bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antiferroelectric behavior in a liquid crystalline polymer
Authors: Skarp Kent , Andersson Gunnar , Gouda Fathi , Lagerwall Sven T. , Poths Holger , Zentel Rudolf 
Published: April 2003

AbstractElectro‐optic and polarization reversal measurements were performed on a side‐chain polymer exhibiting a chiral smectic phase. Based on the observed electro‐optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field‐induced antiferroelectric‐to‐ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side‐chain polyacrylate.
SAXS investigations on chiral liquid crystalline polymers: antiferroelectric and ferrielectric structures?
Authors: Mensinger Hildegard , Biswas Amit 
Published: April 2003

AbstractThe structure and phase behavior of liquid crystalline polymers (LCPs) having a common chiral side chain mesogen but different main chain structures have been investigated using small‐angle X‐ray scattering (SAXS). While the low molecular weight chiral side chain mesogen by itself exhibits ferroelectricity, the SAXS data of the side chain LCP with a flexible polyacrylate backbone contains a bilayered superstructure peak that is indicative of antiferroelectric order. The combined LCP with a nonpolar main chain mesogen also has a bilayered superstructure, but has a different structural organization in the proposed antiferroelectric phase compared to the side chain LCP. Further changes in the phase behavior and structural organization occur when a polar group is introduced into the main chain mesogen. A ferrielectric phase has been proposed to explain the observation of a trilayered superstructure in the corresponding SAXS data. The influence of the chemical structure and connectivity on the phase behavior and superstructure formation in the chiral LCPs is discussed.
Electromechanical effects in ferroelectric liquid crystalline polymers
Authors: Jákli Antal , Éber Nándor , Bata Lajos 
Published: April 2003

AbstractElectric fields can induce mechanical vibrations in planar aligned sandwich cells of ferroelectric liquid crystals. Measurements on a polysiloxane and a polyacrylate side chain polymer proved that the electromechanical effect also exists in ferroelectric liquid crystalline polymers. The main characteristics of the electromechanical responses of these polymers are described and compared to the response of low molecular weight ferroelectric liquid crystals. According to the proposed interpretation, the vibrations in the direction parallel to both the smectic layers and cell substrates are due to coupling between the director rotation and the flow, while the resonances in the vibrations normal to the plates are connected to layer deformations.
Degradable polymers for site‐specific drug delivery
Authors: Domb Abraham , Amselem Shimon , Shah Jaymin , Maniar Manoj 
Published: April 2003

AbstractThe present article was aimed to review the properties and applications of the actually available biodegradable polymers that have been used as targetable drug carriers and site‐specific delivery systems. We have mainly focused on microparticulate or carrier‐based drug delivery systems with little emphasis on implants as site‐specific delivery systems.The review was divided into two major sections. The first section includes a brief description of the properties and applications of the existing biodegradable polymers for site‐specific drug delivery classified in two main categories: synthetic biopolymers (as polyesters, polyanhydrides, polyorthoesters, polyphosphazenes, polycaprolactones), and natural biomaterials (as collagen, albumin and gelatin), which still remains an active area of research in spite of the extensive development of new biodegradable polymers.The second section discusses the mechanistic approaches for the selection of polymeric carriers. General guidelines for the ideal drug carrier complex were summarized. The importance of knowing and understanding the physicochemical properties of the polymer for the optimization of the final formulation and its eventual application were emphasized. The factors governing the effective drug concentration at the specific target site were reviewed. Some of the equations describing the release kinetics of a drug from a polymeric matrix were also examined.The last section of the review describes the preparation and use of polymeric macromolecular prodrugs. A diagrammatic representation of possible polymeric prodrug systems for use in site‐specific delivery was described. The basic requirements from a polymeric prodrug system were also discussed. Finally, clinical applications of polymeric prodrugs as for cancer therapy and colonic delivery were considered.
Site‐specific drug delivery to the lung
Authors: Auerbach Robert , Erdman Boyd , Kubai Louis 
Published: April 2003

