Showing papers in "Polymers for Advanced Technologies in 2000"

Application of sensitive hydrogels in flow control

Abstract: WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW For any polymer gel, the amount of solvent uptake is dependent upon the chemical nature of the gel and the nature of its environment— solvent composition, temperature, pH, and so on. We discuss the use of different hydrogels based on crosslinked poly(N-isopro- pylacrylamide) and copolymers with basic or acidic groups as materials for flow control. The design of a chemo-mechanical valve is described. The liquid flows directly through a gel actuator, which consists of a cylinder filled with small particles of the sensitive crosslinked polymer. The flow rate as well as the pressure drop is measured in dependence on the solvent properties. The sensitivity of the gels as well as the time behavior of the valve-function is correlated with the dependence of the degree of swelling on the environment and the swelling and shrinking kinetics of the gels. The stimulus must permeate the gel itself before a gel can respond to the stimulus. By NMR-imaging it is possible to follow the transport processes inside the gel in real-time. With the presented experimental arrangement we could show that sensitive polymers can be used for controlling the flow in dependence on temperature, pH and content of organic solvents in water. Furthermore, the synthesis of a photo-crosslinkable sensitive polymer is described, synthesized and suggestions for an application of thin layers of this polymer in micro-system techniques are made. Copyright © 2000 John Wiley & Sons, Ltd.

Biodegradation of poly(vinyl alcohol) with different molecular weights and degree of hydrolysis

Abstract: The biodegradability of poly(vinyl alcohol) (PVA) was investigated under different conditions by respirometric determinations, iodometric analysis, and molecular weight evaluation. Microbial inocula derived from the sewage sludge of municipal and paper mill wastewater treatment plants were used. A rather active PVA-degrading bacterial mixed culture was obtained from the paper mill sewage sludge. Significant biodegradation levels within quite short incubation times were obtained in liquid cultures in the presence of acclimated microbial populations. The influence of some polymer properties such as molecular weight and degree of hydrolysis on the biodegradation rate and extent was investigated in the presence of either the acclimated mixed bacterial culture or its sterile filtrate. Kinetic data relevant to PVA mineralization and to the variation of PVA concentration, molecular weight, and molecular weight distribution revealed a moderate effect of the degree of hydrolysis. The molecular weight appeared to be not a limiting factor of microbial attack. Comparison of the degradation process in the presence of either bacterial cells or their culture filtrate highlighted the ability of some microbial strains to utilize polymer chains having 5–10 kD molecular weight. This result suggests the occurrence of two PVA degradation mechanisms: a random-type attack and a terminal unzipping depolymerization process of polymer chains. Copyright © 2000 John Wiley & Sons, Ltd.

Swelling Studies of Copolymeric Acrylamide/Crotonic Acid Hydrogels as Carriers for Agricultural Uses

Abstract: WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW In this study, highly swollen acrylamide/crotonic acid hydrogels (in a rod form) containing some inorganic salts such as ammonium nitrate, potassium nitrate and ammonium sulphate used as fertilizer, an agricultural drug such as Dalapon (sodium 2,2-dichloropropionate) and two crosslinkers such as ethylene glycol dimetha- crylate and 1,4-butandiol dimethacrylate were prepared by copolymerization of acrylamide and crotonic acid with g-radiation. As a result of swelling tests, the influence of g-ray dose and relative content of crotonic acid on the swelling properties, the diffusional behavior of water, diffusion coefficients and network properties of the hydrogel systems were examined. Acrylamide/crotonic acid hydrogels containing these salts and agricultural drug were swollen in the range 2045-400% in water, while polyacrylamide hydrogels swelled in the range 660-700%. Water intake of hydrogels followed a nonFickian-type diffusion. Copyright " 2000 John Wiley & Sons, Ltd.

