Molecular Weight Growth Research Articles

Nanoeffects of Nanocomposites on the Petroleum Recovery and Solar Energy Efficiency

Several polymer inorganic nanocomposites were specially designed for protecting oil formation, enhancing oil recovery in the low permeable strata and solar cell efficicency. The inorganic phase with different load was introduced to the polymer matrix through either the intercalation process of the layered silicates or core-shell particle affinity.Several novel nanoeffects were discovered in such polymers as polyacrylamide, poly(ethylene terephthalate),starch, polynucleic aromatic resins–montmorrilonite or SiO2 nanocomposites. In the nanocomposites, the nano size was 10-70nm, the nanoeffects of particle encapsulation, dispersion, molecular weight growth, barrier, and specially solar absorption and solar power transformation efficiency,etc.were presented and reviewed. The tunable nanoeffects of the nanocomposites and some very obvious practical efficicnecy to traditional and new enenergy were first reported.

A model of particle nucleation in premixed ethylene flames

A detailed model of particle inception is proposed to delve into the physical structure and chemistry of combustion-formed particles. A sectional method is used, from a previously developed kinetic mechanism of particle formation with a double discretization of the particle phase in terms of C and H atom number. The present model also distinguishes between different particle structures based on their state of aggregation; single high molecular mass molecules, cluster of molecules and aggregates of clusters. The model predicts the mass of particles, hydrogen content and internal structure. It represents a first approach in following the chemical evolution and internal structure of the particles formed in flames, coupled with the main pyrolysis and oxidation of the fuel. The model is tested in atmospheric premixed flat flames of ethylene and the effect of fuel equivalence ratio on particle morphology is analyzed. Molecular weight growth of aromatic compounds and the inception of particles are predicted. The morphology of the particles and the number of molecules in the clusters at particle inception are also indicated.

Efficient Synthesis of Poly(acrylic acid) in Aqueous Solution via a RAFT Process

The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, M n with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization.

Progranulin is expressed within motor neurons and promotes neuronal cell survival

BackgroundProgranulin is a secreted high molecular weight growth factor bearing seven and one half copies of the cysteine-rich granulin-epithelin motif. While inappropriate over-expression of the progranulin gene has been associated with many cancers, haploinsufficiency leads to atrophy of the frontotemporal lobes and development of a form of dementia (frontotemporal lobar degeneration with ubiquitin positive inclusions, FTLD-U) associated with the formation of ubiquitinated inclusions. Recent reports indicate that progranulin has neurotrophic effects, which, if confirmed would make progranulin the only neuroprotective growth factor that has been associated genetically with a neurological disease in humans. Preliminary studies indicated high progranulin gene expression in spinal cord motor neurons. However, it is uncertain what the role of Progranulin is in normal or diseased motor neuron function. We have investigated progranulin gene expression and subcellular localization in cultured mouse embryonic motor neurons and examined the effect of progranulin over-expression and knockdown in the NSC-34 immortalized motor neuron cell line upon proliferation and survival.ResultsIn situ hybridisation and immunohistochemical techniques revealed that the progranulin gene is highly expressed by motor neurons within the mouse spinal cord and in primary cultures of dissociated mouse embryonic spinal cord-dorsal root ganglia. Confocal microscopy coupled to immunocytochemistry together with the use of a progranulin-green fluorescent protein fusion construct revealed progranulin to be located within compartments of the secretory pathway including the Golgi apparatus. Stable transfection of the human progranulin gene into the NSC-34 motor neuron cell line stimulates the appearance of dendritic structures and provides sufficient trophic stimulus to survive serum deprivation for long periods (up to two months). This is mediated at least in part through an anti-apoptotic mechanism. Control cells, while expressing basal levels of progranulin do not survive in serum free conditions. Knockdown of progranulin expression using shRNA technology further reduced cell survival.ConclusionNeurons are among the most long-lived cells in the body and are subject to low levels of toxic challenges throughout life. We have demonstrated that progranulin is abundantly expressed in motor neurons and is cytoprotective over prolonged periods when over-expressed in a neuronal cell line. This work highlights the importance of progranulin as neuroprotective growth factor and may represent a therapeutic target for neurodegenerative diseases including motor neuron disease.