AbstractInvestigations were undertaken to determine whether anti‐cancer drugs introduced locally into the lung using bioerodible polyanhydride microspheres as carriers would demonstrate both efficacy and reduced toxicity.BCNU (carmustine) and CDDP (cisplatin), loaded in polyanhydride microspheres, were administered to mice bearing either of two tumors selected for their affinity for the lung: the B16F10 melanoma and the recently established GL26F4 glioma. Following intravenous inoculation of these tumor cells, the number of metastatic foci formed in the lung follows a predictable time course and can readily be determined. Comparisons were made between the efficacy of microspheres introduced into the lung by intratracheal intubation (IT) and of those administered by intraperitoneal injection (IP). Administration of microspheres loaded either with BCNU or cisplatin reduced the detectable metastatic foci by 25–90% depending on the tumor load, both when administered IP and IT.Toxicity was assessed by flow cytometric analysis of bone marrow cellularity as well as by determination of mortality rates. Intratracheal administration of either cisplatin or BCNU reduced the deleterious systemic effects observed when the drug was administered by IP injection. This was seen at high drug levels, where significant mortality occurred only in animals given drug injections IP; and at lower levels where IP injection led to a reduction of bone marrow blast cells, while IT administration caused no detectable effect on marrow cellularity.Since local delivery of BCNU or cisplatin through bioerodible polyanhydride microspheres induces significantly less systemic damage while demonstrating efficacy equal to or exceeding that of IP injection, this mode of drug delivery warrants further and more detailed exploration. Moreover, the method may be applicable to the treatment of other chronic pulmonary pathologies.
Sustained release of acetylcholine in rat hippocampus using a polyanhydride drug‐delivery system
Authors: Mayberg Marc R. , Gross Alan S. , Mathiowitz Edith , Langer Robert 
Published: April 2003

AbstractA biodegradable polymer drug‐delivery system has been developed for the selective localized application of agents to brain parenchyma. The copolymer of poly[bis(p‐carboxyphenoxy)propane] anhydride and sebacic acid (PCPP–SA) was impregnated with [3H]‐acetylcholine (ACh) to form 1–5 μm microspheres. Drug‐loaded microspheres were implanted into hippocampus bilaterally in 25 rats, and brain sections processed for autoradiography in groups of five animals at 2, 5, 10, 20 and 40 days, respectively. By densitometric analysis, the concentration of radiolabelled ACh in polymer and adjacent hippocampus rapidly decreased between 2 and 5 days, after which a gradual decrease in [3H]‐ACh was observed up to 40 days. Between 2 and 40 days the concentration of radiolabelled ACh was reduced by 25.8% in polymer matrix and 40.1% in hippocampus. The spread of [3H]‐label into adjacent brain parenchyma showed a similar temporal relationship, with initially wider dispersion at 2 days (44±3 μm), then a linear decrease in dispersion over the remaining period (10±0.9 μxm at 40 days), suggesting bulk flow of the radiolabel into hippocampus. Brain parenchyma showed only a minimal inflammatory reaction to the polyanhydride implants over all time periods. Polyanhydrides can provide localized continuous release of ACh to brain parenchyma, and may potentially be used to deliver various agents to brain in a number of clinical and experimental applications.
Local release polymeric‐controlled immunotherapy of cardiac transplants in rats
Authors: Bolling Steven F. , Lin Hua , Ning Xue‐han , Levy Robert J. 
Published: April 2003

AbstractSystemic immunosuppression frequently results in severe side effects. To evaluate a method of limiting the adverse effects of immunosuppression, we implanted controlled release matrices containing cyclosporine‐A (Cy) embedded (0.2 or 1 mg/kg/day released), steroid embedded (2%, 0.2% and 0.02% dexamethasone, Dex) or both (Cy 0.2 mg and Dex 0.2%) locally around the transplanted heart at the time of rat heterotopic (neck) heart transplants. Controls received empty (non‐drug) matrix implants. To elucidate a local effect, additional groups received Cy (0.2 mg) or Dex (0.2%) matrix implanted in a subdermal distal leg pouch at the time of heart transplant, without a local neck implant. Rejection was determined by the lack of transplanted heart contractions. Recipient animals received no other form of immunosuppression.The Cy (0.2 mg) animals had whole‐blood Cy levels monitored for 6 weeks following transplantation. Cy levels peaked at 7–10 days after transplant (119 ± 26 ng/ml) and decayed to <50 ng/ml by day 42. At no time did whole‐blood Cy levels reach clinically significant levels. Additional animals had whole‐blood, heart and kidney Cy levels measured at day 6 post‐transplant. Both doses of local Cy demonstrated good survival benefit and were well absorbed locally, resulting in high Cy levels in heart tissue (>9,000 ng/mg). Furthermore, while low‐dose Cy (0.2 mg) demonstrated significant survival benefit, these animals had clinically negligible blood Cy levels on day 6 (<100 ng/ml) and very low kidney Cy levels. Interestingly, the lowest dose of Dex demonstrated no survival benefit, while the mid‐ and high‐Dex doses demonstrated good survival benefit: however, the high‐Dex dose had poor wound healing. Cy and Dex combination did not increase efficacy, perhaps due to release problems from physicochemical interactions.Local immunosuppression with a controlled release matrix resulted in a significant survival advantage and was effective in delaying rejection. This approach may prove advantageous clinically, in extending transplantation and lessening immunosuppression side effects.
Preparation of polyimides utilizing the Diels–Alder reaction, II: Bis[N‐(butadienyl‐2‐methyl)] amino arylenes with bismaleimides
Authors: Smith J. G. , Ottenbrite R. M. 
Published: April 2003

