Polymer Segments Research Articles

Li‐Ion Transfer Mechanism of Ambient‐Temperature Solid Polymer Electrolyte toward Lithium Metal Battery

AbstractThe low ionic conductivity and short service life of solid polymer electrolytes (SPEs) limit the application of ambient‐temperature polymer lithium metal batteries, which is perhaps a result of the inherent restricted segment movement of the polymer at room temperature. Herein, an ambient‐temperature dual‐layer solid polymer electrolyte is developed and the related working mechanisms are innovatively investigated. In the strategy, poly(propylene carbonate) (PPC)/succinonitrile (SN) contacts with the cathode while polyethylene oxide (PEO)/Li7La3Zr2O12 is adopted near the anode. Molecular dynamics simulations demonstrate the formation of solvated sheath‐like structure [SN···Li+], which demonstrates strong interaction with polymers (PPC···[SN···Li+]/PEO···[SN···Li+]). Further density functional theory calculations show that these structures, allow rapid transport of Li ions through polymer segments. These results are confirmed with Fourier transform infrared spectroscopy and nuclear magnetic resonance. Therefore, the Li‐ion transport mechanism for ambient‐temperature SPEs can be reasonably revealed. Remarkably, the binding energy between PPC and SN is stronger than that of PEO, which helps avoid the parasitic reaction between SN and Li. A low overpotential of 55 mV is exhibited for Li/Li symmetrical cells after 1000 h. Notably, a capacity retention of 86.3% is maintained for LiNi0.6Co0.2Mn0.2O2/Li cell at 25 °C, implying good application potential in ambient‐temperature high voltage lithium metal batteries.

Synthesis of colorless polyimides with high Tg and low coefficient of thermal expansion from benzimidazole diamine containing biamide

AbstractColorless polyimides (CPIs) with superheat resistance and low coefficient of thermal expansion (CTE) are required urgently to employ as plastic substrates in flexible‐display devices. To attain the target properties, 2‐(2‐methyl‐4‐(4‐aminobenzamido)phenyl)‐5‐(4‐aminobenzamido)‐N‐phenylbenzimidazol (AB‐MPBZ) that contains biamide was synthesized, and its homo‐ and co‐polyimides were prepared with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (HPMDA) and cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA). The crank‐shaft‐like amide groups effectively increases the linearity and stiffness of polymer segments, providing CPI films with low CTE. On the basis, the CBDA based poly(benzimidazole imide) (PBII) series with dense interchain packing exhibits further reduced CTE down to 22 ppm K−1 and increased glass‐transition temperature (Tg) up to 404 °C. Such good thermal properties indicate that the resultant copolyimides have potential applications as colorless flexible substrates. These provide a feasible approach to balance thermal and optical performance of polyimides.

Short-chain fatty acid-releasing nano-prodrugs for attenuating growth and metastasis of melanoma.

Low-molecular-weight (LMW) short-chain fatty acids (SCFAs), such as propionic and butyric acids, have been reported to possess anti-neoplastic effects; however, rapid renal clearance and high dose-based side effects limit their clinical translation. Hence, in this study, we have designed a new self-assembling nano-prodrugs that can effectively supply SCFAs: endogenous enzyme-metabolizable block copolymer poly(ethylene glycol)block-poly(vinyl ester) possessing several units of SCFAs conjugated as side chains via ester linkages. These amphiphilic polymers spontaneously self-assemble into nanostructures under aqueous conditions to form orally administrable nano-prodrugs (butyric acid: NanoBA and propionic acid: NanoPA). Herein, we show the therapeutic efficacy of SCFA nanoparticles (NanoSCFA) in a mouse model of metastasis (melanoma). Ad libitum intake of our NanoSCFA markedly demonstrated a decrease in the metastatic tumor nodules in the lungs compared with the effect observed after LMW SCFA administration with no discernible toxicity to the GI tract. In contrast, LMW SCFAs, even at a lower concentration than that of the NanoSCFA, facilitated villus atrophy. Taken together, our work suggests that the use of NanoSCFA as a therapeutic intervention for metastatic cancer is preferable over typical LMW SCFAs. STATEMENT OF SIGNIFICANCE: Low-molecular-weight (LMW) short-chain fatty acids (SCFAs) have shown versatile therapeutic effects on various diseases, including anti-tumorigenesis effects. However, their clinical translation is limited due to their poor pharmacokinetic profile and adverse effects. To overcome these limitations, we have developed new amphiphilic block copolymer-based SCFA-prodrugs, which self-assemble into nanoparticles in aqueous media (NanoSCFA). SCFAs are covalently conjugated to the hydrophobic polymer segment via ester linkage, which can be enzymatically metabolized after oral administration. In the present study, we confirmed that ad libitum intake of NanoSCFAs retarded the growth and metastatic potential of B16-F10 tumors compared to the LMW SCFAs with negligible discernible toxicity, reflecting NanoSCFA as a preferable therapeutic intervention to LMW SCFA counterparts.

