Increasing Monomer Concentration Research Articles

Investigating the effect of the perturbation on emulsion polymerization of polystyrene nanospheres

Polystyrene nanospheres (PS spheres) were prepared by soap-less emulsion polymerization. The polymerization reaction with the monomer styrene was initiated using potassium persulfate under nitrogen injection. By adjusting the amount of precursor and the mixing speed of the stirrer during the polymerization process, PS particles of the expected appropriate size can be obtained. This work focuses on the effect of precursor concentration, reaction conditions and stirrer speed on particle size. Samples (C1–C6) were systematically prepared with varying amounts of K2S2O8 and C8H8. The particle sizes ranged from 69.9[Formula: see text]nm to 364.44[Formula: see text]nm. The calculated K2S2O8 to C8H8 ratio remained approximately constant across the samples. This supports the observed trend where increasing monomer concentration leads to larger particle sizes, indicative of bonded spheres. In addition, a correlation between stirring speed and PS bead size is found, with higher speeds resulting in smaller particles. Transmittance analysis of the filtered and sieved process samples showed that better polymerization conditions could be selected for PS beads up to 220[Formula: see text]nm at a stirring speed of 900[Formula: see text]rpm.

Concentration-induced spontaneous polymerization of protic ionic liquids for efficient in situ adhesion

The advancement of contemporary adhesives is often limited by the balancing act between cohesion and interfacial adhesion strength. This study explores an approach to overcome this trade-off by utilizing the spontaneous polymerization of a protic ionic liquid-based monomer obtained through the neutralization of 2-acrylamide-2-methyl propane sulfonic acid and hydroxylamine. The initiator-free polymerization process is carried out through a gradual increase in monomer concentration in aqueous solutions caused by solvent evaporation upon heating, which results in the in-situ formation of a tough and thin adhesive layer with a highly entangled polymeric network and an intimate interface contact between the adhesive and substrate. The abundance of internal and external non-covalent interactions also contributes to both cohesion and interfacial adhesion. Consequently, the produced protic poly(ionic liquid)s exhibit considerable adhesion strength on a variety of substrates. This method also allows for the creation of advanced adhesive composites with electrical conductivity or visualized sensing functionality by incorporating commercially available fillers into the ionic liquid adhesive. This study provides a strategy for creating high-performance ionic liquid-based adhesives and highlights the importance of in-situ polymerization for constructing adhesive composites.

Evolution of morphology, structure, and performance of the COF membranes with monomer concentrations: Enabling effective desalination and kinetics analysis

Fabricating crystalline covalent organic framework (COF) membrane with sub-nanopores for desalination remains challenging. Monomer (p-phenylenediamine (Pa) and 1,3,5-triformylphloroglucinol (Tp)) concentration was crucial to tailor the diffusion-reaction process in the p-toluenesulfonic acid (PTSA)-mediated interfacial catalytic polymerization process for crystalline TpPa-COF membrane fabrication. By increasing monomer concentration, membrane surface color evolved from light yellow to dark orange. TpPa-COF layers with adjustable thickness (90.47–436 nm) transformed from amorphous to crystalline with crystalline and cross-linking degree increasing from 16.47 % to 73.90 %, and 66.40 % to 87.60 %, respectively. Pore size decreased from 1.69 to 0.17 nm, while Na2SO4 rejection significantly increased from 26.7 % to 90.4 %. A 3-day filtration test for RO concentrate demonstrated the stability and robust desalination performance with SO42− rejection ratio of 74.3 ± 1.08 % and Mg2+ rejection ratio of 65.6 ± 1.33 %. Diffusion behavior experiments demonstrated that diffusion coefficient for Pa-PTSA complex (6.49 × 10−5–8.87 × 10−5 cm2 s−1, Pa > 0.05 wt%) higher than Tp (3.53 × 10−6–6.39 × 10−6 cm2 s−1, Tp > 0.006 wt%) by one order of magnitude promoted structural crystallinity and regulated assembly at the interface, resulting in TpPa-COF layer with sub-nanopores. This study highlighted the importance of monomer concentration on the COF membrane formation, providing valuable insights for the highly crystalline COF membrane fabrication.

