Low Monomer Concentration Research Articles

Synergizing radiation-induced emulsion graft polymerization of glycidyl methacrylate on polyethylene-coated polypropylene nonwoven fabric by addition of hydrophobic alcohols

The radiation-induced emulsion graft polymerization method is limited for applying concentrations higher than the monomer concentration that enables stable formation of monomer micelles. Furthermore, foaming may occur because of the presence of the surfactant, which is essential for the formation of micelles, resulting in likely splashing around a highly flammable monomer emulsion. In the present study, to overcome these issues, we investigate the effect of added alcohols on the grafting of glycidyl methacrylate (GMA) in emulsion graft polymerization. By adding hydrophobic alcohols to the GMA monomer emulsion of the given system, we succeeded in increasing polymerization rate at low monomer concentrations and developing a highly safe method of emulsion graft polymerization. By adding 0.5 wt% of hydrophobic alcohol such as 1-octanol to the GMA monomer emulsion, the degree of grafting was 4 times higher than in the case without addition. In addition, we successfully reduced the foamability of the GMA monomer emulsion deriving from the surfactant. This is a novel graft polymerization method with promising wide industrial application, as it brings improvements for the existing issues of the conventional emulsion graft polymerization method — (1) emulsion stability under low concentration monomer and (2) process stability due to foaming of the monomer emulsion during polymerization.

Rapid preparation of nanogels by photopolymerization at 532 nm

The strategy of laser beam expansion was used to rapidly prepare nanogels by photopolymerization at 532 nm under low monomer concentration. According to the unique micellar morphology formed by amphiphilic polyethylene glycol diacrylate (PEGDA) in water, the monomer concentration was largely decreased to increase the distance of micellar aggregates. In this case, the photo-crosslinking could prefer to occur inside the micelles instead of crosslinking between the micellar aggregates. The variations of double bond content with reaction time in different beam expansion experiments were investigated. Finally, nanogels with uniform size could be rapidly prepared by regulating the reaction parameters, including monomer concentration, reaction time and power density.

Synthesis and Structural Characterisation of Dinuclear Aluminium Complexes Supported by NNO‐Tridentate Schiff‐Base Ligands and Their Catalysis in the Ring‐Opening Polymerisation of ϵ‐Caprolactone

AbstractIn this study, we prepared a series of dinuclear aluminium complexes {Bis{2‐OAlMe2‐3‐CH=N[CH2CH2N(CH3)2]‐5‐CH3C6H2}CH2, Bis[2‐OAlMe2‐3‐CH=N(2‐PyCH2)‐5‐CH3C6H2]CH2, and Bis{2‐OAlMe2‐3‐CH=N[2‐N(CH3)2C6H4]‐5‐CH3C6H2}CH2} as well as their corresponding mononuclear aluminium compounds derived from NNO‐tridentate Schiff‐base ligands. The compounds were characterised by 1H and 13C spectroscopy and elemental analyses. Complexes 4 and 7 were additionally characterised by single‐crystal X‐ray diffraction. Their activities toward the ring‐opening polymerisation (ROP) of ϵ‐caprolactone (ϵ‐CL) were investigated. In the presence of benzyl alcohol (BnOH), these complexes are catalytically active for the ROP of ϵ‐CL. The kinetic studies for the polymerisation catalysed by these complexes indicated that the polymerisation was well controlled and produced polymers within a narrow molecular weight distribution. At low monomer concentrations, the catalytic activity of binuclear complexes is considerably greater than that of mononuclear complexes.

Adipose saturation reduces lipotoxic systemic inflammation and explains the obesity paradox.

Obesity sometimes seems protective in disease. This obesity paradox is predominantly described in reports from the Western Hemisphere during acute illnesses. Since adipose triglyceride composition corresponds to long-term dietary patterns, we performed a meta-analysis modeling the effect of obesity on severity of acute pancreatitis, in the context of dietary patterns of the countries from which the studies originated. Increased severity was noted in leaner populations with a higher proportion of unsaturated fat intake. In mice, greater hydrolysis of unsaturated visceral triglyceride caused worse organ failure during pancreatitis, even when the mice were leaner than those having saturated triglyceride. Saturation interfered with triglyceride's interaction and lipolysis by pancreatic triglyceride lipase, which mediates organ failure. Unsaturation increased fatty acid monomers in vivo and aqueous media, resulting in greater lipotoxic cellular responses and organ failure. Therefore, visceral triglyceride saturation reduces the ensuing lipotoxicity despite higher adiposity, thus explaining the obesity paradox.

