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Nanoemulsion polymerization is a novel process for the synthesis of specialty-purpose latexes. In this work, styrene and 1,4-butadiene polymerization are demonstrated through a nanoemulsion-based process. Conventional emulsifiers like rosin soap and fatty soaps are used to prepare base emulsions having 2-10 nm particle size through the sonication process. The high surface area and higher number of micelles allow superior mixing of monomers and initiators leading to more efficient and rapid reaction. Additionally, the use of nanoemulsion improves the efficiency and quality of emulsion with higher productivity. These latexes have unique high molecular weight polymers with smaller particle size which is the most desirable criterion for coating applications. Finally, nanoemulsion-based polymer is compared with conventional macroemulsion-based product. KEYWORDS emulsion, emulsion polymerization, macroemulsion, nanoemulsion, reaction kinetics, sonication, styrene butadiene latex, 1 | INTRODUCTION Emulsion-based process is considered as one of the safest, most eco-friendly, and green approach for the synthesis of high-quality polymers. [1-3] Due to cost economic, green, and [...]

Polyalphaolefins (PAOs) have potential applications as synthetic lubricants in automotive, industrial, and aviation equipment, including motor oils, hydraulic, and transmission fluids. During the present work, the linear higher alpha olefins (LHAOs) ranging from [C.sub.8] to [C.sub.12] present in the refinery stream (RS) are polymerized using Lewis acid catalyst combination of transition metal halide of Group 4, that is, Ti[Cl.sub.4] and Group 13 metal halide, that is, Al[Cl.sub.3]. The influence of Ti:Al (1:1, 1.5:1, 1:2, and 2:1) molar ratios, polymerization time (2-8 h), and polymerization temperature (100-170[degrees]C) on the polymerization behavior of LHAOs were also investigated. The synthesized PAOs were characterized using different analytical techniques, including [sup.1]H-[sup.13]C nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The performance evaluation of PAOs was evaluated in terms of density, pour point, oxidation stability, thermal stability, kinematic viscosity (KV), viscosity index (VI), friction, and corrosion studies. The synthesized PAOs exhibit low pour point ( KEYWORDS cationic polymerization, linear higher alpha olefins, polyalphaolefins, synthetic lubricants, 1 | INTRODUCTION Polyalphaolefins (PAOs) are saturated hydrocarbons widely used in the production of high-performance synthetic lubricants. They are mainly synthesized from linear higher alpha olefins (LHAOs) ranging from [C.sub.8] [...]

In this work, effects of the silicone resins on copolymerization of the acrylated epoxidized soybean oil were investigated. Rheological characteristics, curing behaviors, and thermal properties of acrylate epoxy soybean oil prepolymer (AP), silicone prepolymer (SP), and their hybrids (AP/SP) were studied in detail. Spots in a snowflake pattern were observed on the fracture section surface of cured AP/SP hybrid resins by SEM. According to the change of polymer groups revealed by Fourier transform infrared, a possible reaction between AP and SP was proposed. The curing mechanism of AP/SP hybrids was researched, which was suggested to be an autocatalytic curing process. Furthermore, the degree of cure, the activation energy ([E.sub.[alpha]]) and the reaction frequency factor (A) of the curing reaction were estimated. It was found that the cure kinetic of AP/SP hybrid resins could be well-described by a SesthkBergglen model with the numerical optimization based on the Kissinger method and the Malek approach. The experimental results show that the mass retention rates of AP/SP hybrid resins were significantly increased after curing, indicating that the thermal stability of AP was enhanced with the addition of SP. KEYWORDS copolymerization, curing kinetics, epoxy soybean oil, hybrid resins, prepolymer, silicone resin, orcid.org/0000-0001-6591-9219 1 | INTRODUCTION The white pollution caused by petroleum-based polymers has become more and more serious to the global ecological environment, which also consumed a large amount of petrochemical [...]

This study reports nanocomposite synthesis based on high-density polyethylene with carbon nanotubes through in situ polymerization by coordination, and the use of an aluminohydride zirconocene/MAO system as a catalyst. Nanocomposites of linear polyethylene exhibit higher molar masses than pure high-density polyethylene synthesized under similar conditions; where multiwalled carbon nanotubes (MWCNTs) acted as nucleating agents, shifting the crystallization temperature to higher values than neat high-density polyethylene. Well-dispersed MWCNTs in the HDPE matrices of the obtained nanocomposites are observed by SEM, where most of the nanocomposites showed an improvement in their thermal stability and electric conductivity, besides it is possible to obtain nanocomposites containing up to 41 wt% of nanofiller in the polymeric matrix. The aluminohydride complex n-Bu[Cp.sub.2]Zr[H.sub.3]Al[H.sub.2], activated with MAO at Al/Zr ratios of 2000, produced homogeneous HDPE/MWCNT composites under in situ polymerization conditions, at 70[degrees] C and 2.9 bar of ethylene pressure, with minimal residual alumina in the HDPE matrix. KEYWORDS electrical properties, HDPE nanocomposites, in situ polymerizations, multiwalled carbon nanotubes, thermal properties, 1 | INTRODUCTION Currently, polyethylene (PE) is one of the most used materials for a wide variety of applications in many important areas such as construction, containers and packing, agriculture, [...]

Abstract A series of polyethylene terephthalate-polyethylene naphthalate (PETN) copolymer films with excellent oxygen barrier properties were prepared by introducing trace amounts of hydroxy-terminated polybutadiene (HTPB) into PETN via in-situ polymerization. [...]

Abstract Copolymers of propylene/1-octene and propylene/1-hexene were synthesized in slurry phase polymerization using Mg[Cl.sub.2]/Ti[Cl.sub.4]/Diester based catalyst system. The Al/Do (co-catalyst/external donor), Al/Ti (co-catalyst/catalyst) mole ratio variations were investigated for effect [...]