The comparison of polymerization activity of typical cationic quaternary ammonium salt monomers

AbstractThe cationic water‐soluble polymers, which are widely used in many areas such as papermaking and separation process, are typically synthesized through polymerization of cationic monomers represented by quaternary ammonium salt. In this work, the polymerization reaction kinetics of three typical quaternary ammonium salt cationic monomers including acryloyl oxygen ethyl trimethyl ammonium chloride (DAC), methyl acryloyl oxygen ethyl trimethyl ammonium chloride (DMC), and methyl acrylamide propyl trimethyl ammonium chloride (MAPTAC) was examined by using the dilatometer method. The results showed that the polymerization rate of all three monomers increased with the increase of initiation temperature, monomer concentration, and initiator concentration. Under the same conditions, the polymerization activity of the three monomers followed the order: DAC > DMC > MAPTAC. The activation energies for the polymerization reaction under the specified conditions were EaDAC = 138.97 kJ/mol, EaDMC = 141.24 kJ/mol, and EaMAPTAC = 226.97 kJ/mol, respectively. The polymerization rate equations were RpDAC = k1[M]4.25[I]0.51, RpDMC = k2[M]3.77[I]0.50, and RpMAPTAC = k3[M]3.30[I]0.49. The polymerization activity of the monomers may be influenced by electronic effects and steric hindrance of the monomer structure. This work has provided a theoretical and experimental foundation for the actual work of structural design and preparation of cationic water‐soluble polymers.

Single-molecule FRET imaging and deep learning reveal concentration dependence of aggregation pathways during Aβ aggregation.

Protein aggregation into amyloid fibrils is the hallmark of several devasting neurodegenerative diseases. Gaining an understanding of disease etiology hinges on our ability to understand the molecular mechanics of how soluble monomers assemble to form insoluble fibrils consisting of thousands of constituent monomers. Although amyloid fibril formation is a highly specific self-assembly process, growth patterns and resultant fibril morphologies are highly dependent on solution conditions. Using fluorescence lifetime imaging and deep learning, we have recently shown that amyloid assembly occurs via heterogeneous aggregation pathways resulting in a mixture of co-present mature fibrils with unique morphologies and physicochemical properties (Meng et al., PNAS_2022_e2116736119). Bulk biophysical methods are unable to fully characterize these mixtures of fibril polymorphs. Here, we further develop and use Förster resonance energy transfer (FRET) imaging to monitor the entire aggregation pathway of the Alzheimer's Disease related peptide amyloid β 42 (Aβ42) at the single fibril level in real time. We incubated a mixture of donor-labeled, acceptor-labeled, and unlabeled Aβ42 monomers, which resulted in the formation of fibrils with diverse FRET efficiency values, indicating structural heterogeneity. Single-fibril images reveal that increasing monomer concentration promotes the formation of more homogeneous fibrils. Fibrils formed at lower concentrations show assemble via highly heterogeneous pathways. Deep learning methods (https://github.com/hoisunglab/FNet) enable segmentation of single fibrils within images of highly overlapping fibrils, allowing for quantitative analysis of the aggregation process in terms of fibril growth rate and photon density for each fibril over the course of fibril assembly.

Poly(ionic liquid) nanovesicles via polymerization induced self-assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction

Herein, we report a straightforward, scalable synthetic route towards poly(ionic liquid) (PIL) homopolymer nanovesicles (NVs) with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one-step free radical polymerization induced self-assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs’ internal morphology is studied in detail by coarse-grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra-small (1 ∼ 3 nm in size) copper nanoparticles (CuNPs) and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5-fold enhancement in selectivity towards C1 products (e.g., CH4), compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 products.

