Ethylene Oxide Side Chains Research Articles

Effect of Grafting Density on the Crystallization Behavior of Molecular Bottlebrushes.

A unique case of sterically constrained crystallization arises in bottlebrush polymers bearing semicrystalline side chains. Bottlebrushes with grafted side chains can form crystalline structures governed by the complex interplay between side chain packing and backbone confinement. The confinement effect can be readily tuned by varying the side chain grafting density, thus affording control over the crystallization behavior of these systems. In this work, the grafting density effect on the crystallization behavior of molecular bottlebrushes comprising poly(ethylene oxide) (PEO) side chains grafted to a methacrylate backbone was systematically studied. Thermal analysis using differential scanning calorimetry showed that the bottlebrush polymers displayed suppressed crystallization temperatures, lower melting temperatures, and reduced crystallinities compared to linear homopolymer PEO. The crystalline morphology was investigated using polarized light, atomic force, and scanning electron microscopy. Isothermal crystallization experiments revealed a nonmonotonous dependence of the nucleation density on the side chain grafting density. The grafting density effect was also investigated using self-seeding experiments, revealing an increased clearing temperature and memory retention at higher grafting densities. This work highlights how grafting density influences the crystallization behavior of semicrystalline bottlebrushes, providing information for the processing and application of these unique polymers.

Measuring Heat Dissipation and Entropic Potential in Battery Cathodes Made with Conjugated and Conventional Polymer Binders Using Operando Calorimetry.

This study explores the influence of electronic and ionic conductivities on the behavior of conjugated polymer binders through the measurement of entropic potential and heat generation in an operating lithium-ion battery. Specifically, the traditional poly(vinylidene fluoride) (PVDF) binder in LiNi0.8Co0.15Al0.05O2 (NCA) cathode electrodes was replaced with semiconducting polymer binders based on poly(3,4-propylenedioxythiophene). Two conjugated polymers were explored: one is a homopolymer with all aliphatic side chains, and the other is a copolymer with both aliphatic and ethylene oxide side chains. We have shown previously that both polymers have high electronic conductivity in the potential range of NCA redox, but the copolymer has a higher ionic conductivity and a slightly lower electronic conductivity. Entropic potential measurements during battery cycling revealed consistent trends during delithiation for all of the binders, indicating that the binders did not modify the expected NCA solid solution deintercalation process. The entropic signature of polymer doping to form the conductive state could be clearly observed at potentials below NCA oxidation, however. Operando isothermal calorimetric measurements showed that the conductive binders resulted in less Joule heating compared to PVDF and that the net electrical energy was entirely dissipated as heat. In a comparison of the two conjugated polymer binders, the heat dissipation was lower for the homopolymer binder at lower C-rates, suggesting that electronic conductivity rather than ionic conductivity was the most important for reducing Joule heating at lower rates, but that ionic conductivity became more important at higher rates.

Molecular Dynamics Calculations for the Temperature Response of Poly(alkylated tri(ethylene oxide)isocyanate) Aqueous Solution

Aqueous solutions of conventional temperature-responsive amphiphilic polymers undergo a coil–globule conformational transition around the lower critical solution temperature (LCST) that causes the polymer surfaces to become hydrophobic and the polymers to aggregate together. Isocyanate polymers with alkylated oligo(ethylene oxide) side chains are expected to have rigid main chains and, thus, do not undergo the coil–globule structural transition, but they have recently been reported to exhibit temperature-responsive properties. In this study, molecular dynamics was used to calculate the agglomeration tendencies of two chains of poly(alkylated tri(ethylene oxide)isocyanate) (PRTEOIC, where R = methyl (Me) or ethyl (Et)) in aqueous solution to elucidate the LCST phenomenon in the absence of coil–globule conformational transition. Our MD simulations showed that aggregation also occurs in rod polymers. Furthermore, we found that both (PMeTEOIC)2 and (PEtTEOIC)2 showed parallel agglomeration of the two molecular chains with increasing temperature, but only (PMeTEOIC)2 showed a metastable T-shaped agglomeration in the middle temperature range. The crossing-point temperature (TCRP) at which the density of the first hydrophobic hydration shell around the sidechain alkyl group equals the bulk water density is a useful indicator for predicting the LCST of rod polymers with dense side chains terminated by alkyl groups.

