The influence of the diamine alkyl chain length on the glass transition (Tg) was evaluated by differential scanning calorimetry (DSC, Fig. ). It revealed that Tg decreases with increasing values of n, from 50.3 °C, to 40.2 °C and 22 °C for n = 6, 8 and 12, respectively, as shown in the inset of Fig. . Though this trend is to be expected, it should be noted that some of these variations may also be attributed to the differences in molecular weight, which also influences the position of Tg. It is worth noting that PHU12 exhibits a melting temperature, Tf =59.1 °C. As it displays both the highest Tg and the highest density of dipolar groups, PHU6 was selected for the rest of the study. The dielectric properties of PHU6 were evaluated by casting capacitors from solutions in DMSO. A permittivity of 8.4 was measured on PHU6 at 1 kHz in the vicinity of room temperature (Fig. ). While it is lower than that of the semi-crystalline fluorinated polymers (εr ~ 50), it is high when compared with other amorphous polymers which typically display εr ~ 2-4. Furthermore, this high permittivity was found to be accompanied with low dielectric losses, with tan δ < 0.03 measured in the same conditions, thus promising stable properties at high electric fields for PHU6, as further confirmed by its breakdown strength (Eb). The two-parameter Weibull distribution analysis of PHU6 revealed a high Eb = 428 MV•m -1 , which is comparable with that measured for fluorinated polymers (270-490 MV•m -1 ). The relatively high shape parameter, β = 5.9, also indicates a narrow breakdown strength distribution, which is be expected to increase performance reliability of the devices made from this EDC-based PHU. The high breakdown field of PHU6 allows for high polarization values to be reached, despite its linear dielectric behaviour, with Pmax = 3.2 µC•cm -2 measured at Eb (Fig. ). This remains low compared to fluorinated polymers, in which P ~ 10 µC•cm -2 can be reached at Eb, even if their permittivity decreases significantly at higher field due to their non-linear behaviour. Nonetheless, the combination of high Eb, linear behaviour and low losses (the area inside the "P-E loop" is minimal) maximises the discharged energy density Ue in PHU6, which corresponds to the highlighted area above the "P-E loop", as shown in the inset of Fig. . Monitoring Ue versus E reveals that Ue is much lower in PHU6 than in fluorinated polymers at low fields (E < 300 MV•m -1 ), as expected from the differences in low-field dielectric permittivity. However, when E reaches the vicinity of Eb, the quadratic dependence in E allows PHU6 to reach an impressive value of Ue > 6 J•cm -3 and thus to catch up with the state-of-theart fluorinated polymers. Due to the low volumetric mass density of PHU6, this corresponds to a specific energy of 2 Wh•kg -1 , which is comparable with the performances recorded in electrochemical capacitors, but with a far greater power density of ~ 10 8 W•kg -1 , assuming a full discharge time, τ = 5RC, through a resistor R = 100 kΩ, with C the capacitance of the polymer-based device. Furthermore, the low dielectric losses in PHU6 induces a highly efficient discharge process, with a remarkably high efficiency, η = 85 %, measured in the bio-based PHU, which is much higher than the efficiencies typically measured in high performance fluorinated polymers, with η < 70 % as shown in Fig. . This remarkable efficiency ranks among the best reported values intrinsically measured on linear dielectrics, including biaxially oriented polypropylene (BOPP) and dipolar glasses (DG). The large discrepancies between reported results on fluorinated polymers, even for similar compositions, with Ue ~ 5-10 J•cm -3 and η = 50-70 % at Eb, are most probably due to the strong influence on the dielectric properties of their structural parameters, especially the crystallinity, which are highly dependent on the casting/annealing conditions. The origin of the dielectric enhancement in PHU6 was elucidated by performing broadband dielectric spectroscopy (BDS) at various temperatures (Fig. ). BDS confirms that the high permittivity of PHU6 near RT is maintained over a broad range of frequencies, with 8 < εr < 10 between 0.1 Hz and 100 kHz (Fig. ). Rising the temperature results in a significant change in permittivity with εr increasing by several orders of magnitude, especially at low frequencies. However, a closer inspection of the dielectric losses (Fig. ) reveals that this jump in εr is accompanied with a massive increase in tan δ. This behaviour is related to the increased mobility of space charges, afforded by the proximity of the glass transition temperature. The maximum in dielectric losses gradually shifts to higher temperatures with increasing frequency. Its attribution to the glass transition is confirmed by the Vogel-Tammann-Fulcher (VTF) dependency of the maximum relaxation time τmax with inverse temperature (inset of Fig. ). The extrapolation of the VTF equation to τmax = 100 s, defined as τmax (Tg) by Angell et al., reveals a glass transition temperature Tg = 56.4 °C, which is in good agreement with the static value of Tg = 50.3 °C obtained by DSC measurements.