High Molecular Weight Polymers Research Articles

Perovskite-Initiated Photopolymerization for Singly Dispersed Luminescent Nanocomposites.

Metal halide perovskites have demonstrated rich photophysics and remarkable potential in photovoltaic and electroluminescent devices. However, the photoactivity of perovskite semiconductors in chemical processes remains relatively unexplored. Here, a general approach toward the synthesis of luminescent perovskite-polymer nanocomposites is reported, whereby perovskite nanocrystals are used as photoinitiators in the polymerization of vinyl monomers. The white-light illumination of a perovskite-monomer mixture triggers a free-radical chain-growth polymerization process, giving rise to high molecular weight polymers of ≈200 kDa. The in situ growth of polymer chains from the perovskite crystal surface allows the formation of individually dispersed nanocrystal cores within an encapsulating polymer matrix, and leads to a significant threefold enhancement in photoluminescence quantum yield. This photoluminescence enhancement is attributed to the spatial separation of the perovskite nanocrystals and hence the deactivation of energy transfer to dark crystals. The resulting perovskite-polymer nanocomposites exhibit excellent stability against moisture and are shown to be useful as functional downconversion phosphor films for luminescent displays and lighting.

Effect of viscoelasticity on stability of liquid curtain

The effect of viscoelastic forces on the hole growth speed in a liquid curtain and on the critical flow rate below which a liquid curtain breaks was studied by high-speed visualization. Different Boger-like aqueous solutions were used as the viscoelastic liquids. The expansion of a hole initiated within the liquid curtain leads to the curtain breakup. The results show a strong stabilizing effect of the viscoelastic forces; the minimum flow rate for stable curtain falls drastically by adding small amounts of high molecular weight polymer. The results reveal that the mechanisms for the increased stability are that the initiation of the hole is delayed and the speed at which it expands is also reduced, as the viscoelastic forces become stronger.

A critical review of the application of polymer of low concern and regulatory criteria to fluoropolymers.

Per- and polyfluoroalkyl substances (PFAS) are a group of fluorinated substances that are in the focus of researchers and regulators due to widespread presence in the environment and biota, including humans, of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Fluoropolymers, high molecular weight polymers, have unique properties that constitute a distinct class within the PFAS group. Fluoropolymers have thermal, chemical, photochemical, hydrolytic, oxidative, and biological stability. They have negligible residual monomer and oligomer content and low to no leachables. Fluoropolymers are practically insoluble in water and not subject to long-range transport. With a molecular weight well over 100 000 Da, fluoropolymers cannot cross the cell membrane. Fluoropolymers are not bioavailable or bioaccumulative, as evidenced by toxicology studies on polytetrafluoroethylene (PTFE): acute and subchronic systemic toxicity, irritation, sensitization, local toxicity on implantation, cytotoxicity, in vitro and in vivo genotoxicity, hemolysis, complement activation, and thrombogenicity. Clinical studies of patients receiving permanently implanted PTFE cardiovascular medical devices demonstrate no chronic toxicity or carcinogenicity and no reproductive, developmental, or endocrine toxicity. This paper brings together fluoropolymer toxicity data, human clinical data, and physical, chemical, thermal, and biological data for review and assessment to show that fluoropolymers satisfy widely accepted assessment criteria to be considered as "polymers of low concern" (PLC). This review concludes that fluoropolymers are distinctly different from other polymeric and nonpolymeric PFAS and should be separated from them for hazard assessment or regulatory purposes. Grouping fluoropolymers with all classes of PFAS for "read across" or structure-activity relationship assessment is not scientifically appropriate. Integr Environ Assess Manag 2018;14:316-334. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Sedimentation and consolidation of different density aggregates formed by polymer-bridging flocculation

