Composite materials reinforced with polyoxymethylene whiskers

Various composite samples reinforced with polyoxymethylene (POM) whisker crystals were prepared and their Young's moduli were measured and analysed, on a theoretical equation, to estimate the modulus of the filler itself. Good reinforcement was obtained with matrix resins such as an epoxide and an unsaturated polyester, the results giving the modulus of the whisker to be approximately 1×10¹¹ N m^–2, i.e., almost equivalent to the ideal crystal modulus of POM. Some acoustic properties were investigated for sheet composite materials prepared with a polyolefin polymer for matrix. The sonic velocity attained was more than twice that of the matrix polymer, at larger filler contents, while the internal dynamic loss was maintained at a reasonably high level. Loudspeakers carrying diaphragms of the composite sheets showed improved frequency characteristics in the high-frequency region. Some morphological observations were made for the crystals embedded in resins.     

Study of local intracellular signals regulating axonal morphogenesis using a microfluidic device

The establishment and maintenance of axonal patterning is crucial for neuronal function. To identify the molecular systems that operate locally to control axonal structure, it is important to manipulate molecular functions in restricted subcellular areas for a long period of time. Microfluidic devices can be powerful tools for such purposes. In this study, we demonstrate the application of a microfluidic device to clarify the function of local Ca²⁺ signals in axons. Membrane depolarization significantly induced axonal branch-extension in cultured cerebellar granule neurons (CGNs). Local application of nifedipine using a polydimethylsiloxane (PDMS)-based microfluidic device demonstrated that Ca²⁺ entry from the axonal region via L-type voltage-dependent calcium channels (L-VDCC) is required for branch extension. Furthermore, we developed a method for locally controlling protein levels by combining genetic techniques and use of a microfluidic culture system. A vector for enhanced green fluorescent protein (EGFP) fused to a destabilizing domain derived from E. coli dihydrofolate reductase (ecDHFR) is introduced in neurons by electroporation. By local application of the DHFR ligand, trimethoprim (TMP) using a microfluidic device, we were able to manipulate differentially the level of fusion protein between axons and somatodendrites. The present study revealed the effectiveness of microfluidic devices to address fundamental biological issues at subcellular levels, and the possibility of their development in combination with molecular techniques.     

Chaotic transport in antidot lattices

A review is given of quantum effects and roles of chaos in transport in antidot lattices mainly from a theoretical point of view. The topics include diffusive orbits combined with a magnetic focusing effect as the origin of the commensurability peaks, semiclassical quantization of periodic orbits as the origin of the Aharonov-Bohm type oscillation superimposed, and the importance of inherent disorder in the antidot potential itself.     

Regulation of the polysialylated form of the neural cell adhesion molecule in the developing striatum: effects of cortical lesions

Early in development, the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) is expressed by growth cones, neuronal processes, and neuronal cell bodies. In rat striatum, PSA-NCAM expression becomes progressively restricted to pre- and postsynaptic membranes and is undetectable by postnatal day 25 (P25), i.e., after corticostriatal synaptogenesis. This study examined the effects of cortical lesions performed on P14, when the corticostriatal projection is already primarily unilateral and cortical inputs have not yet formed asymmetric synapses on striatal neurons. Rats were killed on P25, and PSA-NCAM expression was examined by immunoblotting and immunohistochemistry with light and electron microscopy. In contrast to the case in controls, PSA-NCAM expression was maintained in the striatum of lesioned pups. Ultrastructural studies showed that PSA-NCAM was present 1) in growth cone-like structures and neuronal processes and 2) in striatal neurons. Together with the presence of growth cones, the observation that the number of asymmetric synapses was unchanged in the denervated striatum suggests that axonal sprouting occurred in response to the lesion. This was confirmed by axonal labeling in the denervated striatum after injection of Fluoro-Ruby in the contralateral cortex. The data indicate that P14 cortical lesions affect PSA-NCAM expression in the developing striatum 1) by inducing a robust axonal plasticity resulting in the presence of immature presynaptic elements that contain PSA-NCAM and 2) by delaying the loss of PSA-NCAM expression in striatal neurons, suggesting that the lesion affects the time course of striatal maturation.     

Crosslinked polymer from N-vinylcarbazole and formalin

A crosslinked polymer has been synthesized from the reaction of N-vinylcarbazole and formalin in toluene in the presence of dry HCl gas. The copolycondensate is insoluble in all common solvents for poly-N-vinylcarbazole, and exhibits higher thermal stability than the unmodified poly-N-vinylcarbazole. However, this polymer is less thermally stable than the corresponding furfural modified poly-N-vinylcarbazole. A mechanism for the overall reaction has been suggested and the factors affecting the synthesis have been discussed.     

