bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of embryonic exposure to polychlorinated biphenyls on zebrafish (Danio rerio) retinal development
Authors: Wang Yan‐Ping , Hong Qin , Qin Da‐ni , Kou Chun‐Zhao , Zhang Chun‐Mei , Guo Mei , Guo Xi‐Rong , Chi Xia , Tong Mei‐Ling
Published: March 2011

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that affect embryonic development. The purpose of this study was to examine the effects of embryonic exposure to PCBs on early retinal development in zebrafish, Danio rerio. Zebrafish embryos were immediately exposed to different concentrations (0, 0.125, 0.25, 0.5, 1.0 and 2.0 mg) of PCBs per liter of medium at 28.5 °C. Embryos were assessed at 30, 48, 72 and 96 h post‐fertilization (hpf) for changes in embryonic survival rate, development, larval retinal morphology and ultrastructure of the retina. The results show that PCB exposure decreased the survival rate of embryos in a time‐ and dose‐dependent manner. Embryos exposed to the higher concentrations of PCBs (0.5, 1.0 and 2.0 mg l−1) displayed obvious gross morphological deformities. At 72 hpf, the retinal layer development of zebrafish was delayed at higher PCB concentrations (1.0 mg l−1). At 96 hpf, irregularity of photoreceptor cells arrangement and thickening of photoreceptor and ganglionic layers were observed in PCB‐treated larvae at concentrations of 0.25–1 mg l−1. Ultrastructural examination showed signs of growth inhibition of the photoreceptor outer segment at 0.25–1 mg l−1 PCB exposure at 72 hpf, as well as the appearance of massive vacuoles and holes inside the outer segments in the PCB exposure group at 96 hpf. These results suggest that embryonic exposure to moderate and high levels of PCBs induced developmental deficits in zebrafish retinas, particularly in photoreceptor cells. Copyright © 2011 John Wiley & Sons, Ltd.
Increasing strut porosity in silicate‐substituted calcium‐phosphate bone graft substitutes enhances osteogenesis
Authors: Campion Charlie R. , Chander Chaman , Buckland Tom , Hing Karin
Published: March 2011

Synthetic, porous silicate‐substituted calcium phosphate bone graft matrices (SiCaP; 0.8 wt % Si) with varying strut porosity were applied to ovine critical‐sized defect sites as either 1–2 mm microgranules (SiCaP‐23G, SiCaP‐32G, and SiCaP‐46G) or 1–2 mm microgranules in an aqueous poloxamer carrier (SiCaP‐23P, SiCaP‐32P, and SiCaP‐46P). Defect sites treated with SiCaP‐23G or SiCaP‐23P showed evidence of bone formation at 8 and 12 weeks in central zones. More advanced neovascularization and increased bone contact was observed for graft materials with higher strut porosities. At 12 weeks, graft materials with higher strut porosities (32% and 46%) had statistically significantly higher absolute bone volumes (p < 0.05) versus those with a strut porosity of 23%. Absolute bone volume in defects treated with grafts of matched strut porosities as microgranules, or microgranules with poloxamer carrier, were similar at 12 weeks. Absolute graft volume for SiCaP‐46 reduced over 12 weeks (not statistically significant). In conclusion, bone formation patterns in critically‐sized defects confirm strut porosity to be a clinically relevant property of porous silicate‐substituted calcium phosphate bone grafts in promoting osteogenesis. Increasing graft matrix strut porosity encouraged earlier neovascularization and increased the absolute equilibrium volume of bone growth within the graft without compromising graft stability. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.
A comparison of outcomes of general medical inpatient care provided by a hospitalist‐physician assistant model vs a traditional resident‐based model
Authors: Singh Siddhartha , Fletcher Kathlyn E. , Schapira Marilyn M. , Conti Mary , Tarima Sergey , Biblo Lee A. , Whittle Jeff
Published: March 2011

BACKGROUND:

Residency reform in the form of work hour restrictions has forced academic medical centers to develop alternate models of care to provide inpatient care. One such model is the use of physician assistants (PAs) with hospitalists. However, these models of care have not been widely evaluated.

OBJECTIVE:

To compare the outcomes of inpatient care provided by a hospitalist‐PA (H‐PA) model with the traditional resident based model.

DESIGN, SETTING and PATIENTS:

We conducted a retrospective cohort study of 9681 general medical (GM) hospitalizations between January 2005 and December 2006 using a hospital administrative database. We used multivariable mixed models to adjust for a wide variety of potential confounders and account for multiple patient visits to the hospital to compare the outcomes of 2171 hospitalizations to H‐PA teams with those of 7510 hospitalizations to resident teams (RES).

MEASUREMENTS:

Length of stay (LOS), charges, readmission within 7, 14, and 30 days and inpatient mortality.

RESULTS:

Inpatient care provided by H‐PA teams was associated with a 6.73% longer LOS (P = 0.005) but charges, risk of readmission at 7, 14, and 30 days and inpatient mortality were similar to resident‐based teams. The increase in LOS was dependent on the time of admission of the patients.