Pore structure of superporous hydrogels

Abstract: Hydrogels with a fast swelling property have been synthesized using a gas blowing technique. Since those hydrogels possess interconnected pores of which diameters are in the order of a few hundred micrometers, they are called “superporous hydrogels” (SPHs). The fast swelling of SPHs in aqueous solution is due to the absorption of water by capillary pressure through interconnected pores (i.e. open channels). Because of the importance of pore structures on the fast swelling property, effects of surface porosity on the swelling kinetics were examined. The surface chemistry of the polymerization mold made of glass was varied using various silanes, and the surface morphology of the synthesized SPHs was examined by scanning electron microscopy. The porosity was measured using mercury porosimetry. Despite differences in surface morphology and surface porosity of SPHs, the swelling kinetics were not changed significantly. The internal pore structures remained the same as the surface porosity changed. The study indicates that the swelling of SPHs is predominantly determined by the internal pore structures, and small differences in the surface porosity do not alter the overall swelling kinetics of SPHs. Copyright © 2000 John Wiley & Sons, Ltd.

A novel gas sensor from polymer‐grafted carbon black: responsiveness of electric resistance of conducting composite from LDPE and PE‐b‐PEO‐grafted carbon black in various vapors

Abstract: The composite of low-density polyethylene (LDPE) filled with carbon black (CB) having high dispersibility and stability was successfully obtained by the use of poly(ethylene-block-ethylene oxide) (PE-b-PEO)-grafted CB. The response of the electric resistance of the composite against solvent vapors was examined. The electric resistance drastically increased by 104–106 times the initial resistance in a nonpolar solvent vapor such as cyclohexane, and carbon tetrachloride vapor at 40 °C and returned immediately to its initial resistance when the composite was transferred to dry air. However, the electric resistance increased only several times in the polar solvent vapor, such as water and alcohol, at the same temperature. The responsiveness of electric resistance is excellently reproducible and is also stable in cyclohexane vapor and dry air. The effect of temperature on the responsiveness against cyclohexane vapor is also discussed. It is concluded that the composite of LDPE filled with PE-b-PEO-grafted CB could be a promising material to use when preparing gas sensors. Copyright © 2000 John Wiley & Sons, Ltd.

Surface activity and thermodynamic properties of water‐soluble polyester surfactants based on 1,3‐dicarboxymethoxybenzene used for enhanced oil recovery

Abstract: The surface activity and thermodynamic properties for eight low molecular weight nonionic co-polyester (PE) surfactants have been investigated. Surface and interfacial tensions (IFT) of surfactants in aqueous solutions were measured using the spinning drop technique. From these measurements, the critical micelle concentration (CMC), the surface pressure at CMC (YCMC), the maximum surface concentration (Γmax), the minimum area/molecule at the aqueous solution/air interface (Amin), the effectiveness of surface tension reduction (ΠCMC), the alkane carbon number (nmin) and the IFT at nmin (Ymin) were determined. The thermodynamic parameters of micellization (ΔGmic, ΔHmic and ΔSmic) and of adsorption (ΔGad, ΔHad and ΔSad) for these polymeric surfactants were also calculated. Structural effects on micellization and adsorption are discussed in terms of these parameters. The results show that the ΔGad values were more negative than ΔGmic values for these compounds, so that they favored adsorption before the micellization process. They exhibited IFT in the order of 10−3 to 10−4 mN/m against the thin alkane carbon number range 6–9. This range seemed to be prefered for enhanced oil recovery. Copyright © 2000 John Wiley & Sons, Ltd.

Signal‐responsive gating of porous membranes by polymer brushes

Abstract: Various types of signal-responsive polymers were grafted on surfaces of porous membranes as polymer brushes. The grafted polymers shrank and extended in response to environmental signals, such as pH, ionic strength, temperature, redox reaction and photo-irradiation. The pore size was regulated by the extent of the polymer brush. The phenomenon was observed in situ by atomic force microscopy. As a result, the substance permeation through the porous membrane was controlled in response to the signals. The permeation control was rapid in comparison with hygrogel-type membranes, and was reversibly performed. Copyright © 2000 John Wiley & Sons, Ltd.

