Dielectric polymers are the materials of choice for high energy density film capacitors. The increasing demand for advanced electrical systems requires dielectric polymers to operate efficiently under extreme conditions, especially at elevated temperatures. However, the low permittivity and relatively low operating temperature of dielectric polymers limit the high-temperature capacitive energy storage applications. Fortunately, dipolar glass polymers are demonstrated as the preferred materials to achieve high dielectric constant, low dielectric loss and high energy density at elevated temperatures. In this review, we critically elaborate on the recent progress of dipolar glass polymers based on orientational polarization from molecular engineering. In addition, the general design considerations and various dipole moment entities of dipolar glass polymers are described in detail. High dipolar moment, high dipole density and rotation freedom of dipoles are essential for dipolar glass polymers to gain superior dielectric and energy storage properties. Challenges and future opportunities for dipolar glass polymers towards high-temperature energy storage applications are also provided.

With the rapid development of internet of things, self-powered touch sensors made of piezoelectric fluorinated polymers have attracted significant interest because they can constantly convert mechanical energy into electrical energy without external power supply. However, it is still challenging to fabricate fluorinated polymer films with good adhesion and high output performance with a large-scale and low-cost method while maintaining high transparency, which are extremely important for simultaneous optical detection and electromechanical transduction. In this work, we demonstrate that the incorporation of a molecular ferroelectric-dabcoHReO₄ (DH) into poly(vinylidene difluoride) (PVDF) solution enables high-throughput and low-temperature processing of flexible and transparent piezoelectric films by scalable processing method. The effects of multiaxial DH are multiple. First, DH can trigger the phase transition of PVDF from α- to β-phase and realize the orderly orientation of PVDF, which guarantees higher piezoelectric performance without any additional electrical poling process. Second, the hydrophilic nature of DH can improve the adhesion properties of PVDF, which in turn improve the stability and durability of the devices. By optimizing the fabrication processes, the transmittance of the piezoelectric touch sensors based on PVDF films and Ag nanowires coated poly(ethylene terephthalate) electrodes can be higher than 94%. The piezoelectric voltage constant g₃₃ of the transparent films can reach to 1.2 V·m·N⁻¹, which is at least three times higher than the commercially available PVDF films obtained by stretching. These results indicate that the flexible piezoelectric sensors have potential applications in transparent electronic devices for mechanical sensing and energy harvesting.

Polymeric membranes with the integration of various functional performances toward wastewater treatment are urgently required. However, most of the polymeric membranes only exhibit a single function of highly efficiently removing one kind of pollutants. In this work, a biomimetic modification method was introduced to tailor the chemical and topological structure of the porous poly(vinylidene fluoride) (PVDF) fibers prepared by electrospinning. The polydopamine (PDA) nanoparticles were homogeneously introduced onto the surface of PVDF porous fibers via precisely tailoring the concentration of dopamine, which endowed the fibers with more polar groups and bigger roughness but did not destroy the crystalline structures. The fibrous membranes exhibited switchable superhydrophilicity and superlipophilicity characteristics, excellent adsorption abilities toward organic dyes, heavy metal ions and oils. The highest adsorption capacities achieved 917.4 mg/g toward methylene blue (MB), 42.6 mg/g toward Cr(VI) and 74.6 g/g toward silicone oil, respectively. Specifically, the membrane could rapidly remove the trace MB when water flowed through the membrane. The membrane also exhibited excellent sterilization performances, and the bacterial eliminating rate achieved 99.9% for the E. coli and S. aureus. The excellent light-to-heat conversion ability endowed the membrane with the self-heating ability, furtherly intensifying the wastewater treatment efficiency. This work confirms that the PDA nanoparticles-decorated PVDF porous fibers might be the new generation adsorbents used in wastewater treatment.

A series of multiblock sulfonated poly(arylene ether sulfone)s (SPAES) with various block lengths and predictable ion exchange capacity were synthesized from 4,4’-difluorodiphenyl sulfone, 4,4’-dihydrodiphenyl sulfone and 4,4’-biphenol by one-pot and two-pot polymerization. ¹H-NMR and FTIR spectra confirmed the structure that sulfonic acid groups were introduced precisely on the poly(arylene ether sulfone)s by post-sulfonation which resulted in controllable sulfonation degree. The proton exchange membranes (PEMs)-based SPAES displayed excellent dimensional, thermal, antioxidant stability, proton conductivity and mechanical properties (maximum tensile stress >35 MPa). Thermogravimetric analysis indicated the prepared SPAES began to degrade above 310 °C. The effects of polymerization processes, those were, one-pot hydrophobic segment process, one-pot hydrophilic segment process and two-pot process, on the properties of polymers were investigated. The proton conductivity and microphase separation of SPAES PEMs increased in order of those prepared by one-pot hydrophobic segment process, two-pot process and one-pot hydrophilic segment process. The highest conductivities of SPAES synthesized by the above processes under 80 °C and 100% relative humidity were 213 (MS4), 297 (MB3) and 360 mS·cm ⁻¹ (MQ2), respectively.