Preparation of crosslinked microspheres and porous solids from hydrocarbon solutions: A new variation of precipitation polymerization chemistry

AbstractA new variation of precipitation polymerization is described wherein CH bond addition to a triallyl monomer contributes to molecular weight growth, thereby incorporating a significant amount of saturated hydrocarbon into the solid phase. The extent of monomer oligomerization relative to hydrocarbon addition is shown to increase with the concentration of allyl benzoate in cyclooctane. An extension to the trifunctional monomer, triallyl trimesate, results in phase separation of hydrocarbon‐monomer adducts to give a dispersed phase whose continued reactivity leads to crosslinked microspheres. The relationships between reaction conditions and solid‐phase composition and morphology are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6561–6570, 2009

The C7H5 Fulvenallenyl Radical as a Combustion Intermediate: Potential New Pathways to Two- and Three-Ring PAHs

This study proposes the existence of a new, highly resonantly stabilized free radical, fulvenallenyl (C7H5). Fulvenallenyl forms from dissociation or abstraction of the weak H atoms in the C7H6 compounds fulvenallene and 1-ethynylcyclopentadiene, which were recently identified as intermediates in the combustion of aromatic fuels and in sooting flames. The fulvenallenyl radical shares properties of the propargyl and cyclopentadienyl radicals, and like these species, we propose that fulvenallenyl has a significant resonance stabilization energy. This resonance energy is lost upon further reaction, making the fulvenallenyl radical resistant to oxidation and thermal decomposition. As with the resonantly stabilized radicals propargyl and cyclopentadienyl, fulvenallenyl is expected to react with other radicals in molecular weight growth reactions. Several pathways are proposed for self-reaction and cross-reactions of fulvenallenyl that directly produce two- and three-ring PAHs like naphthalene, diphenyl, and phenanthrene. Rate constants are calculated for H atom abstraction from fulvenallene and 1-ethynylcyclopentadiene by the common radicals H, OH, and CH3, to facilitate the inclusion of fulvenallenyl in kinetic models.

Pilot-Scale Gasification of Corn Stover, Switchgrass, Wheat Straw, and Wood: 2. Identification of Global Chemistry Using Multivariate Curve Resolution Techniques

A pilot-scale study was conducted to examine the effect of the steam-to-biomass ratio, the gasification temperature, and the thermal cracker temperature for Vermont wood, wheat straw, switchgrass, and corn stover on the formation and speciation of tars. This study is divided into two parts; the first paper detailed the processing conditions and gives quantitative information on low-molecular-weight species. This paper, which is the second part of this study, uses multivariate curve resolution techniques to correlate process variables with the mass spectra gathered during the study to (1) identify the global chemistry of the system and (2) to identify differences or similarities of the product gas streams for each feedstock. Three main groups of products were identified statistically: (1) primary and secondary pyrolysis products (e.g., guaiacol, furfural), (2) cracking products (e.g., phenol, cresol), and (3) polynuclear aromatic hydrocarbons (PAHs). Our findings support known global reaction mechanisms that delineate the formation of the more-refractory PAHs, whereby oxygenated pyrolysis products are cracked into smaller fragments that contain less oxygen. These crack further into small hydrocarbons and radicals that undergo molecular weight growth to produce PAHs. The results from this statistical analysis indicate that, at high temperatures, where PAHs dominate, there is little variation observed between the feedstocks.

Low-temperature oxidative degradation of PBX 9501 and its components determined via molecular weight analysis of the Poly[ester urethane] binder

The results of following the oxidative degradation of a plastic-bonded explosive (PBX 9501) are reported. Into over 1100 sealed containers were placed samples of PBX 9501 and combinations of its components and aged at relatively low temperatures to induce oxidative degradation of the samples. One of the components of the explosive is a poly(ester urethane) polymer and the oxidative degradation of the samples were following by measuring the molecular weight change of the polymer by gel permeation chromatography (coupled with both differential refractive index and multiangle laser light scattering detectors). Multiple temperatures between 40 and 64 °C were used to accelerate the aging of the samples. Interesting induction period behavior, along with both molecular weight increasing (crosslinking) and decreasing (chain scissioning) processes, were found at these relatively mild conditions. The molecular weight growth rates were fit to a random crosslinking model for all the combinations of components. The fit rate coefficients show Arrhenius behavior and activation energies and frequency factors were obtained. The kinetics of molecular weight growth shows a compensatory effect between the Arrhenius prefactors and activation energies, suggesting a common degradation process between PBX 9501 and the various combinations of its constituents. An oxidative chemical mechanism of the polymer is postulated, consistent with previous experimental results, that involves a competition between urethane radical crosslinking and carbonyl formation.

Ring-expansion metathesis polymerization: catalyst-dependent polymerization profiles.