Correlations in Hard- and Soft-Core Generic Polymer Models

Generic polymer models capturing the chain connectivity and the non-bonded excluded-volume interactions between polymer segments can be classified into hard- and soft-core models depending on their non-bonded pair potential. Here we compared the correlation effects on the structural and thermodynamic properties of the hard- and soft-core models given by the polymer reference interaction site model (PRISM) theory, and found different behaviors of the soft-core models at large invariant degree of polymerization (IDP) depending on how IDP is varied. We also proposed an efficient numerical approach, which enables us to accurately solve the PRISM theory for chain lengths as large as 106.

Synthesis of an all-carbon conjugated polymeric segment of carbon nanotubes and its application for lithium-ion batteries

Synthesis of an all-carbon conjugated polymeric segment of carbon nanotubes and its application for lithium-ion batteries

Counterion Control and the Spectral Signatures of Polarons, Coupled Polarons, and Bipolarons in Doped P3HT Films

AbstractWhen an electron is removed from a conjugated polymer, such as poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), the remaining hole and associated change in the polymer backbone structure from aromatic to quinoidal are referred to as a polaron. Bipolarons are created by removing the unpaired electron from an already‐oxidized polymer segment. In electrochemically‐doped P3HT films, polarons, and bipolarons are readily observed, but in chemically‐doped P3HT films, bipolarons rarely form. This is explained by studying the effects of counterion position on the formation of polarons, strongly coupled polarons, and bipolarons using both spectroscopic and X‐ray diffraction experiments and time‐dependent density functional theory calculations. The counterion positions control whether two polarons spin‐pair to form a bipolaron or whether they strongly couple without spin‐pairing are found. When two counterions lie close to the same polymer segment, bipolarons can form, with an absorption spectrum that is blueshifted from that of a single polaron. Otherwise, polarons at high concentrations do not spin‐pair, but instead J‐couple, leading to a redshifted absorption spectrum. The counterion location needed for bipolaron formation is accompanied by a loss of polymer crystallinity. These results explain the observed formation order of single polarons, coupled single polarons, and singlet bipolarons in electrochemically‐ and chemically‐doped conjugated polymers.

Development of Pneumatic Artificial Rubber Muscle Using Segmented Shape-Memory Polymer Sheets

We have developed a pneumatic artificial rubber muscle using two shape-memory polymer (SMP) sheets. We attached the SMP sheets to a linear pneumatic artificial rubber muscle. Utilizing the large difference in the elastic modulus below and above the glass transition temperature, the shape fixity and shape recovery of SMPs, the bending direction and the initial shape can be changed. In this study, in order to increase the bending motion range, we developed a segmented SMP sheet with embedded electrical heating wires, and evaluated its mechanical properties using bending and tensile tests. Moreover, we attached such sheets to an artificial muscle and evaluated the bending motion. Bending tests showed that segmenting the SMP sheets greatly reduced their bending stiffness. In tensile tests at temperatures below the glass transition temperature, it was found that the artificial muscle with the attached sheet withstood high elongating loads without failure. Attachment of such segmented SMP sheets to an artificial muscle resulted in an increased bending angle. Through isotonic and isometric tests, we showed that the prototype actuator could bend in two directions.