AbstractFour new bisdienes were prepared from 2‐bromomethyl‐1,3‐butadiene and N,N‐diethyl benzidine; bis[4‐(N‐ethyl) aminophenyl]‐p‐diisopropylbenzene, 1,4‐diamino‐2,3,5,6‐tetramethylbenzene and α,α′ bis(4‐amino‐3,5‐dimethyl phenyl)‐p‐diisopropyl benzene. Polyimides were synthesized by the Diels–Alder reaction of these bisdienes and bis(4‐maleimidylphenyl)methane and bis(3‐maleimidylphenyl) sulfone. The polymers were soluble in m‐cresol, dimethyl sulfoxide and chlorinated hydrocarbon solvents. Moderate thermal stability was observed by thermogravimetric analysis in air and nitrogen.
Encapsulation of Hb into unsaturated lipid vesicles and γ‐ray polymerization
Authors: Sakai Hiromi , Takeoka Shinji , Yokohama Hiroaki , Nishide Hiroyuki , Tsuchida Eishun 
Published: April 2003

AbstractA carbonyl hemoglobin (HbCO) solution was stirred with a mixed powder of polymerizable 1,2‐bis(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphocholine (DODPC), cholesterol and stearic acid (7/7/2 by mol). The mixture was extruded through polycarbonate membrane filters (final pore size = 0.2 μm Ø). The average diameter of the resulting vesicles was 203 ± 39 nm. The [Hb]/[Lipid] ratio (the weight ratio of Hb in vesicle to lipid) increased with the Hb concentration, and decreased with the NaCl concentration. A maximum [Hb]/[lipid] ratio was observed at pH 6.9, which was the same as the isoelectric point of Hb. The vesicles were stabilized by γ‐irradiation (60Co) because the bilayer lipids bound each other to yield polyphospholipids. Denaturation of Hb by γ‐irradiation was not detected. These polyphospholipid vesicles encapsulating Hb were stable even against the freeze–thaw cycles and the freeze‐drying procedure.
The effect of curing conditions on the physical and mechanical properties of styrenated polyester
Authors: Nasr Elsayed S. , Abdel‐Azim A.‐A. A. 
Published: April 2003

AbstractThe curing behavior of unsaturated polyester resin was investigated. In the present study, styrene, methyl ethyl keton peroxide (MEKP) and cobalt octoate (CO) have been selected as solvent (monomer), catalyst and accelerator, respectively. The effect of the concentration of both MEKP and CO on the curing exotherm, curing time, hardness and compressive strength of the prepared copolymers was investigated.
Polymerization and photoinitiation behavior in the light‐cured dental composite resins
Authors: Fujimori Yukio , Kaneko Takashi , Kaku Takahiko , Yoshioka Naoki , Nishide Hiroyuki , Tsuchida Eishun 
Published: April 2003

AbstractThe polymerization behavior and photoinitiation process in the visible light‐cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long‐lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post‐curing by the residual radical proceeded effectively in the deeper part of the resin.
Polymer nanocomposites with “ultralow” refractive index
Authors: Zimmermann Lorenz , Weibel Martin , Caseri Walter , Suter Ulrich W. , Walther Paul 
Published: April 2003

