Molecular Weight Characteristics Research Articles

Determination of kinetic constants of the cationic copolymerization of isobutylene with isoprene

A theoretical kinetic model has been developed for cationic isobutylene–isoprene copolymerization in methyl chloride with an AlCl3 catalyst. Kinetic constants of this process have been derived from experimental data available on copolymerization kinetics (isobutylene conversion curve) and on molecular weight characteristics of the isobutylene–isoprene copolymer (butyl rubber). The adequacy of the theoretical kinetic model of the isobutylene–isoprene copolymerization process has been demonstrated by comparing the calculated molecular weight characteristics and degree of unsaturation of butyl rubber to the corresponding independent experimental data.

Macrokinetics of the cationic copolymerization of isobutylene with isoprene

A theoretical model has been developed for the macrokinetics of cationic isobutylene–isoprene copolymerization in a stirred reactor and in a tubular turbulent reactor. The model provides means to calculate the reaction mass temperature, velocity, and turbulence kinetic energy fields. The adequacy of the model has been demonstrated using the Fisher criterion. Computational experiments have been carried out to estimate the effects of the catalyst concentration and the rotational speed of the stirrer (in the case of the synthesis conducted in a stirred reactor) and the effects of reaction mixture velocity and apparatus diameter (in the case of the synthesis conducted in a tubular turbulent reactor) on molecular weight characteristics of the resulting copolymer (butyl rubber).

Investigation of Electron Beam Initiated Reactions of Styrenic Block Copolymers

Electron beam (E-beam) radiation initiated reactions in styrenic block copolymers (SBCs), including poly (styrene-block-butadiene-block-styrene) (SBS), poly (styrene-block-isoprene-block-styrene) (SIS) and a newly developed poly (styrene-block-isoprene/butadiene-block-styrene) (SIBS) were investigated. The gel content of SBCs after E-beam exposure was calculated and the molecular weight characteristic of soluble portion was analyzed by size exclusion chromatography (SEC). The results showed that gel content increased with increasing of E-beam radiation dose and the low molecular weight material was generated after E-beam exposure. This indicated that both crosslinking and chain scission reactions took place during the E-beam exposure. The crosslinking reaction was the predominating reaction. The structures of gel portion of SBCs were analyzed by solid state nuclear magnetic resonance (NMR). Equilibrium swelling showed that a tighter network was formed at higher radiation dose. Cylindrical morphologies were observed by both small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The effect of E-beam on morphologies of ozone etched SBCs was also investigated. It was found that the films of SBCs after E-beam crosslinking were able to maintain a relatively intact morphology after ozonolysis, while SBCs without E-beam cross-linking lost the cylindrical morphology after ozonolysis.

Photoinduced Cu(0)‐Mediated Atom Transfer Radical Polymerization

Photoinduced Cu(0)‐mediated atom transfer radical polymerization (ATRP) of methyl methacrylate is investigated by using Cu(0)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst, ethyl 2‐bromopropionate as the initiator, and dimethyl sulfoxide as the solvent. The effect of light on the conventional Cu(0)‐mediated ATRP and molecular weight characteristics of the obtained polymers are described. Although the polymerization can be achieved in the absence of light, low initiation efficiency of the process is observed. By introducing UV light and additional Cu(II) deactivator, not only the rate of polymerization is increased, but also well‐controlled polymers with narrow‐molecular‐weight distributions at ambient conditions are obtained. The chain extension study clearly confirms high end‐group fidelity of the polymer that is active in the further polymerization process. image

Modeling of continuous free-radical butadiene-styrene copolymerization process by the Monte Carlo method

