Search

Polyimides (PIs) can be synthesized from diisocyanate and dianhydride through a direct heating one-step polymerization process with a lower temperature and shorter reaction time than the traditional stepwise heating route. This study discusses the properties of resulting PIs produced using the direct one-step heating procedure with N-methyl-2-pyrrolidinone (NMP) as the solvent. Based on the structural and property evaluations, the reaction system used yields not only organo-soluble PIs but also ultra-high thermal stability up to 580 °C at 5% weight loss. The obtained PIs have medium molecular weights ranging from 26.6 to 35.6 kg/mol. This reaction system is found to be fast and efficient in producing high thermoresistant PI materials with improved processing ability. These findings provided insights on the energy-efficient one-step synthesis of PIs specifically derived from diisocyanate and dianhydride. [ABSTRACT FROM AUTHOR]

In contrast to convective self-assembly methods for colloidal crystals etc., "convective meniscus splitting method" was developed to fabricate three-dimensionally ordered polymeric structures. By controlling the geometry of evaporative interface of polymer solution, a deposited membrane with uniaxial orientation and layered structures can be prepared. Here it is demonstrated that xanthan gum polysaccharide microparticles with diameter ~ 1 µm can bridge a millimeter-scale gap to form such a membrane because the capillary force among the particles is more dominant than the gravitational force on the evaporative interface. This method is applicable for various substrates with a wide range of wettability (water contact angle, 11°–111°), such as glass, metals, and plastics. The specific deposition can be also confirmed between frosted glasses, functional-molecules-modified glasses, and gold-sputtered substrates. By using such a universal method, the membrane formed on a polydimethylsiloxane surface using this method will provide a new strategy to design a functional polysaccharide wall in microfluidic devices, such as mass-separators. [ABSTRACT FROM AUTHOR]

4-Aminophenylalanine (4APhe), an exotic amino acid which is obtained as a microorganism metabolite of glucose, is polycondensed with various tetracarboxylic dianhydrides as a diamine monomer to obtain poly(amic acid)s. Subsequent thermal imidization of poly(amic acid)s is made at 220 °C with stepwise heating from 100 °C. Some of the obtained polyimides (PIs) exhibited good solubility in organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and more. The progress of imidization was observed by proton nuclear magnetic resonance and infrared spectroscopy to confirm that the imidization ratio was up to 98%. Carboxylate group of the side-chains of PIs affected their solubilities despite the high imidization ratio, and the solubility was lost for any organic solvents by decarboxylation at 280 °C, confirmed from mass-loss of thermogravimetric analysis. Thus, a new series of PIs were obtained with abilities of solvent-molding in PI state and thermal resistivity enhancement by further heating after molding. [ABSTRACT FROM AUTHOR]

Biomass plastics are expected to contribute to the establishment of a carbon-neutral society by replacing conventional plastics derived from petroleum. The biomass-derived aromatic amine 4-aminocinnamic acid (4ACA) produced by recombinant bacteria is applied to the synthesis of high-performance biopolymers such as polyamides and polyimides. Here, we developed a microbial catalyst that hydrogenates the α,β-unsaturated carboxylic acid of 4ACA to generate 4-aminohydrocinnamic acid (4AHCA). The ability of 10 microbial genes for enoate and xenobiotic reductases expressed in Escherichia coli to convert 4ACA to 4AHCA was assessed. A strain producing 2-enoate reductase from Clostridium acetobutylicum (ca2ENR) reduced 4ACA to 4AHCA with a yield of > 95% mol mol and reaction rates of 3.4 ± 0.4 and 4.4 ± 0.6 mM h OD at the optimum pH of 7.0 under aerobic and anaerobic conditions, respectively. This recombinant strain reduced caffeic, cinnamic, coumaric, and 4-nitrocinnamic acids to their corresponding propanoic acid derivatives. We polycondensed 4AHCA generated from biomass-derived 4ACA by dehydration under a catalyst to form high-molecular-weight poly(4AHCA) with a molecular weight of M = 1.94 MDa. This polyamide had high thermal properties as indicated by a 10% reduction in weight at a temperature of T = 394 °C and a glass transition temperature of T = 240 °C. Poly(4AHCA) derived from biomass is stable at high temperatures and could be applicable to the production of high-performance engineering plastics. [ABSTRACT FROM AUTHOR]

