Showing papers in "Macromolecular Research in 2009"

Electrospun Antimicrobial Polyurethane Nanofibers Containing Silver Nanoparticles for Biotechnological Applications

Abstract: In this study, a new class of polyurethane (PU) nanofibers containing silver (Ag) nanoparticles (NPs) was synthesized by electrospinning. A simple method that did not depending on additional foreign chemicals was used to self synthesize the silver NPs in/on PU nanofibers. The synthesis of silver NPs was carried out by exploiting the reduction ability of N,N-dimethylformamide (DMF), which is used mainly to decompose silver nitrate to silver NPs. Typically, a sol-gel consisting of AgNO3/PU was electrospun and aged for one week. Silver NPs were created in/on PU nanofibers. SEM confirmed the well oriented nanofibers and good dispersion of pure silver NPs. TEM indicated that the Ag NPs were 5 to 20 nm in diameter. XRD demonstrated the good crystalline features of silver metal. The mechanical properties of the nanofiber mats showed improvement with increasing silver NPs content. The fixedness of the silver NPs obtained on PU nanofibers was examined by harsh successive washing of the as-prepared mats using a large amount of water. The results confirmed the good stability of the synthesized nanofiber mats. Two model organisms,E. coli andS. typhimurium, were used to check the antimicrobial influence of these nanofiber mats. Subsequently, antimicrobial tests indicated that the prepared nanofibers have a high bactericidal effect. Accordingly, these results highlight the potential use of these nanofiber mats as antimicrobial agents.

Fabrication of PHBV/keratin composite nanofibrous mats for biomedical applications

Abstract: Keratin is an important protein used in wound healing and tissue recovery. In this study, keratin was modified chemically with iodoacetic acid (IAA) to enhance its solubility in organic solvent. Poly(hydroxybutylate-co-hydroxyvalerate) (PHBV) and modified keratin were dissolved in hexafluoroisopropanol (HFIP) and electrospun to produce nanofibrous mats. The resulting mats were surface-characterized by ATR-FTIR, field-emission scanning electron microscopy (FE-SEM) and electron spectroscopy for chemical analysis (ESCA). The purem-keratin mat was cross-linked with glutaraldehyde vapor to make it insoluble in water. The biodegradation testin vitro showed that the mats could be biodegraded by PHB depolymerase and trypsin aqueous solution. The results of the cell adhesion experiment showed that the NIH 3T3 cells adhered more to the PHBV/m-keratin nanofibrous mats than the PHBV film. The BrdU assay showed that the keratin and PHBV/m-keratin nanofibrous mats could accelerate the proliferation of fibroblast cells compared to the PHBV nanofibrous mats.

In Situ Microfluidic Synthesis of Monodisperse PEG Microspheres

Abstract: This study presents a microfluidic method for the production of monodisperse poly(ethylene glycol) (PEG) microspheres using continuous droplet formation and in situ photopolymerization in microfluidic devices. We investigated the flow patterns for the stable formation of droplets using capillary number and the flow rate of the hexadecane phase. Under the stable region, the resulting microspheres showed narrow size distribution having a coefficient of variation (CV) of below 1.8%. The size of microspheres (45∼95 ώm) could be easily controlled by changing the interfacial tension between the two immiscible phases and the flow rates of the dispersed or continuous phase.

Effects of silicone surfactant on the cell size and thermal conductivity of rigid polyurethane foams by environmentally friendly blowing agents

Abstract: Rigid polyurethane foams (PUF)s were synthesized with environmentally friendly blowing agents such as a cyclopentane/distilled water (10.0/1.0, pphp) mixture and distilled water only for four different silicone surfactants having different silicone/polyether ratios. An attempt was made to reduce the thermal conductivities of the PUF samples by varying the concentration and the silicone/polyether ratio of the various silicone surfactants. The scanning electron microscopy (SEM) results indicated an optimum concentration of the silicone surfactant of about 1.5 to 2.5 phpp for various surfactants to reduce the cell size and lower the thermal conductivity. The silicone surfactant having a higher silicone/polymer ratio showed a smaller cell size and, therefore, demonstrated the lower thermal conductivity of the PUF samples. From the relation between the thermal conductivity and the cell size of the PUF samples, the smaller cell size improved the thermal insulation property of the rigid PUF for both the PUF samples blown by the cyclopentane/distilled water (10.0/1.0, pphp) mixture and distilled water only. If the blowing agent is fixed, then the cell size is an important factor to decrease the thermal conductivity of the PUF samples. These results indicated that rigid PUF samples having lower thermal conductivity can be obtained by choosing a silicone surfactant containing a higher silicone/polyether ratio, as well as an optimum content of the surfactant.