CONCLUSIONS:

H‐PA team‐based GM inpatient care was associated with a higher LOS but similar charges, readmission rates, and inpatient mortality to traditional resident‐based teams, a finding that persisted in sensitivity analyses. Journal of Hospital Medicine 2011. © 2011 Society of Hospital Medicine.
Model predictions of increased knee joint loading in regions of thinner articular cartilage after patellar tendon adhesion
Authors: Fernandez Justin W. , Akbarshahi Massoud , Crossley Kay M. , Shelburne Kevin B. , Pandy Marcus G.
Published: March 2011

Patellar tendon adhesion is a complication from anterior cruciate ligament (ACL) reconstruction that may affect patellofemoral and tibiofemoral biomechanics. A computational model was used to investigate the changes in knee joint mechanics due to patellar tendon adhesion under normal physiological loading during gait. The calculations showed that patellar tendon adhesion up to the level of the anterior tibial plateau led to patellar infera, increased patellar flexion, and increased anterior tibial translation. These kinematic changes were associated with increased patellar contact force, a distal shift in peak patellar contact pressure, a posterior shift in peak tibial contact pressure, and increased peak tangential contact sliding distance over one gait cycle (i.e., contact slip). Postadhesion, patellar and tibial contact locations corresponded to regions of thinner cartilage. The predicted distal shift in patellar contact was in contrast to other patellar infera studies. Average patellar and tibial cartilage pressure did not change significantly following patellar tendon adhesion; however, peak medial tibial pressure increased. These results suggest that changes in peak tibial cartilage pressure, contact slip, and the migration of contact to regions of thinner cartilage are associated with patellar tendon adhesion and may be responsible for initiating patellofemoral pain and knee joint structural damage observed following ACL reconstruction. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1168–1177, 2011
Long‐term outcome and cost‐effectiveness of complete versus assisted video‐assisted thoracic surgery for non‐small cell lung cancer
Authors: He Jianxing , Shao Wenlong , Cao Christopher , Yan Tristan , Wang Daoyuan , Xiong Xin‐guo , Yin Weiqiang , Xu Xin , Chen Hanzhang , Qiu Yuan , Zhong Baoliang
Published: March 2011

Background

To compare the outcomes and costs of two methods of video‐assisted thoracoscopic surgery (VATS) major pulmonary resection in patients with clinically resectable non‐small cell lung cancer (NSCLC).

Methods

Between January 2000 and December 2007, 1,058 patients with proven stages I–IIIA NSCLC underwent complete VATS (c‐VATS) or assisted VATS (a‐VATS) major pulmonary resection together with a systematic nodal dissection.

Results

The study cohort consisted of 736 men and 322 women. Mean operative time was shorter for the a‐VATS cohort compared with the c‐VATS group (P = 0.038). Overall survival (OS) at 5 years based on Kaplan–Meier analysis was 55.3% (95%CI, 50.6–60.0%) for those who underwent c‐VATS and 47.7% (95%CI, 41.2–54.2%) for those who underwent a‐VATS (P = 0.404). Gender, final pathology, TNM stage, and pT status were significant predictive factors for OS according to multivariate analysis. The total cost of a‐VATS lobectomy was lower than that of c‐VATS lobectomy.

Conclusions

c‐VATS and a‐VATS yield similar results in patients with clinically resectable NSCLC. a‐VATS, however, may be less expensive and easier to adopt, making it a particularly attractive option for thoracic surgeons in developing countries. J. Surg. Oncol. 2011;104:162–168. © 2011 Wiley‐Liss, Inc.
In vivo volumetric imaging of microcirculation within human skin under psoriatic conditions using optical microangiography
Authors: Qin Jia , Jiang Jingying , An Lin , Gareau Daniel , Wang Ruikang K.
Published: March 2011

Background and Objective

There is a growing body of evidence suggesting that vascular abnormalities may play crucial role in several dermatologic diseases, such as psoriasis, port wine stain, and skin cancer. To improve our understanding of vascular involvement in these skin conditions, there is a need for a non‐invasive imaging modality capable of assessing 3D microcirculations within skin tissue beds in vivo. This study aims to demonstrate whether ultra‐high sensitive optical microangiography (UHS‐OMAG) is feasible to visualize skin microcirculations in 3D and to quantify microvascular vessel density under normal and psoriatic conditions in vivo.

Study Design/Material and Methods

An UHS‐OMAG system operating at 1,310 nm wavelength was used for in vivo imaging of microcirculation in human skin. The system has a spatial resolution of ∼10 µm × 20 µm (axial × lateral), running at 280 fps to acquire 3D imaging dataset to represent morphology and capillary level microvascular blood perfusion within the scanned skin tissue volume. The sensitivity of the system to the blood flow is as low as ∼4 µm/second. With this system, we performed the imaging experiments on the skin of a volunteer with stable plaque‐type psoriasis. The microcirculation and structural information of normal and diseased skins were compared both qualitatively and quantitatively.

Results

The UHS‐OMAG is capable of differentiating the microcirculation within the normal skins from that in the psoriatic skins. The 3D optical images show that the blood vessel elongation and the dense network in the psoriatic lesion skin, the appearance of which is not observed within the normal skin. Based on the results obtained from one subject, the statistical analyses show that higher blood vessel density presented within the psoriasis lesion skin than that of the normal skin.