In the paper the algorithm of modeling of continuous low-temperature free-radical butadiene-styrene copolymerization process in emulsion based on the Monte-Carlo method is offered. This process is the cornerstone of industrial production butadiene – styrene synthetic rubber which is the most widespread large-capacity rubber of general purpose. Imitation of growth of each macromolecule of the formed copolymer and tracking of the processes happening to it is the basis of algorithm of modeling. Modeling is carried out taking into account residence-time distribution of particles in system that gives the chance to research the process proceeding in the battery of consistently connected polymerization reactors. At the same time each polymerization reactor represents the continuous stirred tank reactor. Since the process is continuous, it is considered continuous addition of portions to the reaction mixture in the first reactor of battery. The constructed model allows to research molecular-weight and viscous characteristics of the formed copolymerization product, to predict the mass content of butadiene and styrene in copolymer, to carry out calculation of molecular-weight distribution of the received product at any moment of conducting process. According to the results of computational experiments analyzed the influence of mode of the process of the regulator introduced during the maintaining on change of characteristics of the formed butadiene-styrene copolymer. As the considered process takes place with participation of monomers of two types, besides listed the model allows to research compositional heterogeneity of the received product that is to carry out calculation of composite distribution and distribution of macromolecules for the size and structure. On the basis of the proposed algorithm created the software tool that allows you to keep track of changes in the characteristics of the resulting product in the dynamics.

Two chemically distinct light-absorbing pools of urban organic aerosols: A comprehensive multidimensional analysis of trends

The chemical and light-absorption dynamics of organic aerosols (OAs), a master variable in the atmosphere, have yet to be resolved. This study uses a comprehensive multidimensional analysis approach for exploiting simultaneously the compositional changes over a molecular size continuum and associated light-absorption (ultraviolet absorbance and fluorescence) properties of two chemically distinct pools of urban OAs chromophores. Up to 45% of aerosol organic carbon (OC) is soluble in water and consists of a complex mixture of fluorescent and UV-absorbing constituents, with diverse relative abundances, hydrophobic, and molecular weight (Mw) characteristics between warm and cold periods. In contrast, the refractory alkaline-soluble OC pool (up to 18%) is represented along a similar Mw and light-absorption continuum throughout the different seasons. Results suggest that these alkaline-soluble chromophores may actually originate from primary OAs sources in the urban site. This work shows that the comprehensive multidimensional analysis method is a powerful and complementary tool for the characterization of OAs fractions. The great diversity in the chemical composition and optical properties of OAs chromophores, including both water-soluble and alkaline-soluble OC, may be an important contribution to explain the contrasting photo-reactivity and atmospheric behavior of OAs.

CATIONIC COPOLYMERIZATION OF ISOBUTYLENE WITH ISOPRENE: KINETICS OF THE PROCESS AND DETERMINATION OF KINETIC CONSTANTS

ABSTRACT A theoretical description has been developed of the kinetics of isobutylene with isoprene (IIR) cationic polymerization in the environment of methyl chloride on aluminum trichloride as the catalyst. Based on experimental data on the kinetics of copolymerization (isobutylene conversion curve) and the molecular weight characteristics of the copolymer of IIR, kinetic constants for the process were found. Adequacy of the developed theoretical description of the kinetics of the IIR copolymerization process was confirmed by comparing the experimental molecular-weight characteristics calculated by this description, independent characteristics, and IIR unsaturation.

Pharmacokinetics and Disposition of the Thiouracil Derivative PF-06282999, an Orally Bioavailable, Irreversible Inactivator of Myeloperoxidase Enzyme, Across Animals and Humans.

The thiouracil derivative PF-06282999 [2-(6-(5-chloro-2-methoxyphenyl)-4-oxo-2-thioxo-3,4-dihydropyrimidin-1(2H)-yl)acetamide] is an irreversible inactivator of myeloperoxidase and is currently in clinical trials for the potential treatment of cardiovascular diseases. Concerns over idiosyncratic toxicity arising from bioactivation of the thiouracil motif to reactive species in the liver have been largely mitigated through the physicochemical (molecular weight, lipophilicity, and topological polar surface area) characteristics of PF-06282999, which generally favor elimination via nonmetabolic routes. To test this hypothesis, pharmacokinetics and disposition studies were initiated with PF-06282999 using animals and in vitro assays, with the ultimate goal of predicting human pharmacokinetics and elimination mechanisms. Consistent with its physicochemical properties, PF-06282999 was resistant to metabolic turnover from liver microsomes and hepatocytes from animals and humans and was devoid of cytochrome P450 inhibition. In vitro transport studies suggested moderate intestinal permeability and minimal transporter-mediated hepatobiliary disposition. PF-06282999 demonstrated moderate plasma protein binding across all of the species. Pharmacokinetics in preclinical species characterized by low to moderate plasma clearances, good oral bioavailability at 3- to 5-mg/kg doses, and renal clearance as the projected major clearance mechanism in humans. Human pharmacokinetic predictions using single-species scaling of dog and/or monkey pharmacokinetics were consistent with the parameters observed in the first-in-human study, conducted in healthy volunteers at a dose range of 20-200 mg PF-06282999. In summary, disposition characteristics of PF-06282999 were relatively similar across preclinical species and humans, with renal excretion of the unchanged parent emerging as the principal clearance mechanism in humans, which was anticipated based on its physicochemical properties and supported by preclinical studies.

