Initial Monomer Concentration Research Articles

A qualitative analysis of an A β -monomer model with inflammation processes for Alzheimer’s disease

We introduce and study a new model for the progression of Alzheimer’s disease (AD) incorporating the interactions of A β -monomers, oligomers, microglial cells and interleukins with neurons through different mechanisms such as protein polymerization, inflammation processes and neural stress reactions. To understand the complete interactions between these elements, we study a spatially homogeneous simplified model that allows us to determine the effect of key parameters such as degradation rates in the asymptotic behaviour of the system and the stability of equilibrium. We observe that inflammation appears to be a crucial factor in the initiation and progression of AD through a phenomenon of hysteresis with respect to the oligomer degradation rate d . This means that depending on the advanced state of the disease (given by the value of the A β -monomer degradation rate d : large value for an early stage and low value for an advanced stage) there exists a critical threshold of initial concentration of interleukins that determines if the disease persists or not in the long term. These results give perspectives on possible anti-inflammatory treatments that could be applied to mitigate the progression of AD. We also present numerical simulations that allow us to observe the effect of initial inflammation and monomer concentration in our model.

Zwitterionic ring expansion polymerization of tert‐butyl glycidyl ether with B(C6F5)3 towards the generation of cyclic chains

AbstractThe synthesis of cyclic polymers via zwitterionic ring expansion polymerization is limited to a few number of monomer and catalyst pairs. Herein we report the synthesis of cyclic poly(tert‐butyl glycidyl ether) through the polymerization of tert‐butyl glycidyl ether (tBGE) with B(C6F5)3 in different reaction conditions that include different solvents, monomer to initiator ratio, monomer concentration and temperature. We found that bimodal molecular weight distribution is formed in almost all reaction conditions caused by cyclization of short chains. Subsequent chain elongation leads to the formation of cycles of higher molecular weight, particularly in cyclohexane and under bulk conditions. The formation of non‐cyclic byproducts is common in all the systems investigated. Low molecular weight cyclic chains (Mn = 0.7 kDa, Ð = 1.1) of high topological purity were successfully isolated by preparative gel permeation chromatography. By using a click scavenging protocol, the non‐cyclic byproducts were eliminated from the high molecular weight fraction (Mn = 3 kDa, Ð = 1.3) generating pure cyclic chains. Mechanistic investigation using density functional theory calculations was performed on the formation of zwitterionic intermediates and the transfer reaction to the monomer, which notably affects chain growth by the attack of the glycidyl oxygen of the monomer on the growing chain.

Investigation and Improvement of Thermal and Mechanical Properties of Recycled Polypropylene / Oxidized Polyethylene Composites

In this study, various composites were prepared from synthetic wastes with oxidized polyolefin (OxPO) and the mechanical (elongation, elasticity, tensile strength, etc.) of these composites.) and discusses the results of an experimental study on its thermal characterization. The oxidized polyolefin/Styrene (St) mixture was infused with the melt free radical polymerization method on recycled polypropylene (rPP). The effect of the initial monomer concentration on the mechanical properties of recycled polypropylene was investigated. The mechanical (elongation and tensile strength) properties of the composites produced were made according to the ISO 527-2 standard method. It has been observed that the tensile strength and elongation, which are the mechanical properties of (OxPO/St)/rPP composites, increase compared to RPP. The resulting polymers were then characterized by Fourier transformational infrared spectroscopy (FTIR).

Polymerization of Thermo-Responsive Poly(N-vinylcaprolactam): Effects of Temperature, Initiator and Monomer Concentration on Percent Conversion

Poly(N-vinyl caprolactam) (PNVCL) is a thermally responsive polymer. Its temperature-responsive properties make it an attractive candidate for various applications. A series of temperature-sensitive PNVCL were synthesized through free radical polymerization, using various of amount of Azobisisobutyronitrile (AIBN) as initiator agent and with reaction temperatures set at 60oC, 70oC, 80oC. The percent conversion of polymerization was determined using the Hubl method to investigate the effects of three factors: initiator agent concentration, monomer concentration and reaction temperature. Furthermore, the chemical structure and the responsiveness of the PNVCL polymer were analyzed using Fourier transform infrared spectroscopy (FTIR) and UV-vis spectrometer, respectively. The study revealed that increasing the reaction temperature, initiator concentration, and monomer concentration resulted in higher percent conversion of polymerization. Finally, the obtained polymer demonstrated thermal sensitivity within the range of 32oC to 38oC, which is close to human body temperature, suitable for biomedical applications.