Cholesterol in Membranes Facilitates Aggregation of Amyloid β Protein at Physiologically Relevant Concentrations.

The formation of amyloid β (1-42) (Aβ42) oligomers is considered to be a critical step in the development of Alzheimer's disease (AD). However, the mechanism underlying this process at physiologically low concentrations of Aβ42 remains unclear. We have previously shown that oligomers assemble at such low Aβ42 monomer concentrations in vitro on phospholipid membranes. We hypothesized that membrane composition is the factor controlling the aggregation process. Accumulation of cholesterol in membranes is associated with AD development, suggesting that insertion of cholesterol into membranes may initiate the Aβ42 aggregation, regardless of a low monomer concentration. We used atomic force microscopy (AFM) to test the hypothesis and directly visualize the aggregation process of Aβ42 on the surface of a lipid bilayer depending on the cholesterol presence. Time-lapse AFM imaging unambiguously demonstrates that cholesterol in the lipid bilayer significantly enhances the aggregation process of Aβ42 at nanomolar monomer concentration. Quantitative analysis of the AFM data shows that both the number of Aβ42 oligomers and their sizes grow when cholesterol is present. Importantly, the aggregation process is dynamic, so the aggregates assembled on the membrane can dissociate from the bilayer surface into the bulk solution. Computational modeling demonstrated that the lipid bilayer containing cholesterol had an elevated affinity to Aβ42. Moreover, monomers adopted the aggregation-prone conformations present in amyloid fibrils. The results lead to the model for the on-surface aggregation process in which the self-assembly of Aβ oligomers is controlled by the lipid composition of cellular membranes.

Covalent sizing surface modification as a route to improved interfacial adhesion in carbon fibre-epoxy composites

The polymerisation and attachment of a covalent sizing to the surface of carbon fibres is demonstrated using an electrochemical surface treatment. This treatment proceeds in an aqueous environment at a constant potential of −1 V in 2 min, and thus is within the window of current industrial surface treatments (2–4 min). This treatment demonstrates the ability to significantly increase the tensile strength (up to 25%), Young’s modulus (up to 15%) and interfacial shear strength (IFSS, up to 199%) in an epoxy resin. Optimisation of this process gave similar improvements in carbon fibre properties and IFSS at lower monomer concentrations (0.2 M and 0.5 M vs 1.0 M). This treatment is demonstrated on both bundles of fibres and woven fabrics and the woven fabrics are able to be reversibly moulded into different shapes by simply wetting the surface with an appropriate solvent and allowing to dry.

Does bimolecular termination dominate in benzoyl peroxide initiated styrene free-radical polymerization?

It is believed that polymer chains mainly terminate through bimolecular termination in free-radical polymerization, however, there is few convincing evidence to support it. In benzoyl peroxide (BPO) initiated styrene free-radical polymerization, our studies demonstrate that polymer chain terminates dominantly through primary radical termination rather than by bimolecular termination as described in polymer textbooks. Even at very high primary radical concentration or at very low monomer concentration, primary radical termination still dominates (FPRT&CTI>70%) besides the occurrence of some bimolecular coupling terminations. Two kinds of model polymers were prepared, one for bimolecular coupling termination, and the other for primary radical termination. The 1H-, 13C-, DEPT135-, and 2D HSQC NMR spectra of the polystyrene initiated by BPO are almost the same as those of the model polystyrene for primary radical termination, but they are quite different from those of the model polystyrene for bimolecular coupling termination, demonstrating directly that primary radical termination rather than bimolecular coupling termination dominates in BPO-initiated styrene free-radical polymerization.