Synthesis and Molecular-Weight Characteristics of N-Oxidized Copolymers of N-Vinylpyrrolidone and 2-Methyl-5-Vinylpyridine

Aseries of N-oxides of N-vinylpyrrolidone and 2-methyl-5-vinylpyridine copolymers with various degrees of oxidation were prepared via oxidation of the copolymers by peracetic acid. The N-oxidation kinetic rate constants were calculated using UV spectrophotometry. The temperature dependence of the limiting N-oxidation was determined. The molecular-weight characteristics of the N-oxidized copolymers were established using 13C NMR methods. An approach based on direct UV spectrophotometry was proposed for practical monitoring of the reaction completion (degree of conversion).

ABC Triblock Terpolymers with Orthogonally Deprotectable Blocks: Synthesis, Characterization, and Deprotection

The development and availability of new protecting groups are vital for all branches of synthetic chemistry. Equally vital is the facile and selective removal of these groups, leaving intact other protecting groups which are to be cleaved later. Herein we demonstrate this concept of orthogonal deprotection by combining three different forms of protected methacrylic acid (MAA) in the same terpolymers. One of these protected monomers was 2-(pyridin-2-yl)ethyl methacrylate (PyEMA), recently developed by us, whose units can be readily converted to MAA units either under alkaline hydrolysis conditions or thermally. The second monomer was tetrahydro-2H-pyran-2-yl methacrylate (THPMA) which can be cleaved either via acidic hydrolysis or by thermolysis. The third form of protected MAA was benzyl methacrylate (BzMA) which can be subjected to hydrogenolysis. Two ABC triblock terpolymers based on all three of these monomers were successfully synthesized—one by reversible addition–fragmentation chain transfer (RAFT) polymerization and the other by group transfer polymerization (GTP)—thus proving the feasibility of these demanding three-stage syntheses via both polymerization methods. The molecular weight characteristics and compositions of the terpolymers were determined by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy (1H NMR), respectively. Subsequently, the ABC triblock terpolymers were sequentially subjected to conditions of alkaline hydrolysis, acidic hydrolysis, and hydrogenolysis, leading to the selective cleavage of the PyEMA, the THPMA and the BzMA units, respectively, without affecting the remaining types of protecting groups, according to analysis using 1H NMR spectroscopy. Similarly selective was the acidic hydrolysis followed by alkaline hydrolysis. Thermal treatment at 130 °C of the terpolymers led to the conversion of both the PyEMA and the THPMA units to MAA units, without affecting the BzMA units, yielding amphiphilic diblock copolymers whose self-assembly properties in water were investigated.

Poly(vinylpyrrolidone) as dispersing agent for cerium-gadolinium oxide (CGO) suspensions

The behaviour of selected poly(vinylpyrrolidone) grades to act as dispersant for ethanol-based cerium-gadolinium oxide suspensions was investigated and related to the molecular weight characteristics. The number, weight, and z-average molecular weights M n, M w, and M z were determined by gel permeation chromatography and then used in a numerical method to evaluate the viscosity average molecular weight (M v) via an empirically modified Mark–Houwink–Sakurada (MHS) equation. The MHS equation parameters (a and K) and the polydispersity correction factor (q MHS) were also evaluated. Three grades with different molecular weight features were selected and further studied as dispersants by means of rheology. Despite the differences, only slight shifts in the amount of polymer required for achieving fully stabilized dispersions were observed, whereas comparable packing properties were obtained. This was explained as an effect of the polydispersity, expressed as q MHS.