Ring-expansion metathesis polymerization (REMP) mediated by recently developed cyclic Ru catalysts has been studied in detail with a focus on the polymer products obtained under varied reaction conditions and catalyst architectures. Depending upon the nature of the catalyst structure, two distinct molecular weight evolutions were observed. Polymerization conducted with catalysts bearing six-carbon tethers displayed rapid polymer molecular weight growth which reached a maximum value at ca. 70% monomer conversion, resembling a chain-growth polymerization mechanism. In contrast, five-carbon-tethered catalysts led to molecular weight growth that resembled a step-growth mechanism with a steep increase occurring only after 95% monomer conversion. The underlying reason for these mechanistic differences appeared to be ready release of five-carbon-tethered catalysts from growing polymer rings, which competed significantly with propagation. Owing to reversible chain transfer and the lack of end groups in REMP, the final molecular weights of cyclic polymers was controlled by thermodynamic equilibria. Large ring sizes in the range of 60-120 kDa were observed at equilibrium for polycyclooctene and polycyclododecatriene, which were found to be independent of catalyst structure and initial monomer/catalyst ratio. While six-carbon-tethered catalysts were slowly incorporated into the formed cyclic polymer, the incorporation of five-carbon-tethered catalysts was minimal, as revealed by ICP-MS. Further polymer analysis was conducted using melt-state magic-angle spinning (13)C NMR spectroscopy of both linear and cyclic polymers, which revealed little or no chain ends for the latter topology.

Isomer-specific product detection of CN radical reactions with ethene and propene by tunable VUV photoionization mass spectrometry

Product detection studies of CN reactions with ethene and propene are conducted at room temperature (4 Torr, 533.3 Pa) using multiplexed time-resolved mass spectrometry with tunable synchrotron photoionization. Photoionization efficiency curves, i.e., the ion signal as a function of photon energy, are used to determine the products and distinguish isomers. Both reactions proceed predominantly via CN addition to the π orbital of the olefin. For CN + ethene, cyanoethene (C 2H 3CN) is detected as the sole product in agreement with recent studies on this reaction. Multiple products are identified for the CN + propene reaction with 75(±15)% of the detected products in the form of cyanoethene from a CH 3 elimination channel and 25(±15)% forming different isomers of C 4H 5N via H elimination. The C 4H 5N comprises 57(±15)% 1-cyanopropene, 43(±15)% 2-cyanopropene and <15% 3-cyanopropene. No evidence of direct H abstraction or indirect HCN formation is detected for either reaction. The results have relevance to the molecular weight growth chemistry on Saturn's largest moon Titan, where the formation of small unsaturated nitriles are proposed to be key steps in the early chemical stages of haze formation.

RAFT with Bulk and Solution Polymerization: An Approach to Mathematical Modelling and Validation

Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel technique used to impart a living character in free radical polymerization. A mathematical model accounting for the concentrations of the propagating, intermediate, dormant and dead chains is developed based on their reaction pathways. The kinetic scheme used includes initiation, propagation, pre-equilibrium, core-equilibrium and termination of the propagating radicals along with termination reactions of the carbon-centered intermediate radical. This model is combined with chain-length dependant termination model in order to account for the decreased termination rate. The model has been validated against experimental data for solution polymerization of styrene with dithiobenzoate at 80°C. The fragmentation rate coefficient was used as a model parameter and a value equal to 6×104 sec−1 was found to provide a good agreement with the experimental data. The model predictions indicate that the observed retardation can be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The hypothesised irreversible self termination was found to have a negligible effect on the polymerization rate. While the linear growth of the number average molecular weight along with the low polydispersity, reveal the living nature of RAFT agent and the importance of the transfer constant in controlling these properties.

Synthesis of branched polystyrene by ATRP exploiting divinylbenzene as branching comonomer

Branched polystyrenes have been synthesized using atom transfer radical polymerization (ATRP) of styrene in the presence of divinyllbenzene (DVB) as branching comonomer. The synthesis was completed via facile one pot approach. Mole ratio of styrene to DVB in range of 5:1–30:1 was employed to obtain soluble polymers. The kinetics of the polymerization and evolution of polymer compositions were revealed by determining the conversions of reactants by gas chromatography (GC). The growth of molecular weight was monitored by GPC and the results indicate that the branched polymers were formed by self-condensing vinyl polymerization (SCVP) of AB ∗ monomer or macromonomers. The branched structure of the resulting polymers was confirmed by the remarkable discrepancies of the weight average molecular weights determined by GPC and multi angle laser light scattering (MALLS). The specific viscosity of the resulting polymer is also much lower compared with that of linear analogues. The influence of dosage of initiator and catalyst on the yield and molecular weights of the resulting polymers was also investigated.