There are numerous models of sedimentation in fine particle suspensions, derived from or validated with physical measurements. Such models could be applied to optimise and control gravity thickeners used for solid-liquid separation in mineral processing. However, these applications rely upon particle bridging by high molecular weight polymers to form large, low density and fragile aggregates. The evolution and refinement of sedimentation modelling for flocculated systems is restricted by a lack of meaningful control of flocculation conditions and inadequate detail in the experimental sedimentation data used for validation.To address this problem, an experimental system was built to give high fidelity sedimentation data, its use demonstrated for flocculated calcium carbonate suspensions. Turbulent pipe flow flocculation offers tight control of dosage, mean shear rate and reaction time, with aggregate size monitored in-line. The pipe discharges into the base of a wide (190 mm ID) transparent column for which the contents can be isolated, with mudlines then determined from image capture and bed profiles by γ-attenuation. The use of wide columns minimised wall effects that can limit consolidation, while simultaneous efforts to maximise measurement reproducibility and sensitivity led to a greater ability to distinguish subtle impacts from variations in flocculation. Duplicate columns with detachable lower sections enable direct vane yield stress measurement at known bed depths and thereby plots of yield stress vs. solids fraction.Modelling of such data will be described in subsequent publications, with the present study focusing on key experimental requirements and limitations, the form of data outputs and insights into flocculation impacts. For the latter, off-line determination of individual aggregate settling rate vs. size after bed sampling confirmed that higher solids volume fractions low within beds occurred through removal of both inter- and intra-aggregate liquor, i.e. there is a contribution from aggregate densification. Bed profiles and yield stress responses also indicate flocculant functional chemistry can alter how aggregation limits the solids volume fractions attained.

FABRICATION OF BIODEGRADABLE POLYESTER MICROSPHERES BY ELECTROSPRAYING METHODS FOR DRUG CARRIER APPLICATION

This research investigated the effects of polymer concentration, molecular weight polymer and type of polymer on the morphology of electrosprayed microparticles by Scanning Electron Microscopy. Electrospraying process has been studied to produce nano- and micro- particles for drug carrier application because of high loading capacity and high encapsulation efficiency. Controlling morphology and structure of electrosprayed particles can decide the release of drug from these particles. Particles were hollow and wrinkled semi-spheres as using low polymer concentration while wrinkled spheres as using higher polymer concentration. The electrosprayed particles obtained spherical morphology when the polymer concentration is high enough to generate significant chain entanglements. The results also indicated that high molecular weight polymer could produce spherical microspheres, even with low polymer concentration. The electrospraying process fabricated the microspheres from biodegradable PLA and PCL for drug carrier application.

Viscometric analysis of the hydration of a surface cross-linked EM-HEC polymer

Hydrophilic polymers are used in many different products and processes, in which they function, for example, as rheology control agents, steric stabilizers, water retention agents, or flocculants. When the application requires dissolution of polymer powders in water, this occurs through hydration of the hydrophilic chains, and is accompanied by an increase in solution viscosity through a combination of chain entanglement, hydrophobic interactions and hydrogen bonding. On a practical level, however, the addition of high molecular weight polymer powder to water can result in the formation of a surface gel layer leading to partial hydration and particle agglomeration, creating operational and formulation problems. One way of overcoming this is by chemically crosslinking hydroxyl groups on the particle surfaces, for example, by reaction with dialdehydes, such as glyoxal. This retards the initial hydration rate, thereby allowing more time for effective powder dispersion. The present study is concerned with factors affecting the hydration of a commercial non-ionic glyoxal-crosslinked methyl ethyl hydroxyethylcellulose, in the concentration range 0.15–0.5 wt%. Hydration kinetics have been determined by monitoring the increase in solution viscosity with time using low shear rotational viscometry. Experimental variables include polymer concentration, temperature, pH, the presence of anionic, cationic and non-ionic surfactants, and ionic strength (sodium chloride concentrations in the range 0–5 mol/L). In deionised water, the hydration process is shown to involve two kinetic steps, assigned to breakage of hemiacetal crosslinks and polymer hydration. The kinetic studies enabled the various stages in the overall hydration process to be analysed, and mechanistic implications and activation parameters to be assigned.

Exceeding the Asymptotic Limit of Polymer Drag Reduction.

The drag of turbulent flows can be drastically decreased by adding small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) asymptote; this asymptote is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. Contrary to this accepted view, we show that, for an appropriate choice of parameters, polymers can reduce the drag beyond the suggested asymptotic limit, eliminating turbulence and giving way to laminar flow. At higher polymer concentrations, however, the laminar state becomes unstable, resulting in a fluctuating flow with the characteristic drag of the MDR asymptote. Our findings indicate that the asymptotic state is hence dynamically disconnected from ordinary turbulence.

Review of Viscosity Modifier Lubricant Additives

This article reviews viscosity modifiers, additives that increase the viscosity of lubricating oils. Viscosity modifiers are high molecular weight polymers whose functionality is derived from their thickening efficiency, viscosity–temperature relationship, and shear stability. There are now many different additive chemistries and architectures available, all of which have advantages and disadvantages, and affect solution viscosity through different mechanisms. Understanding these mechanisms and how they impart additive function is critical to the development of new viscosity modifiers that enable lubricants to function more efficiently over a wide range of temperatures.