Characteristics and antioxidant of Ulva intestinalis sulphated polysaccharides extracted with different solvents

Ulva intestinalis, a tubular green seaweed, is a rich source of nutrient, especially sulphated polysaccharides. Sulphated polysaccharides from U. intestinalis were extracted with distilled water, 0.1N HCl, and 0.1N NaOH at 80°C for 1, 3, 6, 12, and 24h to study the effect of the extraction solvent and time on their chemical composition and antioxidant activity. Different types of solvents and extraction time had a significant influence on the chemical characteristics and antioxidant activity (p<0.05). Monosaccharide composition and FT-IR spectra analyses revealed that sulphated polysaccharides from all solvent extractions have a typical sugar backbone (glucose, rhamnose, and sulphate attached at C-2 or C-3 of rhamnose). Sulphated polysaccharides extracted with acid exhibited greater antioxidant activity than did those extracted with distilled water and alkali. The results indicated that solvent extraction could be an efficacious method for enhancing antioxidant activity by distinct molecular weight and chemical characteristic of sulphated polysaccharides.

In vivo oxidative degradation of polypropylene pelvic mesh

Commercial polypropylene pelvic mesh products were characterized in terms of their chemical compositions and molecular weight characteristics before and after implantation. These isotactic polypropylene mesh materials showed clear signs of oxidation by both Fourier-transform infrared spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The oxidation was accompanied by a decrease in both weight-average and z-average molecular weights and narrowing of the polydispersity index relative to that of the non-implanted material. SEM revealed the formation of transverse cracking of the fibers which generally, but with some exceptions, increased with implantation time. Collectively these results, as well as the loss of flexibility and embrittlement of polypropylene upon implantation as reported by other workers, may only be explained by in vivo oxidative degradation of polypropylene.

Prediction of melt rheological properties from GPC molecular weights

The SCLAIR® solution polymerization platform produces a wide variety of ethylene-α-olefin copolymers and polyethylene homopolymers. Commercial products exhibit density and melt index values ranging from about 0.920 to 0.962 g/cm3 and 0.3–75 g/10 min respectively. Polymer molecular weight distributions can be tailored to meet a broad selection of end-use requirements. In this study, we have used a chemometric analysis approach using The Unscrambler® software to demonstrate statistical correlations between rheological properties and fundamental structural parameters for thirty-three commercial SCLAIR polyethylenes. We demonstrate that molten rheological properties such as melt index, stress exponent, zero-shear viscosity, characteristic relaxation time, cross-over modulus and frequency show good non-linear correlations with molecular weight characteristics of SCLAIR products as determined by gel permeation chromatography (GPC). We also show that, with the use of Partial Least Squares (PLS) regression techniques, most melt rheological properties can be accurately predicted on the basis of GPC data.

Algal Lectins and their Potential Uses

Lectins (hemagglutinins), or carbohydrate-binding proteins, are ubiquitous in nature and play important roles in many biological processes. They bind mono- and oligosaccharides reversibly with high specificity, but are devoid of catalytic activity, and in contrast to antibodies, are not products of an immune response. The erythrocyte agglutination or hemagglutination activity of lectins is a major attribute of these proteins and is used routinely for their detection and characterization. Due to their biochemical and biological properties, lectins attract a great deal of attention in the fields of medicine, molecular biology, biochemistry, and glycobiology. Lectins have been isolated and characterized from marine algae. Many of algal lectins generally have common characteristics of low molecular weight, no divalent cations requirements for their activity, and have an affinity for glycoproteins but not for monosaccharides. These properties imply that they may possess molecular structures and carbohydrate-binding specificities distinct from known lectins from other sources. Recent investigations revealed that algal lectins have the strict binding specificity to some definite oligosaccharide structures and are grouped into several types on the basis of oligosaccharide-binding specificity. Thus, marine algae are promising sources of novel lectin molecules for basic research and application. In spite of the progress made in biochemical characterization of algal lectins, additional information are still needed for a more comprehensive understanding of their molecular structures and possible biological functions for the future applications.

