Mixtures Of Macromolecules Research Articles

Semibatch Terpolymerization of Ethylene, Propylene, and 5-Ethylidene-2-norbornene: Heterogeneous High-Ethylene EPDM Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) are materials combining the processability of thermoplastics and the elasticity of rubbers. The global value and demand of TPEs are expected to grow in the coming years, and advancement in synthetic chemistry is the key driving force. This contribution provides a simple synthesis of high-ethylene EPDMs with high molecular weight, narrow molecular weight distribution (1.9 < Mw/Mn < 2.3), and properties which can be adjusted from soft thermoplastic to elastomer. EPDMs are prepared through the terpolymerization of ethylene with propylene and 5-ethylidene-2-norbornene (ENB), where ethylene is continuously supplied to the reaction bath, while propylene and ENB are added only at the beginning. Polymerizations are catalyzed by three known imido vanadium­(IV) complexes, differing in the imido substituent and coligand, in combination with Et2AlCl and Cl3CCO2Et. The obtained EPDMs are a mixture of macromolecules, each of them featuring a nonrandom comonomer distribution and nonuniform composition. Each chain likely contains multiblocks where the comonomers are segmented, i.e., blocks with high ethylene content that may crystallize and blocks with high propylene and ENB content that may not crystallize. This broad chemical composition distribution is due to time drift that occurs during the polymerization, which in turn depends on the experimental conditions and ligand set. Composition drift causes variation in the instantaneous feed comonomer ratio and hence in the chemical composition of the terpolymer over the period of conversion. In proper experimental conditions, EPDMs behave as TPEs without the need of vulcanization, polymer blending, and reinforcement through the addition of fillers. They exhibit high elongation at break, strain hardening at large deformation, remarkable shape retention properties (up to 76% recovery after 10 cycles at 300% and about 90% at 410% strain), and remelting processability with no fall in properties for recycle and reuse.

Measuring translational diffusion of 15N-enriched biomolecules in complex solutions with a simplified 1H-15N HMQC-filtered BEST sequence.

Pulsed-field gradient nuclear magnetic resonance has seen an increase in applications spanning a broad range of disciplines where molecular translational diffusion properties are of interest. The current study introduces and experimentally evaluates the measurement of translational diffusion coefficients of 15N-enriched biomolecules using a 1H-15N HMQC-filtered band-selective excitation short transient (BEST) sequence as an alternative to the previously described SOFAST-XSTE sequence. The results demonstrate that accurate translational diffusion coefficients of 15N-labelled peptides and proteins can be obtained using this alternative 1H-15N HMQC-filtered BEST sequence which is implementable on NMR spectrometers equipped with probes fitted with a single-axis field gradient, including most cryoprobes dedicated to bio-NMR. The sequence is of potential use for direct quantification of protein or peptide translational diffusion within complex systems, such as in mixtures of macromolecules, crowded solutions, membrane-mimicking media and in bicontinuous cubic phases, where conventional sequences may not be readily applicable due to the presence of intense signals arising from sources other than the protein or peptide under investigation.

Surfactant-Induced Patterns in Polymer Brushes.

The properties of surfaces with grafted macromolecules are determined by a fine structure of the macromolecular layer, whereas the mixtures of macromolecules with surfactants are very rich in structure types. Using the scaling mean-field theory, we consider the self-assembly in polymer brushes into various patterns induced by interactions with low-molecular surfactants. The interaction energies of the parts of a surfactant molecule with the polymer units are assumed to be greatly different. With increasing the grafting density, the formation of lamellae perpendicular to the grafting plane, a continuous layer with oblong or round pores, or a homogeneous brush is predicted. The driving force of the pattern formation is a gain in the interaction energy of surfactant molecules oriented at the lateral surfaces of lamellae or pores. The process of pore formation in a homogeneous brush caused by a temperature change at definite grafting densities is described as the first-order phase transition. It is accompanied by a stepwise extension of the brush and by orientational ordering of surfactant molecules. The transitions between the other patterns are of the second order. The thickness of lamellae and the distance between pores are approximately twice the surfactant molecule size except for the extremely high grafting densities. The diagrams of brush patterns are presented and discussed.