Synthesis of Heterogeneously Conductive Polypyrrole Layer from Non-Aqueous Solution Using The Double-Step Potential Technique

In this research we have investigated electrochemical formation of conducting polymer—polypryrrole (Ppy)—by multi-pulse/double-step potential (MpDsP) mode. Ppy layers were electrochemically formed from different concentrations of pyrrole, tetrabutylammonium hexafluorophosphate salt (TBAPF6) in acetonitrile-based (AcN) electrolyte (AcN-TBAPF6). It was determined that during the first anodic potential step the discharge current is significantly higher in comparison to that observed during the next anodic potential step. We conclude that this effect is related to the formation of pyrrole “ad-layer” before the engagement of electrochemical oxidation of pyrrole. During long-lasting formation of Ppy layer the capacitance of double-layer has increased significantly. Electrochemical impedance spectroscopy (EIS) data also showed that double-layer capacitance increases. Such increase of double-layer capacitance is determined by increasing effective electrochemically active surface area of conducting polymer—polypyrrole. However, at the same time, during the formation of Ppy layer by MpDsP approach the increase of reactive impedance (Zreal) has been observed. This effect was the most significant when higher concentrations (25 and 50 mM) of pyrrole in AcN-TBAPF6 based solutions were applied for the formation of Ppy layer. Therefore, we conclude that at increased pyrrole concentrations more homogenous and smooth Ppy layer is formed. However, at the same time the surface of Au-based electrode becomes homogenously blocked by overoxidized Ppy (Ppy(overox)), which has lower conductivity in comparison to that of initially formed Ppy. At low concentration of pyrrole monomer, the Au-based electrode surface is covered by heterogenic layer of Ppy, which is composed of different clusters, which are forming Ppy/Ppy(overox) zones of different conductivity.

Microwave heating assistant preparation of high permselectivity polypiperazine-amide nanofiltration membrane during the interfacial polymerization process with low monomer concentration

By causing the water molecule vibration to generate heat, microwave has become a rapid and efficient heating method which is widely used in industrial production. Herein, microwave heating assistant interfacial polymerization (IP) process was innovatively applied to fabricate polypiperazine-amide nanofiltration (NF) membrane for the first time. With microwave heating, a uniform and faultless polyamide (PA) layer could be generated with low monomer concentration. The pure water flux (PWF) of the NF membrane fabricated with microwave heating was 157.1 L m-2 h-1 with the Na2SO4 rejection of 97.7% under 0.6 MPa. Meanwhile, such NF membrane showed extraordinary selectivity to Cl- and SO42− for a series of mixing solution with different concentrations. This new insight into microwave heating assistant IP provides a feasible method for the high-permselectivity NF membranes fabrication.

Ring-opening (co)polymerization of γ-butyrolactone: a review

With increased environmental concerns and the rising demands for sustainable polymers, e.g., degradable polymers and chemically recyclable polymers, studies on ring-opening polymerization (ROP) of cyclic esters have been developed in recent decades. Biorenewable five-membered γ-butyrolactone (γBL) may be a desirable feedstock for the chemical synthesis of poly(γ-butyrolactone) (PγBL) or for the incorporation of γBL units into polyester chains to modify their properties. Although γBL is traditionally considered to be “nonpolymerizable”, some progress was recently made concerning the ROP of γBL. This mini-review is thus specifically focused on the ROP of γBL and its copolymerization with other cyclic esters. Recent progress in ring-opening (co)polymerization of γ-butyrolactone (γBL) in the presence of various initiating/catalyst systems has been reviewed. Low reaction temperatures and high monomer concentrations are critical for the success of such polymerization, regardless of the different initiating/catalyst systems.

The Formation Mechanism of Segmented Ring-Shaped Aβ Oligomers and Protofibrils.

A clear understanding of amyloid formation with diverse morphologies is critical to overcoming the fatal disease amyloidosis. Studies have revealed that monomer concentration is a crucial factor for determining amyloid morphologies, such as protofibrils, annular, or spherical oligomers. However, gaining a complete understanding of the mechanism of formation of the various amyloid morphologies has been limited by the lack of experimental devices and insufficient knowledge. In this study, we demonstrate that the monomer concentration is an essential factor in determining the morphology of beta-amyloid (Aβ) oligomers or protofibrils. By computational and experimental approaches, we investigated the strategies for structural stabilization of amyloid protein, the morphological changes, and amyloid aggregation. In particular, we found unprecedented conformations, e.g., single bent oligomers and segmented ring-shaped protofibrils, the formation of which was explained by the computational analysis. Our findings provide insight into the structural features of amyloid molecules formed at low concentrations of monomer, which will help determine the clinical targets (in therapy) to effectively inhibit amyloid formation in the early stages of the amyloid growth phase.

