Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

Rational strategies combining computational and experimental procedures accelerate the process of designing and predicting properties of new materials for a specific application. Here, a systematic study is presented on polythioureas for high energy density capacitor applications combining a newly developed modelling strategy with synthesis and processing. Synthesis was guided by implementation of a high throughput hierarchical modelling with combinatorial exploration and successive screening, followed by an evolutionary structure search based on density functional theory (DFT). Crystalline structures of polymer films were found to be in agreement with DFT predicted results. Dielectric constants of $4.5 and energy densities of $10 J cm À3 were achieved in accordance with Weibull characteristic breakdown fields of $700 MV m À1 . The variation of polymer backbone using aromatic, aliphatic and oligoether segments allowed for tuning dielectric properties through introduction of additional permanent dipoles, conjugation, and better control of morphology.

Poly(4‐methyl‐1‐pentene) (P4MP) was characterized to evaluate its viability as a high‐temperature dielectric film for capacitors. Detailed investigation of thermal, mechanical, rheological, and dielectric properties was carried out to assess its high‐temperature performance and processability. P4MP was melt‐processable below 270 °C without degradation and application temperatures as high as 160–190 °C can be achieved. The dielectric constant and loss of melt‐processed P4MP films was comparable to biaxially oriented polypropylene (BOPP) capacitor films, although the dielectric strength was lower. Enhancements in dielectric strength up to 250–300% were achieved via solution‐processing P4MP films, which could be easily scaled up on a roll‐to‐roll platform to yield isotropic, free‐standing films as thin as 3–5 μm. The influence of crystal structure, crystallinity, and surface morphology of these films on the dielectric properties was examined. The dielectric strength was further increased by 450% through biaxial stretching of solution‐cast films, and a Weibull breakdown field of 514 V/μm was obtained. The dielectric constant was very stable as a function of frequency and temperature and the dielectric loss was restricted to <1–2%. Overall, these results suggest that BOP4MP is a promising candidate to obtain similar energy density as a BOPP capacitor film but at much higher operating temperatures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1497–1515

Real-time uniaxial strain-induced birefringence in loosely crosslinked double-network (DN) hydrogels synthesized from acrylamide (AAm) and N,N-dimethyl(acrylamide) (DMA) was measured. Tensile tests were performed at different extension rates from quasi-static conditions to very rapid tests followed by a holding for relaxation. Both DN hydrogels exhibit negative birefringence whose absolute value increased with extension and remained constant during relaxation. DN hydrogel synthesized from AAm displayed a linear stress optical (birefringencetrue stress) behavior, however, a nonlinear trend was observed for the DN gel synthesized from DMA. A simple photoelastic model was developed based on the mechanical behavior of the gels using Fung elastic potential and Brewster's stress-optical law, and the model was compared with the experimental data.