bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and Molecular Weight Development of Dithiolactone‐Mediated Radical Polymerization of Styrene
Authors: Soriano‐Moro Jesús Guillermo , Jaramillo‐Soto Gabriel , Guerrero‐Santos Ramiro , Vivaldo‐Lima Eduardo
Published: April 2009

Calculations of polymerization kinetics and molecular weight development in the dithiolactone‐mediated polymerization of styrene at 60 °C, using 2,2′‐azobisisobutyronitrile (AIBN) as initiator and γ‐phenyl‐γ‐butirodithiolactone (DTL1) as controller, are presented. The calculations were based on a polymerization mechanism based on the persistent radical effect, considering reverse addition only, implemented in the PREDICI® commercial software. Kinetic rate constants for the reverse addition step were estimated. The equilibrium constant (K = kadd/k‐add) fell into the range of 105–106 L · mol−1. Fairly good agreement between model calculations and experimental data was obtained.

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A placebo arm is not always necessary in clinical trials of amyotrophic lateral sclerosis
Authors: Gordon Paul H.
Published: April 2009

Riluzole is currently the only approved medication for amyotrophic lateral sclerosis (ALS). While other potential neuroprotective agents have been tested in clinical trials, none has been effective, and few symptomatic treatments have been studied. Randomized placebo‐controlled trials are necessary to establish the effectiveness of a drug, but an increasing number of potential therapies combined with limited resources means that only a few drugs at a time can be tested for efficacy in ALS. Therefore, priority must be given to agents that show an advantage in early phase trials before proceeding to Phase III efficacy trials. New strategies are being used to screen different agents, along with their correct dose, in a variety of neurological illnesses, including ALS. Early phase trial designs conducted without a placebo arm improve efficiency, reduce cost, and appeal to patients. Dose‐ranging, futility, and selection trials are examples of Phase I and II trial designs that can be conducted without placebo groups. Muscle Nerve, 2009
Can we eliminate placebo in ALS clinical Trials?
Authors: Simmons Zachary
Published: April 2009

Amyotrophic lateral sclerosis (ALS) is a fatal disease with limited treatment options. Controlled studies are a necessary part of Phase II and Phase III assessments of proposed therapies. Due to the relatively small number of patients with ALS, several study designs have been proposed to improve the efficiency of Phase II studies. Some of these advocate the use of historical controls in place of placebo controls. However, the characteristics of historical controls may not mirror those of patients in the treatment group. Novel study designs can be used to decrease the number of patients required for Phase II studies. The use of placebo controls rather than historical controls in these novel study designs likely leads to better predictions of treatments that will be successful in Phase III studies. There is general agreement on the necessity of placebo controls in Phase III studies. Muscle Nerve, 2009
Fast planar slides. A closed‐form thermo‐hydro‐mechanical solution
Authors: Pinyol N. M. , Alonso E. E.
Published: April 2009

Heat‐induced excess pore pressures on the failure surface of a planar slide have been calculated by solving the mass and heat balance equations on the shear band. The set of differential equations and the equation of motion of the slide have been solved in closed form for the case of incompressible fluid and incompressible soil skeleton. The solution describes the accelerated motion of the slide. It has been compared with the numerical solution when soil and water stiffness terms are not disregarded. A case study, based on a well‐known translational slide (Cortes slide) has been solved. Numerical and analytical solutions are compared. Results of a sensitivity analysis indicate that the permeability of the shear band is the key parameter to control the onset of a rapid motion. For a band permeability above a threshold value, in the vicinity of 10−15m2 (10−8m/s), fast accelerated motions are very unlikely. Copyright © 2009 John Wiley & Sons, Ltd.
Asymmetric spin‐echo (ASE) spiral improves BOLD fMRI in inhomogeneous regions
Authors: Brewer Kimberly D. , Rioux James A. , D'Arcy Ryan C. N. , Bowen Chris V. , Beyea Steven D.
Published: April 2009

Functional MRI (fMRI) is of limited use in areas such as the orbitofrontal and inferior temporal lobes due to the presence of local susceptibility‐induced field gradients (SFGs), which result in severe image artifacts. Several techniques have been developed to reduce these artifacts, the most common being the dual‐echo spiral sequences (spiral‐in/out and spiral‐in/in). In this study, a new multiple spiral acquisition technique was developed, in which the later spiral acquisitions are acquired asymmetrically with the peak of a spin‐echo causing increased R2‐weighting but matched R2′‐weighting. This sequence, called asymmetric spin‐echo (ASE) spiral, has demonstrated significant improvements in minimizing the signal loss and increasing the image quality as well as optimal blood‐oxygen‐level‐dependent (BOLD)‐weighting. The ASE spiral is compared to conventional spiral‐out using both signal‐to‐noise ratio (SNR) and whole brain fMRI activation volumes from a breath‐hold task acquired at 4 Tesla. The ASE dual spiral has exhibited SNR increases of up to 300% in areas where strong SFGs are present. As a result, the ASE spiral is highly efficient for recovering lost activation in areas of SFGs, as demonstrated by a 16% increase in the total number of activated voxels over the whole brain. Post spin‐echo ASE spiral images have decreasing SNR due to R2 signal losses, however the increase in R2‐weighting leads to a higher percentage of signal changes producing ASE spiral images with equivalent contrast‐to‐noise ratio (CNR) for each echo. The use of this sequence allows for recovery of BOLD activation in areas of SFG without sacrificing the CNR over the whole brain. Copyright © 2009 John Wiley & Sons, Ltd.
An optimal‐order error estimate on an H1‐Galerkin mixed method for a nonlinear parabolic equation in porous medium flow
Authors: Chen Huan‐Zhen , Wang Hong
Published: April 2009