Novel optical oxygen sensing material: Platinum porphyrin-fluoropolymer film

Abstract: New fluoropolymers, poly(isobutylmethacrylate-co-trifluoroethylmethacrylate) (poly-IBM-co-TFEM) and poly(styrene-co-trifluoroethylmethacrylate) (poly-styrene-co-TFEM) are synthesized and applied to the matrix of optical oxygen pressure sensing based on phosphorescence quenching of platinum porphyrin, platinum octaethylporphyrin (PtOEP), by oxygen. The I0/I100, as a sensitivity of the sensing film, where I0 and I100 represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively, of PtOEP-poly-IBM film and polystyrene film, as the reference, are estimated to be 69.0 and 4.5, respectively. However, the I0/I100 of poly-IBM-co-TFEM film and poly-styrene-co-TFEM film are estimated to be 288 and 296, respectively, and large Stern–Volmer constants are obtained. This result indicates that PtOEP-fluoropolymer films are highly sensitive devices for oxygen. For PtOEP-poly-IBM-co-TFEM film, response times are 6.0 sec for deoxygenated to oxygenated conditions and 35.1 sec for reverse conditions. For PtOEP-poly-styrene-co-TFEM film, however, response times are 4.4 sec for deoxygenated to oxygenated conditions and 30.2 sec for reverse conditions. The rapid response for switching between oxygenated and deoxygenated condition is accomplished using PtOEP-fluoropolymer film. Copyright © 2000 John Wiley & Sons, Ltd.

Design of polyimides for liquid crystal alignment films

Abstract: Recent developments in the chemistry of polyimides (PIs) for liquid crystal (LC) alignment films are reviewed. Some important properties, such as low temperature curing, generation of pretilt angles, and electrical properties, are summarized with respect to the chemical structures of the PI materials. In addition, the future prospect of alignment films for enhanced LC display is also described. Copyright © 2000 John Wiley & Sons, Ltd.

Polymerization of molten salt monomers having a phenylimidazolium group

Abstract: Several kinds of imidazolium salts having a phenyl group were prepared to investigate the property of room temperature molten salts. N-Alkylimidazoles were neutralized to obtain mono-alkylimidazolium salts (RImX) as model compounds of 1,3-dialkylimidazolium salts (R,R′ImX). Some of RImX salts formed room temperature molten salts. According to the data of RImX, alkyl group was selected for the design of R,R′ImX. R,R′ImX obtained through this procedure showed relatively high ionic conductivity about 10−4 S cm−1 at 30 °C. The polymers having these molten salt structures in the side chains were also prepared. The ionic conductivity of the obtained polymers in the bulk decreased to 10−6 S cm−1 at 30 °C. When lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added equimolarly to polymers, the glass transition temperature (Tg) decreased and their mechanical properties were improved from glassy solids to adhesive film. The ionic conductivity was improved up to 10−5 S cm−1. The introduction of a phenyl group into imidazolium salts was confirmed to be effective to improve the film property of molten salt polymers. Copyright © 2000 John Wiley & Sons, Ltd.

Molecular design and biosynthesis of biodegradable polyesters

Abstract: The last two decades have witnessed major discoveries in the field of bacterial polyesters, which makes it all the more promising as a potential biodegradable and biocompatible material. Based on the knowledge obtained, it is now possible to formulate methods to design and synthesize a particular type of bacterial polyester by manipulating biological systems. Poly([R]-3-hydroxybutyrate) [P(3HB)] is the most common bacterial homopolyester synthesized by almost all genera of the bacterial kingdom. The incorporation of other hydroxyalkanoate monomers into this homopolyester has resulted in the formation of various copolyesters with a common name polyhydroxyalkanoates (PHAs). Depending on the type and composition of the incorporated hydroxyalkanoate monomers, PHAs having a wide range of physical properties from crystalline polymers to rubber-like elastomers have been produced. In this paper, we have attempted to give an overview of recent developments in this field with particular emphasis on the findings that was made by our research group. In addition, we have also outlined the possible methods that can be used to design and synthesize biologically some of the PHAs of interest. Copyright © 2000 John Wiley & Sons, Ltd.