Fine-tuning morphology via oligo(ethylene oxide) side chain engineering for squaraine-based organic solar cells

Two squaraine dyes (SQs), USQ-O bearing oligo(ethylene oxide) (OE) chain, and USQ-C bearing alkyl chain, were synthesized. The influence of OE side chain on photovoltaic performances was systematically investigated. USQ-C and USQ-O show similar absorption spectra in dilute solutions, energy levels, charge mobility and the molecular electrostatic potential (ESP) on the conjugated skeleton. However, USQ-O exhibits hypsochromic absorption band compared to that of USQ-C in the film, and the distribution of positive and negative alternating ESP on the OE side chain. Significantly different electrostatic interactions and multiple hydrogen bonds among OE side chains could greatly affect the behaviors of intermolecular interactions, and, in turn, influence the photophysical properties of pristine/blend films and the miscibility with PC71BM acceptor. USQ-O-based devices exhibit higher short circuit current than that of USQ-C-based (13.94 vs 12.36 mA cm−2), which could be principally put down to the effective improvement of the blending morphology. These results indicate that simply substituted alkyl chain by OE chain for SQ is an effective strategy for optimizing morphology.

Highly Conductive Polyoxanorbornene-Based Polymer Electrolyte for Lithium-Metal Batteries.

This present study illustrates the synthesis and preparation of polyoxanorbornene-based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring-opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li-ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10-4 S cm-1 at room temperature and excellent electrochemical performance, including high-rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO4 cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium-metal batteries (LMB).

Novel concrete superplasticizers with sterically hindered amines as stabilizing pendant side chains

In this work, a sterically hindered amine, 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TMPMA), is introduced as a bulky pendant group to achieve steric hindrance, replacing the traditional poly(ethylene oxide) (PEO) side chains of traditional polycarboxylate ether (PCE) superplasticizers (SPs). Note that PCE is the common name for concrete superplasticizers having both carboxylic acid and PEO side-chains in which the bulky PEO pendant group exert large steric hindrance leading to good dispersion and stabilization of cement particles. In this work, the PEO side chains are replaced by a sterically hindered amine. Therefore, copolymers of methacrylic acid (MAA) and TMPMA with different molar ratios were prepared by Reversible-Addition Fragmentation Chain Transfer polymerization (RAFT). The prepared copolymers were characterized by proton nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC) to elucidate the chemical structure and molecular weights. Rheological studies and fluidity measurements revealed that poly(MAA-co-TMPMA) SPs, which we introduce here as polycarboxylate amine (PCA) SPs, enhanced cement flowability, workability, and slump retention. Free radical polymerization (FRP) was also employed, as an industrially more relevant, more straightforward and more cost-effective synthesis technique, for the preparation of PCA SPs to reflect the possibility of scaling up these SPs via conventional polymerization methods. The resulting FRP PCA analog exhibited the same plasticizing efficacy as those prepared by RAFT polymerization, demonstrating that these polymers could have high potential in the concrete industry.

Polyethylenimine-Conjugated Hydroxyethyl Cellulose for Doxorubicin/Bcl-2 siRNA Co-Delivery Systems

Hydroxyethyl cellulose (HEC), widely known for its biocompatibility and water solubility, is a polysaccharide with potential for pharmaceutical applications. Here, we synthesized polyethylenimine2k (PEI2k)-conjugated hydroxyethyl cellulose (HECP2k) for doxorubicin/Bcl-2 siRNA co-delivery systems. HECP2ks were synthesized by reductive amination of PEI2k with periodate-oxidized HEC. The synthesis of the polymers was characterized using 1H NMR, 13C NMR, primary amine quantification, FT-IR, and GPC. Via agarose gel electrophoresis and Zeta-sizer measurement, it was found that HECP2ks condensed pDNA to positively charged and nano-sized complexes (100-300 nm, ~30 mV). The cytotoxicity of HECP2ks was low and HECP2k 10X exhibited higher transfection efficiency than PEI25k even in serum condition, showing its high serum stability from ethylene oxide side chains. Flow cytometry analysis and confocal laser microscopy observation verified the superior cellular uptake and efficient endosome escape of HECP2k 10X. HECP2k 10X also could load Dox and Bcl-2 siRNA, forming nano-particles (HECP2k 10X@Dox/siRNA). By median effect analysis and annexin V staining analysis, it was found that HECP2k 10X@Dox/siRNA complexes could cause synergistically enhanced anti-cancer effects to cancer cells via induction of apoptosis. Consequently, it was concluded that HECP2k possesses great potential as a promising Dox/Bcl-2 siRNA co-delivery carrier.