We present an H1‐Galerkin mixed finite element method for a nonlinear parabolic equation, which models a compressible fluid flow process in subsurface porous media. The method possesses the advantages of mixed finite element methods while avoiding directly inverting the permeability tensor, which is important especially in a low permeability zone. We conducted theoretical analysis to study the existence and uniqueness of the numerical solutions of the scheme and prove an optimal‐order error estimate for the method. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010
On the computation of the solution of perturbed nonlinear Schrödinger equations
Authors: Subaşı Murat
Published: April 2009

We introduce a numerical treatment for solving nonlinear Schrödinger equations in the form
$i\, \psi_{t} + a_{0}\psi_{xx} - v (x) \psi - a_{1} |\psi|^{2}\psi = f (x, \, t),$
where f(x,t) is an arbitrary function, being perturbative, dependent on ψ. For this purpose, we developed a MAPLE® procedure and examined the effectiveness of the method on two problems. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010
An efficient explicit/implicit domain decomposition method for convection‐diffusion equations
Authors: Zhu Liyong , Yuan Guangwei , Du Qiang
Published: April 2009

A nonoverlapping domain decomposition method for some time‐dependent convection‐diffusion equations is presented. It combines predictor‐corrector technique, modified upwind differences with explicit/implicit coupling to provide intrinsic parallelism, and unconditional stability while improving the accuracy. Both rigorous mathematical analysis and numerical experiments are carried out to illustrate the stability, accuracy, and parallelism. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010
Effect of film thickness controlled by ink‐jet printing method on the optical properties of an electroluminescent polymer
Authors: Wang Meng , Yang Gui‐Zhong , Wang Min , Liu Tianxi
Published: April 2009

Ink‐jet printing (IJP) represents a highly promising liquid processed polymer deposition method for the film preparation of functional polymers in photo‐electronic devices. In this report, the results on the IJP of a fluorene‐based electroluminescent polymer, poly(9,9‐dihexylfluorene‐alt‐2,5‐dioctyloxybenzene) (PF6OC8), from a piezoelectric droplet generator are presented. The polymer film thickness has been found to show an approximate linear relation with the number of droplets per unit area; it is thus convenient to control the film thickness by the space of printed dots in IJP process. In comparison, spin coating approach is also used to prepare polymer films with different thicknesses by varying solution concentration and spinning speed. However, it is found that spin coating is difficult to control the film thickness quantitatively. The influence of film thickness on the photoluminescence (PL) properties of PF6OC8 films prepared by IJP and spin coating is comparatively investigated. For both ink‐jet printed and spin coated films, the intensity of PL spectra first increases and then decreases with increase in the film thickness, probably due to the exciton quenching in thicker films. When the polymer film thickness is at nanoscale, the major peak in the PL spectrum is the 0–0 vibronic emission at about 420 nm, and with increase in the film thickness, the 0–1 vibronic peak at about 440 nm becomes dominant. The red‐shifted PL spectra with increase in film thickness show the change from the 2D exciton state to the 3D one. Copyright © 2009 John Wiley & Sons, Ltd.
Brittle–ductile transition in the PETG/PC blends by adding PTW elastomer
Authors: Zhang Xinlan , Wang Ke , Li Bo , Chen Feng , Fu Qiang
Published: April 2009

In this paper, an elastomer containing epoxy groups, ethylene‐butylacrylate‐glycidylmethacrylate (PTW), was used as toughening modifier for the poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) (PETG)/polycarbonate (PC) blends. A remarkable improvement of toughness was achieved by addition of only 5 wt% PTW. In particular, an obvious brittle–ductile (B–D) transition in impact toughness was found when the PTW content increased from 3 to 5 wt%. The toughening mechanism and observed B–D transition have been explored in detail, combining with electronic microscopy observation, melt rheological investigation and dynamic mechanical analysis (DMA). It is suggested that the B–D transition can be attributed to a better interfacial adhesion between different phases, and importantly, to a continuum percolation dispersed‐phases network formed at appropriate PTW content, in which PC particles are connected with each other by PTW phase. Our present study offers new, profound insight on the toughening mechanism for the elastomer modified amorphous/amorphous plastic blends. Copyright © 2009 John Wiley & Sons, Ltd.
Metal complexes of natural and synthetic fabrics grafted with vinyl monomers by gamma irradiation
Authors: Hassan Mahmoud S. , Atteia Rehab M. , Zohdy Maged H.
Published: April 2009