A role for N-methyl-D-aspartate receptors in the regulation of synaptogenesis and expression of the polysialylated form of the neural cell adhesion molecule in the developing striatum

Striatal development proceeds during a protracted postnatal period in rats. In the dorsolateral striatum, the number of asymmetric synapses, formed mostly by glutamatergic afferents innervating the dendritic spines of medium-sized striatal neurons, increases during the 3rd postnatal week and then rapidly declines before reaching adult levels. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM), which is widely expressed along neuronal membranes early in development, becomes progressively localized to synapses, and is no longer detectable in remaining synapses after synaptic pruning has occurred. Administration of MK-801, an antagonist of N-methyl-D-aspartate receptors, on day 20, either peripherally or locally into the striatum, decreases asymmetric synapse number by 30% and totally abolishes immunolabelling for PSA-NCAM in the dorsolateral striatum.     

Preparation and electrooptical properties of liquid crystal dispersed film by electron-beam irradiation

Polymer films consisting of nematic liquid crystal (LC) droplets and polymer networks were prepared by using a low-energy electron beam to irradiate a homogeneous mixture of nematic LC and bifunctional methacrylate monomer. Influences of such polymerization conditions as polymerization temperature, monomer concentration, and radiation energy on electrooptical properties of the compound films were examined. The polymer yield, affecting to a large extent the film properties, depended on the monomer concentration and the radiation energy. Compound films, which have a switching function from the scattering state to transparency by applying approximately 20–30 V between the two sides of the film, were obtained. In addition, it was found that a compound film with excellent electrooptical properties was prepared by changing impure LC in the droplets into pure LC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1675–1681, 1997     

Synthesis of polymer materials by low energy electron beam. I. Polyurethane–acrylate materials prepared by the EB and the UV solid-state polymerization

Structure and properties of films obtained by the electron beam (EB) and the ultraviolet light (UV) solid-state polymerization of polyurethane–acrylate prepolymer were examined to reveal the characteristics of these radiation polymerizations. The prepolymer was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate. EB polymerization behaviors of the prepolymer produced a unique polymer film different from that obtained by UV irradiation. Although polyurethane–acrylate films from the EB and the UV solid-state polymerizations consisted mainly of amorphous and crystalline phases, it was proved that the film from 10 Mrad of EB irradiation at 25°C had higher crystallinity and larger crystallite size than the film from UV irradiation. This is assumed to be due to the reason that EB irradiation below the melting point of the polyurethane–acrylate can lead to crosslinking without the destruction of the original crystalline structure. On the other hand, the UV polymerization proceeded with the melting of the crystalline structure by absorbing other lights than the UV absorbed by a photoinitiator. The EB-polymerized film which was crosslinked more densely than the UV-polymerized film showed higher mechanical strength than the latter film.     

Polymeric reaction of acrylic polymer–monomer system irradiated by low energy electron beam. I. Effects of molecular weight of polymer and polymer-to-monomer ratio

Polymeric reaction of the poly(n-butyl acrylate) (PBA)–benzyl acrylate (BzA) system induced by a low-energy electron beam was investigated. In order to elucidate the reaction behavior of the PBA–BzA system, the gel fraction, molecular weight of soluble part, and molecular weight distributions were examined by means of gel permeation chromatography (GPC) equipped with both ultraviolet (UV) and refractive index (RI) detectors. RI-detected GPC curves represented the molecular weights and their distributions of the total polymers, graft polymer, homopolymer, and unreacted PBA, while UV-detected curves only corresponded to the benzyl groups of graft polymer and homopolymer. Thus, the reaction behavior of the system was able to be followed by GPC. The molecular weight of the added PBA and the mole ratio of PBA/BzA were varied. The crosslinking, the graft reaction and the homopolymerization of BzA proceeded competitively during the polymeric reaction. The proportions of BzA unit incorporated into the crosslinked, graft and homo polymers were estimated by combining of measurement of gel fraction, UV-detected GPC curves, and infrared (IR) spectrum of gel. It was revealed that in the system containing PBA with high molecular weight, the grafting, and the crosslinking reactions predominated. The main reaction was the grafting in the system with a high mole ratio of PBA/BzA, while it was the homopolymerization in the systems with the low mole ratio of PBA/BzA. The reaction mechanism is discussed on the basis of reactivity and mobility of polymer radicals.     

The effect of the counter-anion on the steric structure of poly(alkenyl ether)s in cationic polymerization

Ethyl propenyl and butenyl ethers were polymerized in toluene at –78°C by a variety of catalysts, and effect of a counter-anion on steric structure of the polymer was investigated. The trans monomer produced stereoregular polymer with threo-meso structure and its content was independent of kind of the catalysts. In the polymerization of the cis monomer, the contents of the threo-meso and racemic structures of the poly(cis-propenyl ether) depended on the kind of the catalysts whereas those of the poly (cis-butenyl ether) having bulky -ethyl groups did not. The difference of the counter-anion effect was discussed on the basis of the difference of the -substituent in bulkiness.Stereochemistry in Cationic Polymerization of Alkenyl Ethers. Part 4.