Polymerizable discoticnematic triphenylene derivatives and their application to an optically anisotropic film

Abstract: A novel optically anisotropic film which consists of discotic liquid crystalline molecules aligned and fixed in hybrid mode was invented. The discotic liquid crystalline molecules are polymerizable discotic nematic liquid crystalline triphenylene derivatives. The film is exceedingly useful for improvement in viewing angle of TFT-TN LCD. In the TFT-TN LCD, calamitic liquid crystal molecules which have positive birefringence in refractive property are used. This anisotropy causes light leakage and results in narrow range of the viewing angle of the LCD. It is, therefore, considered that compensation for the positive birefringence by using a negative birefringent material is the essential means for achievement of the wide viewing angle. The triphenylene derivatives are chosen as one of negative birefringent materials. In our study, discotic nematic phase was the most suitable liquid crystalline phase for preparation of the optically anisotropic film. Discotic nematic phase was frequently shown by 2,3,6,7,10,11-hexa-(4-alkoxybenzoyloxy)triphenylene derivatives. Some modification of the alkoxy group brought disappearance of the discotic nematic phase. Introduction of an acryloyl group to the alkoxy group at the terminal position, however, did not cause the disappearance of the discotic nematic phase. 2,3,6,7,10,11-hexa-(4-alkoxybenzoyloxy)triphenylene molecules were able to align on an obliquely vapor deposited SiO film and organic alignment films in the monodomain discotic nematic phase. In this case, the layer of the discotic molecules contacted with the alignment film only on one side and on the other side it contacted with air. Retardation data by an ellipsometric measurement suggested that the molecules aligned in hybrid mode. In the case of the acryloyl derivatives, alignment of the molecules was able to be fixed by photopolymerization of acryloyl moieties. According to the abovementioned method, a novel optically anisotropic film was produced. If alignment of the discotic molecules can be freely controlled, a new area of optically anisotropic film will be produced. Copyright © 2000 John Wiley & Sons, Ltd.

Novel polysaccharide hydrogels: characterization and properties

Abstract: New chemical hydrogels, potentially suitable for biomedical applications, have been synthesized and characterized by 13C NMR, and FT-IR spectroscopy. The polysaccharide components of these hydrogels are hyaluronane, alginate and carboxymethylcellulose, while the novel cross-linking procedure consists of activating the carboxylate moieties by 2-chloro-1-methylpyridinium iodide CMPJ and using 1,3-diaminopropane as a chemical bridge. Varying the amount of CMPJ three series of hydrogels were obtained with different cross-linking degrees (5, 50, 100%). Their percentages were determined by 13C NMR and FT-IR analysis. The morphology of the gels was studied by scanning electron-microscopy and the pore sizes were determined in order to find a relationship with the swelling properties. Cell adhesion, using human hepatocytes, and platelet adhesion studies on the different series of cross-linked compounds allowed us to envisage their utilization as extracellular matrix materials and cardiovascular biomaterials. Copyright © 2000 John Wiley & Sons, Ltd.

Modification of porous silica particles with poly(acrylic acid)

Abstract: The surface of porous silica particles was modified with poly(acrylic acid) by reacting the carboxyl groups on poly(acrylic acid) with the amino groups of pregrafted aminopropyltriethoxysilane (APS). The chemical modifications by APS and polymer were characterized by infrared spectroscopy and the amount of APS and poly(acrylic acid) grafted to the surface were determined by thermal gravimetric analyses. The wettability of the modified silica particles, based on the rate of water penetration, was pH-dependent with PAA; at pH 1.5 the wettability increased but at pH 5.5 it decreased dramatically. The pore size and size distribution of the silica particles decreased with APS and polymer grafting. Copyright © 2000 John Wiley & Sons, Ltd.