Post‐curing and structural relaxation of epoxy networks during early stages of aging for civil engineering applications

AbstractIn this work, epoxy networks used for civil engineering constructions are aged at ambient temperature, and the impact of the early stages of aging on mechanical properties is analyzed. It is observed that Young's modulus and the yield stress increase with the aging time whereas the strain at break and the toughness decrease. The structural causes for these variations are investigated by swelling experiments, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. By combining experimental results, it is deduced that the aging process occurs in two stages. During the first 7 days of aging, the change in mechanical properties should essentially be attributed to the postcuring, which results in additional crosslinking reactions. When increasing the aging time to 21 days, the crosslinking density reaches a plateau, but a second stage emerges, in which the mechanical properties continue evolving in the same way, with variations of the mechanical parameters being of comparable amplitude. This second stage is attributed to the evolution of the thermodynamic state of the glass, leading to a densification of the epoxy network through minimization of the free volume, and favoring the creation of physical interactions between polymer segments. Therefore, structural relaxation is shown to have a significant impact on the mechanical properties.

Modelling strategy for tailorable mechanics and thermochemically driven shape memory effect in amorphous polymers

Thermochemically responsive shape-memory polymers (SMPs) with biocompatibility and variable stiffness have shown great potential in biomedical applications. However, it is difficult to characterize the relaxation behavior and visco-elastoplastic deformation of this kind of SMPs due to the complex interactions between polymer segments and solvent molecules. Herein, a thermo-chemo-mechanical coupling model was proposed to predict the shape-memory behavior and thermomechanical properties of SMPs at different solvent volume fractions and temperatures. By combining the Vrentas–Duta free volume theory and the Flory-Huggins theory, the effect of free volume change on the Gibbs free energy, chemical potential, thermal expansion coefficient, and relaxation time of SMPs was investigated. Subsequently, these functions were substituted into the Maxwell and Boyce models to characterize the visco-elastoplastic mechanical behavior of thermochemically responsive SMPs under large deformation. Based on the phase transition model, the chemical plasticizing effect of solvent molecules on the glass transition temperature, shape-recovery strain, and yield strength of SMPs was further investigated. The numerical results are in good agreement with the experimental results. The proposed model is expected to provide theoretical guidance for designing SMPs with tailorable mechanics.

Diffusion kinetics of vitamin B6 from phase-separated gelatin and agarose gels using blending law modelling

This study was conducted to understand the diffusion kinetics of vitamin B6 from composite gels of gelatin and agarose via blending law and diffusion modelling. Fourier-transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), confocal laser scanning microscopy (CLSM) and small-deformation dynamic oscillation in shear were used to analyse the structural properties of the composite gels. UV–vis spectroscopy was employed to study the diffusion kinetics of vitamin B6 from the gelatin-agarose gels. FTIR confirmed the absence of chemical interactions between gelatin and agarose in the mixture. XRD demonstrated that vitamin B6 was thoroughly hydrated in the polymeric mixture that balanced disordered polymer segments with structured junction zones. CLSM provided tangible evidence of the phase-separated nature of the two macromolecules, and blending law predicted the phase volume and their effective concentrations in the system. The diffusion of vitamin B6 from composite gels, prepared with estimated phase volumes and effective concentrations of the individual components according to rheological blending law, was measured with UV–vis spectroscopy. As far as we are aware, for the first time, rheological blending law was recast to provide the corresponding blending law for diffusion. Thus, theoretical diffusion coefficients were calculated and compared favourably with those from the experimental studies. Results argue for the presence of a blending law-based diffusion theory that can predict the diffusion kinetics of bioactive compounds in aqueous composite gels.

Solution characterization of a hyperbranched polysaccharide carbamate derivative and specific phase separation behavior due to chain branching.

A hyperbranched polymer consisting of rigid helical part chains was prepared as highly branched cyclic dextrin tris(phenylcarbamate) (HTPC) with the weight-average molar masses of 880 and 590 kg mol-1. Small-angle X-ray scattering (SAXS) measurement and viscometry were performed on the samples in good and poor solvents to determine the dimensional and hydrodynamic properties in solution. The HTPC molecule has a much more compact conformation than the linear chain with the same molar mass as expected for the hyperbranched architecture. While the corresponding linear polymer is soluble in methyl acetate (MEA) over a wide temperature range, HTPC is only soluble in the solvent at low temperatures. A typical LCST-type phase diagram was observed for the HTPC-MEA system, indicating that the interactions between the polymer segment of HTPC and the MEA molecules are substantially different from those of the linear chains. This is most likely due to the bending helical chains near the branching point of HTPC having different interactions with solvent molecules.