Synthesis of cyclic polymers containing various backbones by means of non-stoichiometric Suzuki-Miyaura polycondensation through intramolecular catalyst transfer

Cyclic polymers bearing various backbones are selectively synthesized by means of non-stoichiometric Suzuki-Miyaura polycondensation of 1.0 equivalent of diboronate monomers containing carbon–carbon double bond (C=C), ester, ether, and carbonate linkages with 1.3 equivalents of meta- or para-dibromophenylene in the presence of t-Bu3PPd G2 precatalyst and CsF/18-crown-6 as a base. The molecular weight of the cyclic polymers increases with increasing monomer concentration. The obtained polymer containing C=C is cyclic even in the high-molecular-weight region, as confirmed by end-group analysis after degradative cross-metathesis reaction of the obtained polymer with an excess of an olefinic small molecule. This non-stoichiometric A2 + B2 Suzuki-Miyaura polycondensation is expected to be a powerful tool for the synthesis of cyclic polymers containing various functional groups in the backbone.

"ENHANCEMENT OF ANTIBACTERIAL AND WATER ABSORPTION PROPERTIES OF WOOD PULP BY GAMMA RADIATION INDUCED GRAFTING WITH QUATERNARY AMMONIUM SALT FOR APPLICATION IN HYGIENE PRODUCTS"

"The present work reported the enhancement of antibacterial and water absorption properties of mutually grafted wood pulp with quaternary ammonium-based salts containing 3-acrylamidopropyltrimethyl ammonium chloride (APTAC) monomer induced by gamma radiation. Grafting was qualitatively confirmed by FTIR-ATR, TGA, SEM and quantified by calculating the grafting yield and the grafting efficiency. The performance was examined for water absorbency and antibacterial efficacy (R) against gram-negative bacteria Escherichia coli (E. coli) and and gram-positive bacteria Staphylococcus aureus (S. aureus). The results showed that water absorption, grafting yield and grafting efficiency increased steadily with the increase in monomer concentration and absorbed gamma radiation dose up to a certain level, followed by either slowing down or leveling off the increasing trend. The water absorption and antibacterial activity of grafted wood pulp was found to be substantially enhanced compared to its pristine counterpart, showing a remarkable 357% increase in water absorption and four-log cycle decrease in the number of living bacteria after 24 hours of incubation."

RAFT Polymerization of a Biorenewable/Sustainable Monomer via a Green Process.

A biorenewable polymer is synthesized via a green process using the RAFT principle for the first time in supercritical CO2 at 300bar and 80°C. α-Methylene-γ-butyrolactone polymers of various chain lengths and molecular weights are obtained. The molecular weights vary from 10000 up to 20000 with low polydispersity indexes (PDI <1.5). Furthermore, the monomer conversion in supercritical CO2 is substantially higher, respectively 85% for ScCO2 compared to ≈65% for polymerizations conducted in dimethyl formamide (DMF) solvent. Chain extensions are carried out to confirm the livingness of the formed polymers in ScCO2 . This opens up future possibilities of the formation of different polymer architectures in ScCO2 . The polymers synthesized in ScCO2 have glass transition temperature (Tg ) values ranging from 155 up to 190°C. However, the presence of residual monomer encapsulated inside the formed polymer matrix affects the glass transition of the polymer that is lowered by increasing monomer concentrations. Hence, additional research is required to eliminate the remaining monomer concentration in the polymer matrix in order to arrive at the optimal Tg .

Capturing Free-Radical Polymerization by Synergetic Ab Initio Calculations and Topological Reactive Molecular Dynamics.

Photocurable polymers are used ubiquitously in 3D printing, coatings, adhesives, and composite fillers. In the present work, the free radical polymerization of photocurable compounds is studied using reactive classical molecular dynamics combined with a dynamical approach of the nonequilibrium molecular dynamics (D-NEMD). Different concentrations of radicals and reaction velocities are considered. The mechanical properties of the polymer resulting from 1,6-hexanediol dimethacrylate systems are characterized in terms of viscosity, diffusion constant, and activation energy, whereas the topological ones through the number of cycles (polymer loops) and cyclomatic complexity. Effects like volume shrinkage and delaying of the gel point for increasing monomer concentration are also predicted, as well as the stress-strain curve and Young's modulus. Combining ab initio, reactive molecular dynamics, and the D-NEMD method might lead to a novel and powerful tool to describe photopolymerization processes and to original routes to optimize additive manufacturing methods relying on photosensitive macromolecular systems.