Bio-based polybenzoxazoles (PBOs) are prepared by polycondensation of diacid monomer derived from 3-amino-4-hydroxybenzoic acid with a series of aliphatic diamines. Resulting bio-based PBOs have high weight average molecular weight ranging 5.70-7.20 × 10 g/mol and show ultrahigh thermal resistance with T values over 400 °C and T values over 170 °C, which are higher than those of conventional bio-based polymers, polyamides 11 (around 60 °C) or poly(lactic acid) (56 °C). Especially hydrazide group of the bio-based PBO were cyclized to form diazole ring by annealing at 330 °C for 20 min. The resultant PBO show liquid crystalline (LC) behavior to spin fiber in a melting state. The resultant PBO fibers showed high values of Young's modulus and mechanical strength as compared with conventional polymers polyamide 11 and poly(lactic acid) (PLA). [ABSTRACT FROM AUTHOR]

Fully bio-based chitosan derivative was synthesized using 3-benzyl-2,5-diketopiperazine-6-acetic acid (DKP) activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. From IR and H NMR spectra, the structure of the bioconjugated chitosan and the quantitative modification were confirmed. Oil-in-water (o/w) emulsion of the obtained product was presented with the various ratios of water and benzene solution. Continuously the obtained o/w emulsions were freeze-dried to produce the mesoporous sponge, depended on the ratio of the water and benzene. These amphiphilic properties were observed by the property of the pendant DKP moieties in chitosan. The pore size in the sponges was controlled in a range from 0.1 to 0.3 μm by changing the solvent ratios. [ABSTRACT FROM AUTHOR]

The association of congenital pelvic kidney with abdominal aortoiliac aneurysm is an extremely rare clinical finding. Previous reports have described various methods of aneurysm repair with successful preservation of the function of pelvic kidney. However, to our knowledge, reconstruction of more than two renal arteries has not been established. We report a case of abdominal aortic aneurysm complicated by congenital right pelvic kidney in a 72-year-old man. Computed tomography (CT) revealed an abdominal aortic aneurysm with a maximum diameter of 54 mm and a right common iliac aneurysm of 45 mm. In addition, he had a congenital right pelvic kidney and CT angiography identified three right pelvic renal arteries. The upper artery originated from the bifurcation of the terminal aorta and the lower two originated from the right common iliac artery. Three-dimensional CT was helpful for the accurate planning of the operation. Open surgical repair of the aortoiliac aneurysm with a Dacron bifurcated graft replacement was decided and reimplantation of all three right pelvic kidney arteries to the right limb of the graft was also performed. For renal preservation, the right pelvic kidney arteries were perfused with cold Ringer's lactate using a rapid infusion pump and coronary perfusion cannula. The patient's postoperative course was uneventful, and worsening of renal function was not observed. The perfusion of renal arteries with cold Ringer's solution was thought to be a simple and appropriate procedure for renal protection. [ABSTRACT FROM AUTHOR]

Oriented films of the thermotropic liquid-crystalline (LC) polymer, poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)- co- trans-4-hydroxycinnamic acid (4HCA)} (Poly(3,4-BAHBA- co-4HCA)), were prepared by shearing the LC melt. X-Ray and polarized microscopy analyses indicated that the main chains were oriented perpendicularly to the shear direction, and the benzylidene amino side chains were parallely oriented. Furthermore, the oriented film showed polarized fluorescence in which the analyzer rotation changed the emission color when the polarizer was set perpendicular to the sheared direction. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A unicellular cyanobacterium that produces a large amount of exopolysaccharide (EPS) was isolated from a rice field in Phu Tho Province, Vietnam. Morphological characteristics and phylogenetic analysis using a partial sequence of the 16S rRNA gene revealed that the isolate was closely related to the genus Cyanothece. The isolate, named Cyanothece sp. Viet Nam 01, grew at a wide range of temperatures (25-40 °C), but was not viable below 20 °C. The isolate had an ability of aerobic nitrogen fixation. The EPS was purified using NaOH extraction and ethanol precipitation, and the absolute molecular weight was estimated to be 4.5 × 10 kDa. The pattern of the Fourier transform infrared spectrum indicated that the EPS had carbonyl and sulfate groups, as well as the typical functional groups of sugars. The uronic acid and sulfur contents were 23 and 8.4 mol% per total monosaccharide, respectively. The EPS constituent monosaccharides were rhamnose, glucose, galactose, xylose, mannose, fucose, arabinose, ribose, and unknown sugar, with molar compositions of 38.6:13.8:4.8:4.8:2.4:3.5:2.0:0.6:6.5, respectively. [ABSTRACT FROM AUTHOR]

