RESUMO
A dielectric polymer with high energy density is in high demand in modern electric and electronic systems. The current polymer dielectrics are facing the tradeoff between high energy density and low energy loss. Although many efforts have been devoted to solving the problem by modifying biaxially oriented polypropylene (BOPP), poly(vinylidene fluoride) (PVDF) and glassy polymers, limited success has been achieved. In the present work, we disperse the high polar nitrile units in a low polar polystyrene (PSt) matrix to avoid the strong coupling force among the adjacent polar groups and reduce the relaxation-induced high dielectric loss. In addition, the possible charge transportation offered by phenyl groups could be blocked by the enlarged bandgap. Notably, the induced polarization is established between the nitrile and phenyl groups, which may lead to the copolymer chain being more densely packed. As a result, excellent energy storage performances, including the high energy density and low loss, are achieved in the resultant poly(styrene-co-acrylonitrile) (AS). For instance, AS-4 exhibits a Ue of 11.4 J cm-3 and η of 91% at ambient temperature and 550 MV m-1. Manipulating the dipole polarization in the low polar glassy polymer matrix is verified to be a facile strategy for the design of a high-energy storage dielectric polymer.
RESUMO
Polymer dielectrics with high energy density can be realized in high-k polymers, but undesirable energy loss always occurs, especially at high electric field and elevated temperature application. By systematically comparing the dielectric and energy storage properties of poly(styrene-methyl methacrylate)s (P(St-MMA)s) with PSt and PMMA homopolymers, the positive roles of the MMA units in the improvement of their dielectric and energy storage properties are well addressed. The best electric performance, including the largest Ue of 12.2 J cm-3, η of 92%, and Eb of 530 MV m-1 at ambient temperature, was obtained in the copolymer bearing 45 mol% MMA. Considering the different types of dipoles and the generated intermolecular forces, the influence of MMA on the dielectric performances of the copolymers is well illustrated. Instead of permanent dipoles alone, the combination of isolated permanent dipoles together with induced dipoles may be promising for realizing high-k, high energy density and low loss. This conclusion helps to understand the dielectric performances of polymer dielectrics from an intermolecular force point of view and proposes a strategy for realizing high energy density but low loss under a high electric field in polymer dielectrics.
