Polymers which display high dielectric permittivity (DP) and low dissipation factor (DF) are important in the area of energy storage using film capacitors. Polarization based on dipole orientation is the main mechanism defining dielectric constant in this case. 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<sub>g</sub> ~ 50<sup>o</sup>C) 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. For comparison, often used for electronic applications high dielectric constant ferroelectric polyvinylidene fluoride (PVDF) films in similar frequency range exhibit comparable dielectric constant, e = 9.2, but much greater DF= 0.071. A question was posed in regards to the dipole relaxation mechanism responsible for this unusual dielectric response in D2 dendrimer. The dipole relaxation mechanism which constitutes the so called g - relaxation in the dendrimer films was 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.

Dendrimer approach toward high permittivity polymer dielectrics for electrical energy storage

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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