Aromatic polymers include novel and extant functional materials although none has been produced from biotic building blocks derived from primary biomass glucose. Here we screened microbial aromatic metabolites, engineered bacterial metabolism and fermented the aromatic lactic acid derivative β-phenyllactic acid (PhLA). We expressed the Wickerhamia fluorescens gene ( pprA) encoding a phenylpyruvate reductase in Escherichia coli strains producing high levels of phenylalanine, and fermented optically pure (>99.9 %) D-PhLA. Replacing pprA with bacterial ldhA encoding lactate dehydrogenase generated L-PhLA, indicating that the produced enzymes converted phenylpyruvate, which is an intermediate of phenylalanine synthesis, to these chiral PhLAs. Glucose was converted under optimized fermentation conditions to yield 29 g/l d-PhLA, which was purified from fermentation broth. The product satisfied the laboratory-scale chemical synthesis of poly( d-PhLA) with M 28,000 and allowed initial physiochemical characterization. Poly( d-PhLA) absorbed near ultraviolet light, and has the same potential as all other biomass-derived aromatic bioplastics of phenylated derivatives of poly(lactic acid). This approach to screening and fermenting aromatic monomers from glucose exploits a new era of bio-based aromatic polymer design and will contribute to petroleum conservation and carbon dioxide fixation. [ABSTRACT FROM AUTHOR]

Anionic polysaccharide (PS) was extracted from Aphanothece stagnina biomaterials where trivalent metal ions were remarkably condensed from environmental water. Structural analyses indicated that the PS was considered to be a kind of sulfated rhamnoglucan-containing uronic acid at a composition of 23 mol% and that the total composition of anionic groups such as sulfate and carboxylate was 31 mol% to the monosaccharide residues. Since the PS was found to be a huge macromolecule with an ultra-high molecular weight (3.14 × 10 g/mol), the simple calculation indicated that about 9.5 × 10 anions exist on one chain of the PS. The electric conductivity of the highly anionic PS solutions indicated that the metal ions such as Ga, La, and Ca complexed ionically with PS chains. The PS formed the gels as a result of trivalent metal complexation, but the gelation behavior of the PS was different from that of the representative metal-complexable polysaccharide, alginate, in terms of the minimum gel formation concentration and the average molecular weight between cross-linking points. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Micromorphology memory was observed using thin films of PEGylated polypeptides, poly{(β-benzyl- L-aspartate) (BLA)-block-ethylene glycol (EG)-block-BLA}. The slow vaporization of polymer dichloromethane solutions led to the formation of multi-spherulite films, which disappeared upon heating above the PEG melting temperature, 57°C, but reappeared by successive cooling, down to 30 °C. thereby changing the spherulite interface morphology. The water-immersion of recrystallized films caused the self-assembly of peptide chains to form water-swollen networks with spherulites, but surprisingly, spherulite interface morphologies remained completely the same as once-disappeared morphologies in the original dry films. A similar memory behavior was also observed in the pattern inside a millisealed spherulite which entirely occupied the network. Spectroscopic and microscopic studies suggest that appropriate peptide conformations are very important for memorized micromorphology. [ABSTRACT FROM AUTHOR]

Aliphatic polyesters, such as poly(lactic acid), which degrade by hydrolysis, from naturally occurring molecules form the main components of biodegradable plastics. However, these polyesters have become substitutes for only a small percentage of the currently used plastic materials because of their poor thermal and mechanical properties. Polymers that degrade into natural molecules and have a performance closer to that of engineering plastics would be highly desirable. Although the use of a high-strength filler such as a bacterial cellulose or modified lignin greatly increases the plastic properties, it is the matrix polymer that determines the intrinsic properties of the composite. The introduction of an aromatic component into the thermoplastic polymer backbone is an efficient method to intrinsically improve the material performance. Here, we report the preparation of environmentally degradable, liquid crystalline, wholly aromatic polyesters. The polyesters were derived from polymerizable plant-derived chemicals—in other words, ‘phytomonomers’ that are widely present as lignin biosynthetic precursors. The mechanical performance of these materials surpasses that of current biodegradable plastics, with a mechanical strength, σ, of 63 MPa, a Young’s modulus, E, of 16 GPa, and a maximum softening temperature of 169 ∘C. On light irradiation, their mechanical properties improved further and the rate of hydrolysis accelerated. [ABSTRACT FROM AUTHOR]