Conclusions

UHS‐OMAG can be a valuable tool for imaging skin microcirculations non‐invasively with high‐speed and high‐sensitivity, and therefore may have a useful role in future clinical diagnosis and treatment of dermatologic diseases such as psoriasis in human subjects. Lasers Surg. Med. 42:122–129, 2011 © 2011 Wiley‐Liss, Inc.
Chain transfer and living functionalization of polymethacrylates by group transfer polymerization using ethyl 2‐Phenyl‐2‐butenoate
Authors: Quirk Roderic P. , Ren Jie
Published: March 2011

A living functionalization method has been investigated for group transfer polymerization (GTP) of poly(alkyl methacrylates) using ethyl 2‐phenyl‐2‐butenoate (EPB). The end‐capping reactions of EPB to living trimethylsilyl ketene acetal‐ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by SEC, VPO, UV‐visible spectrosocopy, 1H and 13c NMR spectroscopy. The results of sequential monomer addition, varying stoichiometry and copolymerization indicate that EPB effects efficient chain end functionalization only at stoichiometric concentrations; chain transfer reactions (chain transfer constant = 0.4) occur with excess EPB and during copolymerization with MMA. Chain transfer reactions (chain transfer constant = 0.1) also occur when copolymerizing ethyl 2‐methyl‐2‐butenoate with MMA.
Intramolecular chelation as a factor in the stereochemistry of anionic vinyl polymerization
Authors: Hogen‐Esch T. E. , Meverden C.
Published: March 2011

The methylation (CH3I) of 1,3‐bis(2‐pyridyl)butyllithium in THF at −78°C is highly meso‐selective (>98%) but the selectivity decreases with increasing cation‐size or ‐coordination. The reaction of 1,3‐bis(2‐pyridyl)butyllithium with other electrophiles such as i‐C3H7Br, PhCH2Cl, Me3SiCl (CD3)2CO and 4‐vinylpyridine is also stereoselective under these conditions giving meso‐like products. On the other hand, addition of 2‐vinylpyridine is only slightly selective (64%) and this is consistent with the 65% meso content of P2VP formed by polymerization in the presence of Li ion. The chemistry of the above reactions is rationalized by intramolecular coordination of Li or other cations by the penultimate 2‐pyridyl group and this is supported by equilibria involving proton abstraction of 1,3‐bis(2‐pyridyl)butane and similar compounds by bases having Li, Na or K counterions. It is shown that the tendency for intramolecular chelation is highest for Li and lowest for K ion. Temperature dependence of the above equilibrium shows that intramolecular chelation of Li and Na ions is exothermic (−1.4 and −1.3 kcal respectively) whereas the AH for K ion is very small (−0.5 kcal). Entropies of chelation are slightly positive for Li (0.8 e.u.) and negative for Na and K ions (‐2.60 and −0.40 e.u. respectively). The lack of stereoregular polymerization of 2‐VP in the presence of Li ion is most likely due to the requirement that the Li ion of the newly formed 2‐pyridyl anion is coordinated with the 2‐pyridyl group of the previous asymmetric center. Thus it would appear that intramolecular coordination of metal ion by penultimate 2‐pyridine does not necessarily lead to isotactic‐polymerization.
Group‐transfer polymerization: Recent advances and applications
Authors: Hertler Walter R.
Published: March 2011

Abstract: Catalysis of GTP of MMA with nucleophilic anions on cross‐linked polystyrene supports was studied. With anion‐bound supported catalyst, evidence is presented for formation in solution of ester enolates as reaction intermediates. Study of the cyanide‐catalyzed initiation of GTP of MMA by TMSCN, has provided quantitative data for the association constant Ka for the complexation of cyanide by TMSCN and, by inference, an upper limit for the Ka for the association of this nucleophilic anion with silyl ketene acetals. The effects of i‐propyl‐ and t‐butoxy‐silyl analogs of TMSCN on anion‐complexation and on initiation and propagation of GTP are discussed. Coordination by hydrogen‐bonding of nucleophilic anions to acetonitrile is shown to be the mechanism for “livingness‐enhancement” of anion‐catalyzed GTP at low concentrations of acetonitrile. GTP was used to prepare an ABC triblock dispersant, poly(methacrylic acid)‐block‐poly(2‐phenylethyl methacrylate)‐block‐poly(ethoxytriethylene glycol methacrylate), and the surface activity of an aqueous solution of the potassum salt was compared with that of other polymer architectures.
Breathing new life into the free radical polymerization process
Authors: Georges Michael K. , Veregin Richard P.N. , Hamer Gordon K. , Kazmaier Peter M.
Published: March 2011

Conventional free radical polymerization processes are limited by their inability to be used for the synthesis of resins of controlled molecular weights and complex architecture. New processes are being developed in which the free radical propagating chain is reversibly terminated, allowing the free radical polymerization to behave in a living fashion. A review of these processes is presented, along with preliminary results of chain extension studies of nitroxide‐terminated polystyrene as a model for block copolymer synthesis.
Novel catalyst system for the synthesis of poly(alkylene oxide) with controlled molecular weight
Authors: Inoue Shohei , Aida Takuzo , Sugimoto Hiroshi , Kawamura Chikara , Kuroki Masakatsu
Published: March 2011

An organoaluminum compound with bulky phenoxide groups as a Lewis acid can accelerate much the living polymerization of alkylene oxide initiated with aluminum porphyrin by the coordinative activation of the monomer. This concept can be extented to the polymerization initiated with aluminum Schiff base and tetraazaannulene complexes.
Starburst® dendrimers: A conceptual approach to nanoscopic chemistry and architecture
Authors: Dvornic Petar R. , Tomalia Donald A.
Published: March 2011