Direct evidence of the impact of aqueous self-assembly on biological behavior of amphiphilic molecules: The case study of molecular immunomodulators Sulfavants

Sulfavant A and Sulfavant R, sulfoquinovoside-glycerol lipids under study as vaccine adjuvants, structurally differ only for the configuration of glyceridic carbon, R/S and R respectively. The in vitro activity of these substances follows a bell-shaped dose–response curve, but Sulfavant A gave the best response around 20 µM, while Sulfavant R at 10 nM. Characterization of aqueous self-assembly of these molecules by a multi-technique approach clarified the divergent and controversial biological outcome. Supramolecular structures were present at concentrations much lower than critical aggregation concentration for both products. The kind and size of these aggregates varied as a function of the concentration differently for Sulfavant A and Sulfavant R. At nanomolar range, Sulfavant A formed cohesive vesicles, while Sulfavant R arranged in spherical micellar particles whose reduced stability was probably responsible for an increase of monomer concentration in accordance with immunomodulatory profile. Instead, at micromolar concentrations transition from micellar to vesicular state of Sulfavant R occurred and thermodynamic stability of the aggregates, assessed by surface tensiometry, correlated with the bioactivity of Sulfavant A at 20 µM and the complete loss of efficacy of Sulfavant R. The study of Sulfavants provides clear evidence of how self-aggregation, often neglected, and the equilibria between monomers and aqueous supramolecular forms of lipophilic molecules deeply determine the overall bio-response.

One-Pot Preparation of Metal-Polymer Nanocomposites in Irradiated Aqueous Solutions of 1-Vinyl-1,2,4-triazole and Silver Ions.

Metal–polymer nanocomposite polyvinyltriazole–silver nanoparticles were obtained using one-pot synthesis in irradiated aqueous solutions of 1-vinyl-1,2,4-triazole (VT) and silver ions. Gel permeation chromatography data show that upon radiation initiation, the molecular weight of poly(1-vinyl-1,2,4-triazole) increases with increasing monomer concentration. To study the kinetics of polymerization and the features of the radiation–chemical formation of nanoparticles, UV-Vis spectroscopy was used. TEM images show a relatively small average size of the forming nanoparticles (2–3 nm) and a narrow size distribution, which shows the effective stabilization of nanoparticles by triazole substituents at a molar ratio of VT and silver ions of 25/1. The addition of ethyl alcohol was used to increase the efficiency of synthesis and suppress the crosslinking of macromolecules in solution. The results of the work show that aqueous–alcoholic solutions of 1 wt.% VT can be used to obtain soluble nanocomposite materials. 10 wt.% monomer solutions have prospects for use in the preparation of polymer gels filled with nanoparticles.

Zwitterionic copolymer modified polyethersulphone/sulfonated polysulphone membranes for enhancing dye/salt selective separation

AbstractTwo monomers, positively charged N,N‐dimethylaminoethyl methacrylate (DMAEMA) and negatively charged monomer sodium vinylsulfonate (VSA), were employed to generate a zwitterionic copolymer layer on the surface of PES/SPSf blend membrane via UV‐light grafting. The effect of monomer concentration and irradiation time on the properties of the modified membranes was studied. Results showed that the degree of grafting (DG) accelerated with the increase in monomer concentration and irradiation time. The zeta potential of the zwitterionic membrane was tailored from negative (−21.4 mV) to positive charge (+30.8 mV) by varying the concentration DMAEMA monomer and irradiation time. Optimized membrane fabrication conditions were 15 g L−1 of DMAEMA and 10 min irradiation time (Mc15). The molecular weight cut‐off of Mc15 was calculated to be 40 kDa, while the zeta potential was found to be +8.56 mV (pH = 7). Mc15 showed excellent rejection rates for both positively and negatively charged dyes. In contrast Mc15 maintained low rejection rates for Na2SO4 (&lt;10%) and high dye/salt selective separation performance (retention rates for basic blue 26 and Na2SO4 were 97 and 6.5%) over long continuous operation (50 h). In summary, our study provides tailoring implementation strategies to enhance dye/salt selective separation of tight ultrafiltration membranes.