α-Synuclein aggregation at low concentrations

BackgroundAggregation of the neuronal protein α-synuclein into amyloid fibrils is a hallmark of Parkinson's disease. The propensity of α-synuclein to aggregate increases with the protein concentration. For the development of efficient inhibitors of α-synuclein aggregation, it is important to know the critical concentration of aggregation (the concentration of monomeric protein, below which the protein does not aggregate). MethodsWe performed in vitro aggregation studies of α-synuclein at low concentrations (0.11–20 μM). Aggregation kinetics was measured by ThT fluorescence. Obtained aggregates were characterized using CD-spectroscopy, fluorescent spectroscopy, dynamic light scattering and AFM imaging. ResultsMonomeric α-synuclein at concentrations 0.45 μM and above was able to bind to fibril ends resulting in fibril growth. At the protein concentrations below 0.4 μM, monomers did not fibrillize, and fibrils disaggregated. In the absence of seeds, fibrils were formed only at monomer concentrations higher than 10 μM. At low micromolar concentrations, we observed formation of prefibrillar amyloid aggregates, which are able to induce fibril formation in α-synuclein solutions of high concentrations. ConclusionsThe critical concentration of α-synuclein fibril growth is ~0.4 μM. Prefibrillar amyloid aggregates appear at concentrations between 0.45 and 3 μM and are an intermediate state between monomers and fibrils. Although morphologically different from fibrils, prefibrillar aggregates have similar properties to those of fibrils. General significanceWe determined the critical concentration of α-synuclein fibril growth. We showed that fibrils can grow at much lower monomer concentrations than that required for de novo fibril formation. We characterized a prefibrillar intermediate species formed upon aggregation of α-synuclein at low micromolar concentration.

Renewable Terpene Derivative as a Biosourced Elastomeric Building Block in the Design of Functional Acrylic Copolymers.

In order to move away from traditional petrochemical-based polymer materials, it is imperative that new monomer systems be sought out based on renewable resources. In this work, the synthesis of a functional terpene-containing acrylate monomer (tetrahydrogeraniol acrylate, THGA) is reported. This monomer was polymerized in toluene and bulk via free-radical polymerizations, achieving high conversion and molecular weights up to 278 kg·mol-1. The synthesized poly(THGA) shows a relatively low Tg (-46 °C), making it useful as a replacement for low Tg acrylic monomers, such as the widely used n-butyl acrylate. RAFT polymerization in toluene ([M]0 = 3.6 mol·L-1) allowed for the well-controlled polymerization of THGA with degrees of polymerization (DP n) from 25 to 500, achieving narrow molecular weight distributions ( D̵ ≈ 1.2) even up to high conversions. At lower monomer concentrations ([M]0 = 1.8 mol·L-1), some evidence of intramolecular chain transfer to polymer was seen by the detection of branching (arising from propagation of midchain radicals) and terminal double bonds (arising from β-scission of midchain radicals). Poly(THGA) was subsequently utilized for the synthesis of poly(THGA)- b-poly(styrene)- b-poly(THGA) and poly(styrene)- b-poly(THGA)- b-poly(styrene) triblock copolymers, demonstrating its potential as a component of thermoplastic elastomers. The phase separation and mechanical properties of the resulting triblock copolymer were studied by atomic force microscopy and rheology.

Poly(Urethane-Acrylate) Aerogels via Radical Polymerization of Dendritic Urethane-Acrylate Monomers.