P14. Extracellular matrix deposition and function in the early chick embryo

Cells within all multicellular organisms are surrounded by a heterogeneous mixture of macromolecules, collectively known as the extracellular matrix (ECM). The ECM is synthesised and organised by cells, providing them with a substrate to interact with, spaces to migrate through and cell–ECM engagement also directly impacts cell polarisation, proliferation, survival and differentiation. ECM molecules are present from the earliest stages of embryo development and the developmentally regulated dynamics of ECM assembly and degradation play key roles in many embryological processes. In this study we addressed how fibronectin, laminin and chondroitin sulphate proteoglycans are deposited in the early (HH12–15) chick embryo, focusing on the developing mesodermal regions and the neural tube. We find that fibronectin is the first ECM molecule to form a complex ECM. Although present in the interstitial space, fibrillar fibronectin matrices are more prominent lining epithelioid (somites, notochord and intermediate mesoderm) and epithelial (neural tube) tissues, before any assembled basement membrane is detected. However, as these epithelioid/epithelial tissues develop, laminin is progressively assembled on their surface. Assembly starts in small patches localized in fibronectin-poor areas and with developmental time, these patches grow in size until the tissues are lined with a laminin basement membrane. Inhibition of fibronectin assembly leads to abnormal cell polarization and containment, suggesting that the fibronectin matrix is essential for the initial epithelial development of these tissues, before the appearance of the basement membrane. Although the interstitial spaces of HH12–15 embryos are only partially filled with a fibronectin matrix, we find that chondroitin sulphate proteoglycans are progressively deposited in these spaces and appear to play a role in separating the early tissue units. In agreement with this, treatment of cultured chick embryo explants with chondroitinase ABC leads to the collapse of all extracellular space and to mesodermal tissue deformations. We conclude that fibronectin matrices play an important role in polarizing cells and containing cell movements in young epithelia before a laminin-containing basement membrane forms, while chondroitin sulphate proteoglycans are crucial for maintaining interstitial spaces. The developmental deposition of these ECMs is thus essential for the correct morphogenesis of the early embryo.

A New Approach for the Solution of the Electrostatic Potential Differential Equations

This paper is focused on deriving an explicit analytical solution for the prediction of the electrostatic potential, commonly used on electrokinetic research and its related applications. Different from all other analytic techniques, this approach provides a simple way to ensure the convergence of series of solution so that one can always get accurate enough approximations. This new approach can be a useful tool in electrical field applications such as the separation of a mixture of macromolecules and the removal of contaminants in soil cleaning processes.

Envelope: interactive software for modeling and fitting complex isotope distributions.

BackgroundAn important aspect of proteomic mass spectrometry involves quantifying and interpreting the isotope distributions arising from mixtures of macromolecules with different isotope labeling patterns. These patterns can be quite complex, in particular with in vivo metabolic labeling experiments producing fractional atomic labeling or fractional residue labeling of peptides or other macromolecules. In general, it can be difficult to distinguish the contributions of species with different labeling patterns to an experimental spectrum and difficult to calculate a theoretical isotope distribution to fit such data. There is a need for interactive and user-friendly software that can calculate and fit the entire isotope distribution of a complex mixture while comparing these calculations with experimental data and extracting the contributions from the differently labeled species.ResultsEnvelope has been developed to be user-friendly while still being as flexible and powerful as possible. Envelope can simultaneously calculate the isotope distributions for any number of different labeling patterns for a given peptide or oligonucleotide, while automatically summing these into a single overall isotope distribution. Envelope can handle fractional or complete atom or residue-based labeling, and the contribution from each different user-defined labeling pattern is clearly illustrated in the interactive display and is individually adjustable. At present, Envelope supports labeling with 2H, 13C, and 15N, and supports adjustments for baseline correction, an instrument accuracy offset in the m/z domain, and peak width. Furthermore, Envelope can display experimental data superimposed on calculated isotope distributions, and calculate a least-squares goodness of fit between the two. All of this information is displayed on the screen in a single graphical user interface. Envelope supports high-quality output of experimental and calculated distributions in PNG or PDF format. Beyond simply comparing calculated distributions to experimental data, Envelope is useful for planning or designing metabolic labeling experiments, by visualizing hypothetical isotope distributions in order to evaluate the feasibility of a labeling strategy. Envelope is also useful as a teaching tool, with its real-time display capabilities providing a straightforward way to illustrate the key variable factors that contribute to an observed isotope distribution.ConclusionEnvelope is a powerful tool for the interactive calculation and visualization of complex isotope distributions for comparison to experimental data. It is available under the GNU General Public License from .

Kinetics of the enzymatic decomposition of macromolecules with a fractal structure

Mechanisms of enzymatic decomposition of an organic substance consisting of fractal macromolecules of different sizes are studied. A kinetic decomposition equation in which the reaction rate coefficient depends on the characteristic of the fractal structure is formulated. The solution for a fraction of macromolecules of the same size and for a mixture of macromolecules of different sizes is analyzed. It is shown that the decomposition kinetics depends on the fractal structure of the macromolecules and the type of their initial distribution by size. Conditions under which the decrease in the concentration of the organic substance obeys the power law are found. The theoretical relations are used for analyzing the literature data on the decomposition kinetics of organic matter in sea sediments in the time interval from several hours to about one million years. It is shown that in this whole interval the concentration decreases with time according to the universal power law with a 0.14 exponent. The kinetics of enzymatic decomposition of lignin (product of the natural decomposition of plant remains or byproduct of wood processing) is also discussed. It is found that the exponent accounting for the concentration decrease is equal to 0.4 to 0.5 for the decomposition of industrial lignin in bulk water and 1 to 2 for its decomposition in the water with bottom sediments.