Influence of monomer concentration on structures of fully condensed polyphenylsilsesquioxanes

Fully condensed polyphenylsilsesquioxanes have been prepared via the hydrolysis and condensation of the same phenyltrimethoxysilane (PTMS) monomer in different concentrations. The effect of monomer concentration on molecular structure of the final products has been thoroughly investigated. Cage structured polyphenylsilsesquioxane (OPS) and ladder-like structured polyphenylsilsesquioxane (L-PPSQ) can be selectively synthesized from the same starting materials at lower and higher initial monomer concentrations. Meanwhile, online infrared detector, React IR TM15 was used to monitor the real time variation of the concentration and characteristic absorption peaks of any intermediate products that may exist. Then, React IR TM15 coupled with 29Si nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) were used to monitor and identify the intermediate species during the reaction. Mechanism studies indicated that the condensation reaction of OPS and L-PPSQ both proceed through a T1 structure dimer, which was formed by the quick hydrolysis of the PTMS monomer. As confirmed by 29Si-NMR, GPC and MALDI-TOF-MS, the synthesis mechanisms of OPS and L-PPSQ during the hydrolysis-condensation reactions were delineated.

Equimolar Polyampholyte Hydrogel Synthesis Strategies with Adaptable Properties.

Polyampholyte hydrogels exhibit great antibacterial and antifouling properties, which make them attractive for biomedical applications, such as drug delivery, wound healing, and tissue engineering. They also have potential applications in food safety, wastewater treatment, and desalination. Since they are based on ionic interactions, polyampholytes are known to require lower amounts of chemical cross-linkers as compared with traditional gels. However, the effects of both chemical and physical interactions on the material's performance are yet to be fully understood and were examined in the present work. Here, four series of equimolar polyampholyte hydrogels were synthesized with anionic (acrylamidomethylpropane sulfonic acid sodium salt) and cationic monomers (acrylamidopropyl-trimethylammonium chloride) along with a cross-linker (N,N'-methylenebisacrylamide). The mechanical and rheological properties of the gels were characterized following changes to the initial monomer concentration and crosslinker ratios, which led to gels with different toughness, stretchability, and compressibility. The direct correlation of the cross-linking degree with the initial monomer concentration showed that the chemical crosslinker could be further reduced at a high monomer concentration of 30% by weight, which creates an inter-chain network at a minimal crosslinker concentration of 0.25%. Lastly, N'N-dimethylacrylamide was added, which resulted in an increase in the number of H-bonds in the structure, noticeably raising material performance.

Self‐Limited Hyperbranching Polymerization of Di‐N‐Phenoxycarbonyl N‐Substituted Diglycines

AbstractHyperbranched poly(α‐amino acid)s have caught great attention due to their excellent biocompatibility, biodegradability, and bioactivity. However, hyperbranched polypeptoids are rarely reported because of the challenge of synthesis. Herein, unique polymerizations of N,N'‐diphenoxycarbonyl‐N,N'‐(1,4‐phenylenebismethylene)–diglycine (di‐NNPC, an A*B*‐A*B*‐type monomer) which uncommonly result in hyperbranched polypeptoids rather than gels after the complete consumption of di‐NNPC are reported. The molecular weights of the hyperbranched polypeptoids are controlled by the degree of branching via tuning the initial concentrations of monomer and basic catalyst. N‐Phenyloxycarbonyl glycine pendant groups plentifully remained on the polymer chains are used for Gd3+ complexation and post‐modification, which makes the hyperbranched polypeptoids multifunctional single molecular micelles applicable as magnetic resonance imaging contrast agents and photoluminescence probes.

Shape-Controlled synthesis of conjugated microporous polymer nanotubes and their implementation in continuous flow polymerization

Flow reactors have materialized as a reliable and sustainable approach toward polymer production and processing to promote efficient and uniform irradiation pathways. However, the disadvantages of existing homogeneous photocatalysts including noxiousness, restricted photocatalytic activity and stability, and difficult separation and purification, still pose a great challenge to the advancement of this technique. Herein, conjugated microporous polymer nanotubes (hPorBDP NTs) were fabricated through Sonogashira-Hagihara cross-coupling polycondensation with silica nanorods as sacrificial templates, followed by etching of the inner cores. The hPorBDP NTs with a hollow nanostructure and a highly porous texture were demonstrated to facilitate the separation procedure and provide more accessible active sites for photocatalytic reactions. The hPorBDP NTs were employed as heterogeneous catalysts to activate photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization in batch and in continuous flow system. Screening of the initial monomer concentrations and pump flow rates, high monomer conversions (ɑ > 80%) and narrow dispersities (Đ < 1.15) were achieved in continuous flow system for upscaled production of polymers. Separation and reutilization of the catalyst-bound NTs were realized through facile centrifugation, which resulted in negligible leaching and maintenance of catalytic performance over multiple polymerization cycles. As such, the development of photosynthesis system using hPorBDP NTs as heterogeneous photocatalysts should broaden the application scope of these fascinating catalysts while benefiting synthetic upscaling by continuous flow polymerization.

