Low Monomer Concentration Research Articles

Effect of acrylamide monomer concentration in low temperature magnesiothermic synthesis of mesoporous silicon carbide from MCM-48/PAAM nanocomposite precursor

Mesoporous silicon carbide with high specific surface area was successfully synthesised from a MCM-48/polyacrylamide nanocomposite precursor in two temperature ranges of 650–700°C and 800–850°C by a magnesiothermic reduction process. The MCM-48/polyacrylamide precursor nanocomposite was prepared by in situ polymerisation. Heat treatment using low concentrations of acrylamide monomer in the temperature range of 650–700°C and using high concentration of acrylamide monomer was carried in two temperature ranges of 650–700°C and 800–850°C. The products were characterised by X-ray diffraction, TEM and N2 adsorption–desorption. The results show that synthesised SiC in both temperature ranges of 650–700°C and 800–850°C is mesoporous and has specific surface of 194/60 and 167/84 m2 g−1 respectively. The results also show that the value of carbon content and the concentration of acrylamide monomer (factor affecting the amount of contact surface of carbon and silica) impress the starting temperature of the reaction.

Pleomorphic Ensembles: Formation of Large Clusters Composed of Weakly Interacting Multivalent Molecules

Molecular interactions of importance to cell biology are subject to sol-gel transitions: large clusters of weakly interacting multivalent molecules (gel phase) are produced at a critical concentration of monomers. Examples include cell-cell and cell-matrix adhesions, nucleoprotein bodies, and cell signaling platforms. We use the term pleomorphic ensembles (PEs) to describe these clusters, because they have dynamic compositions and sizes and have rapid turnover of their molecular constituents; this plasticity can be highly responsive to cellular signals. The classical polymer physical chemistry theory developed by Flory and Stockmayer provides a brilliant framework for treating multivalent interactions for simple idealized systems. But the complexity and variability of PEs challenges existing modeling approaches. Here we describe and validate a computational algorithm that extends the Flory-Stockmayer formalism to overcome the limitations of analytic theories. We divide the problem by deterministically calculating the fraction of bound sites for each type of binding site, followed by the stochastic assignment of the bonds to a finite number of molecules. The method allows for high valency within many different kinds of interacting molecules and site types, permits simulation of steady-state distributions, as well as assembly kinetics, and can treat cooperative binding within one of the interacting molecules. We then apply our method to the analysis of interactions in the nephrin-Nck-N-Wasp signaling system, demonstrating how multivalent layered scaffolds produce PEs at low monomer concentrations despite weak binding interactions. We show how the experimental data for this system are most consistent with synergistic cooperative interactions between Nck and N-Wasp.

Adhesion of ultrahigh molecular weight polyethylene plates photografted with hydrophilic monomers and evaluation of failure location by X‐ray photoelectron spectroscopy

ABSTRACTIn this study, methacrylic acid (MAA) and acrylic acid (AA) were photografted onto the ultrahigh molecular weight polyethylene (UHMWPE) plates at different monomer concentrations and temperatures, and the grafted UHMWPE plates were bonded with aqueous polyvinyl alcohol (PVA) solutions. The tensile shear adhesive strength of both grafted UHMWPE plates was also discussed in relation to wettability and water absorptivity. The location of failure was also estimated by X‐ray photoelectron spectroscopy (XPS). Wettability of the MAA‐grafted UHMWPE plates became constant, when the UHMWPE surface was fully covered with grafted PMAA chains. Conversely, wettability of the AA‐grafted UHMWPE plates passed through the maximum value and then gradually decreased against the grafted amount probably due to aggregation of grafted PAA chains. Water absorptivity of the grafted layers formed at lower monomer concentrations or temperatures sharply increased at lower grafted amounts. The adhesive strength increased with the grafted amount and substrate breaking was observed at higher grafted amounts, indicating that a main factor to increase the adhesive strength is the formation of a grafted layer by shorter grafted polymer chains and/or the restriction of the location of photografting to the outer surface region. In addition, surface analysis by XPS showed that failure occurred in the boundary between the layer composed of grafted polymer chains and PVA chains and the ungrafted layer at a low adhesive strength, and the location of failure was shifted to the grafted layer containing PVA chains at the grafted amount increased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40133.