CHARACTERIZATION OF TEN SEQUENTIALLY EXTRACTED HUMIC ACIDS AND A HUMIN FROM A SOIL IN WESTERN MASSACHUSETTS

Humic substances are mixtures of macromolecules with varied structures and chemical compositions that are affected by differences in parental biomaterials and environmental conditions. This study used elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state 13 C nuclear magnetic resonance spectroscopy (NMR) to identify the chemical and structural heterogeneity of 10 humic acids (HAs) and a humin. The HAs were obtained by progressively extracting solution from a soil in western Massachusetts, eight times with 0.1 M Na 4 P 2 O 7 and two times with 0.1 M NaOH. The humin was the residual fraction after 10 base extractions. As indicated by solid state NMR analysis, the aliphatic carbons (0 ∼ 108 ppm) of the HAs increased gradually from 50% in fraction 1 (F-1) to 62% in fraction 9 (F-9) and 70% for the humin, but the aromatic carbons (108 ∼ 162 ppm) were highest in F-1. The band assigned to aliphatic carbon (2930 cm -1 ) in the DRIFTS spectra gradually increased with further extractions, and the relative intensity of this peak was the highest in humin. The atomic C/H ratio declined from 1.1 for F-1 to 0.6 for F-10 and the humin, consistent with the spectroscopic analyses. In addition, both elemental and spectroscopic data reveal that the last extracted HA and humin contained relatively lower contents of polar functional groups such as carboxylic and phenolic groups. This study shows significant chemical, structural, and molecular differences among the 10 sequentially extracted HAs and humin, even from a single soil.

The detergent octylglucoside neutralizes lipopolysaccharide in a specific manner.

The stimulatory effect of lipopolysaccharide (LPS) on human macrophages was found to be neutralized by the detergent octylglucoside (OG). Both macrophage stimulation and reactivity in a limulus amebocyte lysate test were suppressed by suspension of LPS in OG at concentrations between 0.25 and 2.5 mM, whereas other stimulatory lipopeptides and lipid containing stimulants were unaffected by OG. LPS at concentrations causing maximal stimulation of macrophages could be completely neutralized by non-toxic concentrations of OG. In addition, it was found that the neutralization in complex mixtures of macromolecules, such as bacterial cell lysate, was specific for LPS and that the stimulatory activity of the other substances in the mixture was not affected by the OG.

Reconstruction of histograms of the glass transition temperature of free radical copolymers from DSC thermograms

Most polymeric materials appear as complex mixtures of macromolecules characterized by distributions of specific properties that are essential to the quality of these products. Among such properties, the accurate determination of the glass transition temperature, and therefore, accurate representation of it, is a key issue. When analyzed using dynamic scanning calorimetry (DSC) techniques, many copolymers exhibit a wide range of temperature over which the glass transition takes place, and the width of the transition region is, therefore, not satisfactorily described by average Tg values, for example those computed from tangent curves drawn on thermograms. This article describes a method that allows us to characterize this spreading of the glass transition region by reconstructing weighted Tg distributions from DSC thermograms. As such an objective might appear as questionable from a strictly physical point of view, the significance of what is meant by “distribution” is specified in the text. A model is proposed that accounts for relaxation phenomena. The approach is validated by examining samples of BuA/Sty emulsion copolymers produced at different overall conversions and compositions, and examining the corresponding histograms of Tg were computed. The results show that accurate and consistent information on the glass transition behavior of the copolymer is obtained, and that the effective distribution is clearly connected with the composition drift in the polymer particles. The proposed algorithm allows one to obtain a maximum amount of information from DSC measurements, and provides a deeper insight into the “history” of complex polymer mixtures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 357–367, 2000

Molecular theory of solutions and blends of heteropolymers. I. Thermodynamics of amorphous multicomponent polymer systems

On the basis of a variational principle a quantitative theory is developed enabling a thermodynamic description in terms of mean field approximation of heteropolymer mixtures of macromolecules with an arbitrary distribution for both degree of polymerization and composition. Rather simple general equations are derived to calculate compositions and volume fractions of spatially homogeneous macroscopic phases as well as to find the cloud-point curve, spinodal, and critical points. Potentialities of general theory are illustrated for copolymers synthesized by traditional methods.

