Dendrimer Approach toward High Permittivity Polymer Dielectrics for Electrical Energy Storage

Polymers which display high dielectric permittivity (DP) and low dissipation factor (DF) are important in the area of energy storage using film capacitors. Unfortunately, most polymers, even polar, exhibit fairly low DP, 2-4. It has been shown in this study that well dried films prepared from second generation dendrimer (D2) (T_g ~ 50^oC) synthesized using 2,2-bis(hydroxymethyl)propionic acid monomer (bis-MPA) demonstrate at room temperature a fairly high DP = 10.5 and low DF = 0.014 in the kHz range of frequencies. The dipole relaxation mechanism, which contributes to this unusual dielectric response was found to be linked to numerous hydroxyl groups situated in the periphery of dendrimer molecules. WAXS and computer molecular dynamics (MD) simulation all indicated that these highly mobile hydroxyl groups in bis-MPA D2 glassy films exhibit a very high level of dipole-dipole (OH-OH) correlation mediated by H-bonding. In fact, terminal hydroxyls readily form H-bonded ‘chain-like’ clusters of different lengths which can range from single H-bond associations to clusters containing tens of hydroxyls. This behavior explains why D2 exhibits a high dielectric constant.