The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur RE) triisocyanate core. The terminal acrylate groups (three at the tip of each of the three branches, nine in total) were polymerized with 2,2′-azobis(isobutyronitrile) (AIBN) via free radical chemistry. The resulting wet-gels were dried with supercritical fluid (SCF) CO2. Aerogels were characterized with ATR-FTIR and solid-state 13C NMR. The porous network was probed with N2-sorption and scanning electron microscopy (SEM). The thermal stability of aerogels was studied with thermogravimetric analysis (TGA). Most aerogels were macroporous materials (porosity > 80%), with high thermal stability (up to 300 °C). Aerogels were softer at low monomer concentrations and more rigid at higher concentrations. The material properties were compared with those of analogous aerogels bearing only one acrylate moiety at the tip of each branch and the same cores, and with those of analogous aerogels bearing norbornene instead of acrylate moieties. The nine-terminal acrylate-based monomers of this study caused rapid decrease of the solubility of the growing polymer and made possible aerogels with much smaller particles and much higher surface areas. For the first time, aliphatic/flexible triisocyanate-based materials could be made with similar properties in terms of particle size and surface areas to their aromatic/rigid analogues. Finally, it was found that with monomers with a high number of crosslinkable groups, material properties are determined by multifunctionality and thus aerogels based on 9-acrylate- and 9-norbornene-terminated monomers were similar. Materials with aromatic cores are carbonizable with satisfactory yields (20–30% w/w) to mostly microporous materials (BET surface areas: 640–740 m2 g−1; micropore surface areas: 360–430 m2 g−1).

A two-phase stochastic model to describe mass transport and kinetics during reactive processing of polyolefins

Free radical induced grafting (FRIG) of polyolefins is described at industrially relevant time scales at which phase segregation occurs, leading to the formation of a monomer- and polyolefin-rich phase. The mass transfer of oligomeric species is accounted for using overall average mass transfer coefficients. Model validation is illustrated for FRIG with a non-homopolymerizable monomer based on experimental data on monomer conversion and functionalization degrees. Comparison with an approximate single-phase model highlights that due to phase segregation the reaction rate and the functionalization degree significantly decrease due to a different role of diffusional limitation on termination, whereas the grafting degree and density are unaffected on an overall monomer conversion basis. This mismatch with the single-phase model is enlarged with a homopolymerizable monomer. The polyolefin-rich phase is there characterized by lower monomer concentrations whose grafting kinetics are strongly affected by depropagation, compensating for influences caused by diffusional limitations on termination. For such monomers, the functionalization selectivity can display even a maximum as a function of the overall monomer conversion.

Mid-Chain Radical Migration in the Radical Polymerization of n-Butyl Acrylate.

The occurrence of intramolecular transfer to polymer in the radical polymerization of acrylic monomers has been extensively documented in the literature. Whilst it has been largely assumed that intramolecular transfer to polymer leads to short chain branches, there has been some speculation over whether the mid-chain radical can migrate. Herein, by the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) of poly(n-butyl acrylate) synthesized by solution polymerization under a range of conditions, it is shown that this mid-chain radical migration does occur in the radical polymerization of acrylates conducted at high temperatures, as is evident from the shape of the molecular weight distribution. Using a mathematical model, an initial approximation of the rate at which migration occurs is made and the distribution of branching lengths formed in this scenario is explored. It is shown that the polymerizations carried out under a low monomer concentration and at high temperatures are particularly prone to radical migration reactions, which may affect the rheological properties of the polymer.

Poly(urethane-norbornene) Aerogels via Ring Opening Metathesis Polymerization of Dendritic Urethane-Norbornene Monomers: Structure-Property Relationships as a Function of an Aliphatic Versus an Aromatic Core and the Number of Peripheral Norbornene Moieties.