Reversing the direction of galvanotaxis with controlled increases in boundary layer viscosity

Weak external electric fields (EFs) polarize cellular structure and direct most migrating cells (galvanotaxis) toward the cathode, making it a useful tool during tissue engineering and for healing epidermal wounds. However, the biophysical mechanisms for sensing weak EFs remain elusive. We have reinvestigated the mechanism of cathode-directed water flow (electro-osmosis) in the boundary layer of cells, by reducing it with neutral, viscous polymers. We report that increasing viscosity with low molecular weight polymers decreases cathodal migration and promotes anodal migration in a concentration dependent manner. In contrast, increased viscosity with high molecular weight polymers does not affect directionality. We explain the contradictory results in terms of porosity and hydraulic permeability between the polymers rather than in terms of bulk viscosity. These results provide the first evidence for controlled reversal of galvanotaxis using viscous agents and position the field closer to identifying the putative electric field receptor, a fundamental, outside-in signaling receptor that controls cellular polarity for different cell types.

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~ 200 °C), ionic conductivity (6.42 × 10−4 S cm−1), lithium ion conductivity (1.40 × 10−4 S cm−1 at 30 °C), and wide electrochemical stability window (~ 4.10 V versus Li/Li+ at 30 °C). Furthermore, the surface of LiFePO4 cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO4 cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO4. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g−1 for graphene oxide-coated LiFePO4 and without coated LiFePO4 at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO4 cathode after coating with graphene oxide.

Anomalies in the coil-stretch transition of flexible polymers

The flow-induced coil-stretch transition of high molecular weight polymers has generally been held to be of first order. But evidence of significant slowing down in the rate at which the polymers relax to equilibrium in the vicinity of the transition suggests that the thermodynamic character of the transition may be less clear-cut. The above slowing down effect is actually characteristic of a second-order transition, and it points to the existence of a broad spectrum of conformational states in the transition region, analogous to the existence of fluctuations of all length scales at a critical point. In this paper, using a path integral approach based on a free-draining finitely extensible chain model, we calculate various polymer properties as a function of elongational flow as a way of exploring different statistical mechanical details of the coil-stretch transition. These properties include the molecular weight dependence of the flow-extension curve of the polymer, the distribution of its steady-state end-to-end distances, and the characteristic relaxation time τR of these distances. Among other findings, our calculations indicate that the coil-stretch transition is discontinuous in the N → ∞ limit, that the effective free energy of the chain is unimodal at all values of the flow, becoming broad and flat in the immediate vicinity of the transition, and that the ratio of τR to the Rouse relaxation time increases abruptly at the transition before eventually reaching a plateau value at large flow strengths. These aspects of the coil-stretch transition place it among a larger class of unconventional nominally first-order single chain transitions that include the adsorption transition of surface-tethered polymers and the escape transition of compressed polymers.

The Effects of Two Phthalate Esters on Toxicity and Gene Expression After an Acute Exposure of Oryzias latipes

Phthalates are industrial chemicals used primarily to increase flexibility of high molecular-weight polymers. These compounds are not covalently bound to the polymeric matrix and are easily able to leach out and contaminate the environment. It is important to learn more about how these toxicants are affecting the environment and vertebrate health. Diisoheptyl phthalate (DIHepP) and Diisononyl phthalate (DINP) are among the substances being assessed by Environment Canada’s Chemical Management Plan, which assesses and manages chemicals that are used in commerce in Canada. This study examines the effect of DIHepP and DINP in the fish Oryzias latipes. At 1 day-post-hatching, fish were exposed to a range of environmentally relevant low concentrations of DIHepP (37-300 ppb ) and DINP (12-100 ppb DINP). Fish were exposed to phthalates under semi-static conditions for 7 days. None of the treatments significantly induced mortality or malformation. Gene expression analysis was performed in order to assess possible endocrine disruption of these compounds in O. latipes. The transcripts of interest include thyroid hormone-related genes (deiodinases, thyroid receptors alpha and beta), and steroid-related genes (cholesterol transporter, 5-reductases, androgen receptor, aromatase, and estrogen receptor). Data on mortality, malformation, and gene expression will be presented.

