Search results for "tetrahydrofuran"

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

2000

The kinetics of the anionic polymerization of methyl methacrylate in presence of N,N,N', -tetramethylethylenediamine (TMEDA) in THF are investigated using 1,1-diphenyl-hexyllithium as initiator in a temperature range between -20°C and 0°C in a flow-tube reactor. The rate constants of propagation determined in the presence of TMEDA are compared to those obtained in the absence of a chelating agent. For propagation, the reaction order with respect to active centers is found to be 0.5 in both cases which indicates that the chelation of the lithium cation does not effectively perturb the aggregation of the enolate ion pair. Both the rate constants of propagation via non-aggregated ion pairs, k …

Pyrrole Studies XXVII.1Utilisation of 1-Methyl-2-pyrrolyl Lithium in the Synthesis of 1-Methyl-2-substituted Pyrroles

1982

Abstract Although metallation of 1-substituted pyrroles with alkyl lithium reagents to give the lithiated derivatives has been recorded by several research groups,4–6 only limited use has been made of these derivatives in the synthesis of 1,2-disubstituted pyrroles. Subsequent to ourinitial studies,7 it was reported that tetrahydrofuran was the solvent of choice for the formation of the mono-lithiated pyrrole derivative and that the rate of the metallation was accelerated by the presence of TMEDA.6 We had noted,7 however, that prolonged reaction of n-butyl lithium with 1-methylpyrrole in a 2:1 mixture of tetrahydrofuran:hexaneat ca 18°C in the absence of TMEDA gave 1-methyl-2-pyrrolyl lithi…

Dilute solution properties of polybutadiene modified by 4-phenyl-1,2,4-triazoline-3,5-dione

1996

The dilute solution properties of 4-phenyl-1,2,4-triazoline-3,5-dione-modified polybutadienes were studied in tetrahydrofuran by static and dynamic light scattering and compared with those from unmodified polybutadiene chains. For the unmodified polymer, the scaling laws were established and the coil interpenetration parameter k f0 was determined in the thermodynamically good solvent tetrahydrofuran ; the chains exhibited common flexible chain behavior. For the modified polybutadiene, the results indicate at infinite dilution a weak extent of intermolecular crosslinking via the urazole groups, coupled with a very high extent of intramolecular ring formation. In order to evaluate the fractio…

On the viscosity of moderately concentrated solutions of poly(ether imide) in a mixed solvent of marginal quality

2000

Abstract Viscosities η were measured for moderately concentrated (15.5 wt%) solutions of poly(ether imide) (PEI) as a function of the composition of the cosolvent tetrahydrofuran (THF) plus γ-butyrolactone (γ-BL). The solutions are almost by a factor of four less viscous when THF predominates than when γ-BL is the major component of the solvent mixture. Furthermore, the viscosity passes a minimum as the composition of the mixed solvent is varied. Both observations can be well understood in terms of the viscosities of the mixed solvents and the hydrodynamic interaction between the polymer molecules. The pronounced dissymmetry of η as a function of the composition of the mixed solvent η resul…

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…

1982

1985

Viscosity measurements were carried out as a function of pressure and temperature with solutions of 8 wt.-% PVC (Mw ≈ 75 000) in ten thermodynamically good solvents by means of a Searle-type viscometer. A rollingxyhball viscometer was used for the investigation of the pure solvents. In all cases the viscosity increases in a more or less exponential manner when the pressure is raised. The viscosity ratio f1000 = η1000 bar/η1bar can be varied by the choice of the solvent from ca. 2 (tetrahydrofuran) to 3,0 (cyclohexanone) at 40°C. For a constant temperature of 40°C, the volumes of activation for the viscous flow of the solutions, V≠, or f1000 exceed that of the pure solvent, by typically 25%.…

1981

Cyclodehydration of Diols in Acidic Ionic Liquids

2011

Cyclodehydration of Diols in Acidic Ionic Liquids In the presence of sulfonic acid group functionalized Bronsted-acidic ionic liquids, cyclodehydration of 1,2-ethanediol and 1,4-butanediol is investigated. The role of structure and catalytic activity of ionic liquids on the formation of cyclic ethers: 1,4-dioxane and tetrahydrofuran - is determined.