The nanoscopic domain of structural complexity, which ranges from 1 to 100 run on a particle size scale includes a relatively unexplored area of science which resides between classical chemistry and molecular biology. This rapidly growing area of science is referred to as nanoscopic chemistry and architecture. Concepts evolving in this area lead to a rich variety of precise structures, architecture and properties. These concepts are based on dendritic macromolecules in general and on Starburst® dendrimers in particular. They envision dendrimers as fundamental building blocks which may be used to synthesize nanoscopic compounds, clusters, polymers, etc. Accordingly, dendrimers are regarded architecturally as functional analogues of atoms; therefore, their potential role in nanoscopic chemistry may be compared to that of the atoms in classical chemistry.
Heterogeneous catalysis for ring opening anionic oligomerisation
Authors: Hamaide T. , Spitz R. , Letourneux J. P. , Clavene J. , Guyot A.
Published: March 2011

New heterogeneous catalysts for ring opening oligomerization are obtained by grafting alkyl aluminium moieties on silica. Adding alcohol in excess causes the formation of aluminium alkoxides and allows the catalytic mode, because of a rapid exchange reaction between the grafted active centers and the free alcohols present in the medium. All the polymer chains are end‐capped by these alcohol molecules, which give functionalized oligomers.
Novel evidence on the chemistry of β‐Lactone anionic polymerization
Authors: Jedliński Zbigniew J. , Kowalczuk Marek , Kurcok Piotr
Published: March 2011

The mechanistic aspects of the β‐lactones anionic polymerization initiated by both classical initiators, i.e. alkali metal alkoxides, and non‐traditional ones, such as supramolecular complexes of alkali metals and alkali metal naphthalenes, are discussed in this paper.
Polymerization of glycolide promoted by ω‐Al‐alkoxide poly(ϵ‐caprolactone) macro‐initiators and formation of stable colloidal dispersions
Authors: Barakat Ibrahim , Dubois Philippe , Jérǒme Robert , Teyssié Philippe , Mazurek Mieczyslaw
Published: March 2011

Block polymerization of glycolide (GA) and ϵ‐caprolactone (ϵ‐CL) has been initiated with aluminum alkoxides, such as Al(OiPr)3 and Et2AlOCH2X (where X = ‐CH2‐Br and ‐CH2O‐C(O)‐C(Me)=CH2), in THF at 40°C. Structure and composition of block copolyesters have been characterized with respect to the molecular weight by NMR spectroscopy and thermal analysis. Copolymerization is typically living, so that block copolyesters have been synthesized with predictable molecular weight and composition. The inherent insolubility of polyglycolide block is responsible for the heterogeneity of the polymerization medium and formation of stable, non‐aqueous colloidal dispersions. This effect is especially pronounced at high GA/ϵ‐CL molar ratios. Colloidal dispersions have been analyzed by transmission electron microscopy (TEM) and photocorrelation spectroscopy (PCS).
Conditions for secondary particle formation in emulsion polymerization systems
Authors: Morrison Bradley R. , Gilbert Robert G.
Published: March 2011

A simple means is deduced for determining conditions for secondary particle formation in emulsion polymerization systems in systems where the amount of added surfactant is below the cmc. A new radical formed from initiator in the aqueous phase will undergo some polymerization with aqueous‐phase monomer, but must have three possible eventual fates: aqueous‐phase termination, entry into a preexisting particle, or creation of a new particle. The means for determining the onset and extent of secondary nucleation is to modify HUFT theory to take into account a successful model for entry [ Macromolecules, 24, 1629 (1991)] which states that entry occurs if and only if the aqueous‐phase radical has achieved a critical degree of polymerization z. Particle formation below the cmc is by homogeneous/coagulative nucleation which (if coagulation is ignored) gives an upper bound to the rate of formation of precursor particles; these are of a degree of polymerization Jcrit > z. The resulting equations are readily solved, and require only a knowledge of the aqueous‐phase propagation and termination rate coefficients (the latter is very high: ca. 109 dm3 mol−1 s−1 for termination between the very small radicals), z and jcrit. Easily applied means are given for estimating all these quantities. The treatment gives good accord with experimentally observed conditions for the onset of secondary nucleation in low‐surfactant systems (including taking in situ micellization into account).
Pulsed laser polymerization of styrene in compartmentalized systems
Authors: Schweer Johannes , van Herk Alex M. , Pijpers Ralf J. , Manders Bart G. , German Anton L.
Published: March 2011

Pulsed laser polymerizations of styrene were performed in microemulsion droplets and in latex particles. From the molecular weight distribution of the resultant polymer either the propagation rate coefficient in the droplets or the monomer concentration in the particles could be determined. Furthermore for microemulsion droplets with a low initiator concentration the rate coefficient for transfer to monomer could be determined. Because in very small particles the termination rate can be very high, instantaneous termination may occur, leading to a shift of the low molecular weight inflection point as the best measure of the propagation rate coefficient to the maximum in the molecular weight distribution.

forming pulsed laser polymerization experiments directly in emulsion systems gives specific information on the special features associated with doing polymerizations in heterogeneous and compartmentalized systems.
Challenges in predicting and controlling particle morphology in latices of commercial complexity
Authors: Sundberg Donald C. , Durant Yvon G.
Published: March 2011

Independent, quantitative models for free energy associated with crosslinked seed latices, and monomer and surfactant at the polymer/water interface have been integrated into a predictive model for latex particle morphology. It has been found that very low levels of crosslinking are predicted to influence the particle morphology in a dramatic fashion. Free energy calculation also highlight the often critical role played by surfactant. Highly active surfactants tend to equalize the two polymer/water interfacial tensions and allow the polymer/water interfacial energy to significantly influence the particle morphology.
An overview of the preparation and use of emulsion polymer particles for the toughening of plastics
Authors: Lovell Peter A.
Published: March 2011

