[Analyse de la dégradation thermique du Poly(éther imide)]

The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). First of all, the thermal ageing mechanisms have been analysed and elucidated by FTIR spectroscopy and by differential scanning calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, leading to the disappearance of their characteristic IR absorption band at 2970 cm -1 and the growth of a new IR absorption band centered at 3350 cm -1 and attributed to alcohol groups. In addition, oxidation leads successively to a relative predominance of chain scissions (decrease in T g ) and crosslinking (increase in T g ). Finally, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on preliminarily polished cross-sections of PEI plates of 3 mm thickness. However, the increase in Young's modulus in the superficial oxidized layer is mainly due to a physical ageing

Low energy dynamics from deformed conformal symmetry in quantum 4D N = 2 SCFTs

We determine the one-loop deformation of the conformal symmetry of a general N}=2 superconformally invariant Yang-Mills theory. The deformation is computed for several explicit examples which have a realization as world-volume theories on a stack of D3 branes. These include (i) N=4 SYM with gauge groups SU(N), USp(2N) and SO(N); (ii) USp(2N) gauge theory with one hypermultiplet in the traceless antisymmetric representation and four hypermultiplets in the fundamental; (iii) quiver gauge theory with gauge group SU(N)xSU(N) and two hypermultiplets in the bifundamental representations (N,\bar N) and (bar N,N). The existence of quantum corrections to the conformal transformations imposes restrictions on the effective action which we study on a subset of the Coulomb branch corresponding to the separation of one brane from the stack. In the N=4 case, the one-loop corrected transformations provide a realization of the conformal algebra; this deformation is shown to be one-loop exact. For the other two models, higher-loop corrections are necessary to close the algebra. Requiring closure, we infer the two-loop conformal deformation.Comment: 30 pages, 0 figure