Enzymatic polymerization of aniline and phenol derivatives catalyzed by horseradish peroxidase in dioxane

Abstract: Phenylenediamines, 4-aminophenol and 1,4-hydroquinone were polymerized via the catalysis of horseradish peroxidase in dioxane at ambient conditions by using hydrogen peroxide as the oxidant. Polymers formed in good yields are black powders soluble in dimethylformamide and dimethylsulfoxide. Several factors influencing the polymer yield were examined using 2-phenylenediamine as substrate. It was found that pH value gave almost no influence in the range between 6.0 and 7.0, while the polymer yield increased as the concentration of the substrate in dioxane increased. The influence of the oxidant amount was still more obvious; larger excess of the oxidant being necessary in getting higher polymer yield. Using the optimized polymerization conditions, the yield of poly(2-phenylenediamine) was achieved up to 77.8%. Weight average molecular weight of the polymers are higher than 1 × 104 as determined by gel permeation chromatography. The structure of the polymers was characterized by using nuclear magnetic resonance and infrared techniques. Copyright © 2000 John Wiley & Sons, Ltd.

Insulation effect of an inclusion complex formed by polyaniline and ?-cyclodextrin in solution

Abstract: The insulation effect of an inclusion complex formed by polyaniline with emeraldine base as a conducting polymer and β-cyclodextrin as insulators of cyclic form has been studied using the oxidation by iodine in solution of N-methyl-2-pyrrolidone. When polyaniline is oxidized by iodine in the solution, the solution color changes from blue to violet. We observed little change in color at 273 K or a considerable delay of the spectral change at 288 K in the solution of the inclusion complex and iodine in contrast to that in solution of polyaniline and iodine without β-cyclodextrin. This suggests that the conjugated conducting polymer in the inclusion complex is almost completely insulated by the threaded cyclodextrin molecules from the chemical oxidation by iodine and that the oxidation at 288 K proceeds after the inclusion complex dissociates into polyaniline and cyclodextrin in the solution. Copyright © 2000 John Wiley & Sons, Ltd.

Theory on inclusion behavior between cyclodextrin molecules and linear polymer chains in solutions

Abstract: The inclusion–dissociation behavior in the complex formation between cyclodextrin molecules and linear polymer chains in solution is theoretically investigated by using a lattice model. The cyclodextrins cooperatively include or dissociate the linear polymer chain when the interaction energy between the adjacent cyclodextrins is strong. Copyright © 2000 John Wiley & Sons, Ltd.

Polysilane light‐emitting diodes

Abstract: This paper discusses the material factors which have led to a recent breakthrough in polysilane light-emitting diodes (LEDs) made from a diaryl polysilane, poly[bis(p-n-butylphenyl)silane] (PBPS), by comparing them with LEDs which employ a conventional polysilane, poly(methylphenylsilane). In contrast to LEDs based on conventional polysilanes in which a weak ultraviolet electroluminescence (EL) was detected either with a strong broad visible EL or only at low temperatures, room-temperature pure near-ultraviolet EL was observed with a quantum efficiency of 0.1% photons/electron with an electron injecting A1 electrode in PBPS-LEDs. We examined the spectroscopic, electronic and structural properties of PBPS, and ascribed to them the improvements observed in the EL characteristics. We also mention the possible future direction of polysilane LED research and other potential optoelectronics applications of polysilanes to the active medium of lasers. Copyright © 2000 John Wiley & Sons, Ltd.

Relationship between absorbed water and proton conductivity in sulfopropylated poly(benzimidazole)

Abstract: A novel proton-conducting polymer, sulfopropylated poly(benzimidazole) (PBI-PS), was synthesized by the ring-opening reaction of 1,3-propanesultone on the reactive N-H groups of PBI. Cast films of PBI-PS obtained from a dimethylsulfoxide solution of PBI-PS exhibited high water uptake, adequate mechanical strength, and flexibility. The temperature dependence of proton conductivity for PBI-PS films hydrated at 90% R.H. showed high proton conductivity of the order of 10−3 Scm−1 in the temperature range from room temperature to 140 °C, which is superior to those of conventional proton conducting polymers such as Nafion. The physical behavior of absorbed water in hydrous PBI-PS films was evaluated by differential scanning calorimetry (DSC), indicating that the absorbed water in PBI-PS mainly consisted of freezing bound water. Copyright © 2000 John Wiley & Sons, Ltd.