In this work, a series of high strength, thermal stable and antioxidant proton exchange membranes were designed with solution processible polybenzimidazole (PBI) as the matrix and perfluorosulfonic acid (PFSA) as the fortifier for proton exchange. Solution processible PBI was successfully synthesized by introducing 4,4’-dicarboxydiphenyl ether into the molecular chains of PBI. PFSA/PBI composite membranes were obtained by solution blending and film casting. PBI and PFSA/PBI composite membranes exhibited greatly enhanced tensile strength and Young’s modulus compared to PFSA. PFSA/PBI composite membranes are stable below 300 °C which are suitable for practical application in proton exchange membrane fuel cells. The PFSA/PBI composite membranes show good dimensional stability with low water uptake and swelling rate. The PFSA/PBI composite membranes also exhibit excellent antioxidation stability with less than 5% initial mass loss over 120 h in Fenton reagent. The proton conductivity of PBI is greatly enhanced by blending with PFSA and the proton conductivities of the composite membranes are increased with the raise of PFSA content and temperature. This work offers valuable insights into the exploration of PBI based high-performance proton exchange membranes.

Aerogels are special porous materials with low thermal conductivity, light weight, high energy absorption rate and large surface area, which have been applied in many fields. However, controlling the aerogel microstructure remains an academic challenge. Herein, by employing graphene oxide (GO) as the aerogel skeleton and utilizing poly(vinyl alcohol) (PVA) to regulate the ice crystal growth, we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method. We demonstrate that due to the hydrogen bond formed between PVA and water molecules, resulting in the initial crystallization temperature being reduced from −12.60 °C (GO/PVA-0.01) to −16.21 °C (GO/PVA-0.1). Meanwhile, the strong hydrogen bond between PVA and GO limits the diffusion of water molecules, thereby inhibiting the growth of ice crystals, decreasing the pore size of the GO/PVA aerogel from 9.96 nm (GO/PVA-0.01) to 7.19 nm (GO/PVA-0.3), and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13 MPa. Overall, the finding of this study can be extended to other aerogel precursors, and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.

The recent development of flexible display technology raised additional requirements for optical and electric properties of polyimides, accelerating the structure and property tunning of transparent polyimides. The unique electronic effect and steric hindrance effect of fluorine substitutions make fluorine-containing polyimides occupy an important position in the transparent polyimide family. In this work, a series of transparent aromatic polyimides were prepared from a fixed 4,4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and biphenyl diamines with different substitute groups at the 2,2’,6,6’-positions. We systematically studied the effects of pendant groups on the thermal, mechanical, optical and dielectric properties of these 6FDA-based polyimides with the aid of density function theory (DFT) calculation. In particular, we paid special attention to the simple but compact fluoro group substitution. The simple fluoro substitution brought the advantages of maintaining the linearity of the backbone and dense polymer chain packing, which would minimize the weakening of polyimides’ inherent thermal, dimensional and mechanical properties. Comparing with trifluoromethyl substituted polyimides with the best optical transparency, polyimides containing fluoro substitutes exhibited slightly decreased optical transparency, but increased thermal and dimensional stability and higher mechanical strength. These results could shed light on the ultimate transparent polyimide film development toward the application in extreme working condition, e.g., the colorless polyimide substrate film for the flexible display technology.

Antistatic and strength properties are of vital importance for polyurethane rubber used in moving parts of many industrial instruments. Herein, polyurethane was composited with polyaniline and nanosilica based on in situ synthesis of polymer and physical mixing of these fillers to reach desired antistatic and mechanical properties. Chemical, morphological and thermal properties of the polyurethane/polyaniline/nanosilica composites were studied. The electrical resistivity of the composite decreased from 1.1×10⁶ MΩ to 7.6×10⁴ MΩ as a result of the addition of 4% polyaniline. The tensile strength and elongation at break of the polyurethane composites improved by nearly 300% and 100%, respectively, when compared with those of the neat polyurethane. The electronic resistance of PU/PANI/NS ternary is low enough for its antistatic property and decreases with the increase of the added nanosilica, which is unexpectedly and rather significant. Our results would shed light on the development of antistatic PU with excellent mechanical performance.

