On the dynamic mechanical behavior of polyimides based on aromatic and alicyclic dianhydrides

Abstract

Unwersite de Savoie -Batiment m-Campus scientiiue 73376 LA? Bourget-du-Lac Cedex, RaneeA series of polyimides has been synthesized based on different diarhydrides and diamines. The microstructure of polyimide films has been analyzed by performing density measurements, X-ray diffraction and W-visible spectrophotometry. The dynamic mechanical behavior was investigated according to both chemical and microstructural aspects. Thus, it was pointed out that the broadness of the p subglass transition is dependent not only on dianhydride flexibility but also on para-or meta-diamine links. Such behavior is discussed in terms of intra-charge transfer complex. On the contrary, the temperature location of the y-transition appears to be controlled by interchain packing. Based on a statistical approach, a correlation between microstructural data and gamma relaxation temperature is established.ies: Cheng et aL conclude that the molecular motion is mainly connected to the dianhydride moiety (10).

Local and segmental motion in highly transparent and low-k poly(ether-imide) films

“…Moreover, it was demonstrated that lower interchain interactions, as is the case of P1-P4, result in looser chain packing, thus facilitating the molecular process that generates the γ-relaxation [52]. The temperature at which γ relaxation appears is very close for all investigated polymers, respectively between −88 and −101°C at 1Hz.…”

High performance bismaleimide resins modified by novel allyl compounds based on polytriazoles

“…Dipolar relaxation processes corresponding to thermal transitions are evidenced by step increase in dielectric constant representations and loss peaks, which shift to higher temperature with increasing frequency. For polyimide films, the relaxation observed in negative temperature region, called γ transition, has bees associated with phenyl ring oscillations and is influenced by moisture absorption content [29,30]. The studied polymers show γ sub-glass transitions: 7a at −85°C and 7b and 7c at −95°C at 10 Hz.…”

Indication of Local Phase Separation in Polyimide/Silica Hybrid Polymers

“…[14,[23][24][25][26] This is due to the complex molecular architecture of PIs which gives rise to the occurrence of at least three mechanical relaxations. The process with the lowest transition rate (longer timescale) showing up to highest temperatures is designed as a arelaxation and it is ascribed to the cooperative glass/rubber transition (only partially visible here).…”

“…As concerning the g-relaxation, although it was first related to the presence of water molecules linked to the polar groups in polyimides, [28,29] a direct correlation with non-cooperative oscillations and pflipping motion of the phenoxy groups in the diamine sequence has been then proven. [30,31] In particular Bas et al [25,26] relate the g-relaxation to micro-structural parameters and discuss its temperature dependence in terms of the ability to establish charge transfer interactions.…”