Effect of multi-walled carbon nanotube dispersion on the electrical, morphological and rheological properties of polycarbonate/multi-walled carbon nanotube composites

Abstract: The effect of a multiwalled carbon nanotube (MWCNT) dispersion on the electrical, morphological and rheological properties of polycarbonate (PC)/MWCNT composites was investigated, with and without pretreating the MWCNTs with hydrogen peroxide oxidation and lyophilization. The resulting PC/treated MWCNT composites showed higher electrical conductivity than the PC/untreated MWCNT composites. The morphological behavior indicated the treated composites to have greater dispersion of MWCNTs in the PC matrix. In addition, the electromagnetic interference shielding efficiency (EMI SE) of the treated composites was higher than that of the untreated ones. Rheological studies of the composites showed that the complex viscosity of the treated composites was higher than the untreated ones due to increased dispersion of the MWCNTs in the PC matrix, which is consistent with the electrical conductivity, EMI SE and morphological studies of the treated composites. The latter results suggested that the increased electrical conductivity and EMI SE of the treated composites were mainly due to the increased dispersion of MWCNTs in the PC matrix.

Thermal and dynamic-mechanical characterization of rice-husk filled polypropylene composites

Abstract: Natural fiber-filled polymer composites have attracted great interest due to increasing environmental concerns and their low costs. In this study, the properties of rice husk flour-filled polypropylene (PP) were anal- ysed in view of the large quantities of this agricultural product available as residue in Brazil. The rice husk flour (RHF) was characterized by SEM and particle size distribution. The properties of the composites were studied by MFI, DMA, DSC and TGA analyses. A commercial PP modified with maleic anhydride (MAPP) was used as coupling agent. It was verified that RHF decreased the MFI of the composites and that the coupling agent decreased it even more. The efficiency of MAPP was confirmed by the high storage modulus and high loss factor of the coupled composites.

Silk Protein as a Fascinating Biomedical Polymer: Structural Fundamentals and Applications

Abstract: Silk is a textile material, as well as one of the oldest biomaterials. However, the recent progress of biomedical science and technology has led to the replacement of silk by various biomaterials based on synthetic polymers. Despite the wide variety of biomaterials available, these materials suffer certain limitations that prevent them from meeting the various demands of the medical field. Therefore, silk continues to attract considerable interest as a promising biomaterial. This paper explains the fundamentals of silk protein, and reviews the many applications of silk biomedical polymers.

Comparing the Effect of Three Processing Methods for Modification of Filament Yarns with Inorganic Nanocomposite Filler and their Bioactivity against Staphylococcus aureus

Abstract: This research compared three methods for producing and processing nanocomposite polypropylene filament yarns with permanent antimicrobial efficiency. The three methods used to mix antimicrobial agents based on silver nano particles with PP were as follows: 1) mixing of PP powder and inorganic nanocomposite filler with the appropriate concentration using a twin-screw extruder and preparing granules, 2) method 1 with a singlerather than twin-screw extruder, and 3) producing the masterbatch by a twin-screw extruder and blending it with PP in the melt spinning process. All pure polypropylene samples and other combined samples had an acceptable spinnability at the spinning temperature of 240 °C and take-up speed of 2,000 m/min. After producing as-spun filament yarns by a pilot plant, melt spinning machine, the samples were drawn, textured and finally weft knitted. The physical and structural properties (e.g., linear density, tenacity, breaking elongation, initial modulus, rupture work, shrinkage and crystallinity) of the as-spun and drawn yarns with constant and variable draw ratios (the variable draw ratio was used to gain a constant breaking elongation of 50%) were investigated and compared, while DSC, SEM and FTIR techniques were used to characterize the samples. Finally, the antibacterial efficiency of the knitted samples was evaluated. The experimental results revealed that the crystallinity reduction of the as-spun yarn obtained from method 1 (5%) was more than that of method 2 (3%), while the crystallinity of the modified as-spun yarns obtained with method 3 remained unchanged compared to pure yarn. However, the drawing procedure compensated for this difference. By applying methods 2 and 3, the drawing generally improved the tenacity and modulus of the modified fibers, whereas method 1 degraded the constant draw ratio. Although the biostatic efficiency of the nanocomposite yarns was excellent with all three methods, the modified fabrics obtained from methods 1 and 2 showed a higher bioactivity.