Probing the inner local density of complex macromolecules by pyrene excimer formation.

The direct relationship existing between the average rate constant 〈k〉 for pyrene excimer formation and the local concentration [Py]loc of ground-state pyrenyl labels covalently attached to a macromolecule was established for 55 pyrene-labeled macromolecules (PyLM). These PyLM belonged to three different families of macromolecules with the first representing short monodisperse linear chains end-labeled with pyrene (polystyrene, poly(ethylene oxide), and poly(N-isopropyl acrylamide)), the second representing long polydisperse linear chains randomly labeled with pyrene (poly(methyl acrylate), poly(methyl methacrylate), polystyrene, poly(butyl methacrylate), poly(methoxyethyl methacrylate), and poly(N-isopropyl acrylamide)), and the third being comprised of two series of pyrene end-labeled low generation dendrimers with a bis(hydroxymethyl)propionic acid or a polyamidoamine backbone. The assumption, that the polymeric segments probed by an excited pyrenyl label covalently attached to one of these macromolecules obeyed Gaussian statistics, enabled the calculation of their square root average squared end-to-end distance (LPy), which was applied to calculate [Py]loc. The log-log plots of 〈k〉 as a function of [Py]loc yielded straight lines with a slope of unity for all families of macromolecules studied in four different organic solvents demonstrating the validity and generality of the 〈k〉-vs.-[Py]loc relationship. Since an experimentalist knows how the the pyrenyl labels are covalently attached onto a macromolecule, [Py]loc offers a means to probe the local density of a macromolecule, which can be employed to characterize its conformation in solution. Consequently, the 〈k〉-vs.-[Py]loc relationship provides a novel experimental means to probe the conformation of macromolecules which should establish pyrene excimer formation as an appealing method for conformational studies of macromolecules in solution, which should nicely complement scattering techniques.

Hierarchical assembly of foldable polymers and applications in organic optoelectronics and antibacterial or antiviral materials.

Aggregation of amphiphilic polymers in block-selective solvents produces different nanostructures, which have been studied extensively for wide-ranging applications. Nevertheless, such immiscibility-driven aggregation does not endow them with the desired structural precision, predictability or surface functional group exposure, which significantly impact their functional applications. More recently, biomimetic folded structures of synthetic macromolecules (mostly oligomers) have come to the fore, but such studies have been limited to probe the secondary structures. In this article, we have collated hierarchical structures of foldamers, especially highlighting our recent contribution to the field of chain-folding regulated assembly of segmented polyurethanes (PUs) and their functional applications. A series of such PUs have been discussed, which contain a segmented hydrocarbon backbone and alternately placed pendant solvophilic groups. In either water or highly non-polar solvents (TCE, MCH), depending on the nature of the pendant group, they exhibit folded structures stabilized by intra-chain H-bonding. Hierarchical assembly of such folded chains by inter-chain H-bonding and/or π-stacking leads to the formation of well-defined nanostructures with functional applications ranging from organic optoelectronics to biomaterials. For example, a segmented PU with appended naphthalene-diimide (NDI) chromophores showed a pleated structure in MCH, which helped in organization of the NDI chromophores within π-stacking distance. Such folded polymer chains eventually produced nanotubular structures with excellent electron mobility. They also showed efficient intercalation of the pyrene (Py) donor by NDI-Py charge-transfer interaction and in this case the mixed nanotubular structure exhibited prominent room-temperature ferroelectricity. On the other hand, having cationic functionalities as the pendant groups such chain-folding regulated assembly produced unilamellar polymersomes with excellent antibacterial activity with very low minimum inhibitory concentrations (<10 μg mL-1). Replacing the pendant amine functionality with sulphate groups made these polyurethanes highly potent antiviral materials. In the absence of the alternating connectivity of the solvophobic and solvophilic segments or rigid hydrocarbon backbone, such folding propensity is destroyed, leading to structural collapse. While significant efforts have been made in correlating primary structures of wide-ranging polymers with their functional applications, this article demonstrates the direct correlation between the secondary structures of polymers and their functional properties.