The rationale for rubber‐toughening of brittle plastics is presented together with a discussion of the advantages of using pre‐formed toughening particles prepared by emulsion polymerisation. Rubber‐toughened acrylic and epoxy resin materials are used to illustrate the preparation and use of pre‐formed emulsion polymer particles for toughening. For both types of material, tensile properties are controlled by the volume fraction of rubbery polymer, essentially independent of the size and morphology of the toughening particles. However, under the additional constraint ahead of propagating cracks, toughening particle size and morphology are shown to be important, and to have different effects in the two types of material due to inherent differences in the mechanism of yielding of the matrix polymer.
Synthesis and characterization of core‐shell latexes with microscopic and solid‐state NMR methods
Authors: Landfester K. , Boeffel C. , Lambla M. , Spiess H. W.
Published: March 2011

Core‐shell latexes based on poly (butyl acrylate) and poly(methyl methacrylate) were synthesized with varying shell content at high and low temperature. Electron microscopy combined with advanced solid‐state NMR techniques have been used to investigate the entire structure and the interphase morphology in these core‐shell particles depending on the reaction conditions. Distinct differences of the interphase morphology were found for particles synthesized at high and low temperature.
Miniemulsion polymerization: An approach to control copolymer composition
Authors: Kitzmiller Ervin L. , Miller Christopher M. , David Sudol E. , El‐Aasser Mohamed S.
Published: March 2011

The copolymerization of vinyl acetate (VAc) and vinyl 2‐ethylhexanoate (V2EH) via miniemulsion polymerization is being investigated with the goal of better copolymer composition control. The reaction kinetics and final particle sizes were compared for homopolymerizations and copolymerizations of the two monomers. Enhanced polymerization rates were seen for the miniemulsion polymerizations over their conventional counterparts despite a decreased number of particles. This was attributed to the influence of the reactive surfactant sodium dodecyl allyl sulfosuccinate and low water solubility of the V2EH monomer. Increased nucleation of miniemulsion droplets was sought by incorporation of small amounts of polymer into the droplets. This was first shown to be effective for styrene miniemulsion polymerizations and was subsequently successfully extended to the VAc/V2EH system
Characterization of emulsion polymerizations through ultrasound propagation velocity measurements
Authors: Apostolo M. , Canegallo S. , Siani A. , Morbidelli M.
Published: March 2011

The application of the measurement of ultrasound waves propagation velocity for characterizing emulsion polymerization systems is discussed. The ultrasound velocity sensor provides informations about various properties of interest in emulsion polymerization systems. These include the evaluation of monomer solubility and emulsifier critical micellar concentration in water, the in‐situ and on‐line monitoring of conversion in homo‐ and co‐polymerizations, the investigation of the polymer glass transition and finally the measure of monomer solubility in submicron polymer particles.
Modelling of glass transition and molecular weight distribution in emulsion and suspension copolymerisation
Authors: Guillot Jean
Published: March 2011

SUMMARY. Modelling of emulsion copolymerisation is now more and more used for both mechanistic investigations and process control. Many specific characteristics of monomers, as well as polymerisation in heterogeneous medium can be quite accurately taken into account (temperature, pH, gel effect, crosslinking, inhibition, e.g.). However, a major problem is the extensive number of required parameters. But, depending on the main informations sought (kinetics, microstructure or properties), the number of parameters actually required can be decreased considerably by providing the computer either on‐line or even off‐line with global information on conversion and particle size, from reliable sensors. In addtion to kinetics, many distributions characterising the copolymers can be derived, which in turn lead to the accurate simulation and control of end‐use properties such as glass transition or molecular weight distribution, as shown in this work.
Kinetics of polyelectrolyte network formation in free‐radical copolymerization of acrylic acid and bisacrylamide
Authors: Zhao X. , Zhu S. , Hamielec A. E. , Pelton R. H.
Published: March 2011

Recently, a research/development program has been initiated to investigate the kinetics of synthesis, characterization and applications of polyelectrolyte networks. The research on crosslinking involves both theoretical development and experimentation. Herein, is provided a summary of this work. In the experimental polymerization done to date, acrylic acid (AA)/N.N'‐methylenebisacrylamide (BAM) was studied in considerable detail. The polymerization conditions were: temperature, 50°C; initial monomer concentration, 5 wt%, of which 1.0 mol% is BAM; K2S2O8(KPS) as the initiator, 10−3 mol/L; pH range, 1 − 13; sodium chloride concentrations up to 3.1 mol/L. Measurements included: monomer conversion, polymer composition, sol/gel fraction, swelling ratio, and the densities of primary cyclization, secondary cyclization and crosslinking. It was found that the effect of polymerization parameters on the resulting polymer network microstructure was dramatic, and in particular, the pH and ionic strength of the reaction medium were important parameters. In the theoretical studies, the Tobita‐Hamielec kinetic gelation model was extended to incorporate the concept of ion pair interaction and the divinyl loop formation. The system was treated as a multi‐component polymerization of acrylic acid, acrylate ion, acrylate ion pair and bisacrylamide. The model permits one to investigate the development of the crosslinking density distribution among primary polymer chains during the course of polymerization as a function of pH and ionic strength.
Some industrial aspects of the suspension polymerisation process for making expandable polystyrene and the development of a polystyrene ‐ poly(methyl methacrylate) based system
Authors: Dequatre Claude , Duhamel Thierry , Hermant Anne , Pla Fernand
Published: March 2011