Recycling of the actin monomer pool limits the lifetime of network turnover.

Intracellular organization is largely mediated by actin turnover. Cellular actin networks continuously assemble and disassemble, while maintaining their overall appearance. This behavior, called "dynamic steady state," allows cells to sense and adapt to their environment. However, how structural stability can be maintained during the constant turnover of a limited actin monomer pool is poorly understood. To answer this question, we developed an experimental system where polystyrene beads are propelled by an actin comet in a microwell containing a limited amount of components. We used the speed and the size of the actin comet tails to evaluate the system's monomer consumption and its lifetime. We established the relative contribution of actin assembly, disassembly, and recycling for a bead movement over tens of hours. Recycling mediated by cyclase-associated protein (CAP) is the key step in allowing the reuse of monomers for multiple assembly cycles. ATP supply and protein aging are also factors that limit the lifetime of actin turnover. This work reveals the balancing mechanism for long-term network assembly with a limited amount of building blocks.

A fluorescent controllable supramolecular crosslinked polymer constructed by complementary metal coordination interaction.

In this work, two different monomers M1 and M2 were designed and synthesized. M1 + M2 + Zn(OTf)2 could self-assemble to form a supramolecular crosslinked polymer (SCP) based on complementary terpyridine-based metal coordination interaction. The self-assembly of M1 + M2 + Zn(OTf)2 was studied by various techniques, such as 1H NMR, 2D COSY NMR, 2D NOESY NMR, UV-Vis analysis, fluorescence analysis, viscosity measurement, and TEM. The experimental result indicated that the molecular weight of the SCP depended on the initial monomer concentration. The SCP could further turn into supramolecular polymer gel at high concentrations, and the reversible gel-sol transformation could be realized by heating/cooling. Moreover, the fluorescence quenching/enhancement of the SCP could be adjusted by adding base/acid.

Determination of kinetic parameters of N-vinylpyrrolidone radical polymerization in water by Pulsed Electron Polymerization−Size Exclusion Chromatography (PEP−SEC)

Propagation step of radical polymerization of N-vinylpyrrolidone (NVP) in aqueous solutions has been studied by a recently introduced method, Pulsed Electron Polymerization−Size Exclusion Chromatography (PEP−SEC). Propagation rate constants have been determined at various initial monomer concentrations and reaction temperatures. It has been shown that the kinetic data, their concentration dependence, activation energy (Ea) and preexponential factor (A) in the Arrhenius equation obtained by PEP−SEC are very similar to those obtained by the well-established Pulsed Laser Polymerization−Size Exclusion Chromatography (PLP−SEC). These results support the correctness of the new PEP−SEC technique, which is expected to have some advantages over the classical PLP−SEC, in particular by its applicability to studying polymerization in nontransparent systems and lack of any chemical initiators and can be developed into a method alternative or complementary to PLP−SEC.

NIR spectroscopy for reaction monitoring and reaction mixture identification of cycloaliphatic epoxides

The industrially relevant cycloaliphatic epoxides do not have a directly distinguishable band in the NIR spectrum and their polymerisation conversion has so far typically been estimated via the simultaneous polymerisation of vinyl ethers. Here, an analytical procedure is presented for the quantitative inline analysis of 4-epoxycyclohexyl methyl-3,4-epoxycyclohexane carboxylate without the need to mix cycloaliphatic epoxides with vinyl ethers. By employing multivariate data analysis on the reaction spectra, the conversion could be analysed spectroscopically. This resulted in a mean uncertainty of 3.38% conversion in the range between 0 and 40% conversion. In addition, a deviation from the initial monomer concentration of 5 w% over a temperature range of 100 °C can be detected and identified via principal component analysis.

Hydrogen-Bond Topology Is More Important Than Acid/Base Strength in Atmospheric Prenucleation Clusters.

