die polymerisation des trioxane. 20. Mitt. über polyoxymethylene1
1963
Die Polymerisation des Trioxans bei 60°C in Cyclohexan mit verschiedenen kationischen Initiatoren wurde untersucht. Die aktivsten Initiatoren sind Acetylperchlorat, Perchlorsaure, FeCl3 und SnCl4. Die Molekulargewichte der erhaltenen Polyoxymethylene sind bei den aktivsten Initiatoren am hochsten. Der Einflus der ubertragung durch Wasser und der kinetischen Kettenlange auf die Molekulargewichte wird diskutiert. Wahrend der Polymerisation kann durch den Initiator eine Spaltung bereits gebildeter Makromolekule erfolgen, welche die Molekulargewichte stark reduziert. Die Frage der Cokatalyse bei der kationischen Polymerisation des Trioxans mit Ansolvosauren wurde untersucht. Bei der Polymerisat…
Kinetic Analysis of “Living” Polymerization Processes Exhibiting Slow Equilibria. 5. Effect of Monomer Transfer in Cationic Polymerization and Simila…
1996
This work deals with the kinetics of polymerization processes with chain transfer to monomer and reversible formation of dormant species. Such a mechanism is typical for cationic polymerization in the presence of Lewis acids as co-initiators. The expressions of number- and weight-average degrees of polymerization and polydispersity index are derived rigorously for a mechanism with free ions as the active species, but it is also applied to other mechanisms, e.g., ion pairs as active species. Plots of polydispersity index versus monomer conversion can be easily computed on a PC computer even though the expressions for the weight-average degree of polymerization and the concentration of residu…