Tetrafluorinated versus hydrogenated azobenzene polymers in water: Access to visible-ligh stimulus at the expense of responsiveness

Photo-responsive polymers are at the core of numerous applications as actuators in biology but often exhibit the drawback of activation in the UV range. This work describes a methacrylate-based terpolymer presenting tetra-ortho-fluoroazobenzene groups showing activation through visible light illumination. The presence of poly(ethylene oxide) side chains and maleimide functions ensures that it can be easily used for biological applications in aqueous media. The terpolymer was shown to form unimolecular micelles in water. The tetra-ortho-fluoroazobenzene moiety was reversibly switched from trans to cis upon visible light irradiation without significant modification of the unimolecular morphology. The deprotection of the maleimide function resulted in a reactive polymer which was used to obtain hydrogels by reaction with poly(ethylene oxide) tetra-thiols or bioconjugates by reaction with a model peptide or a poly(ethylene oxide) mono-thiol exhibiting a biotin group. Hydrogels incorporating β-cyclodextrin molecules were also obtained. Contrary to polymers bearing hydrogenated azobenzenes, the terpolymer bearing tetra-ortho-fluoroazobenzene moieties did not form a complex with β-cyclodextrin and none of the presented hydrogels exhibited macroscopic changes upon irradiation although the trans/cis isomerization occurred. This was explained by the burial of tetra-ortho-fluoroazobenzene groups towards the polymer backbone, therefore completely hindering its access.

Extending Electrochemical Stability Window As a Result of Carbonate-Ketone Side Chain Modified Polyethylene Glycol Electrolytes for Lithium Batteries

Solid state batteries are of wide interest owing to their high energy density and safety. Their stability with high voltage cathodes is not new to the researchers and are advantageous in various terms. Although ethylene oxide side chains being one of the most studied system also suffers from serious setback with its prime backbone. Here in our work, we studied the effect of terminal group of linear and tri-arm polyethylene glycol (PEG-OH) by converting it to carbonate-ketone (Carb-ket) from hydroxyl. We synthesized the polyethylene carb-ket (TPEG-carb-ket) terminal by ring opening reaction. The carb-ket functionality at the chain end not only increase the electrochemical stability window > 4.47 V but also limits the parasitic reactions with lithium metal stabilising SEI at the interface. The latter demonstrated the superior galvanostatic charge-discharge of LiFePO4 using as synthesized electrolyte loaded with LiTFSI salts as compare to similar chain length PEG-OH. This make the vast impact on controlling the undesired decomposed products at the interface to facilitate the high coulombic efficiency and capacity retention The TPEG-carb-ket also hinted at stable interface with lithium as a result of stripping and plating for more than 1200 h. These experiment results provide important insights backed by AIMD simulations in comparison with hydroxyl terminal system. Our study would aide with the major step on improving the higher voltage cathode with superior performance in the lithium batteries.

Synthesis and Micellization of Bottlebrush Poloxamers.

Bottlebrush polymers are characterized by an expansive parameter space, including graft length and spacing along the backbone, and these features impact various structural and physical properties such as molecular diffusion and bulk viscosity. In this work, we report a synthetic strategy for making grafted block polymers with poly(propylene oxide) and poly(ethylene oxide) side chains, bottlebrush analogues of poloxamers. Combined anionic and sequential ring-opening metathesis polymerization yielded low dispersity polymers, at full conversion of the macromonomers, with control over graft length, graft end-groups, and overall molecular weight. A set of bottlebrush poloxamers (BBPs), with identical graft lengths and composition, was synthesized over a range of molecular weights. Dynamic light scattering and transmission electron microscopy were used to characterize micelle formation in aqueous buffer. The critical micelle concentration scales exponentially with overall molecular weight for both linear and bottlebrush poloxamers; however, the bottlebrush architecture shifts micelle formation to a much higher concentration at a comparable molecular weight. Consequently, BBPs can exist in solution as unimers at significantly higher molecular weights and concentrations than the linear analogues.