Extracellular Matrix: The Cellular Environment

The extracellular matrix consists of a mixture of macromolecules that is specific for any given tissue and makes up a distinct environment for the different cells of the body. The study of these macromolecules and their assembly into complex extracellular matrix structures has focused attention on their physiological importance.

Toward the Development of a General Framework for Modeling Molecular Weight and Compositional Changes in Free-Radical Copolymerization Reactions

Abstract Synthetic copolymers are produced as a mixture of macromolecules with varying degree of polymerization, copolymer composition, and degree of branching. The ability to predict molecular properties in a copolymerization process as a function of the reactor operating conditions is of considerable economic importance to the polymer industry.

Excluded volume effects on the partition of macromolecules between two liquid phases

Partition parameters of several proteins and other macromolecules are measured in an aqueous two-phase liquid system containing polyethylene glycol and phosphate buffer. Distribution of macromolecules is a function of the relative volume excluded to the macromolecules in the two phases. A simple model with no adjustable parameters yields covolumes of the macromolecules with the polyethylene glycol. Covolumes are used to estimate effective molecular volumes and the magnitudes of excluded volume effects. The same approach is applied to mixtures of macromolecules.

Cell transport in model extracellular matrices

The rapid transport of cells has been shown to occur by ordered countercurrent convection. This convection can be created by mixtures of macromolecules which make up the extracellular matrix and by the degradation and aggregation products of these macromolecules. The ordered countercurrent convection is manifested in the form of structured flows and arises in isothermal systems with small concentration gradients of solutes. The flows are gravity driven but may rapidly move at angles close to the horizontal axis if they are mechanically constrained to do so. These flows have been shown to rapidly transport cells at rates ranging from 1 to 100 mm h −1, depending on the conditions of the experiment. The transport of cells is nonspecific in that various cell types (chondrocytes, fibroblasts, endothelial cells, and red blood cells) as well as inert particles of similar size (latex beads 6-μm diam) are transported at similar rates. Latex bead transport by structured flow has also been demonstrated to occur in confined spaces in the form of Teflon tubing down to 200 μm in diameter and at angles in the range of 45–90 ° to the horizontal axis. The flows may also occur over relatively long distances for a prolonged period of time. The conditions for flow formation are simple and widespread. It is suggested that it may contribute to the forces involved in the movement of cells in the extracellular matrix in vivo especially during remodeling and embryogenesis.

Polymerization of isoprene adsorbed on kaolin from gaseous phase

Polymerization of isoprene adsorbed on kaolin from gaseous phase was investigated. In the polymerization process that part of polyisoprene which is in the closest contact with the substrate surface is crosslinked and cannot be extracted by solvents. The extractible polymer fraction is a mixture of macromolecules of normal structure and of polymer chains which carry OH and/or C = O groups in each monomer link. Oxygen-containing groups are also present in the insoluble polyisoprene fraction. The incorporation of oxygen-containing groups into polymer chains is probably due to the reaction of water molecules bonded to the exchangeable cations in kaolin with double bonds in the polyisoprene molecules. The microstructure of the polyisoprene has been elucidated.

The State of Polydispersion of Hevea Latex. I

Abstract The rubber particles in the latex of Hevea brasiliensis are present in the form of a polydispersion, and their diameters lie within the range of 0.1 to 3 microns. The rubber hydrocarbon itself is composed of a mixture of macromolecules of different degrees of polymerization. Rubber latex is, therefore, a system which is at the same time both polydispersed and polymolecular. It is well known that the degree of dispersion of a substance governs to a great extent certain properties of the substance. Moreover, astonishing as it may seem, in the great number of investigations which have been made of the composition and properties of latex and crude rubber, almost no attention has been paid to the part which may be played by the dimensions of the latex particles. However, in an investigation concerned with the centrifugation of latex, Loomis and Stump have called attention to this possibility, and in a study of latex obtained by fractionation, and in which the majority of the latex particles were of large dimensions, McGavack came to the conclusion that the protein content is proportional to the surface area of the globules. This limited knowledge of the subject seemed to warrant a more thorough study of the problem, which is of fundamental importance both from the theoretical and practical points of view. The investigation as a whole divided itself into three essential parts: (1) separation of latex into fractions containing particles of different sizes, and measurement of the state of dispersion in these fractions, (2) a study of the relation of these fractions to the composition of the rubber, i.e., the relation between the content of nonrubber components and the size of the latex particles, and (3) a study of the changes in the properties of the rubber hydrocarbon with change in the size of the latex particles. The latex used in this investigation was ordinary latex, containing 38–40 per cent dry-rubber content and preserved with ammonia. For the most important points, a concentrated latex (creamed latex containing 60 per cent dry-rubber content) was also tested. These two latices were about two years old when the investigation was started, and they gave results which were in good agreement with each other. In the present paper, only the data obtained with the first of the two latices are presented.