Graft copolymers of natural and synthetic fabrics with acrylic acid (AAc) prepared by gamma irradiation were transformed into metal complexes of the divalent metal ions of cobalt, nickel, and copper. The factors that affect the grafting process without affecting the physical properties of fabrics and homogeneous grafting were studied. These factors involved inhibitor (FeCl2) concentration, solvent composition, AAc concentration, and irradiation dose. The results showed that the appropriate irradiation dose in all cases was 20 kGy, whereas the inhibitor concentration was 0.1 wt% in the case of cotton and 0.2 wt% in the case of cotton/polyester blend and polyester fabrics. The suitable solvent composition was H2O (90%)/MeOH(10%) in the case of cotton and H2O (90%)/MeOH(10%) in the cotton/polyester blend and polyester fabrics. On the other hand, the suitable AAc concentration was 30% in the case of cotton and 50% in the cotton/polyester blend and polyester fabrics. The homogenous grafting and subsequent distribution of metal complexation was illustrated by a method based on the measurement of color parameters. Moreover, the effect of radiation grafting and metal complexation on the water absorption and mechanical properties of fabrics was investigated. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers
Thermal decomposition behavior of poly(ethylene 2,6‐naphthalate)/silica nanocomposites
Authors: Kim Jun Young , Kim Duk Ki , Kim Seong Hun
Published: April 2009

Poly(ethylene 2,6‐naphthalate) (PEN) nanocomposites reinforced with silica nanoparticles were prepared by direct melt compounding. Dynamic thermogravimetric analysis was conducted on the PEN/silica nanocomposites to clarify the effect of silica nanoparticle on the thermal decomposition behavior of the resultant nanocomposites. There is a significant dependence of thermal decomposition behavior for PEN/silica nanocomposites on the content of silica nanoparticles and heating rate. The variation of the activation energy for thermal decomposition reflected the improvement of the thermal stability of the PEN/silica nanocomposites. The unique characteristics of silica nanoparticles resulted in physical barrier effect against the thermal decomposition, leading to the enhancement of the thermal stability of the PEN/silica nanocomposites. The incorporation of silica nanoparticles into the PEN matrix increased the storage modulus of the PEN/silica nanocomposites and made it possible for them to sustain higher modulus at higher temperature relative to pure PEN. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers
Effects of the accelerated freeze‐thaw cycling on physical and mechanical properties of wood flour‐recycled thermoplastic composites
Authors: Adhikary Kamal Babu , Pang Shusheng , Staiger Mark P.
Published: April 2009

This study investigated durability performance of wood‐plastic composites (WPCs) that were exposed to accelerated cycling of water immersion followed by freeze thaw (FT). The WPCs used in this study were made of high‐density polyethylene (HDPE) or polypropylene (PP) with radiata pine (Pinus radiata) wood flour using hot‐press molding. These two types of plastics included both recycled and virgin forms in the formulation. In the experiments, surface color, flexural properties, and dimensional stability properties (water absorption and thickness swelling) were measured for the FT cycled composites and the control samples. Interface microstructures and thermal properties of the composites were also investigated. The results show that the water absorption and the thickness swelling of the composites increased with the FT weathering. In the meantime, the flexural strength and stiffness decreased. Scanning electron microscopy (SEM) images of the fractured surfaces confirmed a loss of interface bonding between the wood flour and the polymer matrix. Differential scanning calorimetry (DSC) showed a decrease in crystallization enthalpy and crystallinity of the wood flour‐plastic composites as compared with the neat PP and HDPE samples. The crystallinity of the FT cycled composites using the virgin plastics (vPP and vHDPE) increased; however, the composites with the recycled plastics decreased in comparison with corresponding control samples. In general, the properties of the composites were degraded significantly after the accelerated FT cycling. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Effects of silane grafting on the morphology and thermal stability of poly(ethylene terephthalate)/clay nanocomposites
Authors: Xu Xinfeng , Ding Yanfen , Wang Feng , Wen Bin , Zhang Junhua , Zhang Shimin , Yang Mingshu
Published: April 2009

An alkylammonium intercalated montmorillonite (A‐MMT) was modified by edge grafting with 3‐glycidoxypropyltrimethoxysilane. In comparison with poly(ethylene terephthalate) (PET)/A‐MMT, the resultant grafted clay, S‐A‐MMT, exhibited improved miscibility with PET matrix and revealed better dispersion state in the melting compounded PET/S‐A‐MMT nanocomposites. As a result, the PET/S‐A‐MMT nanocomposite had slower degradation rate owing to the enhanced clay barrier effect. Meanwhile, the nanocomposite exhibited lower degradation onset temperature under nitrogen because of the clay catalysis effect, which can be explained by the decreasing degradation reaction energy calculated from Coats–Redfern method of degradation kinetics. In the other hand, nanocomposite with better clay dispersion state exhibited increasing thermal oxidative stability due to clay barrier effect of hindering oxygen to diffuse in, which accorded with the continuous and compact char surface formed during polymer degradation. The clay catalysis and barrier effect of silicate layers were presented directly in isothermal oxidative TGA experiment. Furthermore, the mechanical and crystallization properties of PET/clay nanocomposites were investigated as well. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Influence of modified carbon nanotube on physical properties and crystallization behavior of poly(ethylene terephthalate) nanocomposite
Authors: Kim Jun Young , Choi Hee Jun , Kang Chang Soo , Kim Seong Hun
Published: April 2009

