【正文】 mode has a more strong behaviour according to Angell [22 e 24]. It is consistent with the fact that a constrained amorphous phase has a higher density of hydrogen bonds than a free amorphous phase. The molecular mobility of dipolar entities in the amorphous phase of PA 6,9 has a similar behaviour than odd to these observations and to the chemical structure of PA6,9 we might expect a piezoelectric activity. . Ferroelectric behaviour Prior to polarization process, polyamide 6,9 films were colddrawn to a ratio 3:1. The resulting stretched films were about 50 mmthick. Then, a high electric field was applied to polarize the PA 6,9films. The variation of the electricalfield versus time has a triangular g the polar izati on process, the cur rent is measured versus appl ied field and it is reported on Fi g. 6 . The measured cur rent increases with the applied elect ricfield. The non lin ear behaviour of I( E ) is observed. For a polin g fi eld of 100 kV/ mm, a shoul derappearsat 25 kV/m m. The ampli tude of the s hould er in creases with the electric field. For an appliedel ectric field up to 100 kV/mm ,the s hape of I( E ) curve is character istic of afer roelectric maximu m ele ctri c fi el d that co uld be appl ied on the PA 6,9sample is 125 kV/ mm. For upper el ectri cfi el d voltage, a breakdown is observed. As th e ampli tude of the shoul de r in creases up to anelect ric fi eld of 125 kV/m m, we assume that the sample is not fully polar ized. 3。 modes are equivalent to VFT parameters measured on PA 11. The strength index D=1/ ɑ VTFT0,generally used as a quantitative measure of fragility, of the ɑ39。relaxations are attributed to the dielectric manifestation of glass transition in the free amorphous phase and the amorphous phase constrained by the crystallites respectively [18] .The MWS mode is associated with heterogeneities induced by crystalline/amorphous inter faces [19] . 24 Fig. 1. 3D relaxation map of the dielectric modulus losses of PA 6,9 from DDS. . Thermo stimulated dielectric response The d yn am i c of di pol ar en ti ti es of polyamid6 ,9 i n th elow frequency range has been studied using the TSC technique. The plex T SC thermogram is reported in Fi g. 2 . Four relaxation 25 26 modes are pointed out. The low temperature grelaxation at150℃ has been at tributed to the molecular mobility of al ip ha tics equences of polyamid 6 ,9 . The β relaxations involve the am ide groups of macromolecules. In order to establish the molecular origin of the two ponents of this mode ( β 1andβ 2), the sampl e was dehydrated at 120℃ for 30 min. The in sert of Fig. 2 repre sents the TSC thermograms of PA 6 ,9 be fo re (dashed li ne )and after (solid line) dehyd ration , respe ctively. A mide groups are known to i nterac twith water mole cules. For adehyd rateds ample, the amplitude of the β 2 mode decreases and the one ofβ 1 in creases . Moreover, we note an antiplast cization phenomenon for theβ 1 mode. These evolutions of β modes allow us to attribute theβ 1 ponent to free amide groups and the β 2 ponent to the wateramide plex relaxation [11] . The main dipolar relax ation called ɑ mode is located a t Tɑ= 70℃ . This relaxation occurs in the temperature range of the polyamid 6, 9 glass transition Tg as 27 alreadyobs erved by differentials cann in gcalorimetry [ 12] . In deed all ɑ and βrelaxations are as sociaed with polaramide groups, the large relaxation magnitude of the ɑ mode regarding theβ one is due to the delocal is at i on of the molecular mobility along the mainchain over a sequence of s everala no meters . C on trarly the β mode only impli s oscillation of the am ide group or am ide water plex. Fig. 3 shows the fractional TSC thermograms of thea mode of PA6,9. From the elementary processes, activation enthalpy (ΔH) andpreexponentional factor (τ0) has been extracted. Activation entropy DS has been calculated from τ0 values. The values of ΔS andΔH report in insert of Fig. 3 are consistent with the values usually report in the literature for semicrystalline polymers [20] .We observe a linear relationship between activation enthalpy and activation entropy associated with 28 pensation phenomenon[ 20] . The corresponding relaxation times obey a pensation law: where R is the universal gas constant,τc is the pensation time and Tc is the pensation temperature. For the a mode,τc = and Tc = 84℃ . Tg+ 25℃ . Such a pensation phenomenon is characteristic of the distribution of relaxation times associated with the dielectric manifestation of glass transition. Fig. 4 represents the activation enthalpy (ΔH) versus temperature for theb and amodes. TheΔH variation corresponding to a null activation entropy (also noted “ Starkweather line” [21] )is symbolized by the dashed line. The enthalpies of the 29 β relaxation are practically described by the “ Starkweather line ” . Contrarily,activation enthalpies associated with the a relaxation depart from the“ Starkweather line” . It ascertains the localized behaviour of theβ relaxation mode and the delocalised mobility of the a mode. The temperature range, the amplitude of the depolarization current and the cooperativity of this relaxation mode allow us to associate this relaxation with the dielectric manifestation of the glass transition of PA 6,9. . Dielectric relaxation map The relaxation times extracted from the dissipative part of the dielectric permittivity by DDS are plotted on the Arrhenius diagram of Fig. 5 . The relaxation times of b and a modes extracted from fractional TSC measurements are also reported on Fig. 5. The three sub vitreous dielectric relaxations have Arrhenius behaviour. The preexponential factors and the activation energies associated with these modes are reported in Table