Various types of polydiacetylene microcrystals fabricated by reprecipitation technique and some applications

Abstract: The reprecipitation method is a useful technique to fabricate organic microcrystals such as polydiacetylene (PDA), low-molecular-weight aromatic compounds, organic functional dyes, which features are located in a mesoscopic phase between a single molecule and bulk crystals, and organic microcrystals are expected to exhibit peculiar optical and electronic properties. In the present article, the effects of added surfactants and temperature were investigated to develop and establish further the reprecipitation method to control crystal size, shape of PDA microcrystals. Especially, we were much interested in reprecipitation conditions and formation mechanism to form fibrous PDA microcrystals. In addition, as some trial applications, it has been successful to trap an isolated PDA microcrystal and to prepare well-defined PDA microcrystal thin film, using a layer-by-layer procedure. This technique utilized an electrostatic adsorption between microcrystals with highly negative ζ-potential in an aqueous dispersion liquid and polyelectrolyte (polycation) film. As a result, the value of χ(3)(ω) for the resulting layered PDA microcrystal thin film was confirmed to be enhanced by a factor of about 100, owing to concentration effect. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis and characterization of polycaprolactone (B)–poly(lactide-co-glycolide) (A) ABA block copolymer

Abstract: Novel poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL) ABA block copolymers were synthesized by bulk copolymerization of glycolide and lactide with PCL diols prepolymer using stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques including gel permeation chromatography, IR, 1H nuclear magnetic resonance, differential scanning calorimeter and X-ray diffractometry. Mechanical properties and hydrophilicity of the copolymers were also studied. Data showed that the copolymers presented a part-regular structure, containing both PCL crystalline and amorphous PLGA domains. The properties of these copolymers can be adjusted by changing the compositions of the copolymers. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis and heparin-like biological activity of amino acid-based polymers

Abstract: Biological macromolecules are important regulators of physiological functions. Most of the biologically active macromolecules are charged linear polymers like some proteins, DNA and glycosaminoglycans (GAG). Heparin, the first GAG applied in medicine, is a natural polyanion composed of repeating disaccharide units of glucosamine and uronic acid. The amino and hydroxyl groups of the glucosamine units are partially sulfated. Heparin is a potent anticoagulant, and is also active as an antimethastatic and antiproliferative agent. Sulfatation of other polysaccharides such as laminarin yielded very potent new anticoagulans. It was hypothesized that macromolecules based on N-acryl L-amino acids bearing hydrophobic or charged side groups, such as NH2, COOH, SH, OH and phenols, arranged into a configuration determined by the chirality of the amino acid α-carbon, may express heparin-like biological activities. Homo-poly(N-acryl amino acids) were synthesized from the corresponding monomers. Polymers with different charge densities, nature of the amino acid side group, stereoselectivity and polymeric backbone were tested for their activity as anticoagulants, heparanase inhibition agents, and to basic fibroblast growth factor (b-FGF) release agents bound to the extracellular matrix (ECM). The type of amino acid, the polymer backbone, the charge density and distribution strongly affect the biological activity exerted by these polyanions. All polymers being active either as heparanase inhibitors and/or as b-FGF release agents have at least a negative charge density of 1 per amino acid residue. Polymers bearing hydrophilic side chains that inhibited heparanase, i.e., hydroxyproline, glycine and serine, did not release b-FGF from ECM. The absence of high acidic sulfate-ester groups existing in heparin (hydrophilic) must be compensated by some kind of lipophilic interactions between the polyanion and b-FGF in order to effectively compete with heparan sulfate proteoglycanes, causing its release from ECM. Heparanase inhibitors may have clinical applications in preventing tumor metastasis and inflammatory/autoimmune processes due to the involvement of this enzyme in the extravasation of blood-borne tumor cells and activated cells of the immune system. Molecules that release ECM-bound b-FGF may be applied to accelerate neovascularization and tissue repair. Copyright © 2000 John Wiley & Sons, Ltd.