Poly(ethylene terephthalate) (PET) nanocomposites reinforced with a very small quantity of modified carbon nanotube (CNT) were prepared by melt compounding using a twin‐screw extruder. The introduction of carboxylic acid groups on the surfaces of the nanotube leads to the enhanced interactions between the nanotube and the polymer matrix through hydrogen bonding formation. The thermal stability, mechanical, and rheological properties of the PET nanocomposites are strongly dependent on the interfacial interactions between the PET and the modified CNT as well as the dispersion of the modified CNT in the PET. The introduction of the nanotube can significantly influence the non‐isothermal crystallization behavior of the PET nanocomposites. This study demonstrates that a very small quantity of the modified CNT can substantially improve the thermal stability and mechanical properties of the PET nanocomposites, depending on the dispersion of the modified CNT and the interfacial interactions between the polymer matrix and the modified CNT. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Structure and properties of polypropylene/hydrotalcite nanocomposites
Authors: Ardanuy M. , Velasco J.I. , Antunes M. , Rodriguez‐Perez M.A. , de Saja J.A.
Published: April 2009

This article presents the study of the modification of the particle/matrix interface region and its effects on the structure and dynamic mechanical behavior of polypropylene (PP)/hydrotalcite nanocomposites prepared by melt extrusion. The interface modification was promoted by combinying the organophillization of the hydrotalcite particles with blending the PP with a maleic anhydride‐grafted‐PP (PP‐g‐MAH) or a maleic anhydride‐grafted‐poly(styrene‐co‐ethylenebutylene‐co‐styrene) (SEBS‐g‐MAH). Sodium dodecyl sulphate was used to promote the organophillization of the hydrotalcite particles. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) showed a partially exfoliated hydrotalcite structure, with an increasing exfoliation being achieved by adding a compatibilizer and organo‐modifying the particles. Values of the Young's modulus (E), storage modulus (E′), maximum tensile strength (σmax), neck propagation strength (σneck), and elongation at break (εb) were found to depend both on the nature of the particle matrix interface as well as on the type of compatibilizer. Also, nanocomposites prepared with the organophillized particles showed lower Tg and loss factor values. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Moisture absorption in foam‐cored composite sandwich structures
Authors: Avilés F. , Aguilar‐Montero M.
Published: April 2009

The hygroscopic behavior of sandwich structures composed of E‐glass/polyester face sheets bonded to a PVC foam core exposed to 95% relative humidity and immersed in sea‐water is examined herein. Moisture uptake was monitored for 11 months yielding absorption curves for samples of polyester resin, laminated composites, PVC foam core, and a sandwich structure. The coefficients of diffusion and moisture saturation values extracted from the curves are significantly greater for the water immersed condition than for the exposed to elevated moisture one, and point to the foam core as the most absorbing material in the sandwich structure. The measured absorption curves are compared to a diffusion model which employs the calculated coefficient of diffusion, showing good agreement. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Thermal and morphological characterization of composites prepared by solution crystallization method of high‐density polyethylene on carbon nanotubes
Authors: He Linghao , Xu Qun , Song Rui , Hua Chengwu
Published: April 2009

The morphology, nucleation, and crystallization of polyethylene/carbon nanotubes composites prepared by solution crystallization method of high density polyethylene on Multiwall Carbon Nanotubes (MWNTs) are studied. Transmission electron microscopy (TEM) results show that the center stems of MWNTs are decorated with lamellar crystals. The nonisothermal crystallization kinetics of pure PE and PE/MWNTs composites are investigated by differential scanning calorimetry at various cooling rates. It is found that the Avrami analysis modified by Jeziorny and Mo can describe the nonisothermal crystallization process of pure PE and PE/MWNTs very well. The difference in the value of exponent between PE and PE/MWNTs suggests that addition of the MWNTs influences the mechanism of nucleation and the growth of PE crystallites. On one hand, the increasing of temperature corresponding to the maximum rate of crystallization and the onset crystallization temperature and the study of the nucleation activity reveal that the inorganic component (MWNTs) can act as the nucleating agent to facilitate the crystallization of PE in the hybrids. On the other hand, the decreasing degree of crystallinity and the increasing of half‐crystallization time imply that the MWNTs networks confine the crystallization of PE. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Effect of multi‐walled carbon nanotubes on crystallization, thermal, and mechanical properties of poly(vinylidene fluoride)
Authors: He Linghao , Xu Qun , Hua Chengwu , Song Rui
Published: April 2009