In this contribution, we reported the investigation of natural rubber (NR) reinforced by silicon dioxide-graft-polyisoprene (Si[O.sub.2]-g-PIP) core-shell nanoparticle. First, the hydroxyl on the surface of the Si[O.sub.2] nanoparticles was reacted with 2-methyl2-[(dodecylsulfanylthiocarbonyl) sulfanyl] propanoic acid to produce trithioester-capped Si[O.sub.2] (denoted as Si[O.sub.2]-CTA). Si[O.sub.2]-CTA was used as a nanoparticle chain transfer agent, and Si[O.sub.2]-g-PIP core-shell nanoparticles were synthesized via reversible addition-fragmentation chain transfer polymerization (RAFT). The results of FTIR spectroscopy and TGA showed that the grafting weight of the PIP block in Si[O.sub.2]-g-PIP was 2.1 wt%. Si[O.sub.2]-g-PIP and Si[O.sub.2] were simultaneously incorporated into NR. The curing properties of the NR compounds showed that the vulcanization rates of the NR/Si[O.sub.2]-g-PIP compounds were much higher than those of NR/silica compounds. The results of scanning electron microscopy showed that Si[O.sub.2] microdomains in the NR/Si[O.sub.2]-g-PIP vulcanizate were much better disperse and distribute than Si[O.sub.2] microdomains in the NR/Si[O.sub.2] composite. The filler-rubber interaction of the NR/Si[O.sub.2]-g-PIP composite endowed the composite with improved mechanical properties., INTRODUCTION Nanosilica (Si[O.sub.2]) is an important nanofiller and has been widely used for the reinforcement of rubbers and plastics. Nano-Si[O.sub.2] improves the mechanical properties of rubbers and plastics [1--4]; however, [...]

Copper(II) complexes carrying pyridylmethyleneaminobenzoate or -propanoate ligands, LCuX, were prepared in one-pot reactions from pyridinecarboxaldehyde, aminobenzoic acid or [beta]-alanine, and Cu[X.sub.2] (X = Cl, N[O.sub.3], OAc, or OTf). All complexes were characterized by single-crystal X-ray diffraction studies and formed either dimers, tetramers, or coordination polymers. Attempted preparation of the respective alkoxide complexes, LCu(OR), was unsuccessful, but use of LCuX/NaOMe mixtures in rac-lactide polymerization indicated under some conditions coordination-insertion polymerization via a copper alkoxide as the mechanism. The complexes performed poorly in rac-lactide polymerization, showing low activities (12 h to completion at 140 [degrees]C), low to moderate heterotacticity ([P.sub.r] = 0.6-0.8), and poor polymer molecular weight control (intramolecular transesterification). They were competent catalysts for Chan-Evans-Lam couplings with phenylboronic acid, without any indication of side reactions such as deboration or aryl homocoupling. The complexes were active in undried methanol, without addition of base, ligand, or molecular sieves. Aniline, n-octylamine, and cyclohexylamine were coupled quantitatively under identical reaction conditions. There is only little influence of the anion on activities (less than a factor of 2) but a strong influence on induction periods. The complexes were not active in CEL coupling with alcohols, phenols, or alkylboronic acids. Key words: copper complexes, homogenous catalysis, Chan-Evans-Lam coupling, lactide polymerization, mechanism. Nous avons prepare des complexes de cuivre(II) de formule LCuX portant des ligands pyridylmethyleneaminobenzoate ou -propanoate par reactions en recipient unique entre le pyridinecarboxaldehyde et l'acide aminobenzoique ou la b-alanine, en presence de Cu[X.sub.2] (X = Cl, N[O.sub.3], OAc ou OTf). Tous les complexes ont ete caracterises par diffraction des rayons X sur monocristal et se presentaient sous forme soit de dimeres, de tetrameres ou de polymeres de coordination. Les tentatives de preparation des complexes d'alcoolate correspondants, de formule LCu(OR), ont echoue. Cependant, l'utilisation de melanges de LCuX/NaOMe pour la polymerisation du rac-lactide indiquait, dans certaines conditions, une polymerisation de type coordination-insertion dont le mecanisme ferait intervenir un alcoolate de cuivre comme intermediaire. Les complexes ont produit de pietres resultats pour effectuer la polymerisation du rac-lactide, presentant une faible activite (12 h pour une reaction complete a 140 [degré]C), un heterotacticite faible a moderee ([P.sub.r] = 0,6-0,8) et offrant un faible controle sur le poids moleculaire du polymere (transesterification intrmoleculaire). Cependant, ils se sont reveles aptes a catalyser des couplages de Chan-Evans-Lam avec l'acide phenylboronique, et ce, sans aucun signe de reaction secondaire telle que la deboration ou l'homocouplage d'aryles. Les complexes etaient actifs dans le methanol non asseche, sans base, ligand ou tamis moleculaires ajoutes. L'aniline, la n-octylamine et la cyclohexylamine ont procede au couplage de maniere quantitative dans les memes conditions reactionnelles. L'anion n'exerce que peu d'influence sur l'activite (par un facteur inferieur a 2), mais exerce une forte influence sur la periode d'induction. Les complexes se sont reveles inactifs dans le couplage de Chan-Evans-Lam avec des alcools, des phenols ou des acides alkylboroniques. [Traduit par la Redaction] Mots-cles : complexes de cuivre, catalyse homogene, couplage de Chan-Evans-Lam, polymerisation de lactide, mecanisme., Introduction Copper has found widespread use in catalytic transformations, (1,2) but its application in polymerization catalysis has caused some controversy. It has been widely employed in radical polymerizations involving a [...]

The graft polymerization of 4-imidazole acrylic acid (IA) onto polyurethane (PU) was conducted to prepare antifungal PU with enhanced water compatibilities. Poly(IA) chains with different IA content were grafted onto PU in an IA series, whereas they were not grafted onto PU in a control CIA series. The carboxyl contents of the IA and CIA series, as determined by acid/base titration, proportionally increased with an increase in the IA feed, but the water contact angles of only the IA series significantly decreased compared with those of the CIA series and plain PU. The maximum tensile stress of the IA series sharply increased because of the chemical linking of the grafted poly(IA) chains, whereas the tensile strain at break was not affected by the grafted poly(IA) chains. The shape recovery of the IA series at 10[degrees]C notably improved with the grafting of poly(IA) chains, whereas that of the CIA series did not increase at all. The IA series samples completely suppressed fungal growth on PU because of the grafted imidazole groups and hydrophilic carboxyl groups., INTRODUCTIONAntimicrobial polymers have been the focus of research in various fields, including healthcare products, textiles, food packaging, appliances, and medical supplies [1,2]. Numerous types of antimicrobial polymers were introduced and [...]