The main industrial concerns associated with the suspension polymerisation process for making expandable polystyrene are given and a polystyrene‐poly(methyl methacrylate) based system prepared by this process is described, characterized by transmission and scanning electron microscopy and glass transition temperature measurements.
Ring opening metathesis polymerization catalysts
Authors: Grubbs R. H. , Hillmyer M. , Li R. , Diaz E. , Nguyen S. T.
Published: March 2011

Over the past eight years, early transition metal catalysts for the ring opening metathesis polymerization of cyclic olefins have been developed. These catalysts are simple organometallic complexes containing metal carbon multiple bonds that in most cases polymerize olefins by a living process. These catalysts have been used to prepare a family of near monodispersed and structurally homogeneous polymers. A series of group VIII ROMP catalysts that allow a wide range of functionality to be incorporated into the polymer side chains have recently been prepared. This most important members of this family of complexes are the bisphosphinedihaloruthenium carbene complexes. These catalysts show excellent functional group stability and can be used to prepare well defined telechelic polymers, polyolefins with ordered functionality, and highly functionalized block copolymers.
Synthesis of ultrathin polymer films by self assembly
Authors: Kunitake Toyoki
Published: March 2011

Recent progresses in the self assembly of ultrathin polymer films are described. Bilayer membranes of polymeric hydrogen‐bond networks are formed in water. Two‐dimensional networks of organic and inorganic polymers are formed in cast films of synthetic bilayer membranes to give stable multilayer films upon removal of the matrices. The monolayer at the air‐water interface constitutes suitable templates for 2D polymer networks, and it may be either removed or part of the 2D film. Successive adsorption of polycations and polyanions under carefully controlled conditions produces layered polyion complexes in the stepwise manner. Various polymer chains are epitaxially adsorbed onto graphite. All these results indicate that molecularly defined 2D polymer structures are readily available.
Detailed mechanism of radical high polymerization of sterically hindered dialkyl fumarates
Authors: Matsumoto Akikazu , Otsu Takayuki
Published: March 2011

The radical polymerization kinetics and mechanism of sterically hindered dialkyl fumarates (DRF) bearing various ester alkyl groups are described comprehensively. The overall polymerization reactivity of DRF, the initiation mechanism and the reactivity of the primary radicals in the polymerizations with azo initiators, the determination of the propagation and termination rate constants by means of electron spin resonance spectroscopy, the propagation mechanism and the microstructure of the polymers, and the chain rigidity of poly(DRF) and bimolecular termination process are discussed.
Titanium‐based lewis acids for living cationic polymerizations of vinyl ethers and styrene: Control of lewis acidity in design of initiating systems
Authors: Sawamoto Mitsuo , Kamigaito Masami
Published: March 2011

This brief account discusses the development of HCl/TiCl4‐n(OR)n (n = 1–4), the titanium‐based new initiating systems for living cationic polymerizations of vinyl ethers and styrene. The focus of this development is controlling the Lewis acidity of the metal halide components [TiCl4‐n(OR)n] or “activators” in relation to the structure of the monomers. Thus, for vinyl ethers, relatively mild Lewis acids such as TiCl(OiPr)3 and TiCl2(OiPr)2 are effective, whereas for styrene, a stronger Lewis acid such as TiCl3(OiPr) is employed along with an added salt (nBu4N+Cl−). In both cases, living polymers of controlled molecular weights can be obtained in methylene chloride solvent at −15°C.
Polymerizations with contribution of covalent and ionic species
Authors: Penczek Stanislaw , Szymanski Ryszard , Duda Andrzej
Published: March 2011

The similarities and dissimilarities between the ring‐opening and vinyl cationic polymerizations are discussed for systems with simultaneous presence of covalent and ionic species. The common denominator in comparing kinetics of polymerization of these systems is the comparison of the total times of polymerization with the time elapsing when a given macromolecule is active (i.e. ionic) and inactive (e.g. covalent in cationic vinyl and ring‐opening polymerization). In the cationic ring‐opening polymerization the reactivation of covalent species proceeds mostly by intramolecular nucleophilic dipole‐dipole reaction (conformationally assisted) involving the chain unit adjacent to growing ester chain end. This reaction is fast (e.g. in THF polymerization) and is responsible for covalent ion‐pair interconversion. In the cationic vinyl polymerization this path does not exist but covalent species (esters) can be faster ionized by using of the nucleophile, increasing thus the rate of exchange between esters and ions. This process provides one of the possible ways for converting the non‐living polymerization into the living‐dormant process. The cationic polymerizations are then compared with covalent (pseudoanionic) polymerization of cyclic esters, initiated with covalent metal alkoxides like R2AlOR' or Al(OR)3.
Hydrogen bonding and the self‐assembly of supramolecular liquid‐crystalline materials
Authors: Kato Takashi , Fréchet Jean M. J.
Published: March 2011

Novel supramolecular liquid‐crystalline materials have been obtained by the hydrogen bond formation between different and independent molecules. The self‐assembly of carboxylic acid and pyridine moieties that function as H‐bond donors and acceptors, respectively, results in the formation of mesogenic complex structures. A wide variety of liquid‐crystalline low molecular weight complexes have been prepared using this approach. This concept has been extended to the polymeric systems. Hydrogen‐bonded liquid‐crystalline polymers that exhibit mesophases over wide temperature ranges, ferroelectricity or photo‐responsibility have been prepared by the molecular association. Moreover, liquid‐crystalline polymer networks that show reversible smectic‐isotropic phase transitions have been formed by the hydrogen bonds. The dynamics of the hydrogen bonding may contribute to the induction of the mesomorphism of the networks.
Design and synthesis of macromolecular structures from self‐assembling building blocks
Authors: van Nunen J. L. M. , Schenning A. P. H. J. , Hafkamp R. J. H. , van Nostrum C. F. , Feiters M. C. , Nolte R. J. M.
Published: March 2011