Composites were prepared by solution blending poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWNTs). Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) results showed that the crystalline structure of PVDF was changed by the addition of MWNTs and a MWNTs‐induced crystal transformation from α‐phase to β‐phase of PVDF was confirmed. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMA) techniques, thermal and mechanical properties of the composite films were examined. As the DSC results showed, addition of MWNTs would lead to the increased cooling crystallization temperature (Tc), implying that MWNTs nanoparticles could act as nucleating agents, which is further proved with the help of polarized optical microphotographs. On the other hand, the decreasing of Dd (degree of crystallinity) implied that the MWNTs networks can confine the crystallization of PVDF. Through the curve analysis of the dynamic mechanical measurements, it was found that the storage modulus (E′) is significantly enhanced, revealing that a strong interaction should exist between PVDF and MWNTs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Prenatal features of Costello syndrome: ultrasonographic findings and atrial tachycardia
Authors: Lin Angela E. , O'Brien Barbara , Demmer Laurie A. , Almeda Kristina K. , Blanco Cynthia L. , Glasow Patrick F. , Berul Charles I. , Hamilton Robert , Micheil Innes A. , Lauzon Julie L. , Sol‐Church Katia , Gripp Karen W.
Published: April 2009

Objective

Delineate prenatal features of Costello syndrome (caused by HRAS mutations), which consists of mental retardation, facial, cardiovascular, skin, and musculoskeletal anomalies, and tumor predisposition.

Methods

Literature and new cases classified as Group I (pre‐HRAS), Group II (HRAS confirmed), and Group III (HRAS confirmed in natural history study, plus three contributed cases).

Results

Polyhydramnios occurred in most (mean 79%) pregnancies of cases in Groups I (98), II (107), and III (17); advanced paternal age and prematurity were noted in approximately half. Less frequent were nuchal thickening, ascites, shortened long bones, abnormal hand posture, ventriculomegaly, macrosomia, and macrocephaly. Fetal arrhythmia occurred in nine cases (six supraventricular or unspecified tachycardia, one unspecified arrhythmia, and two premature atrial contractions, PACs); excluding three new cases and two with PACs, the estimated prenatal frequency is 4/222 (2%).

Conclusion

Costello syndrome can be suspected prenatally when polyhydramnios is accompanied by nuchal thickening, hydrops, shortened long bones, abnormal hand posture, ventriculomegaly, large size, and macrocephaly, and especially fetal atrial tachycardia. Consideration should be given for timely prenatal diagnostic studies for confirmative HRAS gene mutations and for maternal treatment of serious fetal arrhythmia. Copyright © 2009 John Wiley & Sons, Ltd.
Morphological, thermal, and mechanical characteristics of polymer/layered silicate nanocomposites: The role of filler modification level
Authors: Marras S.I. , Tsimpliaraki A. , Zuburtikudis I. , Panayiotou C.
Published: April 2009

Composite materials consisting of poly(L‐lactic acid) and montmorillonite modified to a different extent, using various contents of hexadecylammonium cation, were prepared by the solution intercalation method. Investigation of the composites' morphology revealed that a surfactant quantity higher than the mineral's cation exchange capacity (CEC) was necessary for the organomodified clay to be dispersed at nanoscale level into the polymer matrix. The surfactant content in organoclay was found to play a major role in controlling the composite's mechanical properties. Thus, although increase of the alkylammonium concentration initially enhanced these properties, even higher concentrations corresponding to higher modification levels had a negative impact to them causing their dramatic deterioration. Observation of the deformed surfaces showed that the deformation process mechanism of the material is directly related to the degree of clay modification. Thermal degradation studies revealed that the intermediate surfactant excess reinforces the thermal stability of the nanocomposite by increasing the onset decomposition temperature. Additionally, the alkylammonium concentration was found to affect the crystallization temperature and the glass transition temperature of the polymer. In conclusion, an ideal balance between thermal and mechanical properties can be obtained at surfactant quantity equivalent to 1.5 times the clay CEC. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Polystyrene/Sr2Ce2Ti5O15 composites with low dielectric loss for microwave substrate applications
Authors: Subodh G. , Deepu V. , Mohanan P. , Sebastian M.T.
Published: April 2009

Sr2Ce2Ti5O15 (Strontium Cerium Titanate or SCT) ceramic was prepared by solid‐state route. A composite of polystyrene/Sr2Ce2Ti5O15 was made using melt mixing technique in a Kneading machine. The microstructure of the composite was investigated using a Scanning Electron Microscope. The dielectric properties of the composites were studied at radio frequency and microwave frequencies. It is observed that relative permittivity and loss tangent increase with volume fraction of the ceramics. The mechanical properties of the composites were investigated using microhardness tester. For 50 volume percentage loading of the ceramic, the composite has relative permittivity of 13.6and dielectric loss of 4.28 × 10−4. The experimentally observed permittivity was compared with the theoretical models. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Stretching induced steric interaction between backbone and side chain in a novel polyimide fiber
Authors: Liu Xiangyang , Pan Rui , Xu Wei , Ye Guangdou , Gu Yi
Published: April 2009