Covalent segmented polymer networks composed of poly(2-isopropenyl-2-oxazoline) and selected aliphatic polyesters: designing biocompatible amphiphilic materials containing degradable blocks.

To promote facile and efficient synthesis of segmented covalent networks, we developed a cross-linking process with reactive polymeric components in a system without catalysts or side products. To achieve the direct formation of amphiphilic networks, an addition reaction was performed between the polyesters containing carboxyl terminal groups with pendant groups distributed along poly(2-isopropenyl-2-oxazoline) chains. Covalent cross-linking was achieved from predetermined amounts of components dissolved in DMSO at 140 °C. To tune the properties of the resulting networks, the composition and length of the polyester segments and the degree of cross-linking were changed in the feed. The chemical structure of the networks was characterized using Fourier transform infrared-attenuated total reflection spectroscopy and 13C magic-angle spinning NMR. The swelling ability of the formed networks was investigated in aqueous and organic media. Moreover, mechanical properties were tested during uniaxial compression. The cytocompatibility of the scaffolds was confirmed by MTT assay. Through the results obtained, the first report describing the cross-linking of polyesters on hydrophilic PiPOx was provided to prepare new, biocompatible materials with tuneable properties that are promising for potential biomedical applications.

Fabrication of amphiphilic self-healing coatings with high mechanical properties and their antifouling performance

A self-healing antifouling coating with excellent mechanical strength was prepared via a simple “one-step” method. A series of well-designed amphiphilic block copolymer polydimethylsiloxane-poly(2-(dimethylamino) ethyl methacrylate) (PDMS-PDMAEMA) synthesized by atom transfer radical polymerization was introduced to the self-healing polydimethylsiloxane-based polyurethane (PDMS-PU) system, which was further zwitterionized during solidification. The slight swelling resulting from zwitterionic segments promoted the contact fusion rate of the mechanically damaged parts, which improved the underwater self-healing ability of the resulting coating. The PDMS segments in both amphiphilic polymer and PU were entangled with each other to form a semi-interpenetrating network while the zwitterionic segments migrated externally when being immersed underwater, thus a micro-phase separation structure was obtained for antifouling coating. Qualitative and quantitative tests have also proved that the coating can significantly resist the adhesion of proteins (156 μg/cm2 vs 14 μg/cm2) and marine microorganisms (425 × 103 n/cm2 vs 12 × 103 n/cm2). In addition, the organically modified montmorillonite (MMT) effectively improved the coating's mechanical properties via coordination bonding, as the resulting coating's fracture strength was increased by 50 % compared with the initial PU coating. In this study, an inherent problem in underwater self-healing antifouling coatings is solved perfectly, that is to achieve self-healing properties without loss of mechanical properties, which provides inspiration for the research and development of novel self-healing antifouling coatings.

Directional Ion Transport Enabled by Self‐Luminous Framework for High‐Performance Quasi‐Solid‐State Lithium Metal Batteries

Composite gel polymer electrolyte (CGPE), derived from ceramic fillers has emerged as one of the most promising candidates to improve the safety and cycling stability of lithium metal batteries. However, the poor interface compatibility between the ceramic phase and polymer phase in CGPE severely deteriorates lithium-ion pathways and cell performances. In this work, a fluorescent ceramic nanowire network that can palliate the energy barrier of photoinitiators and contribute to preferential nucleation and growth of polymer monomers is developed, thus inducing polymer segment orderly arrangement and tightly combination. A proof-of-concept study lies on fabrications of poly(ethylene oxide) closely coating on the ceramic nanowires, thus dividing the matrix into mesh units that contribute to directional lithium-ion fluxand dendrite-free deposition on the metallic anode. The CGPE, based on the state-of-the-art self-luminous framework, facilitates high-performance quasi-solid-state Li||LiFePO4 cell, registering a high capacity of 143.3 mAh g-1 after 120 cycles at a mass loading of 12mg cm-2 . X-ray computed tomography provides an insight into the relationship between directional lithium-ion diffusion and lithium deposition behavior over the electrochemical processes. The results open a door to improve the electrochemical performances of composite electrolytes in various applications.