Effects of PP-g-MAH on the Mechanical, morphological and rheological properties of polypropylene and poly(acrylonitrile-butadiene-styrene) blends

Abstract: The effects of maleic anhydride-grafted polypropylene (PP-g-MAH) addition on polypropylene (PP) and poly(acrylonitrile-butadiene-styrene) (ABS) blends were studied. Blends of PP/ABS (70/30, wt%) with PP-g-MAH were prepared by a twin-screw extruder. From the results of mechanical testing, the impact, tensile and flexural strengths of the blends were maximized at a PP-g-MAH content 3 phr. The increased mechanical strength of the blends with the PP-g-MAH addition was attributed to the compatibilizing effect of the PP and ABS blends. In the morphological studies, the droplet size of ABS was minimized (6.6 μm) at a PP-g-MAH content of 3 phr. From the rheological examination, the complex viscosity was maximized at a PP-g-MAH content of 3 phr. These mechanical, morphological and rheological results indicated that the compatibility of the PP/ABS (70/30) blends is increased with PP-g-MAH addition to an optimum blend at a PP-g-MAH content of 3 phr.

SBR/organoclay nanocomposites for the application on tire tread compounds

Abstract: N,N-dimethyldodecylamine (tertiary amine)-modified MMT (DDA-MMT) was prepared as an organically modified layered silicate (OLS), after which styrene-butadiene rubber (SBR) nanocomposites reinforced with the OLS were manufactured via the latex method. The layer distance of the OLS and the morphology of the nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). By increasing the amount ofN,N-dimethyldodecylamine (DDA) up to 2.5 g, the maximum values of torque, tensile strength and wear resistance of the SBR nanocomposites were increased due to the increased dispersion of the silicate layers in the rubber matrix and the increased crosslinking of the SBR nanocomposites by DDA itself. When SBR nanocomposites were manufactured by using the ternary filler system (carbon black/silica/OLS) to improve their dynamic properties as a tire tread compound, the tan δ (at 0 °C and 60 °C) property of the compounds was improved by using metal stearates instead of stearic acid. The mechanical properties and wear resistance were increased by direct substitution of calcium stearate for stearic acid because the filler-rubber interaction was increased by the strong ionic effect between the calcium cation and silicates with anionic surface. However, as the amount of calcium stearate was further increased above 0.5 phr, the mechanical properties and wear resistance were degraded due to the lubrication effect of the excessive amount of calcium stearate. Consequently, the SBR/organoclay nanocomposites that used carbon black, silica, and organoclay as their ternary filler system showed excellent dynamic properties, mechanical properties and wear resistance as a tire tread compound for passenger cars when 0.5 phr of calcium stearate was substituted for the conventionally used stearic acid.

Preparation, Properties and Application of Polyamide/Carbon Nanotube Nanocomposites

Abstract: The discovery of carbon nanotubes (CNTs) has opened up exciting opportunities for the development of novel materials with desirable properties. The superior mechanical properties and excellent electrical conductivity make CNTs a good filler material for composite reinforcement. However, the dispersal of CNTs in a polymer solution or melt is difficult due to their tendency to agglomerate. Many attempts have been made to fully utilize CNTs for the reinforcement of polymeric media. Therefore, different types of polymer/CNTs nanocomposites have been synthesized and investigated. This paper reviews the current progress in the preparation, properties and application of polyamide/CNTs (nylon/CNTs) nanocomposites. The effectiveness of different processing methods has increased the dispersive properties of CNTs and the amelioration of their poor interfacial bonding. Moreover, the mechanical properties are significantly enhanced even with a small amount of CNTs. This paper also discusses how reinforcement with CNTs improves the electrical thermal and optical properties of nylon/CNTs nanocomposites.