AbstractNanocomposites of gelatine and gold were prepared by reduction of AuCl4H in a gelatine solution, followed by a spin coating process and a brief washing. The thickness of the films thus obtained was typically 200–400 nm. The surface of the nanocomposites was investigated by scanning electron microscopy (SEM) and surface profilometry. The size of the gold particles is in the range of ca. 2–10 nm, as elucidated by transmission electron microscopy (TEM). Refractive indices were measured by ellipsometry at wavelengths of 632.8 and 1300 nm. The refractive index depends linearly on the volume fraction of gold, at least at 1300 nm. The lowest refractive indices measured are 1.008±0.060 at 1300 nm and 0.963±0.062 at 632.8 nm (limits are 95% confidence interval). These values are, to our best knowledge, the lowest reported for a polymer or polymer composite.
Computational examination of the electrophilic reaction on oxidative polymerization of phenyltrimethylsilane with sulfur chloride
Authors: Shouji E. , Yamamoto K. , Katoh J. , Nishide H. , Tsuchida E. 
Published: April 2003

AbstractPhenyltrimethylsilane possesses a higher HOMO energy (–9.34 eV) than nonsubstituted benzene (>0.41 eV). The π electron of the phenyltrimethylsilane localizes on the benzene ring at the ipso position rather than at the para position. Two center energies calculated by the MNDO‐PM3 method indicate that the CSi bond is facilitated to cleave in comparison with the CH (para position) one of the benzene ring. Phenyltrimethylsilane and phenyl bis(trimethylsilane) were polymerized with sulfur chloride through the cationic oxidative polymerization. The product is isolated as oligo(p‐phenylene sulfide), with a melting point of 150–190°C. An electrophile attacks the carbon atom linked to the Si atom in phenyltrimethylsilane. The new synthetic route of PPS can be established on the basis of the computational calculation.
Oxygen dissolution and transport in cobaltporphyrin‐bound organophosphazene membranes
Authors: Nishide H. , Kawakami H. , Nishihara S. , Tsuda K. , Suzuki T. , Tsuchida E. 
Published: April 2003

AbstractRubbery poly(organophosphazene)s were synthesized, and were combined with cobaltporphyrin (CoP) which binds molecular oxygen rapidly and reversibly. The apparent oxygen‐binding equilibrium constant (Kapp) is in proportion to the physical solubility coefficient of oxygen in the polymer, although the reduced equilibrium and thermodynamic parameters are not dependent on the polymer matrix species. Diffusivity of oxygen via the fixed CoP(DC) is enhanced for poly(organophosphazene) membranes with a larger oxygen diffusion constant. Poly(organophosphazene) membranes with both a large Kapp and DC yield high oxygen permeability.
γ radiolysis of neat 2‐phenylheptamethyltrisilane as a model of polysilastyrene
Authors: Nakao Ren , Oka Kunio , Dohmaru Takaaki , Abe Yasuo , Horii Toyokazu , Kitao Teijiro 
Published: April 2003

Abstract2‐Phenylheptamethyltrisilane as a model compound of polysilastyrene was irradiated at a high dose (1440 kGy) of γ‐rays without any additive. The trisilane was found to be resistant to γ‐rays, while it gave small amounts of Me6Si2, Me3SiSiMe2Ph, Me3SiH, Me3SiSiHMePh and (Me3Si)2 SiMeC6H4SiMe3. These products can be interpreted as being due to a chain contraction of the trisilane with the extrusion of methylphenylsilylene, a methyl migration with the extrusion of dimethylsilylene, a scission of an Si–Si bond due to an attack by hydrogen atoms, and a substitution of a hydrogen atom on the phenyl group by a trimethylsilyl radical. The same reactions, except the chain contraction, are observed in the cases of pentamethylphenyldisilane and 1,2‐diphenyltetramethyldisilane. On the basis of the data obtained, the chemical behavior of polysilastyrene during the irradiation is discussed.
Polyaniline: evidence of oxygen–polarons interactions to explain the high selectivity values in oxygen/nitrogen gas permeation experiments
Authors: Rebattet L. , Geniès E. , Allegraud J.‐J. , Pinéri M. , Escoubes M. 
Published: April 2003