Poly(cyclohexane-1,4-dimethylene cyclohexane-1,4-dicarboxylate) has been prepared by solid-state polymerization using 1,4-cyclohexanedicarboxylic acid or its di-methylester and 1,4-cyclohexanedimethanol as monomers. The process consists in a first step in which a prepolymer with high crystallinity is prepared by melt polycondensation and then submitted to solid-state polymerization (SSP) at a temperature below the melting temperature of the polymer. The use of the solid state process permits to minimize the isomerization from the trans to the cis form in the polymer chain and therefore a polyester with higher crystallinity and melting temperature, compared to those synthesized by the traditional polycondensation routes, can be obtained. For this reason, the SSP process allows to obtain materials with thermo-mechanical properties that cannot be achieved using the standard polycondensation method. Moreover, the process does not involve a complex multi-step temperature ramp as in the case of the polycondensation process., INTRODUCTIONPoly(cyclohexane-1,4-dimethylene cyclohexane-1,4-dicarboxylate) (PCCD) polymers are of current interest as weatherable materials, due to the fact that they are completely aliphatic [1-3], do not absorb UV, and provide resistance to light [...]

Pathogenic bacteria such as Escherichia coli assemble surface structures termed pili, or fimbriae, to mediate binding to host-cell receptors.sup.1. Type 1 pili are assembled via the conserved chaperone-usher pathway.sup.2-5. The outer-membrane usher FimD recruits pilus subunits bound by the chaperone FimC via the periplasmic N-terminal domain of the usher. Subunit translocation through the [beta]-barrel channel of the usher occurs at the two C-terminal domains (which we label CTD1 and CTD2) of this protein. How the chaperone-subunit complex bound to the N-terminal domain is handed over to the C-terminal domains, as well as the timing of subunit polymerization into the growing pilus, have previously been unclear. Here we use cryo-electron microscopy to capture a pilus assembly intermediate (FimD-FimC-FimF-FimG-FimH) in a conformation in which FimD is in the process of handing over the chaperone-bound end of the growing pilus to the C-terminal domains. In this structure, FimF has already polymerized with FimG, and the N-terminal domain of FimD swings over to bind CTD2; the N-terminal domain maintains contact with FimC-FimF, while at the same time permitting access to the C-terminal domains. FimD has an intrinsically disordered N-terminal tail that precedes the N-terminal domain. This N-terminal tail folds into a helical motif upon recruiting the FimC-subunit complex, but reorganizes into a loop to bind CTD2 during handover. Because both the N-terminal and C-terminal domains of FimD are bound to the end of the growing pilus, the structure further suggests a mechanism for stabilizing the assembly intermediate to prevent the pilus fibre diffusing away during the incorporation of thousands of subunits.The structure of a pilus assembly intermediate reveals the timing of subunit polymerization and how chaperone-subunit complexes are transferred from N-terminal to C-terminal domains of the usher in the formation of bacterial pili., Author(s): Minge Du [sup.1] , Zuanning Yuan [sup.1] , Hongjun Yu [sup.1] , Nadine Henderson [sup.2] [sup.3] , Samema Sarowar [sup.4] , Gongpu Zhao [sup.5] , Glenn T. Werneburg [sup.2] [...]

Collagen is a natural polymer that cannot be applied freely to specific end uses due to its inherent drawbacks. Grafting polymerization of methyl methacrylate-co-ethyl acrylate was applied to modify the surface of acid soluble collagen (ASC). The main objective of this work is not only reducing the hydrophilic behavior of collagen on which has been concentrated so far but also successfully showed that the introduced co-monomers onto ASC can alter the thermal behavior of the resulted copolymer. The level of branched copolymer significantly influenced the initial viscosity in studied co-monomer feed ratios. The graft polymerization of collagen demonstrated the meaningful change in conductivity value of branched copolymer, where the copolymer in side chain with low dielectric constant covalently bonded onto the ASC. The increase in the co-monomer feed ratio had no significant effect on conductivity value of copolymer, afterwards. The novelty of this work was determined to achieve the new copolymer onto the backbone of collagen to be used in specific thermally stabled end uses that the sufficient chain entanglements improve the flexibility of final product., INTRODUCTION An idealistic approach in modern life is gradual replacement of natural resources with synthetics for achieving a sustainable living environment [1, 2]. In materials and particularly in polymers, it [...]

We demonstrated a practical microfluidic approach to fabricate extremely monodisperse millimeter-sized poly(divinylbenzene) (PDVB) foam shells with the comparable double emulsion templates. At millimeter scale, the emulsification process was more complex and more difficult to control due to the very large characteristic sizes and velocities. A new kind of three-dimension co-axial microfluidic chip including a Y-shaped compound channels was designed to maintain more stable and robust flow field and regular emulsification. The hydrodynamic features of the double-emulsion droplet formation were investigated. The results showed perfect encapsulation and continuous emulsification could be obtained by one-step dripping ([Ca.sub.outer] [member of] (0.018,0.09)). The size of the outlet channel would be comparable with the target droplet. Besides, droplet diameters could similarly be plotted as a function of capillary number close to the general microfluidic ones. After photo-polymerization and supercritical drying, spherical and concentric PDVB foam shells were obtained to satisfy the inertial fusion energy experiments with large diameter (3-5.45 mm), thin wall thickness (50-250 [micro]m), low density (50-300 mg/[cm.sup.3]), and a less than 0.1% polydispersity., INTRODUCTION Due to the particular core-shell structures, millimeter-scale porous polymeric foam shells have a broad range of applications, such as controlled-release, micro-reactors, carriers of biologically active species, ion exchange resins [...]