Ionic liquid plasticizers comprising solvating cations for lithium metal polymer batteries

Ternary solid polymer electrolytes (TSPEs) with ionic liquids (ILs) including alkyl-based ammonium cations and low coordinating anions suffer from the lack of Li+ ion coordination by the ILs compared to the immobile polymer backbone, in terms of Li+ ion transport. Thus, solvating ionic liquids (SILs) with an oligo(ethylene oxide) side chain attached onto the cation were prepared to improve the interaction between Li+ and the IL and accelerate Li+ transport in TSPEs. A variety of methods, such as pulsed field gradient nuclear magnetic resonance spectroscopy, Li metal plating/stripping and measurements of Sand's times were used to show that Li+ ion transference numbers increase with the oligo(ethylene oxide) side chain length in SIL-based TSPEs, which results in faster Li+ ion transport and translates into much slower lithium depletion at a given current, thereby delaying the onset of fast dendrite growth of lithium metal.

Engineering Li/Na selectivity in 12-Crown-4–functionalized polymer membranes

Lithium is widely used in contemporary energy applications, but its isolation from natural reserves is plagued by time-consuming and costly processes. While polymer membranes could, in principle, circumvent these challenges by efficiently extracting lithium from aqueous solutions, they usually exhibit poor ion-specific selectivity. Toward this end, we have incorporated host-guest interactions into a tunable polynorbornene network by copolymerizing 1) 12-crown-4 ligands to impart ion selectivity, 2) poly(ethylene oxide) side chains to control water content, and 3) a crosslinker to form robust solids at room temperature. Single salt transport measurements indicate these materials exhibit unprecedented reverse permeability selectivity (∼2.3) for LiCl over NaCl-the highest documented to date for a dense, water-swollen polymer. As demonstrated by molecular dynamics simulations, this behavior originates from the ability of 12-crown-4 to bind Na+ ions more strongly than Li+ in an aqueous environment, which reduces Na+ mobility (relative to Li+) and offsets the increase in Na+ solubility due to binding with crown ethers. Under mixed salt conditions, 12-crown-4 functionalized membranes showed identical solubility selectivity relative to single salt conditions; however, the permeability and diffusivity selectivity of LiCl over NaCl decreased, presumably due to flux coupling. These results reveal insights for designing advanced membranes with solute-specific selectivity by utilizing host-guest interactions.

Random copolymerization of macromonomers as a versatile strategy to synthesize mixed‐graft block copolymers

AbstractThe random copolymerization of norbornene‐functionalized macromonomers was explored as a method of synthesizing mixed‐graft block copolymers (mGBCPs). The copolymerization kinetics of a model system of polystyrene (PS) and poly(lactic acid) (PLA) macromonomers was first analyzed, revealing a gradient composition of side chains along the mGBCP backbone. The phase separation behavior of mGBCPs with PS and PLA side chains of various backbone lengths and side chain molar ratios was investigated, and increasing the backbone length was found to stabilize the phase‐separated nanostructures. The graft architecture was also demonstrated to improve the processability of the mGBCP, compared to a linear counterpart. Investigations of mGBCPs comprised of polydimethylsiloxane and poly(ethylene oxide) side chains exemplified the diverse self‐assembled morphologies, including a Frank‐Kasper A15 phase, that can be obtained with mGBCPs synthesized by random copolymerization of macromonomers. Lastly, a ternary mGBCP was synthesized by the copolymerization of three macromonomers.

Synthesis, Phase Structure, and Ion Conductivity of Poly(p-phenylene) Functionalized with Lithium Trifluoromethanesulfonimide and Tetra(ethylene Oxide) Side Chains

Rigid-rod polymers tethered with delocalized anions and flexible ion conductive side chains present a synthetic pathway toward thin, single-ion conducting electrolyte membranes with low bulk resist...