We explored the hypothesis that on the nanoscale level, acids and bases might exhibit different behavior than in bulk solution. Our study system consisted of sulfuric acid, formic acid, ammonia, and water. We calculated highly accurate Domain-based Local pair-Natural Orbital- Coupled-Cluster/Complete Basis Set (DLPNO-CCSD(T)/CBS) energies on DFT geometries and used the resulting Gibbs free energies for cluster formation to compute the overall equilibrium constants for every possible cluster. The equilibrium constants combined with the initial monomer concentrations were used to predict the formation of clusters at the top and the bottom of the troposphere. Our results show that formic acid is as effective as ammonia at forming clusters with sulfuric acid and water. The structure of formic acid is uniquely suited to form hydrogen bonds with sulfuric acid. Additionally, it can partner with water to form bridges from one side of sulfuric acid to the other, hence demonstrating that hydrogen bonding topology is more important than acid/base strength in these atmospheric prenucleation clusters.

DOE-based synthesis of gellan gum-acrylic acid-based biodegradable hydrogels: screening of significant process variables and in situ field studies.

The current study uses the free radical graft copolymerization of acrylic acid as a monomer, N,N-methylene-bis-(acrylamide) as a crosslinker and ammonium persulfate as an initiator to synthesise GG-cl-poly(AA) hydrogels based on gellan gum utilising response surface methodology (RSM). A full factorial design was used to obtain the greatest percent swelling (Ps), and key process variables were determined using the Pareto chart. To make the procedure cost-effective, a multiple regression model employing ANOVA projected a linear model with a maximum percentage swelling of 556 at the lowest concentration of all three studied factors. As a result, the sequential experimental design was successful in obtaining two-fold increases in the percentage swelling in a systematic way. An RSM-based central composite design was used to optimize the percentage swelling of the three most important synthesis parameters: initiator concentration, monomer concentration, and crosslinker concentration. The best process conditions are 7.3 mM L−1 initiator, 44 μM L−1 monomer, and 21.6 mM L−1 crosslinker. The effective synthesis of GG-cl-poly(AA) was validated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, field emission scanning electron microscopy (FE-SEM), and 1H-nuclear magnetic resonance. The swelling behavior of GG-cl-poly(AA) in water and saline solutions, as well as its water retention capability, was investigated. In comparison to distilled water, the swelling potential of optimized hydrogel was shown to be significantly reduced in saline solutions. The addition of GG-cl-poly(AA) significantly improved the moisture properties of plant growth media (clay, sandy, and clay–soil combination), implying that it has great potential in moisture stress agriculture. GG-cl-poly(AA) biodegradation was studied by soil burial and vermicomposting methods. The composting approach showed 89.95% deterioration after 22 days, while the soil burial method showed 86.71% degradation after 22 days. The synthesized hydrogel may be beneficial for agricultural applications because of its considerable degradation behaviour, strong water retention capacity, low cost, and environmental friendliness.

Cisplatin uptake and release assessment from hydrogel synthesized in acidic and neutral medium: An experimental and molecular dynamics simulation study

Targeted drug delivery systems (TDDS) are currently considered to overcome traditional drug delivery systems’ criticisms and weaknesses. Biodegradable hydrogels are widely used for the design of appropriate TDDS. Among them, the gum-based hydrogel is known as a proper material to produce drug delivery systems. The present research aimed to design a biodegradable hydrogel with maximum swelling rate, optimum drug loading, and efficient release rate. The acquired experimental findings have been compared to the molecular dynamics (MD) simulation results. Therefore, a response surface methodology (D-optimal method) was used to optimize the guar gum-based hydrogel’s physicochemical properties. The D-optimal method was employed to design an experiment (DOE) to evaluate significant variables, including initiator concentration, monomer concentration, cross-linker, pH, reaction temperature, and reaction time. Findings showed the optimum swelling rate was 4903.876%. Then, the loading and release of cisplatin, selected as the hydrogel structure model drug, were investigated using the molecular dynamics simulation technique. Cisplatin’s uptake and release from the hydrogel structure were higher in an acidic environment than in a neutral medium.

Effects of network structures on the fracture of hydrogel

The polymer network structures and topologies in hydrogels can significantly affect their mechanical properties. The network structures can vary dramatically with different synthetic conditions of hydrogels. Herein, we study the effects of the polymer network structures on mechanical properties of poly(acrylamide) (PAAm) hydrogels synthesized through free radical polymerizations. We focus on investigating how the initial monomer concentration ϕ0 during the synthesis influences the network structures and thus their mechanical properties. Specifically, we measure the swelling capability of the polymer network, the elasticity and fracture of swollen hydrogels with a fixed volume fraction of polymer. Our results have revealed that for PAAm hydrogels with the same volume fraction of polymer, their elasticity, stretchability, work of rupture and fracture toughness can vary significantly if ϕ0 during the synthesis is different. Our study may provide important guideline for synthesizing hydrogels with tailorable mechanical properties without changing the chemistry and synthesis procedure.