Depolymerization is a potentially viable means of recycling waste polymers, converting them back into monomers or other useful compounds. Terephthalic acid (TPA) and 1,4-butanediol (1,4-BD) are the depolymerization monomer products of polybutylene terephthalate. Their yields from depolymerization in hot compressed water (HCW) were previously found to be lower than reported theoretical values. Thus, the phase behavior, stability, and mechanism of monomers in HCW were investigated in a fused silica capillary reactor (FSCR) and a stainless steel autoclave reactor. Phase change observations showed that TPA was completely dissolved in water at 300[degrees]C, was relatively stable at 320 to 350[degrees]C, and that its recovery significantly decreased at temperatures above 350[degrees]C. The decomposition of TPA increased with increasing heating time. However, the recovery of 1,4-BD decreased rapidly with increasing temperature or heating time. A mechanism for the stability of TPA and 1,4-BD is proposed based on their depolymerization products. The products were quantified by Fourier transform-infrared spectroscopy, high-performance liquid chromatography, and gas chromatography coupled with mass spectrometry. The wall effect of the stainless steel autoclave promoted the decomposition of TPA and 1,4-BD in HCW. POLYM. ENG. SCI., 57:544-549, 2017. [C] 2016 Society of Plastics Engineers, INTRODUCTION Polybutylene terephthalate (PBT) is an important engineering thermoplastic in automotive and electrical applications. It exhibits favorable electrical and mechanical properties, including thermal stability, low moisture absorption, good solvent resistance, [...]

Abstract: The compound 5-aminoquinoline (AQ) was treated with horseradish peroxidase (HRP) and [H.sub.2][O.sub.2] in a reaction medium containing a dioxane:phosphate buffer mixture (70:30). Products (OAQ) with a degree of polymerization [...]

The creep behavior and solid and melt linear viscoelasticity of novel polyamide 6 (PA6) nanocomposites reinforced with cellulose nanocrystals (CNCs) prepared via in situ anionic ring-opening polymerization (ROP) were investigated to accelerate research efforts to develop new polymeric materials with improved properties for lightweight, load-bearing applications. The obtained results showed that incorporation of relatively small amounts of, INTRODUCTION Polymer nanocomposites are an important class of polymer based materials that have found numerous applications in science, engineering and advanced technologies due to their unique properties that are attainable [...]

The focus of this research is a special technique to investigate the polymerization of the water soluble monomer acrylic acid in a rheometer. The rheokinetics is an approach to measure the viscosity of reactive solutions during polymerization and consequently monitor the reaction kinetics. Results are presented on the initial stage of acrylic acid polymerization in water at different temperatures, 50, 60, and 70°C with mass fractions between 12.5% and 35% and two different initiator ratios, 0.8 and 1.2 mmol/mol. An empirical viscosity model to describe the shear viscosity over time is available. With reaction kinetics from literature and the viscosity model, a determination of the exponents a and b of a rheokinetics model is undertaken; a is 1.5 and b is 1.9-2.8. Further investigations show that it is possible to analyze the monomer conversion at a certain time when quenching the reaction and measure the polymer concentration. With the use of a simple reaction model, the conversion is calculated like in a batch reactor, representing the gap in the rheometer. Differences with the stepwise measured conversions are not very high. A rheokinetics approach is consequently useful for optimizing processes, where fast reactions in a continuous flow are present., INTRODUCTION Many investigations focus on the reaction kinetics of acrylic acid in water applying different methods of analysis. Usually the reaction is set in an isothermal batch reactor and the [...]

Due to its inertness and solubility in vinylidene fluoride, (VF2), supercritical carbon dioxide is used as a replacement solvent for producing polyvinylidene fluoride (PVDF). tertbutyl peroxyacetate (TBPA) was evaluated for the first time as a free radical initiator for radical chain polymerization of VF2 producing PVDF without use of a dispersion agent in a semibatch reactor using supercritical carbon dioxide. Diethyl peroxydicarbonate (DEPDC) at 75°C has been evaluated in many publications as an initiator in batch and continuous reactors for polymerization of VF2 in supercritical carbon dioxide. The effects of monomer and initiator concentration, agitation, and reaction time upon average molecular weight and polydispersity were evaluated using TBPA as an initiator at 104°C and compared with DEPDC initiated polymerization. It was found that as agitation rate, monomer concentration, and reaction time increased, the average molecular weight of PVDF using TBPA as an initiator increased. Lower concentrations of TBPA were needed compared to DEPDC to produce comparable molecular weights of PVDF. Using TBPA as an initiator at the conditions investigated resulted in lower polydispersity at similar monomer concentrations compared to DEPDC. Average molecular weights using TBPA ranged from 49,900 g/mol to 1.3 million g/mol and polydispersity ranged from 1.3 to 5.4., INTRODUCTION Due to being nontoxic, low cost, and an excellent solvent, supercritical carbon dioxide (scC[O.sub.2]) is used as an environmentally friendly replacement solvent for hydrocarbons. Successful applications of scC[O.sub.2] include [...]

The on-line monitoring of the droplet/particle size distributions is very important to ensure the quality and applicability of various products in heterogeneous systems. For this reason, the main objective of the present work was to study the usage of the focused beam reflectance measurement (FBRM) technique for monitoring of liquid-liquid dispersions (styrene dispersion in aqueous solutions) and suspension polymerization of styrene. To do better understand the FBRM technique in these systems, the effects of surfactant concentrations, agitation speed and ambient light were evaluated during the in-line monitoring of average chord lengths and chord-length distributions (CLD) at different operation conditions in batch experiments. In addition, a preliminary investigation of the optimal probe position was conducted in the polymerization experiments. It is shown that the FBRM technique is sensitive to variations of particle sizes in the characteristic ranges of particle diameters of typical styrene suspension polymerizations, being useful for monitoring and also control applications that require the on-line characterization of CLD in real time in liquid-liquid dispersions and polymerization systems., INTRODUCTION Several techniques have been developed since the second half of the twentieth century to study the bubbles/droplets/particle size distributions [1-3] in heterogeneous systems (gas-liquid, liquid-liquid and solid-liquid) to understand [...]

