There is a need for polymeric capacitors with improved energy storage density and thermal stability. In this work, the effect of polymer molecular structure and symmetry on T-g, breakdown strength, and relative permittivity were investigated. A systematic series of four amorphous poly(arylene ether ketone)s were compared. Two of the polymers had symmetric bisphenols while the remaining two had asymmetric bisphenols. Two contained trifluoromethyl groups while the other two had methyl groups. The symmetric polymers had T-g's of approximately 160 degrees C while the asymmetric polymers showed higher T-g's near 180 degrees C. The symmetric polymers had breakdown strengths near 380 kV/mm at 150 degrees C. The asymmetric counterparts had breakdown strengths near 520 kV/mm even at 175 degrees C, with the fluorinated polymers performing slightly better in both cases. The non-fluorinated polymers had higher relative permittivities than the fluorinated materials, with the asymmetric polymers being better in both cases. (C) 2015 Elsevier Ltd. All rights reserved.