High pressure RAFT of sterically hindered ionic monomers. Studying relationship between rigidity of the polymer backbone and conductivity

The synthesis of poly(ionic liquid)s (PILs), a new class of polymers with numerous possible applications and tailored thermorheological properties, is quite a challenging task. To achieve that goal, different strategies have been proposed and developed. However, in the majority of cases macromolecules with relatively low molecular weights and high dispersities were produced, probably due to the strong intermolecular coulombic interactions that determine the behavior of monomeric ionic liquids. In this paper, we proposed a completely new approach that relies on the pressure-induced reversible addition fragmentation chain transfer polymerization (RAFT) to produce PILs of desired properties. For this purpose, a series of model imidazolium-based ionic monomers, with different lengths of aliphatic side chains as additional steric hindrances, have been successfully polymerized under high pressure (p = 250, 500 and 800 MPa). In contrast to results obtained at ambient pressure, all monomers yielded high molecular weight polymers (degrees of polymerization DPn ≤ 10 000) with narrow dispersities (Ð∼1.10). From the kinetic data obtained at various thermodynamic conditions, the rate of polymerization, Rp, and overall activation volumes, ΔV, were estimated, which in the limit of low pressures varied as follows −16.7, −18.1, −32.6 and −35.6 cm mol−1 for [MVIM][NTf2], [EVIM][NTf2], [BVIM][NTf2] and [OVIM][NTf2], respectively. An unexpected significant jump in ΔV can be correlated with the nanostructure organization that, accordingly to the literature, starts to dominate in the latter two monomers. It was also demonstrated that below p = 500 MPa, the termination reaction is almost completely suppressed, independently on the sample. On the other hand, above that pressure both the polymerization rate and the control over the reaction decreased due to the high viscosity preventing diffusion of the monomers. Moreover, taking advantage of the high pressure polymerization, we had a unique opportunity of exploring and better understanding a correlation among molecular weight, Mn, the glass transition temperature, Tg, and the dc conductivity, σdc, for a very wide range of Mn (up to 430 kg/mol) polymers of various backbone rigidity. We observed that the evolution of Tg with Mn follows a typical Fox-Flory relation. Nevertheless, Tg decreases with an increase in the size of the monomer. Additionally, a similar chemical structure dependence was observed for the dc conductivity, which seems to strongly depend on the rigidity of the produced polymers. It can be seen that the higher rigidity of the polymer (longer alkyl chain of side group), the higher σdc. We believe the results reported herein offer an easy alternative way to synthesis of well-defined polyelectrolytes of moderate/high conductivity in shorter reaction times, and expand our knowledge of their properties and the correlations among them.

Metabolism and mechanisms of action of hyaluronan in human biology.

Hyaluronan is a ubiquitous high-molecular weight polymer of repeated disaccharides of glucuronic acid and N-acetylglucosamine. It is a membrane-bound, viscous material extruded into the extracellular matrix after being synthesized in the cytoplasm by hyaluronan synthases complex and a regulated degradation by a group of enzymes called hyaluronidases. Hyaluronan has varied biological roles on many vital organismal functions, such as cellular and tissue development, migration and repair after injury or inflammation and cancer genesis. Hyaluronan in the tissue microenvironment is regulated by its concentration as well as the chain length of the polysaccharide. Many functions of hyaluronan are mediated by specific receptors at the cellular level, though its general physiochemical properties facilitate and coordinate many organ functions as well as in development. These fundamental characteristics of hyaluronan are reviewed, focusing on human biological context.

Inactivation of an intracellular poly-3-hydroxybutyrate depolymerase of Azotobacter vinelandii allows to obtain a polymer of uniform high molecular mass

A novel poly-3-hydroxybutyrate depolymerase was identified in Azotobacter vinelandii. This enzyme, now designated PhbZ1, is associated to the poly-3-hydroxybutyrate (PHB) granules and when expressed in Escherichia coli, it showed in vitro PHB depolymerizing activity on native or artificial PHB granules, but not on crystalline PHB. Native PHB (nPHB) granules isolated from a PhbZ1 mutant had a diminished endogenous in vitro hydrolysis of the polyester, when compared to the granules of the wild-type strain. This in vitro degradation was also tested in the presence of free coenzyme A. Thiolytic degradation of the polymer was observed in the nPHB granules of the wild type, resulting in the formation of 3-hydroxybutyryl-CoA, but was absent in the granules of the mutant. It was previously reported that cultures of A. vinelandii OP grown in a bioreactor showed a decrease in the weight average molecular weight (Mw) of the PHB after 20h of culture, with an increase in the fraction of polymers of lower molecular weight. This decrease was correlated with an increase in the PHB depolymerase activity during the culture. Here, we show that in the phbZ1 mutant, neither the decrease in the Mw nor the appearance of a low molecular weight polymers occurred. In addition, a higher PHB accumulation was observed in the cultures of the phbZ1 mutant. These results suggest that PhbZ1 has a role in the degradation of PHB in cultures in bioreactors and its inactivation allows the production of a polymer of a uniform high molecular weight.