Polymeric materials for devices in optical fibre systems

Abstract: This paper reviews recent developments of polymers as materials for optical communication systems, including both fibres and components such as modulators, switches and sources. Optical communication systems involve a wide variety of component types for which the materials must combine high optical transparency at the transmission wavelength(s) with special functionality for the particular component concerned. Where the main fibres are themselves made of polymeric materials, the primary requirement is for the materials to have the lowest possible attenuation, but together with a high degree of mechanical strength, flexibility and durability. For optical modulators and switches, the more important property is a non-linear optical response to applied electric field. This behaviour is, however, linked to optical absorption processes, and careful materials design is necessary to achieve high non-linear response with acceptable attenuation at the operational wavelength. In other devices like arrayed waveguides and sources, the ability to undertake precision microfabrication is of paramount importance. The chief advantages of organic, polymeric materials over ceramics for these applications are undoubtedly their ease of use in device fabrication by conventional spin-coating and moulding methods, together with the potential to tune their optical properties by tailoring their molecular structure. The main challenge is to achieve the necessary lifetime and stability for commercial use. Copyright © 2000 John Wiley & Sons, Ltd.

Organic dye-doped polymer optical fiber laser

Abstract: We report on the lasing action of the graded-index polymer optical fibers containing dyes, such as Rhodamine B, Rhodamine 6G, Perylene orange and Pyrromethene 567. These dyes have been incorporated into poly(methyl methacrylate-co-2-hydroxyethyl methacrylate). These fibers were transversely pumped at 532 nm with a frequency-doubled Q-switched Nd–YAG laser. Slope efficiency of 24% and output of 1.2 mJ were obtained with a Rhodamine 6G-doped fiber. Lifetime of 200,000 pulses at 10 Hz was achieved with a Rhodamine B-doped fiber. Copyright © 2000 John Wiley & Sons, Ltd.

Nano-scale control of composite polymer films by mass-controlled layer-by-layer sequential adsorption of polyelectrolytes

Abstract: The mass of polyelectrolyte films adsorbed onto a surface during the deposition of a thin polymer film by a layer-by-layer sequential adsorption process was systematically controlled using a feedback system with a computer. For the deposition process, a quartz crystal microbalance (QCM) with an integrated oscillation circuit was attached to the arm of an automatic slide stainer and the frequency shift during adsorption or rinsing of the polyelectrolytes was monitored by a computer attached to a frequency counter. By feeding back the data acquired by the in situ QCM measurement, the mass of material deposited was controlled and a high quality self-assembly film was produced. This method is termed mass-controlled layer-by-layer sequential adsorption. The accuracy of the layer thickness in the multiplayer film was found to be approximately 1 nm. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis of novel fluorine-containing poly(aryl ether ketone)s

Abstract: The high-performance fluorinated polymers have been receiving considerable attention as interesting advanced materials. The incorporation of fluorine atoms into polymer chains leads to polymers with increased solubility, flame resistance, thermal stability and glass transition temperature while also leading to decreased color, crystallinity, dielectric constant and moisture absorption. 2,3,4,5,6-Pentafluorobenzoic acid (PFBA) is a valuable intermediate for pharmaceuticals, pesticides, perfumes, cosmetics and so on, and it is available as a commercial product. However, the polymers derived from PFBA have not been reported so far. In this paper, we report the synthesis and characterization of novel fluorinated poly(aryl ether ketone)s (PEKs) containing 2,3,5,6-tetrafluoro-1,4-phenylene moieties derived from PFBA. Novel fluorinated PEKs are prepared from PFBA by aromatic nucleophilic substitution reaction, of which Mn values range from 2.28 × 104 to 1.04 × 105. They have all para connected linear structures. The aromatic fluorine of the para position to the carbonyl groups of monomers is preferentially substituted by phenoxide and this para orientation is mainly attributed to the steric effect rather than π-electron density. The obtained PEKs except 8F-PEKEK (BP) show excellent solubilities in common solvents and can be cast into tough transparent films. They also exhibit high glass transition temperatures depending on the structures and outstanding thermal stabilities. Furthermore, these fluorine-containing PEKs exhibit low dielectric constants from 2.87 to 3.52 at 1 MHz. Copyright © 2000 John Wiley & Sons, Ltd.

