Monomer Concentration In Solution Research Articles

Microscopic characteristics of Janus nanoparticles prepared via a grafting-from reaction at the immiscible liquid interface.

The dynamic process of synthesizing Janus nanoparticles (JNPs) at a water/oil two-phase interface using a grafting-from reaction is investigated via dissipative particle dynamics simulations. We find that the interfacial tension, the initial monomer concentration, and the reaction probability can greatly influence the microscopic characteristics of JNP structure. It is difficult to synthesize a symmetric JNP with an equal volume ratio between hydrophilic and hydrophobic parts by grafting-from methods unless the physical chemical conditions in the two phases are strictly symmetric, and there is always a disordered domain on the JNP at a two immiscible solvents interface. Interestingly, for certain routes for synthesizing JNPs with a grafting-from method, the higher interfacial tension between the water and oil phases may enhance the degree of disorder of the grafted chains. The asymmetric initial monomer concentration in solution and the reaction probability can be used to control the syntheses of asymmetric JNPs.

Synthesis of polyamides from sugar derived d‐glucaric acid and xylylenediamines

ABSTRACTd‐Glucaric acid (GA) is the one of aldaric acids and is an important bio‐based building block for polymers. In this study, poly(m‐xylylene‐acetyl glucaramide) and poly(p‐xylylene‐acetyl glucaramide) were synthesized from GA acetate and two kind of aromatic diamines by solution polymerization. The chemical structures of the polyamides were analyzed by nuclear magnetic resonance spectroscopy. The weight‐average molecular weights ranged from 3.3 × 103 to 1.15 × 104 with a polydispersity of 1.6–1.9, depending on monomer ratio or monomer concentration in solution. The 10% decomposition temperature of the polymers was about 210 °C. Differential scanning calorimetry revealed that the polyamides exhibited no peaks attributed to crystallization or melting point, which indicated that the polyamides were amorphous. No crystalline pattern was observed in the X‐ray diffractograms, supporting this result. Polarized optical microscopy observation revealed that the polyamides exhibited melting‐like behavior at above 150 °C, which was attributed to glass‐transition behavior. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47255.

Mechanisms and rates of nucleation of amyloid fibrils.

The classical nucleation theory finds the rate of nucleation proportional to the monomer concentration raised to the power, which is the "critical nucleus size," nc. The implicit assumption, that amyloids nucleate in the same way, has been recently challenged by an alternative two-step mechanism, when the soluble monomers first form a metastable aggregate (micelle) and then undergo conversion into the conformation rich in β-strands that are able to form a stable growing nucleus for the protofilament. Here we put together the elements of extensive knowledge about aggregation and nucleation kinetics, using a specific case of Aβ1-42 amyloidogenic peptide for illustration, to find theoretical expressions for the effective rate of amyloid nucleation. We find that at low monomer concentrations in solution and also at low interaction energy between two peptide conformations in the micelle, the nucleation occurs via the classical route. At higher monomer concentrations, and a range of other interaction parameters between peptides, the two-step "aggregation-conversion" mechanism of nucleation takes over. In this regime, the effective rate of the process can be interpreted as a power of monomer concentration in a certain range of parameters; however, the exponent is determined by a complicated interplay of interaction parameters and is not related to the minimum size of the growing nucleus (which we find to be ∼7-8 for Aβ1-42).

Tungsten Oxide and Polyaniline Composite Fabricated by Surfactant‐Templated Electrodeposition and Its Use in Supercapacitors

Composite nanostructures of tungsten oxide and polyaniline (PANI) were fabricated on carbon electrode by electrocodeposition using sodium dodecylbenzene sulfonate (SDBS) as the template. The morphology of the composite can be controlled by changing SDBS surfactant and aniline monomer concentrations in solution. With increasing concentration of aniline in surfactant solution, the morphological change from nanoparticles to nanofibers was observed. The nanostructured WO3/PANI composite exhibited enhanced capacitive charge storage with the specific capacitance of 201 F g−1 at 1.28 mA cm−2 in large potential window of −0.5~ 0.65 V versus SCE compared to the bulk composite film. The capacitance retained about 78% when the sweeping potential rate increased from 10 to 150 mV/s.

Polystyrene-coated micro-sized particles by “in situ” surface initiated polymerization in accord with Langmuir model adsorption

This study describes the mechanism of adsorption of polystyrene chains PS “in situ” growth from micro-sized commercial silicate particles, i.e. Feldspar. The main aim is to derive adsorption isotherms from thermal gravimetric analysis (TGA) and size exclusion chromatography (SEC) data obtained during the direct polymerization of PS initiated by a pre-adsorbed radical initiator onto the inorganic surface. The adsorption isotherm plot indicates that the PS adsorption is in accord with the Langmuir Model. The amount of PS monolayer coverage increases with polymerization time, and it is highly dependent on the monomer diffusion to the surface during the hybrid inorganic/organic synthesis. Such behavior depends on the concentration gradient between monomer concentration in solution and that adsorbed by polymerization onto the micro-sized particles surface of Feldspar.