Stretching induces to form electric interaction between backbone and mesogenic side chain in the bulk of a novel polyimide fiber that was synthesized from 4,4′‐oxydiphthalicanhydride (ODPA) and 6‐(4‐phenyl phenoxy) hexyl‐3,5‐diaminobenzoate (DABBE6), which results in unusual in situ self‐reinforced function, and surprisingly, zigzag undulation of mechanical properties of the annealed polyimide fibers with increasing draw ratios. X‐ray scattering and differential scanning calorimetry (DSC) results indicate that some order structures develop in the annealed fibers under tensile stress. Dynamic thermomechanical analysis (DMA) and DSC results also indicate that no phase separation is observed between backbone and side chain. Further results of experiments and computer molecular simulation prove that the biphenyl side chain can be parallel to the backbone via methylene spacers bending and together align orientationally under tensile stress to develop electronic interaction, and the molecular conformations are stabilized to form binding‐like molecular structures by the interaction to enhance strength and rigidity of backbone. Meanwhile, formation of the interaction depends on the relative position between backbone and the trail phenyl group of side chain, which contributes to the zigzag undulation of tensile strength and initial modulus of the polyimide fibers. In addition, relationship of draw ratios and formation of the interaction was established, and a corresponding backbone‐side chain‐packing model was suggested. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Simulation of phase‐change heat transfer during cooling stage of gas‐assisted injection molding of high‐density polyethylene via enthalpy transformation approach
Authors: Yang Bin , Fu Xiao‐Rong , Yang Wei , Liang Shui‐Po , Hu Shen , Yang Ming‐Bo
Published: April 2009

Gas‐assisted injection molding (GAIM) is one of the significant fabricating technologies of plastics in modern industry, mainly owing to the light weight of products, good structural rigidity and dimensional stability, as well as shorter molding cycles. The objective of this article is to explore the temperature profiles during the cooling stage of gas‐assisted injection molded high‐density polyethylene (HDPE) parts using a transient heat transfer model of the enthalpy transformation method, which could always be utilized for the numerical studies of the phase‐change heat transfer issues. The simulated results were validated by the in situ measurement of temperature decay, and good agreement has been observed. The comparison between GAIM and conventional injection molding (CIM) reveals that it is the rapid cooling rate (because of thin wall‐thickness) and the inner gas cooling effects that together lead to the shortening of molding cycles. As cooling rate plays a part in the stabilization of the crystalline structure during the GAIM process according to our previous studies, this work is of significance for the operational designs in GAIM industrial applications and further investigation on the detailed mechanisms of various crystalline structures in GAIM parts. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
A new explicit simulation for injection molding and its validation
Authors: Cheng Zhiqiang , Barriere Thierry , Liu Baosheng , Gelin Jean‐Claude
Published: April 2009

The simulation of injection molding involves the filling of cavities and runners in complicated shapes. The 3D elements in large numbers are generally required to satisfy the precise simulation of real processes. It results in the computation in large scales, so that the efficiency of computation becomes very important. On the basis of previous explicit software realized by the authors, the new algorithm avoids the global solution for pressure fields to improve its efficiency. Another feature of the new algorithm is the use of same order interpolation elements instead of MINI elements, which simplifies significantly the software procedures. Except for the operations at element level, neither global solution nor the construction of global matrix is required in simulation. A special feedback regulation strategy is used to meet the incompressibility in filled domain at each time step. In case of the mold filling problems, this method provides a fast way to simulate the filling processes. The computational cost is about linearly proportional to the degree of freedom number. Comparison of velocity field obtained by the previous algorithm using MINI element and analytical theoretical solution proves that the feedback regulation strategy in the new algorithm can satisfy well incompressibility. Moreover, comparison with the results of filling process and temperature field obtained by the previous algorithm proves the validity of the new algorithm. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Synthesis and characterization of a thermotropic liquid crystalline hyperbranched polyester
Authors: Cai Liming , Lu Yafei
Published: April 2009

BACKGROUND: Hyperbranched polymers have received increasing attention in the fields of medicine, homogeneous catalysis and materials science. Hydroxyl‐functional aliphatic polyesters are one of the most widely investigated families of hyperbranched polymers. The research reported here is based on the preparation of a novel hyperbranched polyester and the modification of its terminal hydroxyl groups by biphenyl mesogenic units.

RESULTS: 2,2,6,6‐Tetramethylolcyclohexanol as a core and 8‐[4′‐propoxy(1,1‐biphenyl)yloxy]octanoic acid as a mesogenic unit were synthesized. A hyperbranched polyester (HPE) was synthesized in one step and subsequently substituted by reaction of its terminal hydroxyl groups with the biphenyl mesogenic units to yield a novel liquid crystalline hyperbranched polyester (HPE‐LC). The chemical structures of all compounds were confirmed using Fourier transform infrared, 1H NMR and 13C NMR spectroscopy. The thermal behavior and the mesogenic properties of the biphenyl mesogenic unit and HPE‐LC were investigated using differential scanning calorimetry, polarized optical microscopy and wide‐angle X‐ray diffraction. The results demonstrated that the degree of branching of the HPE is ca 0.63. Both HPE‐LC and the biphenyl mesogenic unit exhibit mesomorphic properties, but HPE‐LC has a lower isotropic transition temperature and a wider transition temperature range than the biphenyl mesogenic unit.