Rapid degeneration of rod photoreceptors expressing self-association-deficient arrestin-1 mutant

Arrestin-1 binds light-activated phosphorhodopsin and ensures timely signal shutoff. We show that high transgenic expression of an arrestin-1 mutant with enhanced rhodopsin binding and impaired oligomerization causes apoptotic rod death in mice. Dark rearing does not prevent mutant-induced cell death, ruling out the role of arrestin complexes with light-activated rhodopsin. Similar expression of WT arrestin-1 that robustly oligomerizes, which leads to only modest increase in the monomer concentration, does not affect rod survival. Moreover, WT arrestin-1 co-expressed with the mutant delays retinal degeneration. Thus, arrestin-1 mutant directly affects cell survival via binding partner(s) other than light-activated rhodopsin. Due to impaired self-association of the mutant its high expression dramatically increases the concentration of the monomer. The data suggest that monomeric arrestin-1 is cytotoxic and WT arrestin-1 protects rods by forming mixed oligomers with the mutant and/or competing with it for the binding to non-receptor partners. Thus, arrestin-1 self-association likely serves to keep low concentration of the toxic monomer. The reduction of the concentration of harmful monomer is an earlier unappreciated biological function of protein oligomerization.

Adhesion of grafted polypropylene plates with enzymatically modified chitosan solutions and analysis of failed surfaces by X‐ray photoelectron spectroscopy

ABSTRACTIn this study, hydrophilic monomers were photografted onto the PP plates at different monomer concentrations and temperatures, and grafted PP plates were bonded with enzymatically modified chitosan solutions. Their adhesive strength properties were discussed in relation to the grafting conditions and hydrophilic properties such as wettability and water‐absorptivity. In addition, the location of failure was investigated by X‐ray photoelectron spectroscopy analysis of failed surfaces. Wettability of the grafted PP plates except for the PP grafted with acrylic acid (PP‐g‐PAA) plates remained constant above the grafted amounts at which the PP surfaces were fully covered with grafted polymer chains. On the other hand, wettability of the PP‐g‐PAA plates passed through the maximum value and then gradually decreased with the grafted amount probably because of the aggregation of grafted PAA chains. Water‐absorptivity of the grafted layers formed at lower monomer concentrations or temperatures sharply increased at lower grafted amounts. The adhesive strength increased with an increase in the grafted amount and substrate breaking was observed for PP‐g‐PAA plates because enzymatically modified chitosan solutions were successfully penetrated in the grafted layers and quinone derivatives reacted with carboxy groups of grafted PAA chains. Failure occurred in the layers composed of grafted PAA chains and components containing in enzymatically modified chitosan solutions and the location was shifted to the inside of grafted layer, as the grafted amount increased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1369‐1376, 2013

Surface-bound basement membrane components accelerate amyloid-β peptide nucleation in air-free wells: An in vitro model of cerebral amyloid angiopathy

Cerebral amyloid angiopathy is caused by deposition of the amyloid β-peptide which consists of mainly 39–40 residues to the cortical and leptomeningeal vessel walls. There are no definite in vitro systems to support the hypothesis that the vascular basement membrane may act as a scaffold of amyloid β-peptide carried by perivascular drainage flow and accelerate its amyloid fibril formation in vivo. We previously reported the critical roles of interfaces and agitation on the nucleation of amyloid fibrils at low concentrations of amyloid β-peptide monomers. Here, we reproduced the perivascular drainage flow in vitro by using N-hydroxysuccinimide-Sepharose 4 Fast flow beads as an inert stirrer in air-free wells rotated at 1rpm. We then reproduced the basement membranes in the media of cerebral arteries in vitro by conjugating Matrigel and other proteins on the surface of Sepharose beads. These beads were incubated with 5μM amyloid β(1–40) at 37°C without air, where amyloid β(1–40) alone does not form amyloid fibrils. Using the initiation time of fibril growth kinetics (i.e., the lag time of fibril growth during which nuclei, on-pathway oligomers and protofibrils are successively formed) as a parameter of the efficiency of biological molecules to induce amyloid fibril formation, we found that basement membrane components including Matrigel, laminin, fibronectin, collagen type IV and fibrinogen accelerate the initiation of amyloid β-peptide fibril growth in vitro. These data support the essential role of vascular basement membranes in the development of cerebral amyloid angiopathy.