We report the synthesis and characterization of synthetic polymer aerogels based on dendritic-type urethane-norbornene monomers. The core of those monomers is based either on an aromatic/rigid (TIPM/Desmodur RE), or an aliphatic/flexible (Desmodur N3300) triisocyanate. The terminal norbornene groups (three at the tip of each of the three branches) were polymerized via ROMP using the inexpensive 1st generation Grubbs catalyst. The polymerization/gelation conditions were optimized by varying the amount of the catalyst. The resulting wet-gels were dried either from pentane under ambient pressure at 50 °C, or from t-butanol via freeze-drying, or by using supercritical fluid (SCF) CO2. Monomers were characterized with high resolution mass spectrometry (HRMS), 1H- and solid-state 13C-NMR. Aerogels were characterized with ATR-FTIR and solid-state 13C-NMR. The porous network was probed with N2-sorption and SEM. The thermal stability of monomers and aerogels was studied with TGA, which also provides evidence for the number of norbornene groups that reacted via ROMP. At low densities (<0.1 g cm−3) all aerogels were highly porous (porosity > 90%), mostly macroporous materials; aerogels based on the aliphatic/flexible core were fragile, whereas aerogels containing the aromatic/rigid core were plastic, and at even lower densities (0.03 g cm−3) foamy. At higher densities (0.2–0.7 g cm−3) all materials were stiff, strong, and hard. At low monomer concentrations all aerogels consisted of discrete primary particles that formed spherical secondary aggregates. At higher monomer concentrations the structure consisted of fused particles with the size of the previous secondary aggregates, due to the low solubility of the developing polymer, which phase-separated and formed a primary particle network. Same-size fused aggregates were observed for both aliphatic and aromatic triisocyanate-derived aerogels, leading to the conclusion that it is not the aliphatic or aromatic core that determines phase separation, but rather the solubility of the polymeric backbone (polynorbornene) that is in both cases the same. The material properties were compared to those of analogous aerogels bearing only one norbornene moiety at the tip of each branch deriving from the same cores.

Morphological Study of Nascent Growth of α‐Olefin Polymers on Spatially Unconstrained Silica Surfaces

AbstractThe experimental study of polymer growth on spatially unconstrained flat silica surfaces is presented for propylene and ethylene polymerization in liquid and gas phases with high activity metallocene catalyst (rac‐Et(Indenyl)2ZrCl2/ methylaluminoxane at 30–70 °C and 30–50 psig. The study shows a surprisingly rich spectrum of nascent morphologies for each polymer synthesized in two different reaction phases. In propylene polymerization in a liquid phase, polypropylene nanofibrils are first formed at the catalyst sites and quickly develop into microglobular morphology, whereas in ethylene polymerization in a liquid phase, polyethylene nanofibrils formed at the catalyst sites grow to a ribbon‐like morphology. In gas phase polymerization where polymerization rate is much lower due to low monomer concentration, both polymers grow to compact aggregates of globules. Unlike in liquid phase polymerization, no ribbon‐like structure is formed in ethylene polymerization. The sequential polymerization of these olefin monomers has also been carried out and the experimental data show two distinct regions of corresponding polymers as observed in separate ethylene and propylene homopolymerization experiments.

Synthesis of Janus Particle Arrays and Janus Films through an Interfacial Polymerization Method

We report the fabrication of Janus particle arrays and Janus films through the combination of selfassembly of spheres on a water surface and interfacial polymerization of pyrrole or aniline around the spheres. With a low concentration of monomer, it is found that only the water-exposed side of the spheres are coated with a thin layer of polypyrrole (PPy) or polyaniline (PANI), leading to the formation of Janus particle arrays. At an elevated monomer concentration an additional PPy or PANI layer forms on the water surface and further increase in the concentration leads to the coalescence of the layers on water surface and on the waterexposed side of spheres, both of which produce Janus films with PS spheres embedded in a structured conducting polymer.

Evolutionary advantage of directional symmetry breaking in self-replicating polymers

Due to the asymmetric nature of the nucleotides, the extant informational biomolecule, DNA, is constrained to replicate unidirectionally on a template. As a product of molecular evolution that sought to maximize replicative potential, DNA’s unidirectional replication poses a mystery since symmetric bidirectional self-replicators obviously would replicate faster than unidirectional self-replicators and hence would have been evolutionarily more successful. Here we carefully examine the physico-chemical requirements for evolutionarily successful primordial self-replicators and theoretically show that at low monomer concentrations that possibly prevailed in the primordial oceans, asymmetric unidirectional self-replicators would have an evolutionary advantage over bidirectional self-replicators. The competing requirements of low and high kinetic barriers for formation and long lifetime of inter-strand bonds respectively are simultaneously satisfied through asymmetric kinetic influence of inter-strand bonds, resulting in evolutionarily successful unidirectional self-replicators. Within our model, circular strands, the configuration prefered by primitive life forms, have higher replicative potential compared to linear strands.