Isobutylalumoxanes as high-performance activators of rac-Et(2-MeInd)2ZrMe2 in copolymerization of ethylene with propylene and ternary copolymerization of ethylene, propylene, and 5-ethylidene-2-norbornene

Isobutylalumoxanes have been obtained by hydrolysis of triisobutylaluminium (TIBA) with water in the form of vapour (1) or ice particles (2) at AlTIBA/H2O = 2 mol/mol. 1H NMR spectra of hydrolyzates showed the presence of unreacted TIBA indicating the formation of alumoxanes larger than i Bu2Al-O-Al i Bu2 which one can expect based on the molar ratio of reagents. Alumoxanes 1 and 2 demonstrate high activating ability for rac-Et(2-MeInd)2ZrMe2 in copolymerization reactions of ethylene with propylene and terpolymerization of ethylene with propylene and 5-ethylidene-2-norbornene. Alumoxane 1 demonstrates high structural and chemical stability during long-term storage (for 1 year) that results in consistent activating ability and similarity of molecular weight characteristics of polymer formed. Alumoxane 2 is much less structurally stable which is manifested in considerable changes of 1H NMR spectra of the product even after several days of storage. It essentially loses activating ability after 3 months’ storage. The alumoxanes with high activating ability have been also obtained by in situ TIBA hydrolysis with water intentionally incorporated into toluene (~1 × 10−2 mol/l) prior to polymerization also at AlTIBA/H2O = 2 mol/mol. The differences of catalytic systems with different activators are also reflected in differences in microstructure, molecular-weight, thermal-physical characteristics and physical-mechanical properties of copolymers formed.

Polyurethanes with Different Molecular Weight Characteristics as Materials for Assessing the Damaging Effects of Ozone

Polyurethanes with Different Molecular Weight Characteristics as Materials for Assessing the Damaging Effects of Ozone

Iron-based catalytic systems in atom-transfer controlled-radical-polymerization processes

The literature data about the use of catalytic systems and compositions based on iron and its complexes for the controlled synthesis of polymers via the atom-transfer mechanism are generalized and analyzed. The effects of the oxidation number of a metal atom, the ligand environment, the structure of a radical initiator, the activating additives, and other factors on the molecular-weight characteristics of the polymers and the kinetics of vinyl polymerization are considered.

Comparative Study of Polyethylene Composites Containing Industrial Lignins

In this work, free-radical grafting was investigated in order to enhance the compatibility between lignins and polyolefins. High density polyethylene (HDPE) was used as the matrix and two types of industrial lignins were selected as eco-friendly fillers: Kraft lignin which represents most of the global lignin production, but lacks adequate applications; and organosolv lignin which has received increasing attention for its low molecular weight, homogeneity and sulfur-free characteristics. The compounds were produced by batch mixing, and were compression molded. From these samples, morphological, tensile and thermal properties were studied. The results show that incorporation of different lignins into HDPE yielded materials of different tensile behavior, but improvement in morphological and mechanical properties through free-radical grafting was obtained. Furthermore, free-radical grafting was found to decrease the thermal oxidation resistance and the crystallinity of the composites.

The relationship between wheat baking properties, specific high molecular weight glutenin components and characteristics of varieties

The main objective of this study was to compare the aeration level of ring shaped breads, produced from flour made from different winter wheat varieties with different glutenins composition. Analysis of the qualitative and quantitative composition of low molecular weight glutenins (LMW-glutenins), high molecular weight glutenins (HMW-glutenins) and wheat gluten protein fractions α-, γ-, ω-gliadins was performed by electrophoresis in polyacrylamide gel using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). For qualitative evaluation of HMW-glutenin subunits, the obtained electrophoregrams were compared with the standard electrophoretic spectrums of the glutenin components presented in the catalogue. In particular, the indirect acoustic echolocation method can be applied in measurements of the structures of ring shaped breads. Correlations between wheat gluten fractions and some quality parameters characterizing the raw grain material show that HMW-glutenins have the strongest influence on the wheat flour baking properties, and the acoustic method allowed us to assess the quality of ring shaped breads according to the amount of water absorbed and the nature of swelling. This made it possible to classify the ring shaped breads into three quality categories: good (the amount of water absorbed from 37.5 to 50.75 relative units), medium (the amount of water absorbed from 2.54 to 6.28 and from 23.45 to 24.91 relative units), and poor (the amount of water absorbed from 3.6 to 14.7 relative units). According to the specific HMW-glutenin components, it is possible to select the best quality wheat varieties for flour production which could be recommended for ring shaped breads production.