Sintering and consolidation of silver nanoparticles printed on polyimide substrate films

Abstract: We investigated the sintering and consolidation phenomena of silver nanoparticles under various thermal treatment conditions when they were patterned by a contact printing technique on polyimide substrate films. The sintering of metastable silver nanoparticles commenced at 180 °C, where the point necks were formed at the contact points of the nanoparticles to reduce the overall surface area and the overall surface energy. As the temperature was increased up to 250 °C, silver atoms diffused from the grain boundaries at the intersections and continued to deposit on the interior surface of the pores, thereby filling up the remaining space. When the consolidation temperature exceeded 270 °C, the capillary force between the spherical silver particles and polyimide flat surface induced the permanent deformation of the polyimide films, leaving crater-shaped indentation marks. The bonding force between the patterned silver metal and polyimide substrate was greatly increased by the heat treatment temperature and the mechanical interlocking by the metal particle indentation.

effects of Nucleating Agents on the Morphological, Mechanical and Thermal Insulating Properties of Rigid Polyurethane Foams

Abstract: This study examined the effects of liquid and solid additives on the morphological, mechanical and thermal insulating properties of rigid polyurethane foams (PUFs). The PUFs synthesized with tetramethylsilane (TEMS) as a liquid-type additive showed a smaller average cell size and lower thermal conductivity than those with the aerosil 200 and clay 30B as solid-type additives. When TEMS was added, the average cell size of the PUF became more uniform and finer due to the reduced surface tension of the polymer solution, which increased the nucleation rate and number of bubbles produced and reduced cell size. The PUFs with TEMS showed the highest closed cell contents among the PUFs prepared using TEMS, aerosil 200 and clay 30B. This suggests that the insulation properties of PUF can be determined by both the size of the cell structure and the amount of closed cell contents in the system. The compression and flexural strengths of the PUF increased slightly when the aerosil 200, clay 30B and TEMS were added compared those of the neat PUF. The reaction profiles of the PUFs showed a similar gel and tack free time with the reaction time among the PUFs synthesized with three different additives and neat PUF. This suggests that the nucleating additives used in this study do not affect the bubble growth of the chemical reaction, and the additives may act as nucleating agents during the formation of PUF. From the above results of the cell size, thermal conductivity, closed cell contents and reaction profile of the PUFs, liquid-type nucleating agent, such as TEMS, is more effective in decreasing the thermal conductivity of the PUF than solid-type nucleating agent, such as aerosil 200 and clay 30B.

Polymer inkjet printing: Construction of three-dimensional structures at micro-scale by repeated lamination

Abstract: Solution-based, direct-write patterning by an automated, computer-controlled, inkjet technique is of particular interest in a wide variety of industrial fields. We report the construction of three-dimensional (3D), micropatterned structures by polymer inkjet printing. A piezoelectric, drop-on-demand (DOD) inkjet printing system and a common polymer, PVA (poly(vinyl alcohol)), were explored for 3D construction. After a systematic preliminary study with different solvent systems, a mixture of water and DMSO was chosen as an appropriate solvent for PVA inks. The use of water as a single solvent resulted in frequent PVA clogging when the nozzles were undisturbed. Among the tested polymer ink compositions, the PVA inks in a water/DMSO mixture (4/1 v/v) with concentrations of 3 to 5 g/dL proved to be appropriate for piezoelectric DOD inkjet printing because they were well within the proper viscosity and surface tension range. When a dot was printed, the so-called ‘coffee-ring effect’ was significant, but its appearance was not prominent in line printing. The optimal polymer inkjet printing process was repeated slice after slice up to 200 times, which produced a well-defined, 3D micro-patterned surface. The overall results implied that piezoelectric DOD polymer inkjet printing could be a powerful, solid-freeform, fabrication technology to create a controlled 3D architecture.

Synthesis and properties of novel flame-retardant and thermally stable poly(amideimide) s fromN,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids and phosphine oxide moiety by two different methods

Abstract: N,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids3a-g were synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride1 with two equimolars of Lalanine2a, L-valine2b, L-leucine2c, L-isoleucine2d, L-phenyl alanine2e, L-2-aminobutyric acid2f and L-histidine2g in an acetic acid solution. Seven new poly(amide-imide)s PAIs5a-g were synthesized through the direct polycondensation reaction of seven chiralN,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids3a-g with bis(3-amino phenyl) phenyl phosphine oxide4 by two different methods: direct polycondensation in a medium consisting ofN-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl2)/pyridine (py), and direct polycondensation in a tosyl chloride (TsCl)/pyridine (py)/N,N-dimethylformamide (DMF) system. The polymerization reaction produced a series of flame-retardant and thermally stable poly(amide-imide)s5a-g with high yield. The resulted polymers were fully characterized by FTIR,1H NMR spectroscopy, elemental analyses, inherent viscosity, specific rotation and solubility tests. Data obtained by thermal analysis (TGA and DTG) revealed that the good thermal stability of these polymers. These polymers can be potentially utilized in flame retardant thermoplastic materials.