Highly conductive and semitransparent free-standing polypyrrole films prepared by chemical interfacial polymerization

Chemical interfacial polymerization is a facile and effective way to synthesize large-area free-standing polypyrrole (PPy) films. Unfortunately, the conductivities of the PPy films prepared by ordinary chemical interfacial polymerization are generally very low. In this work, large-area, highly conductive and semitransparent free-standing PPy films are prepared by chemical interfacial polymerization at the interface of cyclohexane/water at a low monomer concentration and/or at a short reaction time. PPy films with a thickness ranging from nanometers to submicrons can be obtained by adjusting the monomer concentration and reaction time. The conductivity of the PPy films is up to 560 S cm−1. And the PPy films exhibit moderate transparency with a transmittance up to 31%. FTIR, Raman and XRD characterizations show that the PPy films have very similar polymer backbones and aggregated structures. XPS analyses indicate that the PPy films are doped with both p-toluenesulfonic acid (PTS) and Cl−. The high doping levels and the compact and smooth surface morphologies are the main reasons for the high conductivities of the PPy films.

The Influence of 4,4’-bis[6-(acryloyloxy)-hexyloxy]biphenyl Contents on the Electro-Optical Properties of Polymer Stabilized Liquid Crystals

The polymer stabilized liquid crystals (PSLC) films was prepared subsequently based on the mesogenic diacrylate monomer 4,4’-bis[6-(acryloyloxy)-hexyloxy]biphenyl (BAB6). The effects of BAB6 on the morphology of polymer network as well as the electro-optical properties of the PSLC films were investigated. The helical structure of liquid crystals was observed in the morphology of polymer network by SEM. Further, a single switching process was observed at lower monomer concentration in this study compared with the former publication. When BAB6 concentration reached 7 %, the response time and contrast ratio of PSLC film were 7 ms and 16.8, respectively.

A new precursor for conducting polymer-based brush interfaces with electroactivity in aqueous solution

We present the synthesis of a novel conducting polymer (CP) incorporating both pyrrole and thiophene units in its monomer, which is also substituted with an initiator for grafting of sidechains by atom-transfer radical polymerisation (ATRP). The precursor monomer for the CP macroinitiator, 2-(2,5-di(pyrrol-2-yl)thiophen-3-yl)ethyl 2-bromopropanoate) (PyThon) is very readily electropolymerised at low monomer concentrations and low applied potentials. Density functional theory (DFT) predictions of ionisation potentials and spin-charge distribution for PyThon are in good agreement with these experimental results. We present also the grafting of sidechains from electropolymerised PolyPyThon (PPyThon) to yield surface-confined polymer brushes. Functionalisation with polystyrene (PS), poly(2,3,4,5,6-pentafluorostyrene) (PFS) and poly(ethylene glycol) methyl ether acrylate (PEGMEA) is demonstrated and confirmed by FT-IR and water contact angle measurements. These PPyThon-based molecular brushes are electroactive in both water and acetonitrile, and show evidence of changes in surface conformation related to the redox state of the CP. The growth of human fibroblasts on PPyThon films is also demonstrated, indicating good biocompatibility of the polymer. We conceive PPyThon-based molecular brushes as a substrate for electrical stimuli-responsive surfaces with application particularly in the biomedical field.

