Structure and properties of the mesophase of syndiotactic polystyrene. VIII. Solvent sorption behavior of syndiotactic polystyrene/p‐chlorotoluene mesophase membranes

A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004     

Electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols in aprotic media.

The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed.     

Oxidation of isoniazid by quinolinium dichromate in an aqueous acid medium and kinetic determination of isoniazid in pure and pharmaceutical formulations.

The kinetics of oxidation of isoniazid in acidic medium was studied spectrophotometrically. The reaction between QDC and isoniazid in acid medium exhibits (4:1) stoichiometry (QDC:isoniazid). The reaction showed first order kinetics in quinolinium dichromate (QDC) concentration and an order of less than unity in isoniazid (INH) and acid concentrations. The oxidation reaction proceeds via a protonated QDC species, which forms a complex with isoniazid. The latter decomposes in a slow step to give a free radical derived from isoniazid and an intermediate chromium(V), which is followed, by subsequent fast steps to give the products. The reaction constants involved in the mechanism are evaluated. Isoniazid was analyzed by kinetic methods in pure and pharmaceutical formulations.     

Influence of surfactant and lipid chain length on the solubilisation of phosphatidylcholine vesicles by micelles comprised of polyoxyethylene sorbitan monoesters

Photon correlation spectroscopy and freeze-fracture electron microscopy have been used to determine the ability of a range of micelle-forming, polyoxyethylene (20) sorbitan monoesters (Tweens) to solubilise vesicles prepared from phosphatidylcholines of different acyl chain lengths and degrees of saturation with a view to rationalising (in terms of their membrane toxicity) which of the micelle-forming surfactants to use as drug delivery vehicles. The phosphatidylcholines used were dimyristoyl-, dipalmitoyl-, distearoyl- and dioleoylphosphatidylcholine (DMPC, DPPC, DSPC and DOPC, respectively) while the nonionic polyoxyethylene sorbitan monoesters studied were polyoxyethylene (20) sorbitan monolaurate (Tween 20), a 9:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 40), a 1:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 60), and polyoxyethylene (20) sorbitan monooleate (Tween 80). The ability of the Tween micelles to solubilise phospholipid vesicles was found to depend both upon the length of the surfactant acyl chain and the length of the acyl chains of the phospholipid comprising the vesicle. Vesicles composed of long saturated diacyl chain phospholipids, namely DSPC and DPPC, were the most resistant to solubilisation, while those prepared from the shorter acyl chained DMPC were more readily solubilised. In terms of their solubilisation behaviour, vesicles made from phospholipids containing long, unsaturated acyl chains, namely DOPC behaved more akin to those vesicles prepared from DMPC. None of the Tween surfactants were effective at solubilising vesicles prepared from DPPC or DSPC. In contrast, there were clear differences in the ability of the various surfactants to solubilise vesicles prepared from DMPC and DOPC, in that micelles formed from Tween 20 were the most effective solubilising agent while those formed by Tween 60 were the least effective. As a consequence of these observations it was considered that Tween 60 was the surfactant least likely to cause membrane damage in vivo and, therefore, is the most suitable surfactant for use as a micellar drug delivery vehicle.     

Desorption behavior of a surfactant in a linear low‐density polyethylene blend at elevated temperatures

The desorption behavior of a surfactant in a linear low‐density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low‐density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN‐40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN‐40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10^?11 to 6.79 × 10^?11 cm²/s, from 1.10 × 10^?11 to 5.75 × 10^?11 cm²/s, and from 0.58 × 10^?11 to 4.75 × 10^?11 cm²/s, respectively. In addition, the calculated activation energies (E_D) of specimens II, III, and IV, from the plotting of ln D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN‐40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm^?1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm^?1. This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN‐40 and retarded the appearance of the 1730 cm^?1 peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1114–1126, 2004     

Structure and properties of the mesophase of syndiotactic polystyrene—III. Selective sorption of the mesophase of syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has various crystalline forms such as α, β, γ, and δ forms, and a mesophase depending on the preparation method. In this study, we focused on the mesophase with the molecular cavity of sPS, which is obtained by step‐wise extraction of the guest molecules from the sPS δ form. To prepare the mesophase containing different shapes and sizes of the cavity, two kinds of the sPS δ form membrane cast from either toluene or chloroform solution were first prepared and then the guest molecules were removed by a step‐wise extraction method using acetone and methanol. We could succeed in the preparation of two kinds of mesophase with different shapes and sizes of the molecular cavity. Either toluene or chloroform vapor sorption to the sPS mesophase membranes was examined at 25 °C. Sorption analysis indicates that the mesophase with large molecular cavities can mainly sorb large molecules; on the other hand, the mesophase with small cavities can sorb only the small molecules, and is unable to sorb a large amount of large molecule because the cavity was too small to sorb the large molecules. Therefore, the sPS mesophase membrane has sorption selectivity based on the size of the molecular cavity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 238–245, 2004     

Ultrahigh‐molecular‐weight‐polyethylene‐fiber surface treatment by electron‐beam‐irradiation‐induced graft polymerization and its effect on adhesion in a styrene–butadiene rubber matrix

Aiming to develop a high‐performance fiber‐reinforced rubber from styrene–butadiene rubber (SBR), we applied a special technique using electron‐beam (EB)‐irradiation‐induced graft polymerization to ultrahigh‐molecular‐weight‐polyethylene (UHMWPE) fibers. The molecular interaction between the grafted UHMWPE fibers and an SBR matrix was studied through the evaluation of the adhesive behavior of the fibers in the SBR matrix. Although UHMWPE was chemically inert, two monomers, styrene and N‐vinyl formamide (NVF), were examined for graft polymerization onto the UHMWPE fiber surface. Styrene was not effective, but NVF was graft‐polymerized onto the UHMWPE fibers with this special method. A methanol/water mixture and dioxane were used as solvents for NVF, and the effects of the solvents on the grafting percentage of NVF were also examined. The methanol/water mixture was more effective. A grafting percentage of 16.4% was the highest obtained. This improved the adhesive force threefold with respect to that of untreated UHMWPE fibers. These results demonstrated that EB irradiation enabled graft polymerization to occur even on the inert surface of UHMWPE fibers. However, the mechanical properties of the fibers could be compromised according to the dose of EB irradiation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2595–2603, 2004     

Crystal structure of the 4-chromanone derivative.

The title compound was extracted from a natural product and its structure was characterized by an X-ray diffraction method. It crystallizes in the tetragonal space group P41 with cell parameters a = 15.832(10)A, c = 11.622(10)A, Z = 4; the final residual factor is R1 = 0.0769. The structure has both intra and intermolecular hydrogen bonds.     

Preparation and characterization of finely dispersed drugs. 5. Ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate

Controlled precipitation of the diagnostic imaging agent ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate has been used to produce fine particles of various sizes, morphologies, and degrees of crystallinity, which depended on experimental conditions. In addition, two distinct polymorphic forms of the drug have been fully characterized by single crystal X-ray diffraction studies, and evidence for a third polymorph was also observed. Some of the so prepared dry particles were coated with a thin layer of silica.