The self‐assembling properties of a variety of building‐blocks are used to generate different types of nanostructures, e.g. molecular golfballs, molecular tubes, and molecular braids.
Design, synthesis and properties of molecular composites of rod‐like polymers
Authors: Wegner Gerhard
Published: March 2011

Processing and performance of fiber reinforced polymers suffer from problems related to the heterogeneous nature of the composites. The strong impact of the nature of the interface between fibers and matrix adds to the complication of the field. Consequently many attempts have been made to reduce the cross‐section of the reinforcing fibers to molecular dimensions and to increase the compatibility between the rod‐like molecules or bundles of molecules and the isotropic matrix of ordinary flexible polymers. All such attempts have failed, mainly for reasons of thermodynamics which predict immiscibility of rods and coils on the molecular level. A possibility to create structures in which molecular rods are embedded in a continuous matrix of flexible chain segments exists nevertheless.1 Rod‐like backbone structures decorated with a skin of flexible side chains of moderate length in terms of the number of carbon atoms (typically C6 ‐ C18‐side chains) have been synthesized and tested for the spontaneous formation of molecular composites. Some of the materials built along this principle can be processed by solution casting or even melt extrusion. The academically more interesting materials can be built up layerwise by a modified Langmuir‐Blodgett technique. The latter process gives rise to monodomain textures which allow for straight‐forward testing of the mechanical properties by optical means (Brillouin‐spectroscopy) and by piezoquartz‐techniques.

Hairy‐rod macromolecules can also be synthesized which contain crosslinkable side chains. Thus, after formation of layered, oriented structures, these can be crosslinked photochemically or by curing. The result is a network, which is unidirectionally reinforced by the rod‐like macromolecules. These novel types of networks can serve as membranes by which size exclusion is achieved via control of the distance between adjacent backbone molecules in the matrix. Recent synthetic advances in the field have concentrated on hairy‐rod macromolecules based on cellulose alkyl ethers and on derivatives of poly‐(p‐phenylene). The latter materials serve as examples of systems which can be processed by casting and extrusion processes. Due to their excellent thermal stability relevant data on the rheological and mechanical‐dynamical data have become available. These data serve to document the unique behavior of the hairy‐rod macromolecules as bulk materials.
Supramolecular devices for targeting dna into cells: Fundamentals and perspectives
Authors: Kabanov V. A. , Kabanov A. V.
Published: March 2011

Interaction of DNA polyanions with polycations results in spontaneous electrostatic coupling of opposite charged macromolecules and formation of interpolyelectrolyte complexes (IPECs). If the appropriate conditions are met such complexes can be obtained in the form of equilibrated and well defined water‐soluble supramolecular (actually supramacromolecular) species. Soluble IPECs formed by coupling of cyclic DNA (plasmid DNA) with various polycations are found to be efficient devices enhencing plasmid penetration into intact cells, probably, due to increase of a membrane activity of the complexed DNA. The strategy based on certain fundamental properties of IPECs seems to be a general approach for effective targeting of a genetic material to cells not only in vitro but also in vivo. These properties including those of DNA containing IPECs as well as the representative examples of gene delivery using IPEC supramacromolecular devices are reviewed and discussed.
Self‐assembled networks of conducting polyaniline in bulk polymers: A new class of conducting polymer blends
Authors: Heeger Alan J. , Smith Paul , Cao Yong
Published: March 2011

This review of the current status of conducting polymers will focus on recent progress which demonstrates that the initial promise of the late 1970's has become reality. Conducting polymers are now available as materials with truly unique properties: They combine the important electronic and optical properties of semiconductors and metals with the attractive mechanical properties and processing advantages of polymers. Conducting polymer blends based upon polyaniline (PANI) are a new class of materials in which the threshold for the onset of electrical conductivity (σ) can be reduced to volume fractions below 1%, well below that required for classical percolation (16% by volume for globular conducting objects dispersed in an insulating matrix in three dimensions). The origin of this remarkably low threshold for the onset of electrical conductivity is the self‐assembled network morphology of the PANI polyblends which forms during the course of liquid‐liquid separation. Since the average density of the conducting network near threshold is small, the conductivity increases smoothly and continuously over many orders of magnitude as the concentration of conducting polymer increases above threshold. The low percolation threshold and the continuous increase of σ(f) above threshold are particularly important; as a result of this combination, conducting polyblends can be reproducibly fabricated with controlled levels of electrical conductivity while retaining the desired mechanical properties of the matrix polymer.1‐3)
High performance nonlinear optical chromophores
Authors: Shi R. F. , Yamada S. , Wu M. H. , Cai Y. M. , Zamani‐Khamiri O. , Garito A. F.
Published: March 2011

Both the linear and nonlinear optical properties of our newly designed high temperature electrooptic chromophores are discussed. In addition to the charge separated mechanism for the new chromophores, isomer effects are equally important in determining the optical properties of the new class.
Electrical field induced phase‐matched second harmonic generation in low Tg polymer waveguides
Authors: Watanabe T. , Zou D. , Mohamed B. , Usui H. , Miyata S. , Claude C. , Okamoto Y.
Published: March 2011