Confinement effect of graphene nanoplatelets on the kinetics of styrene atom transfer radical polymerization was studied by a 'grafting from' reaction. Graphene oxide was modified by different amounts of (3-aminopropyl) triethoxysilane and then alpha-bromoisobutyryl bromide from the hydroxyl groups. Polymerization of styrene in the presence of modified graphene and free initiator, ethyl alpha-bromoisobutyrate, was accomplished at 110 C. Then, effect of various graft densities and different graphene loadings on the heterogeneous graft and free polystyrene chains characteristics and also kinetics of polymerization was studied by gas and gel permeation chromatographies. Efficiency of grafting reactions along with the graft contents was studied by X-ray photoelectron spectroscopy, elemental analysis, and thermogravimetric analysis. Confinement effects of graphene on the relaxation behavior of polystyrene chains and also morphology of the graphenes were studied by differential scanning calorimetry and transmission electron microscopy, respectively. POLYM. ENG. SCI., 55:1720-1732, 2015. © 2014 Society of Plastics Engineers, INTRODUCTION Polymerization techniques based on controlled radical propagation are commonly used for synthesis of well-defined polymers with predetermined molecular weight and low polydispersity index (PDI) [1]. In these methods, radical [...]

Here we report and validate a new method, suitable broadly, for use in differentiated cells and tissues, for the direct visualization of actin polymerization under physiological conditions. We have designed and tested different versions of fluorescently labeled actin, reversibly attached to the protein transduction tag TAT, and have introduced this novel reagent into intact differentiated vascular smooth muscle cells (dVSMCs). A thiol-reactive version of the TAT peptide was synthesized by adding the amino acids glycine and cysteine to its N[H.sub.2]terminus and forming a thionitrobenzoate adduct: viz. TAT-Cys-SSTNB. This peptide reacts readily with G-actin, and the complex is rapidly taken up by freshly enzymatically isolated dVSMC, as indicated by the fluorescence of a FITC tag on the TAT peptide. By comparing different versions of the construct, we determined that the optimal construct for biological applications is a nonfluorescently labeled TAT peptide conjugated to rhodamine-labeled actin. When TAT-Cys-S-STNB-tagged rhodamine actin (TSSAR) was added to live, freshly enzymatically isolated cells, we observed punctae of incorporated actin at the cortex of the cell. The punctae are indistinguishable from those we have previously reported to occur in the same cell type when rhodamine G-actin is added to permeabilized cells. Thus this new method allows the delivery of labeled G-actin into intact cells without disrupting the native state and will allow its further use to study the effect of physiological intracellular [Ca.sup.2+] concentration transients and signal transduction on actin dynamics in intact cells. protein transduction domain; rhodamine G-actin; TAT doi: 10.1152/ajpcell.00210.2010.

The serpinopathies result from the ordered polymerization of mutants of members of the serine proteinase inhibitor (serpin) superfamily. These polymers are retained within the cell of synthesis Where they cause a toxic gain of function. The serpinopathies are exemplified by inclusions that form with the common severe Z mutant of [[alpha].sub.1]-antitrypsin that are associated with liver cirrhosis. There is considerable controversy as to the pathway of serpin polymerization and the structure of pathogenic polymers that cause disease. We have used synthetic peptides, limited proteolysis, monoclonal antibodies, and ion mobility-mass spectrometry to characterize the polymerogenic intermediate and pathological polymers formed by Z [[alpha].sub.1]-antitrypsin. Our data are best explained by a model in which polymers form through a single intermediate and with a reactive center loop-[beta]-sheet A linkage. Our data are not compatible with the recent model in which polymers are linked by a [beta]-hairpin of the reactive center loop and strand 5A. Understanding the structure of the serpin polymer is essential for rational drug design strategies that aim to block polymerization and so treat [[alpha].sub.1]-antitrypsin deficiency and the serpinopathies. alpha-1-antitrypsin deficiency | protein folding | serpins | polymers | cirrhosis doi/ 10.1073/pnas.1004785107

The Kv2.1 [K.sup.+] channel is highly expressed throughout the brain, where it regulates excitability during periods of high-frequency stimulation. Kv2.1 is unique among Kv channels in that it targets to large surface clusters on the neuronal soma and proximal dendrites. These clusters also form in transfected HEK cells. Following excessive excitatory stimulation, Kv2.1 declusters with an accompanying 20- to 30-mV hyperpolarizing shift in the activation threshold. Although most Kv2.1 channels are clustered, there is a pool of Kv2.1 resident outside of these domains. Using the cell-attached patch clamp technique, we investigated the hypothesis that Kv2.1 activity varies as a function of cell surface location. We found that clustered Kv2.1 channels do not efficiently conduct [K.sup.+], whereas the nonclustered channels are responsible for the high threshold delayed rectifier [K.sup.+] current typical of Kv2.1. Comparison.of gating and ionic currents indicates only 2% of the surface channels conduct, suggesting that the clustered channels still respond to membrane potential changes. Declustering induced via either actin depolymerization or alkaline phosphatase treatment did not increase whole-cell currents. Dephosphorylation resulted in a 25-mV hyperpolarizing shift, whereas actin depolymerization did not alter the activation midpoint. Taken together, these data demonstrate that clusters do not contain high threshold Kv2.1 channels whose voltage sensitivity shifts upon declustering; nor are they a reservoir of nonconducting channels that are activated upon release. On the basis of these findings, we propose unique roles for the clustered Kv2.1 that are independent of [K.sup.+] conductance. actin depolymerization | gating currents | Kv2.1 clustering | single-channel activity | confocal imaging doi/10.1073/pnas.1003028107

Plant microtubules are found to be strongly associated with the cell cortex and to experience polymerization/depolymerization processes that are responsible for the organization of microtubule cortical array. Here we propose a minimal model that incorporates the basic assembly dynamics and intermicrotubule interaction to understand the unexplored phase behavior of such a system. Through kinetic Monte Carlo simulations and theoretical calculations, we show that the self-organized patterns of plant cell cortical microtubules can be regulated by controlling single microtubule assembly dynamics. Biologically, this means that the structural reorganization can be regulated by microtubule-associated proteins via changing microtubule dynamic instability parameters, such as the microtubule plus-end growing rate, GTP-tubulin hydrolysis rate, etc. Such regulation is indirectly confirmed by various in vivo experiments. For the physical aspects, we not only construct the phase diagram that determines under what parameters ordered microtubule arrays form, but also predict that the essentially different ordered structures may appear through continuous and discontinuous transitions. The present study will play a central role in our understanding of the basic mechanism of plant cell noncentrosomal microtubule arrays. cortical microtubule array | cytoskeleton | nematic phase | treadmilling | steric interaction doi/ 10.1073/pnas.1007138107

