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Augmentation rotable de la conductivite de 10 a 11 ordres de grandeur par dopage; on suggere que la formation d'un complexe de transfert de charge est responsable de l'augmentation de la conductivite

A combined X-ray diffraction and DSC investigation of the crystalline phase in lamellar low density polyethylene after conventional chlorosulfonation treatment has been carried out. Our results indicate that the acid attack does not involve any heavy group penetration within the lattice. The location of these groups at the basal crystal surface contributes, however, to an enhancement of the melting temperature of the modified lamellae. It turns out that the destruction level of crystalline material at 45 ºC, after 15-20 h is of the order of 20% and progressively increases for longer periods of time.

The hardening of lamellar polyethylene (PE) as a consequence of a controlled chlorosulfonation treatment has been studied using the microindentation technique. The hardness of the polymer turns out to be a linear function of the density of treated PE. The rate of increase is larger for samples with higher crystallinity. This increase is related to the hardening of crystal lamellae due to the surface attachment of electron dense groups. The latter impede the slippage of crystals and substantially reduce the rate of creep of the material under the contact pressure applied.

8 pags., 10 figs., 7 tabs., The isothermal `cold crystallization' of the thermoplastic polyimide (New TPI) has been studied using the microhardness technique to examine the property-microstructure correlation. By using wide- and small-angle X-ray diffraction and differential scanning calorimetry, the influence of the experimental parameters, i.e., treatment temperature Tc and time tc on the micromechanical properties of the `cold crystallized' samples has been examined. It is shown that both macroscopic hardness H and volume crystallinity xc increase with Tc and tc. For the samples prepared in the secondary crystallization range, it is demonstrated that H values strongly depend on the hardness of the crystalline units Hc. In this range, long spacing L, crystal thickness lc and crystallinity (both linear xCL, and derived from density xc) slightly increase with Tc. From the DSC study, it is demonstrated that the proportion of `liquid-like' and `rigid' amorphous fraction present in each sample is directly related with the crystallization conditions. Finally, from the SAXS and DSC combined study, information concerning the secondary crystallization mechanism has been obtained., The authors are indebted to DGICYT (Grant PB94-0049), Madrid (Spain). We wish also to thank NEDO's International Joint Research Programme, Japan, for the generous support of this investigation. Partial financial support was provided by the Polymeric Composites Laboratory Consortium at the University of Washington.

4 pags., 7 figs., The present report is part of a general study aiming to investigate the possible evidence of electron density fluctuations as precursors of crystallization in polymers with different chain stiffness. The present experiments on the thermoplastic polyimide (New-TPI) with varying induction times, studied by small- and wide-angle X-ray scattering (SAXS and WAXS), reveal the onset of long-range ordering prior to crystal growth. Slow crystallization, slightly above Tg indicates the development of well resolved SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. The experimental results suggest that density fluctuations control at sufficiently low temperatures the precrystallization mechanisms during the embryonic period., Grateful acknowledgment is due to the International Research Grant NEDO and to the DGICYT, Spain (Grant PB94-0049) for the support of this investigation. Synchrotron radiation experiments were performed thanks to the support of the TMR Contract ERBFMGECT 950059 of the European Community. We wish to thank Prof. James C. Seferis, PCL (University of Washington) for the supply of the New-TPI films.