Optimization of poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD) preparation for increased crystallinity

A key factor, which affects the crystallization temperature on cooling ( T c) of PCCD is the cis/trans isomer ratio of the cyclohexyl diester in the polymer. Isomerization of pure dimethyl- trans-1,4-cyclohexanedicarboxylate can occur during the polymerization, and the T c on cooling decreases along with the trans content. The isomerization reaction is enhanced with temperature, time and catalyst amount, and these variables should be minimized to prepare PCCD polymers with high T c. However, these same variables also control the molecular weight growth of the polymer, and so a compromise between the best conditions for high T c and those for high M w must be made. A set of optimized conditions were obtained leading to PCCD polymers with M w of 75,000–80,000 and T c on cooling of 164–167 °C. Solid state polymerization was used to prepare high molecular weight PCCD with a high level of crystallinity ( T c on cooling ∼193 °C). It was also shown that adding small amounts of supplementary diols facilitates PCCD preparation by ensuring that high molecular weight PCCD polymers will be obtained even when the stoichiometry of monomer feed is off by >3%, i.e. conditions which would otherwise lead to low M w. Finally, less crystalline PCCD's have been prepared via either incorporation of diethylene glycol or increasing the cis-diester amount in the polymer.

Comparison of conversion and deposit formation of ethanol and butane under SOFC conditions

This paper explores the gas-phase kinetics of butane and ethanol conversion as well as the propensity for molecular-weight growth and deposit formation in the non-catalytic regions of a solid oxide fuel cell (SOFC). Experiments are done where the fuel flows through a quartz reactor heated by a furnace. The primary observables are the extent of fuel conversion and the amount of deposit formed on a YSZ disk placed at the end of the furnace. Experiments are performed at 700, 750 and 800 ° C. The residence times in the hot zone varied from 2 to 4 s. Ethanol is more reactive than butane, and almost all the ethanol is reacted at 750 ° C whereas butane is completely reacted at 800 ° C. Deposit formation is much larger for butane. These results are compared to predictions of a detailed kinetic model. Model predictions for the extent of fuel conversion and molecular-weight growth are in good agreement with the data for both fuels. Butane is predicted to be converted to the lighter hydrocarbons methane, ethylene, propylene and ethane. Hydrogen is also a significant product, especially at higher temperatures. For ethanol, the product distribution is different with lower amounts of hydrocarbons while substantial quantities of water, ethylene, CO and H 2 are predicted. In ethanol pyrolysis there is no significant production of species with more than two carbon atoms, whereas propylene production is significant in butane pyrolysis. Modeling results suggest this is a major reason for increased deposit formation with butane. Equilibrium calculations demonstrate that both the butane and ethanol systems are far removed from equilibrium.

The Influence of Heterogeneous Chemistry and Electrochemistry on Gas-Phase Molecular-Weight Growth and Deposit Formation

This paper explores the effect of surface kinetics and electrochemistry on gas-phase kinetics and the propensity for molecular-weight growth and deposit formation in solid oxide fuel cells (SOFCs). A computational model has been built that combines a homogeneous reaction mechanism with the predicted distance-dependent flux of major species from the anode. Two case studies of methane reactions at 800°C are considered to illustrate the model capabilities. For a 50/50 methane/air mixture, inclusion of only heterogeneous kinetics decreased molecular-weight growth substantially relative to the gas-phase-only predictions. Surprisingly, inclusion of the electrochemical kinetics in addition to the anode catalytic reactions predicted increased growth, but the predicted deposit propensity was still much lower than the gas-phase-only case. The 50/50 methane/steam predictions indicated that both heterogeneous kinetics and electrochemistry increase molecular-weight growth. The level of molecular-weight growth predicted in all cases is well below the level that should result in deposit formation.

Quick atom transfer radical polymerization of N,N-diisopropyl ammonium acrylate in the presence of air

The atom transfer radical polymerization of N,N-diisopropyl ammonium acrylate was successfully carried out, either with continuous exposure to air or in the presence of small amounts of air, which were introduced to the reaction mixture during the polymerization. A linear growth of molecular weight as a function of conversion and low polydispersities of the polymers synthesised here were consistent with the controlled polymerization. Since the polymerization was carried out in the presence of air, oxygen may act as co-catalyst or can be an initiator in a CuBr/bipy/O2 complex.