Dental monomers inhibit LPS-induced cytokine release from the macrophage cell line RAW264.7

Methacrylate monomers have been identified in aqueous extracts of freshly cured dental fillings. The hypothesis tested presently was that low concentrations of triethyleneglycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) alone or in combination interfere with the LPS-induced release of cytokines from the macrophage cell line RAW264.7. The cells were exposed to 5–200μM of monomers for 24h followed by a 24h combined exposure to monomers and LPS. TEGDMA reduced LPS-induced release of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), whereas HEMA only reduced IL-1β release. Co-exposure to the two monomers indicated an additive effect. Moreover, the reduced cytokine release persisted for 24h after termination of the monomer exposure. The LPS-induced activation of proteins in pre-transcriptional signaling pathways (CD14, p-ERK1/2, p-p38, p-JNK, p-IκB-α and p-NFκB-p65) was not altered by monomer exposure, neither were the levels of IL-1β and TNF-α mRNA. However, the LPS-induced level of pro-IL-1β was decreased by the monomer treatment. Thus, HEMA and TEGDMA may interfere with post-transcriptional regulation of synthesis and release of these cytokines. Overall, the results suggest that low concentrations of monomers may cause impaired macrophage responses, and that these effects can persist for up to 24h after exposure.

Supramolecular Polymerization at Low Monomer Concentrations: Enhancing Intermolecular Interactions and Suppressing Cyclization by Rational Molecular Design

We present the construction of long-chain water-soluble supramolecular polymers at low monomer concentrations. Naphthalene-based host-enhanced π-π interactions, which possess high binding constants, were used as the driving force of supramolecular polymerization. A monomer, DNDAB, with a rigid, bulky 1,4-diazabicyclo[2.2.2]octane-1,4-diium linker was designed. The design of the monomer structure strongly influenced the efficiency of the supramolecular polymerization. The rigid, bulky linker in DNDAB effectively eliminates cyclization, promoting the formation of long-chain supramolecular polymers at low monomer concentrations. In contrast, a reference monomer containing a flexible linker (DNPDN) only forms oligomers owing to cyclization.

A novel method of in situ chemical polymerization of polyaniline for synthesis of electrically conductive cotton fabrics

In the present work, a study of two-step in situ chemical polymerization of polyaniline (PANI) on cotton fabric was undertaken by employing the jig-dyeing principle. The important reactant parameters, such as monomer concentration, oxidant/monomer ratio, protonic acid concentration and the duration of polymerization, were studied. The structural and morphological features of the resultant fabric were analyzed by Fourier transform infrared–attenuated total reflectance and scanning electron microscopy studies. The electrical conductivity was expressed as both bulk and surface properties. With the present experimental set up, a minimum electrical surface resistivity of about 103 ohm/square was achieved. The present investigation revealed that key parameters, such as protonic acid concentration, oxidant/monomer ratio and the duration of polymerization, are influential at lower monomer concentrations. Further, the treatment method and fabric construction appear to have a predominant role in the deposition, thereby affecting the resultant conductivity. The PANI-coated cotton fabrics thus produced are suitable in application areas of static protection and sensors for smart textiles. The described method of in situ polymerization has a potential for scaling up for bulk production.

Nanofiltration membrane modification by UV grafting for salt rejection and fouling resistance improvement for brackish water desalination