Second‐harmonic generation in the guided waveguide configuration is very attractive because a high fundamental power density can be coupled over long propagation length therefore remarkably high conversion efficiencies can be expected compared to bulk materials.1 Organic SHG devices in optical waveguides have not been developed extensively because of the difficulty encountered in phase‐matching. To avoid this problem, the use of an artificial periodic structure, Cerenkov radiation, and non‐colinear light path geometry have already been demonstrated. Recently, we reported an electric field‐induced dynamic phase‐matching in a guided wave configuration using a main‐chain polymer in which the effective phase‐matching thickness can be controlled by an applied electric field.2 This technique is able to increase the waveguide dimension tolerances of phase‐matching condition. In the case of a main‐chain polymer, the thermal optic effects due to the heating prevent to satisfy the optimum phase‐matching conditions, which causes a reduction in the conversion efficiency of devices. In order to overcome this problem, we have synthesized novel low glass transition temperature (Tg) nonlinear optical (NLO) polymers.

In this presentation, we will discuss an electric field‐induced dynamic phase‐matching of a multilayer waveguide at room temperature using a low Tg NLO polymer which can increase both the waveguide dimension tolerances and overlap integral. Using this technique, efficient phase‐matched SHG was generated from p‐nitroaniline grafted NLO materials. The dimension tolerance of waveguides under an electric field will be described.
Large‐amplitude motion in polymer crystals and mesophases
Authors: Wunderlich Bernhard
Published: March 2011

Large‐amplitude motion of macromolecules involves mainly rotation about bonds (conformational motion). In the liquid phases, the large‐amplitude motion is coupled with disorder and accounts for the flow and viscoelastic behavior. Perfectly ordered crystals, in contrast, permit only little large‐amplitude motion. The mesophases are intermediate in order and mobility. In crystals, large‐amplitude motion leads initially to gauche defects and kinks (conformational defects), and ultimately may produce conformationally disordered crystals (condis crystals). Molecular dynamics simulations of crystals with up to 30 000 atoms have been carried out. They show the mechanism of defect formation, permit the study of the distribution of defects, and lead to a visualization of the hexagonal crystal phase. The main‐chain liquid‐crystalline macromolecules and condis crystals, the two mesophases of polymers, can be distinguished on the basis of an analysis of the phase separation (partial crystallinity), present in condis crystals and not in liquid crystals. Solid state NMR is the tool of choice for the detection of mobile and rigid phases. In highly drawn fibers one can find four different states of order and mobility. Besides the (defect) crystalline phase and the isotropic amorphous phase, an intermediate oriented phase and a rigid amorphous phase exist.
Anxiety rating scales in Parkinson's disease: A validation study of the Hamilton anxiety rating scale, the Beck anxiety inventory, and the hospital anxiety and depression scale
Authors: Leentjens Albert F.G. , Dujardin Kathy , Marsh Laura , Richard Irene H. , Starkstein Sergio E. , Martinez‐Martin Pablo
Published: March 2011

Background:

Anxiety is a prevalent and disabling condition in Parkinson's disease (PD). The lack of anxiety rating scales validated for this population hampers research into anxiety in PD. The aim of this study is to assess the clinimetric properties of the Hamilton anxiety rating scale (HARS), the Beck anxiety inventory (BAI), and the hospital anxiety and depression scale (HADS) in PD patients.

Design:

Three hundred forty‐two PD patients underwent a standardized assessment including a structured interview for diagnostic and statistical manual diagnoses of anxiety disorders and completion of the HARS, BAI, and HADS. Inter‐rater reliability of the HARS was assessed in 60 patients; test‐retest reliability of the BAI and HADS in 213 and 217 patients, respectively.

Results:

Thirty‐four percent of patients suffered from an anxiety disorder, whereas an additional 11.4% had clinically significant anxiety symptoms in the absence of a diagnosis of anxiety disorder. Acceptability, score distribution, and known groups validity over different levels of anxiety were adequate. Inter‐rater reliability for the HARS and test‐retest reliability for the BAI and HADS were good. The HARS, but not the BAI and HADS, had a satisfactory inter‐item correlation, convergent validity and factorial structure. For all scales, the positive predictive value was poor, and the negative predictive value was moderate.

Conclusions:

Given the adequate known groups validity of all three rating scales, each of these scales is likely to be useful in clinical practice or research for evaluation of symptom severity. Limitations in the construct validity of the anxiety scales in this study raise questions regarding suitability for their use in PD. © 2011 Movement Disorder Society
Anorganische Chemie 2010
Authors: Fischer Roland C. , Weigand Jan J. , Wolf Robert , Rau Sven , Schatzschneider Ulrich
Published: March 2011

Molekülchemie der Hauptgruppenelemente: Trends wie die Stabilisierung ungewöhnlicher Bindungsumgebungen durch Carbene, die Darstellung persistenter Radikale, neuartige komplexchemische Wirtsysteme und Cluster als Liganden setzen sich fort. Koordinationschemie: Neuartige Metall‐Metall‐Bindungen erregten große Aufmerksamkeit; der Trend, metallorganische Gerüstverbindungen als Reaktionsraum oder Modellsystem zu nutzen, setzt sich fort. Bioanorganik: Die Aktivierung kleiner Moleküle wie H2 und CH4 durch Metalloenzyme hielt letztes Jahr einige Überraschungen parat.