Rational Design and Modification of High-k Bis(double-stranded) Block Copolymer for High Electrical Energy Storage Capability

High dielectric constant (high-k) polymers have important application in advanced electronic devices such as energy storage, wearable electronics, artificial muscles, and electrocaloric cooling because of their excellent flexibility and ease of processing. However, most of the commercially available polymers have low-k values and the designed strategies for enhancing k are usually at the cost of the increase of dielectric loss. In this work, novel high-k and low loss bis(double-stranded) block copolymers, containing the ionic-conjugated hybrid conductive segments (HCS) with narrow band gap and the insulating segments with wide band gap, were synthesized by tandem metathesis polymerizations. The novel copolymers exhibited enhanced dielectric constant of 33-28 accompanied by low dielectric loss of 0.055-0.02 at 10²-10⁶ Hz, and thus greatly increased stored energy density of 9.95 J cm^-3 was achieved at relatively low electric field of 370 MV m^-1, which is significantly higher than that of the commercial biaxially oriented polypropylene (BOPP) (about 1.6 J cm^-3 at 400 MV m^-1). In addition, by doping with I₂, the k values of the HCS-contained block copolymer can increase further to 36.5-29 with low dielectric loss of 0.058-0.026, and the stored energy density maintained at a high level of 8.99 J cm^-3 at 300 MV m^-1 with suitable I₂ content. The excellent dielectric and energy storage capability were attributed to the unique macromolecular structure and well-defined nanomorphology, which not only enhanced the dipolar, electronic, and interfacial polarizations but also significantly suppressed the leakage current and increased the breakdown strength by wrapping the narrow band gap segments in the wide band gap segments.