Uniform nanospheres were prepared by dispersion copolymerization of n-butyl methacrylate (BMA) with poly(ethylene glycol) (PEG) macromonomers with p-vinylbenzyl end groups in various ethanol/water media. Particle size effects were investigated as a function of macromonomer molecular weight, solvent composition, and initial monomer and initiator concentrations. Hydrodynamic nanoparticle radii (Rh) followed the exponential law of initial initiator, St-PEG macromonomer and BMA concentrations. When reaction conditions were properly chosen, nanosphere particle size was controlled from ca. 40 to 750 nm in diameter. It was found that nanospheres swelled in ethanol/water dispersion media and the degree of swelling responded sensitively to solvent composition changes and reached a maximum at ethanol contents of 40-50 vol %. [ABSTRACT FROM AUTHOR]

Amphiphilic AB-type block copolymers of poly(styrene-block-N,N-dimethylacrylamide) (PSt-b-PDMAA) were successfully synthesized by atom transfer radical polymerization (ATRP) of DMAA initiated by bromide end-capped PSt (polydispersity = 1.08), PSt-Br, under an appropriate catalyst/ligand system of CuCl/ N,N,N′,N′,N″-pentamethyldiethylenetriamine, where PSt-Br was pre-synthesized by ATRP of St using ethyl-α-bromo-propionate as an initiator under CuCl/2,2-bipyridine. We investigated the self-assembly behavior of PSt-b-PDMAA with different polymerization degree (DP) of hydrophilic PDMAA block and a constant DP of PSt block in various aqueous milieus. The dynamic laser light scattering (DLLS) studies demonstrated that every PSt-b-PDMAA formed the self-assembled matters whose radii depended on both polymer and salt concentrations. Transmission electron microscope (TEM) and the chain length of PSt-b-PDMAA suggested that the present polymers formed vesicular assembly with a size-controllable hollow structure. [ABSTRACT FROM AUTHOR]

The surface sliding friction of chemically cross-linked poly(dimethyl siloxane) (PDMS) swollen with linear PDMS as an oligomer is investigated. The friction force f increases with the normal pressure P in a power-law relation f∝ Pα, where the exponent α changes in a range of 0-1, depending on the degree of polymerization, Npoly, of the linear PDMS oligomer. When Npoly is in a range of 240-320, a dramatic decrease in friction force is observed at a critical normal pressure, Pc, leading to a very low friction coefficient on the order of 10−3 at high-pressure ranges. The Pc increases with decreasing network size Nnetof the gel and also with increasing polymer length related to Npoly. One possible explanation for this transition phenomenon in friction is that linear PDMS molecules are exuded from the gel network beyond a certain pressure and behave as polymer brushes, which are able to reduce the friction. [ABSTRACT FROM AUTHOR]

Taxonomic diversity, physiological tolerance ranges, and nutrient utilization capabilities were determined for bacterial communities in Gulf of Alaska surface waters and sediments. Taxonomic diversity was assessed using Shannon Weaver ( H′) and equitability ( J′) indices. Physiological tolerance and nutritional versatility indices were developed to further assess the state of 'informational heterogeneity' within the bacterial communities. The Gulf of Alaska bacterial communities were characteristically diverse; the bacterial populations in these marine ecosystems generally were eurytolerant and nutritionally versatile. The maintenance of a high degree of informational heterogeneity was found to be characteristic of these bacterial communities. It appears to be of adaptive advantage to maintain diverse populations with physiological tolerances whose ranges exceed those experienced within the natural habitat, and for the bacterial communities to possess a high degree of nutritional versatility within these marine ecosystems. [ABSTRACT FROM AUTHOR]

An ecological study of Vibrio parahaemolyticus was carried out from December 1970 to December 1971 in the Rhode River of Chesapeake Bay. The annual cycle of the organism was elucidated and factors restricting its distribution in the estuary were described, including the association of the organism with zooplankton. Numerical taxonomy was employed for identification and classification of V. parahaemolyticus and related organisms on the basis of substrate utilization tests. From characteristics recorded for V. parahaemolyticus, it is concluded to be an estuarine organism. [ABSTRACT FROM AUTHOR]

This paper presents the results of unidirectional strain-controlled experiments on fibrous electrospun networks used to study damage formation during elongation. The experimental loading curve shows a symmetrical parabolic type dependence at large scale and saw tooth-like force−extension behaviour at small scale. The damage formation was quantified by determining the number and the magnitude of abrupt force drops. The experiments evidenced that damage evolution is a consequence of strain induced random events. The frequency distribution of the number of damages as well as the magnitude of rupture force were represented by histograms. The results of the present study provide a better insight into damage tolerance and complex nonlinear tensile properties of electrospun networks. In addition, it could suggest a possible probabilistic approach to the fiber bundle model which has mainly motivated this study. [ABSTRACT FROM AUTHOR]