Discovery of an Anionic Polymerization Mechanism for High Molecular Weight PPV Derivatives via the Sulfinyl Precursor Route

The polymerization of PPV via the sulfinyl precursor route has been investigated with respect to its mechanism. When polymerized in sec-butanol, a purely radical polymerization mechanism is observed as in most precursor polymerization routes. Accordingly, an increase in the reaction temperature induced an increase in the overall yield alongside with a reduction of the average molecular weight of the polymer. Upon changing the monomer concentration in solution before addition of the base NatBuO, an increase in molecular weight is observed, signifying that the polymerization is faster than the mixing of the two reaction components. When changing the solvent to NMP, a competition of anionic and radical polymerization has been established while in THF an anionic polymerization mechanism occurs exclusively. To prevent termination reactions, LDA and LHMDS were introduced as base whereby LHMDS shows less propensity to initiate anionic chain growth due to higher steric hindrance. With polymerizations in presence of the radical quencher TEMPO, the anionic polymerization mechanism could unambiguously be proven.

Growth Kinetics of Asymmetric Bi2S3 Nanocrystals: Size Distribution Focusing in Nanorods

The growth kinetics of colloidal Bi2S3 nanorods was investigated. After nucleation, the length distribution of the growing Bi2S3 nanorods narrows with the reaction time until a bimodal length distribution appears. From this critical reaction time on, the smallest nanorods of the ensemble dissolve, feeding with monomer the growth of the largest ones. A comprehensive characterization of the size-distribution evolution of Bi2S3 nanorods is used here to illustrate the dependences of the anisotropic growth rates of cylindrical nanoparticles on the nanoparticle dimensions and the monomer concentration in solution. With this goal in mind, a diffusion-reaction model is presented to explain the origin of the experimentally obtained length distribution focusing mechanism. The model is able to reproduce the decrease of the growth rate in the nanorod axial direction with both its thickness and length. On the other hand, low lateral reaction rates prevent the nanorod thickness distribution to be focused. In both crystallographic growth directions, a concentration-dependent critical thickness exists, which discriminates between nanorods with positive growth rates and those dissolving in the reaction solution.

Shape-Controlled Growth and Shape-Dependent Cation Site Occupancy of Monodisperse Fe3O4 Nanoparticles

The shape control and formation mechanism of Fe3O4 nanoparticles (NPs) synthesized by a modified hot-injection method were investigated. Monodisperse Fe3O4 nanocubes terminated at {100} planes with the average size of 16.1 ± 0.9 nm were synthesized by injecting Fe precursor into reaction solution at 290 °C with a slow injection rate of 10 mL/h. When we increased the monomer concentration in solution by increasing the injection rate to 20 mL/h or doubling the precursor concentration with the same reaction time, the main terminated planes of Fe3O4 NPs became {100} and {110} planes leading to a rhombicuboctahedral shape. The shape of NPs was strongly affected by the monomer concentration and the intrinsic surface energy of Fe3O4. The shape-induced crystallographic orientation-ordered superlattices were obtained in both cubic and rhombicuboctahedral Fe3O4 NPs. On the other hand, the shape-dependent occupancy of the cation sites was clearly observed, measured by using X-ray magnetic circular dichroism (XMCD) spectra. The octahedral sites were occupied by more ferric ions, Fe3+, when the shape of Fe3O4 NPs became cubic.

Atom transfer radical polymerization of a novel quinoline derivative monomer and fluorescent property

A novel functional monomer incorporating quinoline derivative moiety as the side group, 2-[4-(2,7,7-trimethyl-3-ethoxycarbonyl-5-oxo-1,4,5,6,7,8-hexhydricquinoline)phenoxyl] ethylmethacrylate (HQPEMA), was synthesized and polymerized utilizing atom transfer radical polymerization (ATRP) technique. 2-(4-Chloromethylphenyl)benzoxazole (CMPB) and CuCl/PMDETA were used as the initiator and catalyst, respectively. GPC, 1H NMR and fluorescent emission spectroscopy were conducted for characterization of polymers. The linear increase of number average molecular weight ( M n) versus conversion and the relatively narrow molecular weight distribution ( M w/ M n) of the obtained polymers confirmed that ATRP of HQPEMA was carried out successfully. In addition, the fluorescence “structural self-quenching effect” was observed in the DMF solution of the monomer HQPEMA, which bearing both electron-donating chromophore group and electron-accepting C C bond. We also found that the fluorescence properties of the newly obtained polymers containing quinoline chromophore depended on both the monomer concentration in solution and the polarity of solvents. The emission of the polymer film showed that the emission peak maxima of the polymer film shifted 50 nm towards high wavelength with respect to the polymer in DMF solution due to the intermolecular or intramolecular interactions of the polymer chains.