NEW AROMATIC DINITRODERIVATIVES OF CHLORAL AS MONOMER FOR SYNTHESYS OF POLYESTER AND POLYHETERO-ARYLENE

The synthesis of aromatic dinitroderivatives of chloral effectively used in production of soluble, heat and fire resistant polyester and polyhetero arylenes using in the reaction of aromatic nucleophilic replacement was studied. The groups of new aromatic dinitroderivatives containing chloral as central groups between the phenyl nuclei: dichlorethelyne, carbonyl, acetylene and methylene groups were considered. The synthesis conditions were improved for polyester polyesterketones, polyesteretherketones, poliftalimides and polynaphtalamids without substantially affecting the thermal and solid characteristics achieved under relatively mild conditions using nucleophilic polynitro substitution. The search of new functional groups used in the condensation reactions, is an urgent task of polymer chemistry. Such groups must be determined by enough high reactivity of the monomers, without reducing their availability and without increasing their toxicity. It has decisive importance in the structure of initial monomers, which would be determined by the properties of polymers and the solubility of the target. In this aspect, dinitro compounds containing diphenyl, phthalimide and naftalimidnye cycles are presented their unique structures. It is known that improvement in meltability and solubility of the polymers without significant effect on the thermal and strength properties achieved by the introduction of these "carded" groups bulky substituents or phenyl phenoxide, flexible "bridge" fragments and introduced into the aromatic nuclei of the starting compounds bulk chlorine atoms. As part of this review it was made an attempt to describe methods of synthesis and properties of aromatic dinitropro- derivatives containing combinations of bulky substituents and flexible "bridged" groups using as initial compounds the simplest derivatives of chloral. The mostly known polyimides and polyetherimides prepared by reacting dianhydrides of aromatic tetracarboxylic acids with aromatic diamines with two-staged process where the first stage, a poly (o-carboxy) imides, and the second, due to thermal or catalytic imidization of polyamides with low solubility in organic solvents. It should be noted that the second stage -thermal or catalytic imidization not always results in a totally cycling polyamides that reduces the possibility of a relatively high molecular weight of polymers. At using aromatic dinitro- compounds containing a phthalimide and naftalimide cycles as comonomers bis-phenols, the problem of the extent of cyclization is absent. It was noted that an important determinant of obtaining high molecular weight of polymers is using nucleophilic polinitro-substitution in a process flow on the first stage under relatively mild conditions in a medium of DMSO or DMSO / toluene at 70 °C for 2 h in a completely dry environment. The review deals with some aspects of activation mechanism of nitro groups in nucleophilic polynitro-substitution. The processes of synthesis of condensation monomers of dinitro-derivatives using chloral were considered in detail. The methods of preparation and some properties of aromatic dinitroarilene, dinitroftalimide and dinitronaftalimide with dichlorethylenes, ketones, acetylene and methylene "bridged" groups between the phenyl nuclei are given. Forcitation:Kumykov R.M., Vologirov A.K. New aromatic dinitroderivatives of chloral as monomer for synthesys of polyester and polyhetero- arylene. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 4-14

Synthesis and characterization of polymer electrolyte membrane containing methylisatin moiety by polyhydroalkylation for fuel cell

High molecular weight polymer containing N-methylisatin was synthesized by superacid-catalyzed polyhydroxyalkylation reactions. Their functionality with sulfonic acid groups and the measurement of apposite parameters for proton exchange membranes (PEMs) were described. Sulfonic acid groups were introduced into the polymer through sulfonation reaction with chlorosulfonic acid. The membranes were casted from the solution of sulfonated polymer in dimethylsulfoxide (DMSO). The structural properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by thermogravimetric analysis (TGA), ion exchange capacity (IEC), water uptake, dimensional stability and proton conductivity assessment. Different levels of sulfonation and ion exchange were tested; the resulting membranes exhibited high proton conductivities of up to 88.63 mS/cm. The sulfonated membranes showed good dimensional stability owing to having all carbon-carbon linkages on polymers' backbone.