Two commercial NF membranes denoted as NF-1 and ASP30 were investigated in terms of applicability to desalinate ground water in Gaza where chloride-based salt concentrations are relatively high (1000mg/l) with 2200mg/l total dissolved solids (TDS). Initially, investigated membranes showed low chloride-based salt rejection as well as resistance to humic acid fouling which required certain improvement. Such improvement could be achieved by surface modification via UV-grafting. UV graft polymerisation is a common method applied to improve nanofiltration (NF) membrane properties due to: 1) lower operational costs 2) milder reaction conditions and 3) enhanced absorption selectivity of UV light without affecting the bulk polymer to increase salt rejection and humic acid fouling resistance was applied. The newly combined monomer of acrylic acid and ethylenediamine dihydrochloride grafted by UV initiated successfully increased NaCl rejection of the NF-1 membrane to 57–60%. Rejection of MgSO4 was increased from 89% to 94%, while for ASP30, NaCl and MgSO4 rejection increased from 33% and 32% to 57% and 71%, respectively. The best rejection for NF-1 was achieved at a low monomer concentration and moderate UV exposure, while ASP30 showed the best rejection at a high monomer concentration and low UV exposure. However, pure water flux was slightly reduced. Irreversible fouling caused by humic acid, common ground water foulant, was measured by the irreversible fouling factor (IRF), which was reduced after modification, indicating improved fouling resistance. These data show that this new combined monomer initiated by UV grafting can successfully improve NF membrane selectivity as well as fouling resistance.

Estimation of surface properties of grafted layers formed on low‐ and high‐density polyethylene plates by photografting of methacrylic acid and acrylic acid at different monomer concentrations and temperatures

AbstractAn investigation was carried out on estimation of hydrophilicity, wettability and water‐absorptivity, and surface analysis by X‐ray photoelectron spectroscopy of the low‐ and high‐density polyethylene (LDPE and HDPE) plates photografted with methacrylic acid (MAA) and acrylic acid (AA) at different monomer concentrations or temperatures. Wettability of the MAA‐grafted LDPE and HDPE plates increased with grafted amounts, and became constant when the substrate surfaces were fully covered with the grafted polymer chains. On the other hand, for the AA‐grafted LDPE and HDPE plates, wettability had the maximum value, and then gradually decreased against the grafted amount probably due to aggregation of grafted PAA chains, although the surfaces were covered with grafted PAA chains at lower grafted amounts compared with grafted PMAA chains. Water‐absorptivity sharply increased at lower grafted amounts due to formation of shorter grafted polymer chains for photografting at lower monomer concentrations or due to restriction of the location of grafting to the outer surface region for photografting at lower temperatures. Therefore, for photograftings of AA or onto the HDPE plates, the substrate surfaces were covered with grafted polymer chains and the grafted layers formed possessed higher water‐absorptivity at lower grafted amounts. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis of Hyperbranched Polymer Using Slow Monomer Addition Method

This paper details the synthesis of a well-defined hyperbranched polymer using a slow monomer addition method. The polymerization under slow monomer addition conditions results in a very low monomer concentration actually present in the reaction mixture, and the exclusive reaction of the monomer with the growing polyfunctional macromolecules occurs, resulting in a high molecular weight and a high degree of branching value. Thus, the slow monomer addition is a versatile and preferential method for the controlled synthesis of a well-defined hyperbranched polymer with both a high molecular weight and a high degree of branching value.

Length Scales Necessary for Proper Averaging to Characterize Polymerization in Nanosystems: Topochemical Polymerization of Diacetylene Nanocrystals Dispersed in a Polystyrene Matrix As Probed by Confocal Raman Microscopy

The scales necessary to make appropriate spatial averaging on solid-state polymerization were investigated by confocal Raman microscopy with a mapping resolution of 2 μm. Nanocrystals of an aliphatic diacetylene with an average size of 0.14 μm, each separated by 0.3 μm on average, were dispersed in a polystyrene matrix and were polymerized by UV irradiation. The distribution of nanocrystals was inhomogeneous over approximately 20 μm scale. A large crystal of the same monomer shows that photoinitiation is already averaged at the microscope resolution, while the color transition from the blue to the red form requires a scale greater than 5 μm. For the nanocrystals at low conversion, UV-vis absorption spectroscopy measured over a centimeter scale indicates linear polymerization kinetics and a higher polymer yield at a higher temperature. By contrast, the Raman microscopy reveals that, whereas the 20 μm region of high monomer concentrations yields more polymers at -24 °C, the region of low monomer concentrations gives more polymers at 20 °C. We propose thermal initiation, which is not efficient in the large crystals, as an additional initiation process for the apparent discrepancy, implying that the initiation process is not averaged below 20 μm scale for the dispersed nanocrystals.