Adsorption of Zwitterionic Drugs on Oxidized Cellulose from Aqueous and Water/Alcohol Solutions

Adsorption of zwitterionic drugs (β-lactam antibiotics and amino acids) on samples of oxidized cellulose (OC) with various carboxyl contents and structure characteristics was investigated from aqueous and water/alcohol solutions. The process is described according to the theory of localized stoichiometric adsorption and represented by Langmuir-like isotherms. The drug uptake increases with increase of alcohol content in the solution and with growth of alcohol molecular weight. The main contribution to the increase of drug uptake with addition of alcohol to the aqueous drug solution is provided by the desolvation of zwitterion ionic groups, which increases with growth of alcohol content. The structural characteristics of OC (degree of crystallinity and carboxyls distribution) and sorbate molecule size have considerable effect on the drug adsorption. It is shown that different drug uptake occurs on the OC samples with similar exchange capacity but various structure characteristics, which can be explained by various accessibility of carboxylic groups of OC, caused by decreased swelling of a sorbent in binary water/alcohol solutions.

Homogeneous kinetics and equilibrium predictions of coking propensity in the anode channels of direct oxidation solid-oxide fuel cells using dry natural gas

Abstract Direct electrochemical oxidation (DECO) solid-oxide fuel cells (SOFCs) offer the potential to generate electrical power from hydrocarbon fuels without the need for upstream fuel processing, such as reforming. However, with pure hydrocarbon fuel entering the flow channels at temperatures typically above 700 °C, fuel pyrolysis can cause molecular-weight growth and the formation of deleterious carbonaceous deposits. This paper, which develops a plug-flow model for fuel (natural gas surrogate) within the anode channels, considers the elementary gas-phase chemical kinetics of fuel pyrolysis and oxidation. It also considers the limiting case of local chemical equilibrium. Formation of cyclic hydrocarbon species is used to indicate deposit propensity. Results show that the likelihood of deposit formation depends strongly on cell temperature, current density, and residence time. Generally speaking, equilibrium favors deposit formation early in the channel whereas, owing to limited residence time, the homogeneous finite-rate kinetics predicts relatively low levels of deposit precursors. In the downstream portions, because of electrochemical oxygen flux though the electrode–electrolyte membrane, chemical equilibrium shifts strongly away from deposit formation to volatile carbon-oxygen species. However, the homogeneous finite-rate kinetics predictions show a continuing increase in coking propensity.

Mitigation of the Fouling by Popcorn Coke

How often is petroleum fouling mitigated by raising temperature? One case is if the fouling is caused by a polymerization reaction. It is shown that popcorn coke is the result of molecular weight growth reactions of conjugated olefins in the oil that were formed by the thermal cracking process. An olefin is conjugated to another olefin when the double bond is one carbon away from a carbon connected to a different double bond or an aromatic. Those conjugated to aromatics are the greater fouling problem in oils formed by thermally cracking petroleum resids. A property of polymerization reactions is that they are greatest over a range of temperatures. At lower temperatures the reaction rate is too slow and at higher temperatures the polymerization bonds thermally crack faster than they are formed (ceiling temperature). Therefore, the recommended mitigation action is to minimize the residence time of the thermally cracked oil in this temperature range (particularly 500–580°F) of greatest polymerization rate. An analytical method to monitor conjugated olefins in thermally cracked oils will be described. In addition, a case study will be given when the coking of a fractionator downstream of a Flexicoker® was mitigated by raising the bottom pool temperature.

Alternatives to the use of fetal bovine serum: Serum-free cell culture

Serum is commonly used as a supplement to cell culture media. It provides a broad spectrum of macromolecules, carrier proteins for lipoid substances and trace elements, attachment and spreading factors, low molecular weight nutrients, and hormones and growth factors. The most widely used animal serum supplement is fetal bovine serum, FBS. Since serum in general is an ill-defined component in cell culture media, a number of chemically defined serum-free media formulations have been developed in the last two decades. Besides modern cell biological advances in cell and tissue culture and efforts towards a standardisation of cell culture protocols in Good Cell Culture Practice, in addition, considerable ethical concerns were raised recently about the harvest and collection of fetal bovine serum. Thus, in order to decrease the annual need for bovine fetuses in terms of the 3Rs through any reduction in the use or partial replacement of serum, as well as in terms of an improvement of cell and tissue culture methodology, serum-free cell culture represents a modern, valuable and scientifically well accepted alternative to the use of FBS in cell and tissue culture.