One of the great challenges in surface chemistry is to assemble aromatic building blocks into ordered structures that are mechanically robust and electronically interlinked--i.e., are held together by covalent bonds. We demonstrate the surface-confined growth of ordered arrays of poly(3,4-ethylenedioxythiophene) (PEDOT) chains, by using the substrate (the 110 facet of copper) simultaneously as template and catalyst for polymerization. Copper acts as promoter for the Ullman coupling reaction, whereas the inherent anisotropy of the fcc 110 facet confines growth to a single dimension. High resolution scanning tunneling microscopy performed under ultrahigh vacuum conditions allows us to simultaneously image PEDOT oligomers and the copper lattice with atomic resolution. Density functional theory calculations confirm an unexpected adsorption geometry of the PEDOToligomers, which stand on the sulfur atom of the thiophene ring rather than lying flat. This polymerization approach can be extended to many other halogen-terminated molecules to produce epitaxially aligned conjugated polymers. Such systems might be of central importance to develop future electronic and optoelectronic devices with high quality active materials, besides representing model systems for basic science investigations. metal-catalyzed coupling reaction | molecular wires | cis-polythiophene | scanning probe microscopy | polymerization mechanism doi/ 10.1073/pnas.1000726107

We synthesize specially designed latex polymer systems by an in situ emulsion polymerization process that yields latex particles with both a high molecular weight polymer phase and a low molecular weight oligomer phase. The oligomer functions as a plastici/er by lowering the glass transition temperature ([T.sub.g]) of the polymer. A polymer system is prepared by blending soft latex and a hard latex where the hard mode consists of a hard, high molecular weight polymer and an oligomer, allowing for facile film formation at ambient conditions. Upon the soft and hard particles coming into contact during the film formation process, the oligomer preferentially diffuses from the hard polymer to the soft polymer, thus recovering the natural Ts of the hard polymer as described in a recent patent application. Oligomer diffusion allows a hard coalesced phase to be incorporated into a latex film without using a coalescing solvent, which would contribute to the volatile organic compound (VOC) content. A well-coalesced hard phase in a latex film contributes to a variety of desirable coatings properties, such as tack, print, block, and scrub resistance properties. Key words: oligomers, diffusion. Designed Diffusion™ Technology, plasticization. On a effectue la synthese de systemes de polymeres de latex concus specialement a cet effet en faisant appel a un processus de polymerisation en emulsion in situ qui conduit a la formation de particules de latex a la fois une phase de polymere de haul poids moleculaire el une phase d'oligomere de faible poids moleculaire. L'oligomere fonctionne comme plastifiant en reduisant la temperature de transition de verre ([T.sub.g]) du polymere. On prepare un systeme de polymere en procedant au melange d'un latex mou el d'un latex dur dans lequel le mode dur est forme d'une polymere dur de poids moleculaire eleve et d'un oligomere qui permet de former facilement un film dans les conditions ambiantes. Lorsque les particules molles et dures viennent en contact durant le processus de formation du film, l'oligomere diffuse d'une facon preferentielle du polymere dur vers le polymere mou et il retrouve la [T.sub.g] naturelle du polymere dur, tel que decrit dans une recente application pour un brevet. La diffusion de l'oligomere permet d'incorporer une phase dure ayant subi une coalescence d'etre incorporee dans un film de latex sans utiliser de solvant de coalescence qui contribuerait a la teneur en compose organique volatil (COV). Une phase dure qui a subi une bonne coalescence dans un film de latex contribue a une variete de proprietes desirables des revetements, telles que les proprietes resistance a la colle, a l'imprimerie, et au frottage. Mots-cles: oligomere, diffusion, technologie Designed Diffusion™, plasticisation. [Traduit par la Redaction], Introduction Demand of low and no volatile organic compound (VOC) binders in latex paints Water-borne latex coatings have been growing in popularity for decades as they offer performance, economic, and [...]

Acetyl-CoA carboxylase (ACC), the first committed enzyme in fatty acid (FA) synthesis, is regulated by phosphorylation/dephosphorylation, transcription, and an unusual mechanism of protein polymerization. Polymerization of ACC increases enzymatic activity and is induced in vitro by supraphysiological concentrations of citrate (>5 mM). Here, we show that MIG12, a 22 kDa cytosolic protein of previously unknown function, binds to ACC and lowers the threshold for citrate activation into the physiological range (50-fold in the presence of 1 mM citrate. In vivo, overexpression of MIG12 in liver induced ACC polymerization, increased FA synthesis, and produced triglyceride accumulation and fatty liver. Thus, in addition to its regulation by phosphorylation and transcription, ACC is regulated at a tertiary level by MIG12, which facilitates ACC polymerization and enhances enzymatic activity. lipogenesis | SREBPs | steatosis www.pnas.org/cgi/doi/10.1073/pnas.1001292107