Silicone‐based hydrogels prepared by interpenetrating polymer network synthesis: Swelling properties and confinements effects on the formation kinetics

AbstractIn this work, interpenetrating polymer networks (IPNs) of polydimethylsiloxane (PDMS) and poly(acrylic acid) or poly(2‐hydroxyethyl methacrylate) (PHEMA) have been synthesized employing a sequential method. Monomeric AAc or HEMA was introduced into the PDMS network by swelling the polymer in solutions of monomer. The polymerization of monomers was then conducted in the swollen network. The swelling properties of the IPNs were investigated by varying the monomer concentrations in the polymerization and more swelling was observed with low monomer concentrations due to the prevalence of cyclization reactions. Multi‐step polymerization used to achieve IPNs with high hydrogel contents, did not improve their water uptake. The kinetics of acrylic acid polymerization was studied under various conditions. Specifically, in the presence of confinement effects imposed by the PDMS network a considerable drop in the rate of reaction was observed. The cross‐linking density of the PDMS network was also studied how to affect the reaction rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and characterization of the novel shape-persistent nanosized cavity macrocycle

The Friedel–Crafts reaction was employed to prepare the shape-persistent macrocycle ( TPAP) 3 with direct cyclization from three monomers of 2-(4′-(Phenyl(4″-methylphenyl)amino) phenyl)-propan-2-ol ( TPAP), which contains two reactive groups of the t-hydroxyl and the p-proton on the triphenylamine. Under a very low monomer concentration (ca. 1%), the yield of the shape-persistent macrocycle ( TPAP) 3 is up to 34%. FT-IR, NMR, MALDI-TOF and MS were applied to determine the structure of macrocycle. It can be a good candidate as the hole-transporting layer because its photoluminescent spectrum appears no emission peaks in the range of 400–600 nm. The geometry of ( TPAP) 3, optimized by the density functional theory (DFT) calculations using Gaussian03 software at the B3LYP/6-31G(d) level, showed that ( TPAP) 3 possesses an approximately 10 Å diameter and 8.4 Å depth molecular inner cavity. Owing to three nitrogenous lone electron pairs and six conjugated large π bonds of the macrocyclic electron-excessive phenylene almost directing into the cavity, the macrocycle is a big electron-rich donor which may be favorable for selective extraction of special diameter metal ions, high effective and selective catalysis and the formation of 1:1 π-donor–π-acceptor (C60) complexes through the host–guest interactions.

A novel protocol for the preparation of uniform polymer microspheres with high yields through step polymerization of isophorone diisocyanate

AbstractUniform polymer microspheres with neat surface are of high interests. Precipitation polymerization of vinylic monomers remains a very limited process owing to very low monomer concentration allowed. Here, a fully novel protocol for the production of uniform polymeric microspheres is presented. Using one single monomer, isophorone diisocyanate, highly monodisperse polyurea microspheres were achieved with very high yield in a very short time period via precipitation polymerization in water–acetone mixed solvent. Results demonstrated that the ratio of water–acetone and polymerization temperature played important roles in the process. The size of the microspheres was readily adjustable by varying monomer concentration, water/acetone ratio or polymerization temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Enhanced electrochemical reversibility of ultrathin aniline oligomer films grown on Pt(111)

Aniline adsorption and the first stages of aniline polymerization on a Pt(111) single-crystal electrode are studied. At low monomer concentration the aniline oxidation process leads to the appearance of two highly reversible redox couples at 0.480 V and 0.820 mV (vs RHE), related to the first redox transition of aniline oligomers from leucomeraldine to emeraldine and to the transition from emeraldine to pernigraniline, respectively. A fast electron transfer constant of 9.1 s − 1 for the redox reaction from leucomeraldine to emeraldine is obtained from the dependence of the peak potential on the voltammetric sweep rate. Finally, it was found that the electropolymerization of aniline is a surface sensitive reaction on basal plane platinum electrodes.