Bioconjugation of Poly(poly(ethylene glycol) methacrylate)-Coated Iron Oxide Magnetic Nanoparticles for Magnetic Capture of Target Proteins

Abstract: Chemical modification of magnetic nanoparticles (MNPs) with functional polymers has recently gained a great deal of attention because of the potential application of MNPs toin vivo andin vitro biotechnology. The potential use of MNPs as capturing agents and sensitive biosensors has been intensively investigated because MNPs exhibit good separation-capability and binding-specificity for biomolecules after suitable surface functionalization processes. In this work, we demonstrate an efficient method for the surface modification of MNPs, by combining surface-initiated polymerization and the subsequent conjugation of the biologically active molecules. The polymeric shells of non-biofouling poly(poly(ethylene glycol) methacrylate) (pPEGMA) were introduced onto the surface of MNPs by surface-initiated, atom transfer radical polymerization (SI-ATRP). With biotin as a model of biologically active compounds, the polymeric shells underwent successful post-functionalization via activation of the polymeric shells and bioconjugation of biotin. The resulting MNP hybrids showed a biospecific binding property for streptavidin and could be separated by magnet capture.

Effect of Crosslinking Agents on the Morphology of Polymer Particles Produced by One-Step Seeded Polymerization

Abstract: One-step seeded polymerization was used to prepare 7∼10 μm of crosslinked monodisperse spheres with four crosslinking agents using 468 μm poly(methyl methacrylate) (PMMA) seed particles in aqueous-alcoholic media in the absence of the swelling process The crosslinking agents used were ethylene glycol dimethacrylate (EGDMA), allyl methacrylate (AMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane trimethacrylate (TMPTMA) The effects of the type and concentration of the crosslinking agents on the swelling, pore size, thermal property of the networks and morphology of the particles were studied The chemical structures and concentrations of the crosslinking agents affected both the swelling ratio and the porosity of the networks In addition, the chemistry of the reactive vinyl group and chain length of the crosslinking agents affected the stability of the monodisperse particles of the ultimate morphology

Formation of poly(ethylene glycol)-poly(ε-caprolactone) Nanoparticles via Nanoprecipitation

Abstract: Size control of therapeutic carriers in drug delivery systems has become important due to its relevance to biodistribution in the human body and therapeutic efficacy. To understand the dependence of particle size on the formation condition during nanoprecipitation method, we prepared nanoparticles from biodegradable, amphiphilic block copolymers and investigated the particle size and structure of the resultant nanoparticles according to various process parameters. We synthesized monomethoxy poly(ethylene glycol)-poly(e-caprolactone) block copolymer, MPEG-PCL, with different MPEG/PCL ratios via ring opening polymerization initiated from the hydroxyl end group of MPEG. Using various formulations with systematic change of the block ratio of MPEG and PCL, solvent choice, and concentration of organic phase, MPEG-PCL nanoparticles were prepared through nanoprecipitation technique. The results indicated that (i) the nanoparticles have a dual structure with an MPEG shell and a PCL core, originating from self-assembly of MPEG-PCL copolymer in aqueous condition, and (ii) the size of nanoparticles is dependent upon two sequential processes: diffusion between the organic and aqueous phases and solidification of the polymer.

Effect of Hot Pressing/Melt Mixing on the Properties of Thermoplastic Polyurethane

Abstract: In-depth understanding of the influence of hot pressing and melt processing on the properties of thermoplastic polyurethane (TPU) is critical for effective mechanical recycling of TPU scraps. Therefore, this study focused on the effects of hot pressing and melt mixing on molecular weight (MW), polydispersity index (PDI), melt index (MI), characteristic IR peaks, hardness, thermal degradation and mechanical properties of TPU. The original TPU pellet (o-TPU) showed two broad peaks at lower and higher MW regions. However, four TPU film samples, TPU-0 prepared only by hot pressing of o-TPU pellet and TPU-1, TPU-2 and TPU-3 obtained by hot pressing of melt mixed TPUs (where the numbers indicate the run number of melt mixing), exhibited only a single peak at higher MW region. The TPU-0 film sample had the highest Mn and the lowest PDI and hardness. The TPU-1 film sample had the highest Mw and tensile modulus. As the run number of melt mixing increased, the peak-intensity of hydrogen bonded C=O stretching increased, however, the free C=O peak intensity, tensile strength/elongation at break and average MW decreased. All the samples showed two stage degradations. The degradation temperatures of TPU-0 sample (359 °C and 394 °C) were higher than those of o-TPU (342 °C and 391 °C). While all the melt mixed samples degraded at almost the same temperature (365 °C and 381 °C). The first round of hot pressing and melt mixing was found to be the critical condition which led to the significant changes ofM n /M w /PDI, MI, mechanical property and thermal degradation of TPU.

