No abstract

Novel polyaniline (PANI)/epoxy hybrids have been fabricated using an absorption-transferring process in which no organic solvent is involved. An epoxy prepolymer cured by aniline monomer (DGEBA-aniline) was added to a freshly prepared PANI nanoparticles (NPs) aqueous solution with vigorous agitation and heating (ca. 90 °C). The PANI NPs were absorbed on the surface of epoxy droplet and then transferred into the whole droplet. The microstructures of the product PANI/epoxy hybrids, characterized using scanning electron microscopy, featured well-dispersed PANI NPs (ca. 40∼60 nm) within epoxy matrixes; no large aggregates were observed. The hybrids exhibited huge negative permittivities; the electromagnetic interference shielding efficiency in an electric field at low frequency (100-1000 MHz) was ca. 30-60 dB. The welldispersed PANI NPs not only provided a continuous conducting network but also a higher level of charge delocalization.

A mechanistic study of the trans%cis isomerization of the azobenzene moiety in a side-chain liquid-crystal polymer system was carried out with six liquidcrystalline polymethacrylates in which different electron-withdrawing substituents were attached to the para-positions of the azobenzene chromophores. Compared to the non-nitro-substituted azo polymers, the nitro-substituted azo polymers exhibited two quite different behaviors: an extraordinarily high reaction rate of the thermal cis-trans isomerization and an unexpected composition of cis-trans isomers obtained from the photochemical trans-cis isomerization process. A potential energy profile for the isomerization process was established on basis of the structures of the proposed transition states and was employed to elucidate the reaction mechanism. The results confirmed that the nitro-substituted azo polymer system proceeded via a rotation mechanism in either direction of the trans%cis isomerization reaction, whereas the non-nitro-substituted species were more likely to follow an inversion mechanism.