Conductivity–modulus–Tg relationships in solvent‐free, single lithium ion conducting network electrolytes

AbstractA model system of single‐ion conducting network electrolytes with acrylic backbone, ethylene oxide (EO) side chains, tethered fluorinated anions, and mobile Li cations was designed and synthesized to investigate structure–property relationships. By systematically tuning four molecular variables, one at a time, we investigated how crosslinker length, mol% of crosslinker added, Li:EO ratio and side‐chain length affect conductivity, Tg, and modulus. Ionic conductivity at 90 °C varied by two orders of magnitude (and by three orders of magnitude at room temperature) depending on the molecular details, while a 70 °C span in glass transition temperature (Tg) was observed. The range of crosslinking, which can be achieved without impacting conductivity was also elucidated, and the modulus of the electrolyte can be increased by a factor of 8, up to 2.4 MPa, without impacting ion transport. Changes in conductivity due to crosslink density and crosslinker length are fully explained in terms of Tg shifts, while comonomer length cannot be accounted for by such a shift. The best performing network exhibited 10−5 S/cm at high temperature, which is comparable to other single‐ion conductors reported in the literature, while the modulus is higher due to crosslinking. Adding 10 wt% propylene carbonate further increased this value to 10−4 S/cm. This work provides insights into the structure–property relationships of solid‐state polymer electrolytes, which retain conductivity but can potentially help suppress dendrites.

Block Copolymer Electrolytes with Excellent Properties in a Wide Temperature Range

A series of block copolymers (BCPs) with a polynorbornene backbone containing short poly(ethylene oxide) (PEO) side chains and rigid side chains were synthesized by tandem ring-opening metathesis p...

The Effect of Oligo(Ethylene Oxide) Side Chains: A Strategy to Improve Contrast and Switching Speed in Electrochromic Polymers.

Solution-processable electrochromic polymers (ECPs) with high performance are urgently needed for extensive applications. Nevertheless, they suffer from slow switching speed because of low ionic conductivities. Herein, we present an effective strategy to improve the contrast and switching speed in ECPs via facile side-chain engineering. A novel electrochromic thieno[3,2-b]thiophene-based polymer (PmOTTBTD) is designed and successfully synthesized by introducing oligo(ethylene oxide) side chains with high ionic conductivity. Compared to the counterpart POTTBTD without modification by oligo(ethylene oxide) chains, PmOTTBTD demonstrates nearly double contrast (42 % vs. 24 %) with a fast oxidation switching process that just takes half of the time when detected under 400 nm, as well as much higher coloration efficiencies (e. g. 239.04 cm2 C-1 vs. 226.26 cm2 C-1 @ 400 nm and 314.04 cm2 C-1 vs. 174.00 cm2 C-1 @ 650∼700 nm). Besides, PmOTTBTD exhibits excellent stability with negligible decay after 3000 cycles. Our work suggests a facile strategy that could be adopted to realize high-performance ECPs via molecular design tuning.

Influence of Addition of Polycarboxylate-Based Superplasticizer on Properties of High Performance Concrete

Nowadays, polycarboxylate-based (PCA) superplasticizer (SP) has become the basic ingredient to prepare high-performance concrete (HPC). PCA SP with carboxylic sulfonic groups and long poly (ethylene oxide) side chain was prepared. The behaviors and economies of PCA SP-blended concrete were investigated. Inclusion of PCA SP improves the initial fluidity and fluidity preservation of concrete. Utilizing PCA SP increased the air content and bleeding water rate and prolonged the setting times of concrete, which have a negative effect on the early-age properties of concrete. At the early curing age (7 days), concrete mixtures with 0.20% and 0.24% PCA SP have the slightly lower mechanical properties and higher water porosity than control concrete. Beyond a certain amount of PCA SP (0.24%), a large reduction in the mechanical properties and a rapid increase in the water porosity can be found in concrete. The introduction of PCA SP to concrete lowers the resistance of concrete against chloride ion penetration and increases the total material costs. The prolonged curing period is an effective method to improve the long-term properties of PCA SP series concrete. Based on the consideration from the early-age properties and the economies of concrete, at the given fluidity, an optimum amount of PCA SP must be chosen in the production of concrete.

Poly(p-phenylene)s tethered with oligo(ethylene oxide): synthesis by Yamamoto polymerization and properties as solid polymer electrolytes

Salt-containing rigid-rod polyphenylenes tethered with ethylene oxide side chains form mechanically and thermally stable “molecular composite electrolytes” reaching high conductivity.

Molecular Brush with Dense PEG Side Chains: Design of a Well-Defined Polymer Electrolyte for Lithium-Ion Batteries

Herein, we designed a series of well-defined bottlebrush-like macromolecules with short and densely grafted poly(ethylene oxide) (PEO) side chains through several controlled radical polymerization ...