Piezoelectric poly(vinylidene fluoride) (PVDF) has received considerable attention due to its ability of interconverting mechanical into electric energies and potential applications in wearable electronics. To achieve piezoelectricity, it is important to simultaneously control the formation of polar phases, crystallinity, and dipole alignments in PVDF-based films. Here we demonstrate that piezoelectricity can be obtained by directly hot-pressing PVDF films sandwiched between chitosan or cellulose films. The electrostatic interactions between PVDF and chitosan or cellulose enabled an exceptional high content of polar phases (β- and γ-phases) up to 90% and a measured piezoelectric charge coefficient d₃₃ of up to −30 pC/N. This study provides a simple and low-cost approach for obtaining piezoelectric PVDF films used for sensors, actuators, and energy harvesters.

It has been established that star polymers with a large number of arms display both the conventional chain relaxation and a slower interchain relaxation due to the formation of hard cores, which is called the local structural relaxation. Here, we demonstrate that this unique relaxation property of multi-arm stars leads to unusual rheological behaviors. We study the response of star polymer melts with various arm numbers to start-up shear flow via nonequilibrium molecular dynamics simulation. Our simulation results indicate that the stress-strain response of multi-arm star polymer melts differs from that of star polymers with a small number of arms in both quantitative and qualitative manners. While the multi-arm star polymer melts exhibit an overshoot peak in the stress-strain curve both at relatively small and sufficiently large shear rates, two overshoot peaks appear when the flow strength is comparable to the relaxation time of the star polymers. This double stress overshoot is absent in linear polymers and star polymers with a small number of arms and is evidently related to the presence of the local structural relaxation in star polymers with a large number of arms. We present a detailed analysis of the conformational and dynamical properties of star polymer melts under start-up shear to gain a molecular understanding of their stress response.

Molecules adsorbed or attached on a surface is a quite basic phenomenon in numerous chemical or biological systems. Grafting-onto is considered as a feasible way to achieve it. The grafting reaction is essentially controlled by the diffusion of the molecules, thus it is more likely a physical issue, instead of a chemical issue. Because of the experimental difficulty in measuring the properties of surface-attached molecules (e.g., the polymeric molecules), the surface-bound molecules are often assumed as with the same properties as that of the start feeding ones in solution. This assumption was even used to guide further characterization, while it is proved to be invalid by different quantifying methods. Consequently, an effective prediction for the properties of surface-bound molecules is still lacking. Based on a microscopic level and a dynamic perspective, the grafting process onto a flat substrate with polydisperse feeding polymeric molecules is investigated in-depth by coarse-grained Brownian dynamics simulation as well as model analysis. We find from simulations that for the final grafting density σ_g and the mean chain length of start feeding molecules < N₀>, the dependence ofσ_g-<N₀>^γ with the constant exponential factor γ may be a determined rule for one-end functionalized flexible linear polymer chains grafting on the flat substrate. Since grafting-onto is a multiple interplayed process, our simulation study indicates that there is an optimized initial concentration of start feeding molecules for achieving high grafting density of surface-bound polymers. We also propose a correctional equation to quantitatively predict the molecular weight distribution (MWD) of surface-bound polymeric molecules, which may be effective for predicting the MWD of the surface-bound ones in specific conditions. This simulation study helps to better understand the kinetics of grafting-onto process, and serves as a theoretical guide to achieve the precise design of surface modification materials via grafting-onto strategy.

Polymer-solvent interaction is a fundamentally important concept routinely described by the Flory-Huggins interaction (χ), Hildebrand solubility (Δδ) and the relative energy difference (RED) determined from Hansen solubility in experimental, theoretical and simulation studies. Here we performed a machine learning study based on a comprehensive and representative dataset covering the interaction pairs from 81 polymers and 1221 solvents. The regression models provide the coefficients of determination in the range of 0.86−0.94 and the classification models deliver the area under the receiver operating characteristic curve (AUCs) better than 0.93. These models were integrated into a newly developed software polySML-PSI. Important features including LogP, molar volume and dipole are identified, and their non-linear, non-monotonic contributions to polymer-solvent interactions are presented. The widely known “like-dissolve-like” rule and two broadly used empirical equations to estimate χ as a function of temperature or Hansen solubility are also evaluated, and the polymer-specified constants are presented. This study provides a quantitative reference and a tool to understand and utilize the concept of polymer-solvent interactions.