The Performance of Nafion-Based IPMC Actuators Containing Polypyrrole/Alumina Composite Fillers

Abstract: A polypyrrole (PPy)/alumina composite filler prepared via in-situ polymerization of pyrrole on alumina particles was incorporated into Nafion® to improve the performance of ionic polymer-metal composite (IPMC) actuators. The IPMCs with the pristine PPy without alumina support did not show bending displacements superior to that of the bare Nafion-based IPMC, except at a high PPy content of 4 wt%. This result was attributed to the low redox efficiency of the PPy alone in the IPMC and may have also been related to the modulus of the IPMC. However, at the optimized filler contents, the cyclic displacement of the IPMCs bearing the PPy/alumina filler was 2.2 times larger than that of the bare Nafion-based IPMC under an applied AC potential of 3 V at 1 Hz. Even under a low AC potential of 1.5 V at 1 Hz, the displacement of the PPy/alumina-based IPMCs was a viable level of performance for actuator applications and was 2.7 times higher than that of the conventional Nafion-based IPMC. The generated blocking force was also improved with the PPy/alumina composite filler. The greatly enhanced performance and the low-voltage-operational characteristic of the IPMCs bearing the PPy/alumina filler were attributed to the synergic effects of the neighboring alumina moiety near the PPy moiety involving electrochemical redox reactions.

Studies on Properties of Polyaniline-Dodecylbenzene Sulfonic Acid Composite Films Synthesized Using Different Oxidants

Abstract: Two types of nano composite were obtained by in situ chemical method in polyaniline (PANI)/dodecyl- benzenesulfonic acid (DBSA) system depending on the use of either ammonium persulfate (APS) or ferric chloride (FeCl ) as the oxidant. In order to study the difference of the two composites in the surface characteristics, thermal stability, and electric properties, the composite films were studied by transmission electron microscopy (TEM), X- ray diffraction (XRD), thermogravimetric analysis (TGA), and temperature dependent DC electrical conductivity. The results revealed a large difference in the surface morphology, thermal stability, and the microstructure properties between the two composites, and these differences were considered responsible for the molecular order and conduc- tivity.

DSC Analysis on Water State of Salvia Hydrogels

Abstract: The role of the water structure present in hydrogels from nutlets of three species of salvias,S. miltiorrhiza (SM),S. sclarea (SS) andS. viridis (SV), was analyzed by differential scanning calorimetry (DSC). The sharp endothermic peaks that appeared at 5.9 °C (SM), 2.8 °C (SS) and 1.8 °C (SV) in each 1.0% hydrogel of 10.4–15.8% were not affected by addition of 0.1 M urea and alkali-metal salts. The order-disorder portions in the network were slightly affected by the distribution of freezable and non-freezable water in the hydrogel networks. The SV hydrogel was further used to investigate the effects of additives (0.1–8.0 M urea and 0.1–5.0 M NaCl) on its melting behavior. At 0.5–4.0 M urea and 1.0–3.0 M NaCl, two endothermic peaks appeared, corresponding to unbound (high temperature) and bound (low temperature) water in the gel networks, and eventually merged into one endothermic peak at 5.0–8.0 M urea and 4.0–4.5 M NaCl. After this merger, the endothermic peak shifted to 3.7, 4.0 and 5.6 °C at 5.0, 6.0 and 8.0 M urea, respectively. In the case of NaCl, a combination of peaks that occurred at 4.0–4.5 M were accompanied by a shift to lower temperature (−14.4 and 15.3 °C) and the endothermic peak finally disappeared at 5.0 M NaCl due to the strong binding of water in the gel networks.