AbstractHigh selectivity between oxygen and nitrogen has been found by gas permeation with doped polyaniline. Because of the small difference in kinetic diameters, solubility rather than diffusion may explain the preferential oxygen permeation. Electron spin resonance (ESR) measurements have been performed to check whether interactions of oxygen with polarons in polyaniline exist. A tenfold decrease in the spin number was observed when the polymer was in the presence of oxygen rather than nitrogen. This result was interpreted as being due to interactions between oxygen triplet states and polarons of polyaniline.
Synthesis of novel polystyrene derivatives with pendant oligo(oxyethylene)cyclo‐triphosphazenes and ionic conductivities of their LiClO4 complexes
Authors: Inoue K. , Tanigaki T. , Yuan Z. 
Published: April 2003

AbstractIonic conductivities of complexes of polystyrene derivatives having a spacer, CH2O(CH2CH2O)n (poly‐(SEDEP), n = 1; poly(SDEDEP), n = 2), between backbone and pendant penta(methoxyethoxyethoxy)cyclotriphosphazene with LiClO4 were investigated as functions of temperature and salt concentration. The glass transition of temperature of poly(SEDEP) and poly(SDEDEP) was observed at −64 and −65°C, respectively. The extent of Tg elevation of the Li+–polymer complexes was not affected by the difference of spacer in the host polymers. The conductivities of the complexes exhibit non‐Arrhenius temperature dependence. The conductivities of poly(SDEDEP)–Li+ complexes were somewhat higher than those of poly(SEDEP) systems and the maximum value close to 10−4 S/cm at 50°C has been achieved at [Li+]/O = 0.08. The results are compared with those obtained previously for the complexes based on polymers which have the similar structures but no spacer, and the correlation between the conduction mechanism and polymer characteristics is discussed.
Ion conduction in mixtures of oligo(ethylene oxide) comb–branch polymer with dipositive cation salts
Authors: Cowie John M. G. , Ferguson Roderick , Billotte Stephane 
Published: April 2003

AbstractA series of polymer–salt, solid solutions have been prepared using a comb–branch polymer with oligo(ethylene oxide) side chains and salts of divalent cations. The salts used were magnesium, zinc and copper triflate, and the copper (I) and copper (II) bromides. Homogeneous, single‐phase, solid solutions were obtained, except for CuBr, which showed poor solubility in the polymer. The addition of salt caused an increase in the glass transition temperature of the system, which was taken to be a reflection of the effective coordination of the cation by the polymer. The a.c. ion conduction was measured using the complex impedance method, and conductivities were obtained as a function of temperature. The magnitude of the conductivity was generally higher in these systems than observed in comparable mixtures when conventional polyethylene oxide was the host polymer. Conductivity was also found to depend on the length of the ethylene oxide side chain in the comb–branch polymers. There is some indication from the present results that the divalent salts may only be partially ionized giving only monovalent species, but this conclusion remains circumstantial until further work is carried out on similar multivalent salt systems.
Constant‐voltage polarization of symmetric polymer electrolyte cells with non‐blocking electrodes
Authors: Vincent Colin A. , Bruce Peter G. , Hardgrave Martin T. , Shi Jie 
Published: April 2003

AbstractThe steady state current flowing in a polymer electrolyte when a constant potential difference, ΔV, is applied to a symmetric cell of the type

has been determined as a function of the magnitude of the d.c. potential, the salt concentration and the temperature in amorphous PEO:LiCF3SO3 and PEO:LiClO4 systems.Such measurements may be used to determine a practical electrolyte parameter, the current fraction, F+, which is defined as the ratio of the current flowing when the cell is passing a steady state current following establishment of a stable concentration gradient, to the current flowing in the absence of a concentration gradient. Under certain circumstances it is possible to identify the limit of the current fraction for ΔV → 0, F, with the transport number of M+. More generally, measurements of F+ yield useful information about the maximum current density which may be maintained at steady state, provided that the electrolyte conductivity is known—a situation which can be rapidly attained in paractical thinfilm devices.It was found that: (i) F fell very significantly as the salt concentration was increased for the two lithiumbased systems; (ii) for these systems, F increased significantly with temperature at concentrations below 2.0 mol dm−3; (iii) F values for the LiCF3SO3‐based electrolytes were significantly higher than those for the LiClO4‐based electrolytes of the same concentration; (iv) F values for the LiCF3SO3‐based electrolytes were independent of the molecular weight of the polymer host.