Reactive Polymers最新文献

In this study, the diffusion characteristics of theophylline through polyurethane (PU), polyvinylchloride (PVC) and polyhydroxyethylmethacrylate (PHEMA) membranes were investigated for their usage as oral controlled-release reservoir systems. PU and PVC membranes were prepared by the solvent-casting method and PHEMA membrane was prepared by bulk polymerization of 2-hydroxyethylmethacrylate in different thicknesses. Diffusion measurements were performed in simulated gastric fluid and simulated intestinal fluid during 10 h at 37°C using a diffusion cell. Permeability coefficients calculated from diffusion experiments were found to be approximately 10 times higher in PHEMA than PU and PVC membranes.

Platinum complexes with poly(vinylpyridine) ligands have been studied as catalysts in the reaction of nitrobenzene and 2-propen-1-ol hydrogenation. Pretreatment of the complexes with NaBH₄ causes the reduction of part of platinum into lower valent states (XPS data) and a decrease of catalytic activity of polymer-metal complexes. The structure of polymer ligands and the position of substituents on the pyridine ring of poly(vinylpyridine) have been shown to affect properties of obtained catalysts. A platinum complex with poly(2-methyl-5-vinylpyridine) was active in hydrogenation reaction.

Insoluble polymer beads bearing pendant norbornadiene (NBD) moieties were synthesized by the substitution reaction of insoluble chloromethylated poly(styrene) beads with potassium salts of certain NBD derivatives having carboxylic acid or phenol groups using a phase transfer catalyst. The reaction proceeded smoothly in high conversions in DMF at 90°C for 72 h to give the corresponding insoluble polymer beads bearing NBD moieties. Rates of photochemical reaction of the obtained insoluble polymer beads were measured by IR spectrometry using KBr disk plates. The photochemical valence isomerization from 3-phehyl-2,5-NBD-2-carboxylate (PNCA) moiety to the corresponding quadricyclane (QC) group and catalytic reversion from QC to the NBD moiety were also examined in dichloromethane, and it was found that the photochemical valence isomerization and the catalytic reversion in insoluble polymer beads can be recycled in high conversions at last for 10 runs.

Lightly crosslinked polystyrenes with ammonium chlorides were ion-exchanged to a fluoride form. The fluoride polymers functioned as good catalysts for several base-catalyzed reactions, such as cyanoethylation, Knoevenagel reaction, Claisen condensation and Michael addition. Their catalytic activity was comparable to that of tetrabutylammonium fluoride (TBAF). The factors controlling the catalytic efficiency for the reaction between ethyl acetoacetate and benzaldehyde were examined in detail. Ionic loading and ammonio structure of the fluoride polymers hardly affected the catalytic efficiency. The reaction was fast in a non-polar solvent, such as octane or toluene. The solvent effect was very similar to that of nucleophilic substitution reactions. These results suggest that the rate-determining step of the base-catalyzed reaction is not the formation of a conjugate base from the reagent acid, but the attack of the nucleophilic anion on electrophiles.

The conditions for the preparation of catalysts based on the interaction of PdCl₂ with poly(vinylpyridine) were studied. The activity of polymer-metal complexes in hydrogenation can be considerably changed by variation in temperature, initial ratio of PdCl₂ and polymer in solution, and contact time of the resulting complexes with the initial solution. The complex, prepared at 25°C from ethanolic solutions of poly(2-vinylpyridine) and PdCl₂ (molar ratio polymer: Pd = 1:1), and kept in the initial solution for 3 days, was found to be an active catalyst for hydrogenation. The reduction of this complex with NaBH₄ leads to an increase in its catalytic activity.

Three kinds of novel β-cyclodextrin (β-CyD) polymers were synthesized by immobilization of β-CyD onto the crosslinked polystyrene supports with different functional groups such as CH₂Cl, SO₂Cl and