Synthesis and Heavy-Metal Sorption Studies of N,N-Dimethylacrylamide-Based Hydrogels.

In this work, a hydrogel system was produced via radical polymerization of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in the presence of N,N-methylene-bis-acrylamide as a crosslinker and ammonium persulfate as an initiator. Parameters that impact the conversion of copolymerization (such as initial concentration of monomers, temperature, initiator dose, and time) were studied. The swelling degree of the hydrogel was investigated with the addition of a crosslinker and initiator at different pH levels. A hydrogel with high conversion and high swelling degree was selected to investigate their ability for adsorption of Pb(II) ions from solutions. Adsorption behavior of Pb(II) ions in a hydrogel was examined as a function of reaction time and concentration of lead ions from a solution of Pb(II) ions.

Highly thermostable high molecular-weight low k PIM polymers based on 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-Tetramethylspirobisindane, decafluorobiphenyl, and bisphenols

High-molecular-weight (number average molecular weight Mn = 11–81 kDa) polymers with intrinsic microporosity (PIM) were prepared by the solution polycondensation of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane, decafluorobiphenyl, and bisphenols in an aprotic polar solvent at an initial monomer concentration of 0.1 mol/L at 100°C-140 °C for 10–144 h. Transparent (minimum cutoff wavelength of 310 nm), highly thermostable (glass transition temperature of 161°C-376 °C by dynamic mechanical analysis, and 5% weight loss temperature in N2 of 410°C-514 °C) polymer films were fabricated using a solvent-cast method. The copolymer films showed good mechanical properties (tensile strengths of 45–67 MPa, breaking elongation of 2.2%–23.1%, and tensile elastic moduli of 1.5–3.3 GPa) and insulating properties (relative permittivity of 2.27–2.59, and dissipation factor of 0.00191–0.00466 at 20 GHz frequency). The prepared new PIM copolymers are candidates for next-generation low k dielectric materials.

Diverse Aggregation Kinetics Predicted by a Coarse-Grained Peptide Model.

Protein and peptide aggregation is a ubiquitous phenomenon with implications in medicine, pharmaceutical industry, and materials science. An important issue in peptide aggregation is the molecular mechanism of aggregate nucleation and growth. In many experimental studies, sigmoidal kinetics curves show a clear lag phase ascribed to nucleation; however, experimental studies also show downhill kinetics curves, where the monomers decay continuously and no lag phase can be seen. In this work, we study peptide aggregation kinetics using a coarse-grained implicit solvent model introduced in our previous work. Our simulations explore the hypothesis that the interplay between interchain attraction and intrachain bending stiffness controls the aggregation kinetics and transient aggregate morphologies. Indeed, our model reproduces the aggregation modes seen in experiment: no observed aggregation, nucleated aggregation, and rapid downhill aggregation. We find that the interaction strength is the primary parameter determining the aggregation mode, whereas the stiffness is a secondary parameter modulating the transient morphologies and aggregation rates: more attractive and stiff chains aggregate more rapidly and the transient morphologies are more ordered. We also explore the effects of the initial monomer concentration and the chain length. As the concentration decreases, the aggregation mode shifts from downhill to nucleated and no-aggregation. This concentration effect is in line with an experimental observation that the transition between downhill and nucleated kinetics is concentration-dependent. We find that longer peptides can aggregate at conditions where short peptides do not aggregate at all. It supports an experimental observation that the elongation of a homopeptide, e.g., polyglutamine, can increase the aggregation propensity.

Self-Initiated Butyl Acrylate Polymerizations in Bulk and in Solution Monitored By In-Line Techniques.

High-temperature acrylate polymerizations are technically relevant, but yet not fully understood. In particular the mechanism and the kinetics of the thermal self-initiation is a topic of current research. To obtain more detailed information the conversion dependence of the polymerization rate, rbr, is determined via in-line DSC and FT-NIR spectroscopy for reactions in bulk and in solution at temperatures ranging from 80 to 160 °C. Solution polymerizations revealed that dioxane is associated with the highest rbr, while aromatic solvents result in the lowest values of rbr. Interestingly, rbr for polymerizations in solution with dioxane depends on the actual monomer concentration at a given time in the system, but is not depending on the initial monomer concentration. The overall rate of polymerization in bulk and in solution is well represented by an equation with three or four parameters, respectively, being estimated by multiple linear regression and the temperature as additional parameter.