Vapor-liquid interfacial polymerization of covalent organic framework membranes for efficient alcohol dehydration

Covalent organic frameworks (COFs) with well-ordered pore structures and versatile functionalities hold tremendous promise as membrane building blocks. The facile and controllable fabrication of COF membranes remains a critical challenge. Herein, we presented a one-step vapor-liquid interfacial polymerization (VLIP) method to in-situ fabricate COF membranes on substrates under mild conditions. This VLIP method features controllable COF growth at the vapor-liquid interface, acquiring COF membranes with tunable physicochemical structure. The time-dependent amorphous-to-crystalline COF growth improved the crystallinity of COF membranes, thus improving the molecular sieving property. The increased monomer concentration endowed COF membranes with higher hydrophilicity, intensifying the water sorption ability. The resultant COF membranes conferred numerous hydrophilic pathways for water-selective transport, exhibited a high and stable n-butanol dehydration performance with permeation flux of 8160 g m−2 h−1 and separation factor of 1023 over 14 days. This VLIP method may evolve into a generic platform technique to fabricate COF membranes for efficient molecular separation.

Charged Polymers: From Polyelectrolyte Solutions to Polyelectrolyte Complexes

Coarse-grained molecular dynamics simulations, random phase approximation (RPA) approach, and scaling analysis are used to study static and dynamic properties of concentrated polyelectrolyte solutions of positively charged chains with the degree of polymerization N+ = 400 and their mixtures with negatively charged chains with degrees of polymerization N– varying between 10 and 400. Simulations show that both the effective chain Kuhn length and mean-square end-to-end distance of a chain decrease with increasing monomer concentration, pointing out screening of the electrostatic interactions by surrounding chains. The structure factor S(q) has a characteristic peak at intermediate wavenumbers q* which location moves toward smaller q values with decreasing monomer concentration. It is demonstrated that the plateau in S(q) at a small q is controlled by system compressibility and increases with increasing degree of polymerization of negatively charged chains. These results are in agreement with S(q) calculated in the framework of the RPA approach considering a solution of neutral chains as a reference system. In the framework of this approach, the location of the maximum in the scattering function at q* scales with monomer concentration as ρ–0.25. Analysis of the chain dynamics in the mixtures of oppositely charged chains shows that chain relaxation is a combination of constraint release and chain reptation processes. Constraint release is demonstrated to be the dominant mechanism in mixtures with negatively charged chains having intermediate degrees of polymerization. The degree of polymerization Ne between entanglements of the tube and super tube for charged systems is found to scale with concentration as Ne ∼ ρ–2 with corresponding packing numbers Pe = 18.45 ± 0.93. This is in contrast with mixtures of neutral chains, where in addition to Ne ∼ ρ–2 scaling, the degree of polymerization between entanglements of the super tube follows scaling Ne ∼ ρ–4/3 with packing number Pe = 6.64 ± 0.19.

MRI diffusion phantoms: ADC and relaxometric measurement comparisons between polyacrylamide and agarose gels

PurposeThe aim of this study is to compare polyacrylamide and agarose gels, as components of a simple MRI phantom, for the measurements of Apparent Diffusion Coefficient (ADC), T1 and T2 relaxation times. Materials and methodsFive (5) test tubes with polyacrylamide gels of different monomer concentrations and six (6) test tubes of different agarose gel concentrations were used as a phantom for ADC, T1 and T2 measurements, which were expressed as 2D color parametric maps, on a 1.5 T clinical MRI system. ADC and T2 maps were calculated utilizing a Weighted Linear (WL) regression fitting algorithm. T1 maps were calculated utilizing a standard non-linear fitting algorithm. ResultsIn agarose gels, ADC measurements are independent of the agarose concentration, whereas the T1 and T2 relaxation times decrease with increasing agarose concentration. On the contrary, in polyacrylamide gels, ADC measurements decrease quadratically while increasing the monomer concentration, whereas the T1 and T2 relaxation times reveal a linear decrease with increasing monomer concentration. ConclusionPolyacrylamide gels can serve as a better means for simulating ADC values, as compared with the agarose gels used in this study.