Droplets of an iron-bearing calcia magnesia aluminosilicate (Fe-CMAS) melt were reacted under distinctly reducing conditions ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] - 2.4 x [10.sup.-13] and 6.4 x [10.sup.-15] atm) at high temperature (~1400[degrees]C) and ambient pressure. The low [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] environment was maintained by a flowing gas mixture of CO and C[O.sub.2], with a high content of CO. Molten metallic iron alloyed with silicon and carbon formed on the surface of the melt; no metal was observed in sample interiors. A color change from brown to pale blue confined to the outer layer of the melt indicated that essentially complete reduction of [Fe.sup.3+] to [Fe.sup.2+] had occurred in this region. Analysis of the reaction kinetics, particularly in comparison to melts of similar polymerization but free of CaO, reveals that the concentration of electron holes has decreased to such an extent that ionic transport in the melt is significantly slowed and the diffusion of CO as a neutral species becomes dominant and rate-limiting: molecular CO, initially incorporated into the melt as a physically dissolved species, subsequently reacts to form chemically dissolved (bonded into the melt structure) C[O.sup.2-.sub.3] anions, consuming electron holes in the process. The chemical diffusion coefficient for CO in the reduced melt at 1400[degrees]C is estimated as [D.sub.CO] [approximately equal to] 4 x [10.sup.-4] [cm.sup.2]/s, consistent with that of other, similarly sized molecular species (e.g., [H.sub.2] and [H.sub.2]O) for similarly polymerized melts, as reported by other investigators. Upon quenching, the droplet acts as a closed system. Internal redox couples see the reduction of the carbonate so as to form bubbles of CO, the composition of which are confirmed with Raman spectroscopy. The open-system reduction and closed-system quenching dynamics are analyzed following an Ellingham-diagram approach. Keywords: Redox, silicate melts, carbon, diffusion, reactions, kinetics DOI: 10.2138/am.2010.3375

Extracellular matrix (ECM) remodeling occurs during normal homeostasis and also plays an important role during development, tissue repair, and in various disease processes. ECM remodeling involves changes in the synthesis, deposition, and degradation of ECM molecules. ECM molecules can be degraded extracellularly, as well as intracellularly following endocytosis. Our data show that the ECM protein fibronectin is an important regulator of ECM remodeling. We previously showed that agents that inhibit the polymerization of fibronectin into ECM fibrils promote the loss of preexisting fibronectin matrix and accelerate fibronectin endocytosis and degradation. In this paper we show that inhibition of fibronectin polymerization leads to the loss of collagen I matrix fibrils and a corresponding increase in the levels of endocytosed collagen I. In contrast, manipulations that stabilize fibronectin matrix fibrils, such as caveolin-1 depletion, stabilize collagen I matrix fibrils and cause a decrease in ECM collagen I endocytosis. Our data also show that endocytosis of ECM collagen I is regulated by both [beta]1 integrins and Endo180/urokinase plasminogen activator associated protein (uPARAP). Unexpectedly, Endo180/uPARAP was also shown to promote the endocytosis of fibronectin from the ECM. These data demonstrate that fibronectin polymerization regulates the remodeling of ECM collagen I, in part, by regulating collagen I endocytosis. Furthermore, these data show that processes that regulate ECM deposition coordinately regulate the removal of proteins from the ECM. These data highlight the complexity of ECM remodeling. This multifaceted regulatory process may be important to ensure tight regulation of ECM fibronectin and collagen I levels. extracellular matrix; integrin; endocytosis; Endo180; urokinase plasminogen activator-associated protein doi: 10.1152/ajpcell.00341.2009.

The generation of membrane curvature in intracellular traffic involves many proteins that can curve lipid bilayers. Among these, dynamin-like proteins were shown to deform membranes into tubules, and thus far are the only proteins known to mechanically drive membrane fission. Because dynamin forms a helical coat circling a membrane tubule, its polymerization is thought to be responsible for this membrane deformation. Here we show that the force generated by dynamin polymerization, 18 pN, is sufficient to deform membranes yet can still be counteracted by high membrane tension. Importantly, we observe that at low dynamin concentration, polymer nucleation strongly depends on membrane curvature. This suggests that dynamin may be precisely recruited to membrane buds' necks because of their high curvature. To understand this curvature dependence, we developed a theory based on the competition between dynamin polymerization and membrane mechanical deformation. This curvature control of dynamin polymerization is predicted for a specific range of concentrations (~0.1-10 [micro]M), which corresponds to our measurements. More generally, we expect that any protein that binds or self-assembles onto membranes in a curvature-coupled way should behave in a qualitatively similar manner, but with its own specific range of concentration. force | nucleation | fission | endocytosis | dynamin-like proteins doi/10.1073/pnas.0913734107

The human recombinase hRad51 is a key protein for the maintenance of genome integrity and for cancer development. Polymerization and depolymerization of hRad51 on duplex DNA were studied here using a new generation of magnetic tweezers, measuring DNA twist in real time with a resolution of 5[degrees]. Our results combined with earlier structural information suggest that DNA is somewhat less extended by hRad51 than by RecA (4.5 vs. 5.1 [Angstrom] per base pair) and untwisted by 18.2[degrees] per base pair. They also confirm a stoichiometry of 3-4 bp per protein in the hRad51-dsDNA nucleoprotein filament. At odds with earlier claims, we show that after initial deposition of a multimeric nucleus, nucleoprotein filament growth occurs by addition/release of single proteins, involving DNA twisting steps of 65[degrees] [+ or -] 5[degrees]. Simple numeric simulations show that this mechanism is an efficient way to minimize nucleoprotein filament defects. Nucleoprotein filament growth from a preformed nucleus was observed at hRad51 concentrations down to 10 nM, whereas nucleation was never observed below 100 nM in the same buffer. This behavior can be associated with the different stoichiometries of nucleation and growth. It may be instrumental in vivo to permit efficient continuation of strand exchange by hRad51 alone while requiring additional proteins such as Rad52 for its initiation, thus keeping the latter under the strict control of regulatory pathways. homologous recombination | magnetic tweezers | nucleation and growth | single molecule | mechanoenzyme www.pnas.org/cgi/doi/10.1073/pnas.0902234106

A variety of contractile stimuli increases actin polymerization, which is essential for smooth muscle contraction. However, the mechanism(s) of actin polymerization associated with smooth muscle contraction is not fully understood. We tested the hypothesis that phosphorylated myosin triggers actin polymerization. The present study was conducted in isolated intact or [beta]-escin-permeabilized rat small ruesenteric arteries. Reductions in the 20-kDa myosin regulatory light chain ([MLC.sub.20]) phosphorylation were achieved by inhibiting MLC kinase with ML-7. Increases in [MLC.sub.20] phosphorylation were achieved by inhibiting myosin light chain phosphatase with microcystin. Isometric force, the degree of actin polymerization as indicated by the F-actin-to-G-actin ratio, and [MLC.sub.20] phosphorylation were determined. Reductions in [MLC.sub.20] phosphorylation were associated with a decreased force development and actin polymerization. Increased [MLC.sub.20] phosphorylation was associated with an increased force generation and actin polymerization. We also found that a heptapeptide that mimics the actin-binding motif of myosin II enhanced microcystin-induced force generation and actin polymerization without affecting [MLC.sub.20] phosphorylation in [beta]-escin-permeabilized vessels. Collectively, our data demonstrate that [MLC.sub.20] phosphorylation is capable of triggering actin polymerization. We further suggest that the binding of myosin to actin triggers actin polymerization and enhances the force development in arterial smooth muscle. isometric force; [beta]-escin; myosin light chain kinase; myosin light chain phosphatase; ML-7; microcystin