Interlayer diffusion of surface segregating additives to improve the isotropy of fused deposition modeling products

It is well known that 3D printed parts prepared by fused deposition modeling (FDM) exhibit large anisotropy of mechanical properties. For instance, the mechanical properties observed of samples printed orthogonal to the print bed (transverse) are significantly weaker than those printed parallel to the bed (longitudinal). This behavior is a result of poor interlayer adhesion from limited diffusion and entanglement of chains across the interlayer interface. To improve the diffusion and entanglement of adjacent layers, our group has implemented a process in which bimodal blends comprised of a parent, high molecular weight polymer blended with an identical but low molecular weight (LMW) polymer is utilized. These bimodal blends lead to significant enhancements in the mechanical properties of samples printed in the transverse orientation. Additionally, the moduli, regardless of print orientation, become nearly identical, indicating a more isotropic part. To more fully understand this behavior, we report the impact of LMW architectures on the improvement of structural properties of 3D printed parts. The decrease in anisotropy of mechanical properties of PLA bimodal blends containing 2-arm (linear), 3-arm and 4-arm PLA stars (Mw of arm- ∼11 k) at loadings of 3, 10, and 15 mol% are tested under the same protocol as previous linear specimens. With the addition of just 3 mol% of each LMW additive, increases in the maximum stress from 15% to 100% are observed for samples printed in the transverse orientation. A significant improvement in layer adhesion and a significantly more isotropic part is thus realized, where the 3-arm star exhibits optimal performance. Interpretation of the data presented leads to the conclusion that this is true because the 3-arm star most efficiently diffuses to the inter-filament interface and entangles with the linear polymer.

The importance of OH− transport through anion exchange membrane in microbial electrolysis cells

In two-chamber microbial electrolysis cells (MECs) with anion exchange membranes (AEMs), a phosphate buffer solution (PBS) is typically used to avoid increases in catholyte pH as Nernst equation calculations indicate that high pHs adversely impact electrochemical performance. However, ion transport between the chambers will also impact performance, which is a factor not included in those calculations. To separate the impacts of pH and ion transport on MEC performance, a high molecular weight polymer buffer (PoB), which was retained in the catholyte due to its low AEM transport and cationic charge, was compared to PBS in MECs and abiotic electrochemical half cells (EHCs). In MECs, catholyte pH control was less important than ion transport. MEC tests using the PoB catholyte, which had a higher buffer capacity and thus maintained a lower catholye pH (<8), resulted in a 50% lower hydrogen production rate (HPR) than that obtained using PBS (HPR = 0.7 m3-H2 m−3 d−1) where the catholyte rapidly increased to pH = 12. The main reason for the decreased performance using PoB was a lack of hydroxide ion transfer into the anolyte to balance pH. The anolyte pH in MECs rapidly decreased to 5.8 due to a lack of hydroxide ion transport, which inhibited current generation by the anode, whereas the pH was maintained at 6.8 using PBS. In abiotic tests in ECHs, where the cathode potential was set at −1.2 V, the HPR was 133% higher using PoB than PBS due to catholyte pH control, as the anolyte pH was not a factor in the performance. These results show that maintaining charge transfer to control anolyte pH is more important than obtaining a more neutral pH catholyte.

Synthesis, characterization and aggregation-induced emission of alternating copolymers containing cyclophanes and tetraphenylethenes

The alternating copolymers containing tetraphenylethenes bonded to pseudo-para or pseudo-meta [2.2]paracyclophanes were synthesized by palladium catalyzed Suzuki-Miyaura cross-coupling reaction. Relatively high molecular weights of polymers were obtained by the reaction of their corresponding comonomers using Pd(OAc)2 as a catalyst with S-Phos as a ligand and K3PO4 as a base under a high base to monomer ratio. The maximum emission intensity of polymer in THF increases gradually as the addition of water fraction increases. The polymers exhibited aggregation-induced emission in aggregated state. In particular, the photoluminescence quantum yield of those tetraphenylethenes bonded to pseudo-meta [2.2]paracyclophanes is up to 0.334 when the water fraction reaches to 90%. The polymers used in the detection of 2,6-dinitrotoluene are more sensitive than that of small molecule containing the same conjugated segment of the polymers. They are promising candidates for potential uses in the optoelectronic applications.