Optically active and organosoluble poly(amide-imide)s derived fromN,N′-(Pyromellitoyl)bis-l-histidine and various diamines: Synthesis and characterization

Abstract: An optically active diacid containing the L-histidine moiety was prepared by reacting pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic acid 1,2,4,5-dianhydride)1 withl-histidine2 in acetic acid, and was polymerized with several aromatic diamines5a-g to obtain a new series of optically active poly(amide-imide)s (PAIs) using two different methods, such as direct polycondensation in a medium consisting ofN-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl2)/pyridine (Py) and direct polycondensation in a tosyl chloride (TsCl)/pyridine (Py)/N,N-dimethylformamide (DMF) system as a condensation agent. The resulting new polymers6a-g with inherent viscosity was obtained in good yield. The polymers were readily soluble in polar organic solvents, such asN,N-dimethyacetamide (DMAc),N,N-dimethyformamide (DMF), and dimethyl sulfoxide (DMSO). The obtained polymers were characterized by FTIR, specific rotation, elemental analysis as well as1HNMR spectroscopy and gel permeation chromatography (GPC). The thermal stability of the resulting PAIs was evaluated with thermogravimetric analysis techniques under a nitrogen atmosphere.

Methotrexate-Incorporated Polymeric Micelles Composed of Methoxy Poly(ethylene glycol)-Grafted Chitosan

Abstract: In this study, methotrexate (MTX)-encapsulated polymeric micelles using methoxy poly(ethylene glycol) (MPEG)-grafted chitosan (ChitoPEG) copolymer were prepared. The MTX-incorporated polymeric micelles of ChitoPEG copolymer has a particle size of around 50-100 nm. In 1H nuclear magnetic resonance (NMR) study, the specific peaks of MTX disappeared in heavy water (D2O) and only the specific peak of MPEG was observed, while all of the peaks were confirmed in dimethyl sulfoxide (DMSO). These results indicated that MTX was complexed with chitosan and then formed an ion complex inner-core of the polymeric micelle in an aqueous environment. The drug contents of the polymeric micelle were around 4∼12% and the loading efficiency of MTX in the polymeric micelles was higher than 60% (w/w) for all of the formulations. The cytotoxicity of MTX and MTX-incorporated polymeric micelle against CT26 tumor cells was not significantly changed.

Effect of Room Temperature Ionic Liquids Adsorption on Electromechanical Behavior of Cellulose Electro-Active Paper

Abstract: The cellulose smart material called electro-active paper (EAPap) is made by regenerating cellulose. However, the actuator performance is degraded at low humidity levels. To solve this drawback, EAPap bending actuators were made by activating wet cellulose films in three different room-temperature ionic liquids: 1-butyl-3-methylimidazolium hexaflurophosphate (BMIPF6), 1-butyl-3-methylimidazolium chloride (BMICL) and 1-butyl-3-methylimidazolium tetrafluroborate (BMIBF4). In the results, the actuator performance was dependent on the type of anions in the ionic liquids, in the order of BF4> Cl > PF6. The BMIBF4-activated actuator showed the maximum displacement of 3.8 mm with low electrical power consumption at relatively low humidity. However, the BMICL-activated actuator showed a slight degradation of actuator performance. Further performance and durability improvement will be possible once various ionic liquids are blended with cellulose.

Synthesis and Characterization of Low Viscosity Aromatic Hyperbranched Polyester Epoxy Resin

Abstract: Low viscosity aromatic hyperbranched polyester epoxy resin (HTBE) was synthesized by the reaction between epichlorohydrin (ECH) and carboxyl-end hyperbranched polyester (HTB) which was prepared from inexpensive materials A2 (1,4-butanediol glycol, BEG) and B3 (trimellitic anhydride, TMA) by pseudo one-step method. The molar mass of the HTB was calculated from its acid value by “Recursive Probability Approach”. The degree of branching (DB) of the HTB was characterized by model compounds and1H NMR-minus spectrum technology, and the DB of the HTB was about 0.47∼0.63. The viscosity and epoxy equivalent weight of the HTBE were 3,600∼5,000 cp and lower than 540 g/mol respectively. The reaction mechanism and structure of the AB2 monomer, HTB and HTBE were investigated by MS,1H NMR and FTIR spectra technology. The molecular size of HTBE is under 8.65 nm and its shape is ellipsoid-like as determined by molecular simulation.

