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The dilute nanocomposite strategy facilitates a promising route for high-temperature polymer dielectrics to achieve high dielectric constant and energy density, robust breakdown strength, and low loss. The dielectric enhancement of the dilute nanocomposites strongly ties to the topological conditions of the nanofiller–polymer interface. Here, atomic force microscopy-based infrared spectroscopy was employed to observe the interfacial region of a high-temperature poly(arylene ether urea) (PEEU) dilute nanocomposite directly. The experimental results showed that the nanoparticles induce morphological changes in PEEU, and the interface region extends over 150 nm away from the nanofiller surfaces. Such nano-morphology changes are highly indicative of generating a large enhancement of the dielectric performance in the PEEU dilute nanocomposite. [ABSTRACT FROM AUTHOR]

A convenient method for preparing high molecular weight polyacrylonitrile (PAN)/poly (acrylonitrile- co -methyl acrylate) (P(AN- co -MA)) using a Lewis base (LB)/dimethyl sulfoxide (DMSO) system for controlled anionic polymerization was explored. Nine systems were shown to achieve high conversion and high molecular weight polymerization while maintaining low molecular weight distribution (polydispersity index, PDI = 1.03–1.57). Among them, the 1,8-Diazabicyclo [5,4,0] undec-7-ene (DBU)/DMSO and P(OEt) 3 /DMSO systems, notably, exhibited quasi-living polymerization allowing us to prepare PAN with ultra-high MW (1,110,000 g/mol), with high linearity while maintaining low PDI (1.49). Evidence has been shown that DMSO can interact with monomers, LB catalysts, and propagating chains during polymerization, unlike other aprotic solvents. Such interactions are found to increase the rate of chain initiation, stabilize chain propagation, and prevent chain transfer, branching and chain termination. P(AN- co -MA) was also prepared with this new method resulting in high M w (880,000 g/mol) and better spinnability. Because of the good scalability of this method, it can be applied to other anionic monomers. Thermogravimetry analysis (TGA) shows lower cyclization temperatures and high thermal stability providing promise towards in the development of high-performance carbon fibers. Image 1 • A metal free method to produce UHMW-PAN and P(AN-co-MA) in DMSO has been demonstrated. • UHMW-PAN with the Mw over 1,000,000 g/mol with better thermostability was obtained. • HMW P(AN-co-MA) with the Mw over 880,000 g/mol with good processability was obtained. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric polymers exhibiting a giant electrocaloric effect (ECE) can potentially be used to create next‐generation solid‐state coolers. Under an electric field, poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) terpolymer goes through a large dipolar entropy change producing a high adiabatic temperature change (ΔTECE). This work resolves the molecular origins of the large entropy change behind the electric field‐induced dipole switching. A Fourier transform infrared spectroscopy equipped with a high voltage source is used to operandoly observe the characteristic molecular vibrational modes. A short‐range trans (T) conformation of the CF2‐CH2 dyads interrupted by a gauche (G) conformation, e.g., TTTG in the terpolymer chain, undergoes a dynamic transformation that leads to a corresponding ΔTECE whenever an electric field is applied. The molecular dynamics simulation also proves that the energy barrier that the transformation from TTTGs into a long T sequence overcomes is smaller than that for all other conformations. A mixed solvent system is used to obtain T3G‐enriched terpolymer films exhibiting a 4.02 K ΔTECE at 60 MV m−1 and these films are employed to manufacture a 2‐layer‐cascaded cooling device that achieves a 6.7 K temperature lift, the highest reported value for a 2‐layer cascaded device made of fluoropolymers. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF)‐based polymers demonstrate great potential for applications in flexible and wearable electronics but show low piezoelectric coefficients (e.g., −d33 < 30 pC N−1). The effective improvement for the piezoelectricity of PVDF is achieved by manipulating its semicrystalline structures. However, there is still a debate about which component is the primary contributor to piezoelectricity. Therefore, current methods to improve the piezoelectricity of PVDF can be classified into modulations of the amorphous phase, the crystalline region, and the crystalline–amorphous interface. Here, the basic principles and measurements of piezoelectric coefficients for soft polymers are first discussed. Then, three different categories of structural modulations are reviewed. In each category, the physical understanding and strategies to improve the piezoelectric performance of PVDF are discussed. In particular, the crucial role of the oriented amorphous fraction at the crystalline–amorphous interface in determining the piezoelectricity of PVDF is emphasized. At last, the future development of high performance piezoelectric polymers is outlooked. [ABSTRACT FROM AUTHOR]

To realize advanced electrical applications for ferroelectric liquid crystalline polymers, high spontaneous polarization (Ps) is highly desired. However, current ferroelectric liquid crystalline polymers usually exhibit a low Ps. In this work, mesogen‐free, chiral polyethers containing sulfonylated methyl‐branched alkyl side chains with a (CH2)3O spacer between the sulfonyl and the branched alkyl groups are designed and synthesized. In contrast to the linear n‐alkyl side chains, the methyl‐branched alkyl side chains induce chain tilting in the smectic layers. When double chirality exists in both the main chain and the side chains, a crystalline structure is observed after mechanical stretching. Intriguingly, when single chirality exists in either the backbone or the side chains, a liquid crystalline smectic C phase is obtained. The electric displacement–electric field study, however, does not show typical ferroelectric switching, although the dielectric constants are relatively high for these liquid crystalline polymers. This is likely because the dipole–dipole interactions among neighboring sulfonyl groups along the main chain are so strong that the ferroelectric switching is hindered in the samples. For the future work, it is desired to weaken the dipole–dipole interaction to achieve ferroelectricity in these mesogen‐free liquid crystalline polymers. [ABSTRACT FROM AUTHOR]