Search results for "counterion"

Metal-free anionic polymerization of methyl methacrylate in tetrahydrofuran using bis(triphenylphosphoranilydene)ammonium (PNP+) as counterion

2000

Bis(triphenylphosphoranilydene)ammonium (PNP + ) triphenylmethanide (Ph 3 C - ) is a new metal-free initiator for the living polymerization of methyl methacrylate (MMA). The kinetics of the polymerization strongly depend on the metal counterion the initiator precursor. When the initiator is made from the metathesis reaction of Ph 3 CK and PNPCl, the polymerization follows first-order kinetics up to 0°C with half-lives below 0.1 s. The propagation rate constants are much higher than those obtained with tetraphenylphosphonium (TPP + ) cations, indicating a smaller fraction of dormant ylides. When the initiator is synthesized from Ph 3 CLi, polymerization proceeds much slower and molecular wei…

Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium (P5+) as counterion in tetrahydrof…

2000

A novel metal-free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) cation with the 1,1-diphenylhexyl (DPH–) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between –20 and +20°C using a flow tube reactor provide nearly linear first-order time-conversion plots with half-lives below 0.1 s, a linear dependence of the number-average degree of polymerization, and rather narrow molecular weight distributions (Mw/Mn ≈ 1.2). 13C NMR measurements on a model of the active chain end (the P5+ salt of ethyl isobutyrate) in THF-d8 show 15 and 25…

Anionic Polymerization of Alkyl (Meth)acrylates Using Metal-Free Initiators:  Effect of Ion Pairing on Initiation Equilibria

1999

Metal-free anionic polymerizations of alkyl (meth)acrylates using tetrabutylammonium salts of diethylphenylmalonate, fluorene, and 9-ethylfluorene as initiators were performed in THF at 30 °C. A poor control of molecular weights, inconsistent initiator efficiencies, and broad or bimodal molecular weight distributions were obtained. The effect of counterion nature was studied from the polymerization of methyl methacrylate using the 1,1-diphenylhexyl anion with tetrabutylammonium, tetramethyldiethylguanidinium, and lithium as counterions under otherwise identical conditions. Metal-free initiators resulted in incomplete initiation which is attributed to the fact that the initiation is an equil…

N,N-Diallylglycidylamine: A Key Monomer for Amino-Functional Poly(ethylene glycol) Architectures

2012

The first application of N,N-diallylglycidylamine (DAGA) as a monomer for anionic ring-opening polymerization is presented. The monomer is obtained in a one-step procedure using epichlorohydrin and N,N-diallylamine. Both random and block copolymers consisting of poly(ethylene glycol) and poly(N,N-diallylglycidylamine) with adjusted DAGA ratios from 2.5 to 24% have been prepared, yielding well-defined materials with low polydispersities (Mw/Mn) in the range 1.04–1.19. Molecular weights ranged between 2600 and 10 300 g mol–1. Isomerization of allylamine to enamine structures during polymerization depending on time, temperature, and counterion has been realized. The kinetics of the formation o…

Synthesis and properties of aromatic ionenes

1993

Cationic polyelectrolytes with aromatic segments can be synthesized by a repetitive alkylation reaction. The structure of the products, their synthesis and their solubility are described. All ionenes are not, or only in small amounts, water soluble. The best solubility can be achieved by mixtures of polar protic and aprotic solvents. Variations of the counterion produces sufficient solubility in THF. All ionenes show a typical polyelectrolyte effect. The thermal stability of aromatic ionenes and the glass transition temperature is dominated by the nature of the counterion. The molecular weight of oligomers can be described by using a combination of a conductive titration method and an ion s…

The anionic copolymerization of 5-(N,N-diisopropylamino)isoprene with styrene

1995

The anionic copolymerization of 5-(N,N-diisopropylamino)isoprene (N,N-diisopropyl-2-vinylallylamine) and styrene initiated with alkyllithium compounds is studied. Copolymers obtained from different compositions are characterized by size-exclusion chromatography (SEC), differential scanning calorimetry and by 1 H NMR and 13 C NMR spectroscopy. Under these conditions the dialkylaminoisoprene, similar to butadiene and isoprene, is more reactive than styrene and is incorporated faster into the polymer backbone. The incomplete conversion of the monomers has been attributed to the formation of intra-or intermolecular complexes between the Li + counterion at the chain end and amino groups. Because…

1982

The role of potassium and hydrogen ions in the Prussian Blue ⇆ Everitt's Salt process

1998

Cyclic voltammetry experiments have proved very useful in the knowledge and understanding of the role of the potassium and hydrogen ions during the Prussian Blue ⇄ Everitt's Salt process. While potassium ions act as a stoichiometric reactant, the hydrogen ions play a very important role in the kinetics of the electron-hopping process. The entropy change for the reaction PB ⇄ ES has proved to be dependent on the degree of crystallinity of the film, indicating that this entropy change is related to the fixation of inner counterions on the crystal structure of the films.

The correlation between electrochemical impedance spectra and voltammograms of PB films in aqueous NH4Cl and CsCl

1998

Abstract Voltammetric curves of reduction of Prussian Blue Films to the Everitt’s Salt form and oxidation to the Prussian Yellow form show important differences depending on the supporting electrolyte countercation. The rate of the overall electron-hopping depends on the countercation. Apparent diffusion coefficients are evaluated from impedance spectra at different stabilization potentials. The dependence of the apparent diffusion coefficients on the stabilization potential can help understand the dependence of the voltammograms shape on the countercation nature.

The role of inner counterions within PB films during electrochemical processes

1999

Abstract The shape of voltammograms of Prussian Blue films (ferric ferrocyanide, PB) deposited on ITO (indium–tin oxide) electrodes in aqueous KCl, CsCl and NH 4 Cl solutions has been studied. These results proved a double role of countercations during these electrochemical processes. Countercations can either be only retained within the zeolitic pores of the PB structure forming part of their inner solution, or can also form part of the crystalline structure of PB films by replacing some iron sites. The different electrochemical behaviour of PB films in the three studied solutions (KCl, CsCl and NH 4 Cl) is analysed from this point of view.