The Aggregation Work and Shape of Molecular Aggregates upon the Transition from Spherical to Globular and Cylindrical Micelles

The transition from spherical to globular and cylindrical equilibrium modifications of micelles in solutions of nonionic surfactants is numerically studied within the framework of the droplet model of molecular aggregates. Two branches of the curve of micelle aggregation work are plotted as a function of aggregation numbers. One of these curves corresponds to the globular micelles; the other, to spherocylindrical micelles. At aggregation numbers corresponding to the limiting spherical packing, both the globules and spherocylinders are transformed into the limiting sphere. It is shown that the ratio between the branches depends on the dimensionless parameter characterizing the ratio of electrostatic and surface contributions to the aggregation work. It is elucidated that, at certain values of this parameter and surfactant monomer concentration in solution, in addition to the maximum in the region of submicellar aggregates for spherical micelles, the second maximum arises on the curve of aggregation work as a function of aggregation numbers in the region of transition to spherocylindrical micelles. The appearance of an additional maximum is shown to be caused by the sum of surface, electrostatic, and concentration contributions to the aggregation work and is not directly related to the conformational contribution to the aggregation work.

Mechanisms for the Shape‐Control and Shape‐Evolution of Colloidal Semiconductor Nanocrystals

AbstractThe shape of CdSe and other semiconductor nanocrystals is controlled, producing dots, rods, rice‐shaped particles, tetrapods, or other elongated shapes. Monomer concentration in the growth solution is the determining factor in shape‐control and shape‐evolution. The elongated shapes could be transformed into more spherical shapes if the monomer concentration in the solution was lowered to a certain level, and spherically shaped nanocrystals could grow to elongated shapes by simply increasing the monomer concentration. The precursors are stable, inexpensive, and relatively non‐toxic, and therefore good choices for the growth of nearly monodisperse and shape‐controlled nanocrystals.

Thermodynamic Characteristics of a Spherical Molecular Surfactant Aggregate in a Quasi-Droplet Model

The model of spherical molecular aggregate of nonionic surfactant is proposed. This model allows for the maximal (in accordance with packing rules) penetration of water molecules into an aggregate and is an alternative to the droplet model of molecular aggregate. Necessary conditions for the applicability of a model named quasi-droplet model are formulated. Based on this model, the dependence of the work of molecular aggregate formation on the aggregation number and surfactant monomer concentration in solution that plays the key role for the theory of micellization is studied. The equation is derived for the coordinates of maximum and minimum of aggregate formation work on the aggregation number axis arising with an increase in the concentration of micellar solution. Model calculations of the thermodynamic characteristics of the kinetics of micellization are performed. The approximation of the work of molecular aggregate formation allowing for the analytical study is constructed.

Thermodynamic Characteristics of Micellization in the Droplet Model of Surfactant Spherical Molecular Aggregate

The dependence of the work of the molecular aggregate formation on the aggregation number and surfactant monomer concentration in solution that has the key role for the theory of micellization was studied on the basis of a simple realistic droplet model of spherical aggregate composed of surfactant molecules (the o/w micelle type). Analytical formulas were derived for the coordinates of maximum and minimum of aggregate formation work on the aggregation number axis arising with an increase in the concentration of micellar solution. Model calculations of the thermodynamic characteristics of the kinetics of micellization were performed for premicellar and micellar regions of aggregate sizes within a wide range of solution concentration including the critical micellization concentration.

Formation of Covalently Attached Polymer Overlayers on Si(111) Surfaces Using Ring-Opening Metathesis Polymerization Methods

We describe a method for growing uniform, covalently attached polymer onto crystalline Si(111) surfaces. H-Terminated Si was first chlorinated, and the surface-bound chlorine was then replaced by a terminal olefin using a Grignard reaction. A ruthenium ring-opening metathesis polymerization catalyst was then crossed onto the terminal olefin, and the resulting surface was subsequently immersed into a solution of monomer to produce the desired surface-attached polymer. The method provides a direct linkage between the polymer and the Si without the presence of an electrically defective oxide layer. Growth of the polymeric layer could be controlled by varying the concentration of monomer in solution, and polynorbornene films between 0.9 and 5500 nm in thickness were produced through the use of 0.01−2.44 M solutions of norbornene.