CONCLUSION: A novel liquid crystalline hyperbranched polyester was successfully synthesized, which exhibits mesomorphic properties. This polymer has good solubility in highly polar solvents and good thermal stability. Copyright © 2009 Society of Chemical Industry
Liquid crystalline conjugated polymers and their applications in organic electronics
Authors: Yang Sheng‐Hsiung , Hsu Chain‐Shu
Published: April 2009

This article describes the syntheses and electro‐optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p‐phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p‐phenylenevinylene)s, the Suzuki‐ or Yamamoto‐coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main‐chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side‐chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field‐effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo‐fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713–2733, 2009
Polyisobutylene‐based polyurethanes. II. Polyureas containing mixed PIB/PTMO soft segments
Authors: Jewrajka Suresh K. , Kang Jungmee , Erdodi Gabor , Kennedy Joseph P. , Yilgor Emel , Yilgor Iskender
Published: April 2009

The design, synthesis, characterization, and structure–property behavior of polyureas containing novel soft segments of mixed polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) chains and conventional hard segments is presented. Modest amounts (12%) of PTMO in the soft PIB phase significantly increase both the tensile strength and elongation of the polyureas. These polyureas exhibit not only oxidative/hydrolytic stabilities far superior to Bionate® and Elast‐Eon® considered the most oxidatively stable polyurethanes on the market but also display mechanical properties (29 MPa tensile strength and 200% elongation) approaching those of conventional thermoplastic polyurethanes. The surfaces of these polyureas are covered/protected by PIB segments, which will lead to excellent biocompatibility. Our results demonstrate that the PTMO segments facilitate stress transfer from the continuous mixed soft phase to the dispersed hard phase, which strengthens and flexibilizes PIB‐based polyureas and thus significantly improves elastomeric properties without compromising oxidative and hydrolytic stability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2787–2797, 2009
Experimentally facile controlled polymerization of N‐carboxyanhydrides (NCAs), including O‐benzyl‐L‐threonine NCA
Authors: Gibson Matthew I. , Cameron Neil R.
Published: April 2009

It is demonstrated here that three different α‐amino N‐carboxyanhydrides (NCAs), including for the first time O‐benzyl‐L‐threonine NCA, can be polymerized in a controlled/“living” fashion without the need for transition metal catalysts or complex custom‐made glassware. Homopolymerizations in tetrahydrofuran gave monomodal distributions, high conversions, predictable Mn values and displayed first‐order kinetics. Chain extension experiments from poly(benzyl‐L‐threonine), using N,N‐dimethylacetamide to avoid the formation of insoluble β‐sheets, was used to create a range of block copolypeptides of controlled structure. Monomodal molecular weight distributions are observed throughout and molecular weights agree well with predicted values, although polydispersities are generally higher than those observed using more experimentally challenging techniques. This method therefore represents a practical approach to the synthesis of well‐defined polypeptides without the requirement for specialized glassware or glove‐box techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2882–2891, 2009
Synthesis and properties of chitosan‐based thermo‐ and pH‐responsive nanoparticles and application in drug release
Authors: Chuang Chung‐Yang , Don Trong‐Ming , Chiu Wen‐Yen
Published: April 2009

In this research, thermo‐ and pH‐responsive nanoparticles with an average diameter of about 50–200 nm were synthesized via the surfactant‐free emulsion polymerization. The thermal/pH dual responsive properties of these nanoparticles were designed by the addition of a pH sensitive monomer, acrylic acid (AA), to be copolymerized with N‐isopropylacrylamide (NIPAAm) in a chitosan (CS) solution. The molar ratio of CS/AA/NIPAAm in the feed was changed to investigate its effect on structure, morphology, thermal‐ and pH‐responsive properties of the nanoparticles. It was found that CS‐PAA‐PNIPAAm nanoparticles could be well dispersed in the aqueous solution and carried positive charges on the surface. The addition of thermal‐sensitive NIPAAm monomer affected the polymerization mechanism and interactions between CS and AA. The particle size of the nanoparticles was found to be varied with the composition of NIPAAm monomer in the feed. The synthesized nanoparticles exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in vitro release experiment. The environmentally responsive nanoparticles are expected to be used in many fields such as drug delivery system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2798–2810, 2009
Synthesis, photophysics, and electroluminescent performance of stable blue‐light‐emitting copoly(9,9‐diarylfluorene)s
Authors: Chen Ruei‐Tang , Chen Shinn‐Horng , Hsieh Bar‐Yuan , Chen Yun
Published: April 2009