Experimental investigation into mechanical destruction of intumescent chars

Abstract: The paper presents a broad discussion on the problem of mechanical destruction of intumescent chars in the application to fire protection of buildings in conditions of fires and protection of rocket engines in conditions of intensive mass and heat flows. Data on mechanical strength of various types of chars in hot and cold states are presented and discussed. Various methods are compared. The rheological approach to destruction is concerned. Some aspects of destruction behavior observed previously are explained. Copyright © 2000 John Wiley & Sons, Ltd.

Structured electrically conductive polyaniline/polymer blends

Abstract: This paper describes electrically conductive polymer blends consisting of polyaniline (PANI) dispersed in a polymer matrix. Melt blending of previously mixed, coagulated and dried aqueous dispersions of PANI and the polymer matrix lead to high conductivities at extremely low PANI concentrations (∼0.5 wt% PANI). In these blends the surface properties (surfactants used) of the PANI and the polymer particles play a major role in the structuring process, in addition to the very small size of the PANI particles. In another approach, i.e. conventional melt blending of PANI powder with a given polymer powder, the success of generating an efficient conductive network depends on the PANI/polymer interaction level. A high interaction level (for example, similar solubility parameters) leads under dynamic hot blending conditions to the formation of conductive networks, but still at relatively high PANI concentration (>10 wt% PANI). To further reduce the PANI conductivity threshold concentration, ternary PANI/polymer/polymer blends can be designed, in which PANI is selectively attracted to the minor polymer component, thus generating double-percolation structures. The threshold PANI concentration in the ternary blends may be reduced by a factor of ∼2 compared to the binary blends. Further reduction can be expected in special ternary blends designed so that the PANI particles will mostly locate at the interfaces, rather than within the dispersed minor polymer particles. The blending method of aqueous dispersions is limited to matrix polymers which can be synthesized by emulsion polymerization. Thus, the conventional melt blending procedure and also the formation of ternary blend systems are particularly beneficial for condensation-type polymers, whereas melt blending of PANI/polymer powders prepared by the aqueous dispersions method is beneficial for the addition-type polymers. Copyright © 2000 John Wiley & Sons, Ltd.

Biological activity of chitosan–sugar hybrids: specific interaction with lectin †

Abstract: The specific interactions between lectins and chitosan–sugar hybrids, the synthesized chitosan derivatives linking carbohydrate residue to the amino group of chitosan, were investigated. The specific bindings of chitosan-L-fucose (Fuc) hybrid with Ulex europaeus agglutinin I (UEA I, a lectin specific to L-Fuc), and chitosan-N-acetyl-D-glucosamine (D-GlcNAc) hybrid with Concanavalin A (Con A, a lectin specific to D-glucose, D-mannose and D-GlcNAc), were confirmed by a surface plasmon resonance technique. The microscopic observation of Pseudomonas aeruginosa, which was preincubated with the fluorescein isothiocyanate-labeled chitosan-L-Fuc hybrid, showed bacteria aggregation. The aggregation was thought to be resulted from the specific interaction of the L-Fuc residue of the hybrid with PA-II lectin on the surface of P. aeruginosa. The chitosan-L-Fuc hybrid inhibited P. aeruginosa growth more effectively in comparison with the other hybrids or unmodified chitosan. The enhancement of antimicrobial activity of chitosan-L-Fuc hybrid could be attributed to the specific binding between PA-II lectin of P. aeruginosa and L-Fuc residue of the L-Fuc hybrid. Copyright © 2000 John Wiley & Sons, Ltd.