Effect of solvent on the rate constants in solution polymerization. Part II. Vinyl acetate

Measurements were made of the value of the lumped kinetic constant kp/k of vinyl acetate in different solvents and with different initiators. This quantity was evaluated using the well-known conversion vs. time approach in dilute solutions using both azo-bis-isobutyronitrile and benzoyl peroxide (AIBN and BPO), and two different solvents (toluene and ethyl acetate) at 60°C. As was found for butyl acrylate in Part 1 of this series, it was found that the value of the lumped rate constant depends very strongly on the concentration of monomer in solution, decreasing as the solution becomes more and more dilute. However, unlike butyl acrylate, vinyl acetate is much more susceptible to changes in the solvent type, with toluene acting as a severe retarding agent of polymerization. The results of the present study suggest that at least two separate effects of solvent exist simultaneously in the case of vinyl acetate polymerization, and that both of them must be taken into account when attempting to model this type of system. The number- and weight-average molecular weights of the different polymers were also measured, and excellent agreement was found between the measurements and model predictions. A linear relationship was shown to exist between the value of the lumped constant and the square root of the number-average chain length. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 589–601, 1999

Surface modification of polymers—I. Grafting initiated by photo-generated hydroperoxides

Grafting of methacrylic acid (and other water-soluble monomers such as acrylic acid and acrylamide) onto the surface of styrene-butadiene-styrene block copolymer films has been performed using polymeric hydroperoxides as initiator. These peroxides are obtained by reaction with the polymer of singlet oxygen, the production of which is photo-sensitized by anthracene. The rate of grafting is first order with respect to the monomer concentration in solution but increase of rate is observed for methacrylic acid concentrations higher than 1 mol 1 −1. The rate of grafting is also proportional to the initial concentration of anthracene in the film.

Radiation‐induced graft polymerization of metal‐containing monomers

AbstractGraft polymerization of acrylates and acrylamide complexes of Mn(II), Cr(III), Fe(III), Co(II), Ni(II), and Cu(II) from alcohol solutions onto a polyethylene powder preirradiated in air up to total doses of 10–300 kJ/kg was studied. Graft copolymers with a metal content of as high as 1.7 mass% were obtained. The addition of a σ‐ or a coordinate‐bound metal atom to the monomer molecule (acrylic acid, acrylamide) was shown to decelerate the process of thermal homopolymerization by 4 to 8 times, significantly reduce the reaction order in respect with monomer concentration in solution, and in most cases produce no effect on the polymer chain termination mechanism. The grafting of metal‐containing monomers was found not to alter the structure of the monomer unit, valent state, and coordination of the metal atom, either. The graft polymerization of the monomers from solution is distinguished by a weak effect of the radical reaction inhibitors. The effective activation energies for the grafting of the metal‐containing monomers lie within 42–60 kJ/mol.

Polymerization of glass-like solutions of N-phenyl maleimide in dimethyl formamide (DMF)

The low temperature radiation-induced polymerization of N-phenylmaleimide solutions in DMF, forming glass at 77°K, has been studied over a wide concentration range. It was shown that with increasing monomer concentration in solution, more and more polymer is formed immediately following γ-irradiation of the glassy solutions at 77°K, as a result of rather high mobility of the monomer molecules in the DMF matrix. By studying the postpolymerization of these solutions, the nature of the active centres was explained and the values of radiochemical yield of radicals, effective activation energy and propagation constant determined.

Evaluation of heats and entropies of polymerization from measurements of equilibrium monomer concentration in solution

AbstractFormulas are derived for the evaluation of heats and entropies of polymerization from measurements of equilibrium monomer concentrations in solution. In contrast to previous work, the heats of mixing of monomer, solvent and polymer are taken into account. The effect of the glass transition in the polymer is considered. The derived relationships successfully predict the observed differences in equilibrium concentration of styrene monomer in different solvents. The effect of varying amounts of solvent and polymer on the equilibrium concentration of α‐methylstyrene is also accounted for, at least semi‐quantitatively.

Polymerization in the system vinylidene chloride‐potassium laurate‐potassium persulfate

AbstractThe persulfate–initiated polymerization of vinylidene chloride in aqueous solutions of potassium laurate has been studied both with amounts of monomer small enough so as not to form a separate phase, and in emulsions of various compositions. In the first case, rates were determined by following the change in vapor pressure over the solution, and a method for obtaining the necessary vapor pressure‐concentration calibration curves was also developed; in the second, rates were determined by dilatometric and gravimetric methods. The rates were found to vary with the square root of the initiator concentration, and with the first power of the monomer concentration in solution, but to be independent of the amount of dispersed monomer in emulsion. They were found to increase with soap concentration, most markedly so in the region of low concentration. Approximate solubilities of monomer in polymer latices were also determined, and found to be about five times greater than solubilities in the original soap solutions; polymerization rates in emulsion and solution differed correspondingly. A high‐temperature viscometric technique has been developed for polyvinylidene chloride; intrinsic viscosity data indicate that chain transfer is appreciable in the reaction investigated.