Mechanical and thermal behavior of polyamide-6/clay nanocomposite using continuum-based micromechanical modeling

Abstract: The mechanical and thermal behaviors of polyamide-6/clay nanocomposites were studied using the continuum-based, micromechanical models such as Mori-Tanaka, Halpin-Tsai and shear lag. Mechanic-based model prediction provides a better understanding regarding the dependence of the nanocomposites’ reinforcement efficiency on conventional filler structural parameters such as filler aspect ratio (α), filler orientation (S), filler weight fraction (ψ f ), and filler/matrix stiffness ratio (E f /E m ). For an intercalated and exfoliated nanocomposite, an effective, filler-based, micromechanical model that includes effective filler structural parameters, the number of platelets per stack (n) and the silicate inter-layer spacing (d 001), is proposed to describe the mesoscopic intercalated filler and the nanoscopic exfoliated filler. The proposed model nicely captures the experimental modulus behaviors for both intercalated and exfoliated nanocomposites. In addition, the model prediction of the heat distortion temperature is examined for nanocomposites with different filler aspect ratio. The predicted heat distortion temperature appears to be reasonable compared to the heat distortion temperature obtained by experimental tests. Based on both the experimental results and model prediction, the reinforcement efficiency and heat resistance of the polyamide-6/clay nanocomposites definitely depend on both conventional (α,S, ψ f ,E f /E m ) and effective (n,d 001) filler structural parameters.

Synthesis and Characterization of Organic Light-Emitting Copolymers Containing Naphthalene

Abstract: Conjugated PPV-derived block copolymers containing 2-ethylhexyloxynaphthalene unit were synthesized and characterized in this study. The resulting polymers were soluble in common organic solvents and showed good thermal stabilities. The weight-average molecular weights (M w ) of the copolymers ranged from 246,000 to 475,000 with PDIs of 1.3∼2.1. The optical properties of these polymers, measured both in a chloroform solution and on a film, showed a maximum absorption at 405∼476 nm for Copolymers I∼VIII. In the PL spectra, Copolymers I∼VIII showed maximum peaks at 510∼566 nm. The HOMOs, LUMOs and band gaps of the PPV derivatives of Copolymers I∼VIII were 5.30∼5.77, 3.04∼3.24, and 2.5∼2.2 eV, respectively. The multi-layered, light-emitting diodes of ITO/PEDOT/copolymers/LiF/Al exhibited turn-on voltages of 6∼2.5 V. Copolymer VIII exhibited the maximum brightness of 3,657 cd/m2. Particularly, Copolymer VII, with an identical composition of MEH-PPV and naphthalene-PPV, showed a maximum luminance efficiency and power efficiency of 2.63 cd/A and 1.06 lm/W, respectively.

Compatibilizing effect of graphite oxide in graphene/PMMA nanocomposites

Abstract: The structure of single graphene sheets, which are the basal plane of graphite, can be best visualized by making a longitudinal scission on a single wall carbon nanotube (SWCNT) along the tube axis and flattening the resulting sheet. These sheets have electric conductivity, thermal conductivity, and tensile modulus values similar to SWCNTs, and can be used as alternatives to SWCNTs in various applications. Graphite shows a sharp X-ray diffraction peak at 2θ=26.5 because it has a layered structure composed of graphene sheets and the typical interlayer spacing is 3.35 A. These sheets are one-atom-thick and are composed of hexagonal carbon rings. Graphite oxide (GO), prepared by oxidizing graphite, is a graphite-derived compound with a layered structure. GO has a broad X-ray diffraction peak at lower angles than graphite, normally 2θ=10~15, because polar groups such as hydroxyl, epoxide, ether, and carboxylate groups are present on graphene sheets as a result of oxidation and expand the interlayer spacing. Recently, it has been reported that exfoliation of graphite into a single graphene sheet can be achieved from sufficiently oxidized GO, if inter-graphene spacing associated with native graphite is completely eliminated in the oxidation stage, and if adequate pressure builds up at the gallery between the GO sheets by rapid heating. The pressure results from CO2 evolved by the thermal decomposition of functional groups. This exfoliated graphite, where the inter-graphene spaces associated with GO and graphite are completely excluded after thermal expansion, has an affinity for polar solvents and polymers, as well as good conductivity, because this exfoliated graphite is composed of functionalized graphene sheets (FGSs) having polar functional groups remained even after thermal treatment. Normally, carbon nanotubes need surface treatment if they are to be used as a nanofiller for fine dispersion in a polymer matrix. However, FGS can offer comparable or better electrical conductivity enhancement than carbon nanotubes without further surface treatment, owing to the polar functional groups. Our laboratory has prepared and examined FGS nanocomposites with various polymers. During these studies, we discovered that the fine dispersion of FGS in a polymer matrix can be improved when GO is used as a compatibilizer. This paper reports the compatibilizing effect of GO in FGS/poly(methyl methacrylate) (PMMA) nanocomposites.