Synthesis and Ring-Opening Metathesis Polymerization of o-Dialkoxy Paracyclophanedienes.

The highly strained ortho-diethylhexyloxy [2.2]paracyclophane-1,9-diene (M1) can be synthesized by ring contraction of a dithia[3.3]paracyclophane using a benzyne-induced Stevens rearrangement. This paracyclophanediene undergoes ring-opening metathesis polymerization to give well-defined 2,3-dialkoxyphenylenevinylene polymers with an alternating cis/trans alkene stereochemistry and controllable molecular weight. Fully conjugated block copolymers with electron-rich and electron-deficient phenylene vinylene polymer segments can be prepared by sequential monomer additions. These polymers can be readily isomerized to the all-trans stereochemistry polymer. The optical and electrochemical properties of these polymers were investigated by theory and experiment.

Effects of Chemical Composition on the Shape Memory Property of Poly(dl-lactide-co-trimethylene carbonate) as Self-Morphing Small-Diameter Vascular Scaffolds.

Smart materials have great potential in many biomedical applications, in which biodegradable shape memory polymers (SMPs) can be used as surgical sutures, implants, and stents. Poly(dl-lactide-co-trimethylene carbonate) (PDLLTC) represents one of the promising SMPs and is widely used in biomedical applications. However, the relationship between its shape memory property and chemical structure has not been fully studied and needs further elaboration. In this work, PDLLTC copolymers in different compositions have been synthesized, and their shape memory properties have been investigated. It has been found that the shape memory property is related to the chemical composition and polymeric chain segments. The copolymer with a DLLA/TMC ratio of 75:25 (PDLLTC7525) has been demonstrated with great shape fixation and recovery ratio at human body temperature. Furthermore, PDLLTC7525-based self-morphing small-diameter vascular scaffolds adhered with inner electrospun aligned gelatin/hyaluronic acid (Gel/HA) nanofibers have been constructed, as a merit of its shape memory property. The scaffolds have been demonstrated to facilitate the proliferation and adhesion of endothelial cells on the inner layer. Therefore, PDLLTC with tailorable shape memory properties represents a promising candidate for the development of SMPs, as well as for small-diameter vascular scaffolds construction.

Isothermal Crystallization of Poly(ε–Caprolactone) PCL in Three‐Armed Copolymers

AbstractBranched copolymers are a special class of polymeric materials in which are reflected the combined effects of polymer segments and architectural constraints of the branched architecture. In this work, three‐armed graft copolymers, poly (hydroxyethyl methacrylate‐graft‐poly(caprolactone), [P(HEMA‐g‐PCL)]3, are synthesized by combination of reversible addition‐fragmentation chain‐transfer (RAFT) and ring opening polymerization (ROP) mechanisms in a one‐pot/one‐step protocol. The resulting macromolecules are characterized by 1H Nuclear Magnetic Resonance (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The preliminary results indicate the success of the methodology and are in agreement with literature reports. In addition, DSC isothermal crystallization are performed, and Avrami's theory is employed in order to obtain kinetics parameters of interest, such as the half‐life for the crystallization process (t1/2), the bulk crystallization constant (k), and the Avrami's exponent (n). Thermal analysis evidences a noticeable reduction in the melting temperature compared with linear PCL homopolymer. However, the presence of branches does not modify the values of the maximum degradation temperatures significantly. Finally, the synthesized copolymers adopt a two‐dimensional crystallization type (disk and cylindrical).

Intrinsically Stretchable Block Copolymer Composed of Polyisobutene and Naphthalenediimide–Bithiophene-Based π-Conjugated Polymer Segments for Field-Effect Transistors

Intrinsically Stretchable Block Copolymer Composed of Polyisobutene and Naphthalenediimide–Bithiophene-Based π-Conjugated Polymer Segments for Field-Effect Transistors