Preparation and characterization of polyacrylonitrile for carbon fiber manufacture by photo-induced polymerization

The control of the molecular weight of polyacrylonitrile and its distribution is important for carbon fiber preparation. Polyacrylonitrile was synthesized by photo-induced solution polymerization using acrylonitrile as the monomer and dimethyl sulfoxide as a solvent. The molecular weight and molecular weight distribution of the polyacrylonitrile were respectively determined by a viscosity method with an Ubbelohde viscometer and gel permeation chromatography. The functional groups on and the chain structure of polyacrylonitrile were analyzed by infrared spectroscopy and nuclear magnetic resonance spectroscopy. Results showed that with an increase of polymerization temperature or monomer concentration, the conversion of the monomer and the molecular weight increased. Compared with the traditional initiator-induced radical polymerization of acrylonitrile, photo-induced polymerization significantly narrows the molecular weight distribution. Polyacrylonitrile with both a high molecular weight and a relatively narrow molecular weight distribution was manufactured by photo-induced solution polymerization.

Effect of Polymer Viscosity and Polymerization Kinetics on the Electrical Response of Carbon Nanotube Yarn/Vinyl Ester Monofilament Composites.

The effect of polymerization kinetics and resin viscosity on the electrical response of a single carbon nanotube yarn (CNTY) embedded in a vinyl ester resin (VER) during polymerization was investigated. To analyze the effect of the polymerization kinetics, the concentration of initiator (methyl ethyl ketone peroxide) was varied at three levels, 0.6, 0.9, and 1.2 wt.%. Styrene monomer was added to VER, to reduce the polymer viscosity and to determine its effect on the electrical response of the CNTY upon resin wetting and infiltration. Upon wetting and wicking of the CNTY by VER, a transient decrease in the CNTY electrical resistance (ca. −8%) was observed for all initiator concentrations. For longer times, this initial decrease in electrical resistance may become a monotonic decrease (up to ca. −17%) or change its trend, depending on the initiator concentration. A higher concentration of initiator showed faster and more negative electrical resistance changes, which correlate with faster gel times and higher build-up of residual stresses. An increase in styrene monomer concentration (reduced viscosity) resulted in an upward shift of the electrical resistance to less negative values. Several mechanisms, including wetting, wicking, infiltration, electronic transfer, and shrinkage, are attributed to the complex electrical response of the CNTY upon resin wetting and infiltration.

Low cost highly efficient natural polymer-based radiation grafted adsorbent-I: Synthesis and characterization

High energy Co-60 gamma radiation was used to graft cationic and anionic monomers onto radiation crosslinked chitosan through mutual radiation grafting technique. The absorbed dose for synthesizing adsorbent of good strength and adsorption capacity was monomer specific. The grafting extent increased with the increase in radiation dose, dose rate and monomer concentration. While a decrease in grafting extent was observed with the increase in crosslinking density of chitosan backbone. The grafted products were characterized for water uptake capacity, surface morphology, thermal stability and elemental analysis by SEM, TGA and EDXA respectively.

Synthesis of Block Copolymers of Acrylic Acid and N-Butyl Acrylate under Reversible Chain-Transfer Conditions in a Water-Alcohol Medium

The laws of dispersion polymerization of n-butyl acrylate in an aqueous-alcoholic medium in the presence of a hydrophilic reversible addition-fragmentation chain-transfer poly(acrylic acid)-based polymeric agent with a trithiocarbonate group within the chain are investigated. It is shown that the portioned introduction of the monomer into the synthesis makes it possible to achieve higher maximum conversions. The resulting block copolymers are characterized by a relatively narrow molecular weight distribution and their number-average molecular weight increases linearly with increasing monomer concentration. The obtained dispersions of triblock copolymer poly(acrylic acid)–block-poly(n-butyl acrylate)–block-poly(acrylic acid) have a unimodal particle size distribution that persists after dialysis against water. It is shown that the synthesized dispersions may be used as a polymer matrix for immobilizing zinc oxide nanoparticles and as a polymer precursor in the process of the seeded polymerization of styrene.