A series of fluorene derivatives containing nonsymmetric and bulky aromatic groups at C‐9 position were synthesized and used for the preparation of blue‐light‐emitting copolyfluorenes (P1–P4) by the Suzuki coupling polycondensation. The copolymers were characterized by molecular weight determination, elemental analysis, differential scanning calorimeter, thermogravimetric analysis, absorption and emission spectroscopy, cyclic voltammetry, and differential pulse voltammetry. Their decomposition temperatures and glass transition temperatures are 423–441 °C and >120 °C, respectively. In film state, the copolyfluorenes exhibit blue photoluminescence at 425–450 nm, which remains almost unchanged after annealing at 200 °C in air for 60 min. Polymer light‐emitting diodes [ITO/PEDOT:PSS/P1–P4/Ca(50 nm)/Al(100 nm)] show stable blue‐light emission under device operation with the CIE co‐ordinates being between (0.16, 0.07) and (0.17, 0.09). The light‐emitting diodes devices from P1 and P3 containing electron‐deficient oxadiazole units display enhanced performance, with the maximum brightness and maximum current efficiency being (4510 cd/m2 and 2.40 cd/A) and (2930 cd/m2, 1.19 cd/A), respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2821–2834, 2009
Thermosensitive polymer brush‐supported 4‐N,N‐dialkylaminopyridine on silica particles as catalyst for hydrolysis of an activated ester in aqueous buffers: Comparison of activity with linear polymer‐supported version and effect of LCST transition
Authors: Jiang Xiaoming , Wang Bingbing , Li Christopher Y. , Zhao Bin
Published: April 2009

We report on the synthesis of a thermosensitive polymer brush‐supported 4‐N,N‐dialkylaminopyridine catalyst and the comparison of its catalytic activity with the corresponding linear polymer‐supported version in the hydrolysis of p‐nitrophenyl acetate (NPA) as well as the effect of lower critical solution temperature (LCST) transition on catalytic activity. The polymer brushes were synthesized from initiator‐functionalized silica particles by surface‐initiated atom transfer radical polymerization of methoxytri(ethylene glycol) methacrylate and 2‐(N‐methyl‐N‐(4‐pyridyl)amino)ethyl methacrylate in the presence of a free initiator. Dynamic light scattering studies showed that the onset temperatures of the LCST transition of polymer brushes in pH 7.52 and 7.82 buffers were 42 and 38 °C, respectively. Under the same reaction conditions, the net initial rate of the hydrolysis of NPA catalyzed by hairy particles was 70–80% of that catalyzed by the free copolymer at the temperature below the LCST of polymer brushes. With further increasing the temperature above the LCST, the plot of logarithm of net initial rate versus inverse temperature exhibited a shift for the reactions catalyzed by hairy particles and leveled off or decreased slightly in the case of using the free copolymer as catalyst, presumably because the structures of the aggregates of hairy particles and free copolymer chains were different. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2853–2870, 2009
Fluorinated hydroxytelechelic polybutadiene as additive in cationic photopolymerization of an epoxy resin
Authors: Ameduri B. , Bongiovanni R. , Sangermano M. , Priola A.
Published: April 2009

Fluorinated hydroxytelechelic polybutadiene (PBF), which is synthesized from the radical addition of a fluorinated mercaptan onto a hydroxytelechelic polybutadiene was used as an efficient surface and mechanical modifier in original formulations to enable the UV cationic polymerization of a telechelic diepoxy cycloaliphatic oligomer, leading to crosslinked polymers. Various amounts of PBF were used (ranging between 0 and 15 wt %). The kinetics of photocrosslinking revealed that the diepoxyde conversion reached 70% only in the absence of PBF, whereas it was about 90% in the presence of 10 wt % of PBF. When the PBF content increased, the dynamic mechanical measurements showed that: (i) the glass transition temperature values decreased and (ii) the resilience increased. The hydrophobicity of these polymers was investigated from the water contact angle (WCA) values showing a surface modification of the epoxy‐based system. Indeed, great modifications were noted on the extreme surface (i.e., air side) of the polymers (with WCA values as high as 120°) in contrast to those observed on the substrate side. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2835–2842, 2009
Discussion of substantially identical gel points among multiallyl monomers based on characterization of resultant network polymer precursors consisting of oligomeric primary polymer chains
Authors: Matsumoto Akira , Hamamoto Hiroyuki , Miwa Yuta , Aota Hiroyuki , Inoue Satoshi , Yokoyama Katsutoshi , Matoba Yasuo , Shibano Michirou
Published: April 2009

No difference in the actual gel points was substantially observed among three isomeric diallyl phthalates such as diallyl phthalate (DAP), diallyl isophthalate, and diallyl terephthalate (DAT); this interesting gelation behavior was discussed further in terms of the correlation between gelation and the difference in cyclization modes, and also, the difference in reactivity between the uncyclized and cyclized radicals for cross‐linking. In the present work, we tried to extend the preceding discussion to the polymerization of triallyl trimellitate (TAT) because the molecular structure of TAT is presumed to essentially involve the characteristics of three isomeric diallyl phthalates and, therefore, the enhanced gelation was expected in TAT polymerization. However, no enhancement of gelation was observed. For a full understanding of the gelation in multiallyl cross‐linking polymerization, we explored further the polymerizations of DAP, DAT, and TAT, especially focusing on the characterization of resultant network polymer precursors (NPPs) using SEC‐MALLS‐viscometry providing the correlation of [η] versus Mw of fractionated samples. Notably, the structure of NPP consisting of oligomeric primary polymer chains generated from specific allyl polymerization would become core‐shell type dendritic with the progress of polymerization. The correlation between delayed gelation and decreased reactivity of dendritic NPP for intermolecular cross‐linking is discussed. Conclusively, the reactivity for intermolecular cross‐linking between NPPs decreased with the progress of polymerization leading to a delayed gelation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2871–2881, 2009