We report on polydimethylsiloxane (PDMS) microlens arrays fabricated through liquid-phase photopolymerization and molding. The gist of this fabrication process is to form liquid menisci of variable radii of curvature at an array of apertures through pneumatic control, followed by photopolymerization under ultraviolet radiance. The resultant polymerized structures are then transferred to PDMS utilizing two molding steps. By adjusting the pneumatic pressure during the process, a single aperture array can be used to fabricate PDMS microlens arrays with variant focal lengths. The liquid menisci are formed by liquid-air interfaces that are pinned at the top edges of the apertures along hydrophobic-hydrophilic boundaries generated through surface chemical treatments. The microlens arrays are optically characterized. Variant focal lengths from 2.35 to 5.54 mm and f-numbers from 1.27 to 5.88, dependent on the diameter of apertures and the applied pressure to form the liquid menisci, are achieved with this relatively simple process and match well with the physical model. Owing to the formation from the liquid-air interfaces, the surface roughness of microlenses is measured to be around 25 nm. [2007-0293] Index Terms--Hydrophobic-hydrophilic boundary, microlens array, photopolymerization, pneumatic control, polydimethylsiloxane (PDMS).

In Escherichia coli FtsZ organizes into a cytoskeletal ring structure, the Z ring, which effects cell division. FtsZ is a GTPase, but the free energy of GTP hydrolysis does not appear to be used for generation of the constriction force, leaving open the question of the function of the GTPase activity of FtsZ. Here we study the mechanism by which SulA, an inhibitor of FtsZ induced during the SOS response, inhibits FtsZ function. We studied the effects of SulA on the in vitro activities of FtsZ, on Z rings in vivo, and on a kinetic model for FtsZ polymerization in silico. We found that the binding of SulA to FtsZ is necessary but not sufficient for inhibition of polymerization, since the assembly of FtsZ polymers in the absence of the GTPase activity was not inhibited by SulA. We developed a new model for FtsZ polymerization that accounts for the cooperativity of FtsZ and could account for cooperativity observed in other linear polymers. When SulA was included in the kinetic scheme, simulations revealed that SulA with strong affinity for FtsZ delayed, but did not prevent, the assembly of polymers when they were not hydrolyzing GTP. Furthermore, the simulations indicated that SulA controls the assembly of FtsZ by binding to a polymerization-competent form of the FtsZ molecule and preventing it from participating in assembly. In vivo stoichiometry of the disruption of Z rings by SulA suggests that FtsZ may undergo two cooperative transitions in forming the Z ring.

A study is conducted to characterize the conditions that govern the monomer-polymer reaction of MreB from the thermophile Thermotoga maritima. The influence of temperature, nucleotides and ions on the polymerization properties is reported.

Vesicular trafficking and actin dynamics on Golgi membranes are both regulated by ADP-ribosylation factor 1 (ARF1) through the recruitment of various effectors, including vesicular coats. Actin assembly on Golgi membranes contributes to the architecture of the Golgi complex, vesicle formation, and trafficking and is mediated by ARF1 through a cascade that leads to Arp2/3 complex activation. Here we addressed the role of Golgi actin downstream of ARF1 by using a biomimetic assay consisting of liposomes of defined lipid composition, carrying an activated form of ARF1 incubated in cytosolic cell extracts. We observed actin polymerization around the liposomes resulting in thick actin shells and actin comet tails that pushed the ARF1 liposomes forward. The assay was used to characterize the ARF1-dependent pathway, leading to actin polymerization, and confirmed a dependency on CDC42 and its downstream effector N-WASP. Overall, this study demonstrates that actin polymerization driven by the complex multicomponent signaling cascade of the Golgi apparatus can be reproduced with a biomimetic system. Moreover, our results are consistent with the view that actin-based force generation at the site of vesicle formation contributes to the mechanism of fission. In addition to its well established function in coat recruitment, the ARF1 machinery also might produce movement- and fission-promoting forces through actin polymerization. transport vesicle | Golgi | membrane scission | motility | CDC42

A study on the copolymerization of these sugar monomers with styrene and methyl methacrylate, as well as some physical properties of the resulting polymeric materials is discussed. New chiral copolymers containing sucrose have been synthesized by radical polymerization, and some of their physical properties is determined.

The evolution of defect annihilation and the dynamics and mechanisms of reorganizations of disclinations during the thin film polymerization of various aromatic LC polyesters is detailed. In contradiction to conventional rules, a faster annihilation rate in the late stage of annihilation process in some samples is observed and an increase in the distance of a disclination pair is found due to the surroundings and polymerization effects.

A new approach in the manipulation of the size and chemistry of nanoscopic characteristics using contact molding and living free radical polymerization is presented. A focus is also laid on creating templates for pattern replication and the development of process steps for transferring images into molecular electronics applications.

The photoinitiated polymerization of phenyl benzoate-based liquid crystalline (LC) thiol-ene monomers in isotropic and anisotropic solvents is reported. The mixing behavior of the thiol-ene monomers with anisotropic cyanobiphenyl solvents was investigated, and unique reactive LC mixtures are formed that exhibit variable mesophases at ambient temperatures.

The chemistry of controlled/living radical polymerizations from surfaces is investigated in terms of atom transfer radical polymerization from nanoparticles.

Microhardness of C70 crystals was studied in terms of temperature dependence and photopolymerization effects.

The consecutive chain transfer reaction to p-methylstyrene and to hydrogen during polymerization is reported.