Polymer/clay nanocomposite materials based on poly(propylene-graft-maleic anhydride) (PPgMAH) and two different organophilic modified clays were investigated by dielectric relaxation spectroscopy (DRS). In contrast to ungrafted polypropylene (PP), PPgMAH shows a dielectrically active relaxation process which can be assigned to localized fluctuations of the polar maleic anhydride groups. Its relaxation rate exhibits an unusual temperature dependence, which could be attributed to a redistribution of water molecules in the polymeric matrix. This is confirmed by a combination of Raman spectroscopy and thermogravimetric experiments (TGA) with real-time dielectric measurements under controlled atmospheres. In the nanocomposites this relaxation process is shifted to higher frequencies up to 3 orders of magnitude compared to the unfilled polymer. This indicates a significantly enhanced molecular mobility in the interfacial regions. In the nanocomposite materials a separate high-temperature process due to Maxwell-Wagner-Sillars (MWS) polarization was observed. The time constant of this MWS process can be correlated with characteristic length scales in nanocomposites and therefore provides additional information on dispersion and delamination/exfoliation of clay platelets in these materials. These properties also influence the diffusivity of the water molecules as revealed by real-time dielectric investigations.

No abstract

Photochromic liquid crystalline main chain poly(ester imide)s with cinnamoyl moieties and chiral groups as part of the backbone were characterized concerning their liquid crystalline, molecular dynamical, and photochemical properties. Homo-and copolymers were synthesized by polycondensation of mixtures containing isosorbide, tert-butylhydroquinone, or catechol. The copolyesters were cholesteric, but exclusively the polymers containing the tert-butylhydroquinone moiety form Grandjean textures on annealing. These polymer films show blue iridescent color. UV irradiation causes photo-cross-linking of the polymers via the (2 + 2) photocycloaddition of the cinnamoyl moieties, resulting in insoluble films in which the iridescent supramolecular structure is frozen in without any changes compared to the initial films. Dichroism of about 0.07 is induced upon irradiation with linearly polarized UV light. In contact with liquid crystals, the photoinduced anisotropic interface of the films causes an efficient alignment of liquid crystals.

No abstract

SUMMARY: A series of amorphous photochromic homo-and copolymethacrylates with an azobenzene moiety in the side group is investigated systematically by optical and dielectric spectroscopy. The aliphatic ester component of the comonomer unit and the concentration of the azobenzene groups within the copolymer are varied. The kinetics and the temperature dependence of the E/Z (trans/cis) photoisomerization and of the thermal Z/E (cis/trans) isomerization is studied for spin-coated films of the polymers. To understand the polarity of the polymeric materials as well as the matrix dependence of the reactions and of the photoinduced reorientation processes in the steady state molecular dynamics is investigated by dielectric spectroscopy. A variety of relaxation processes is observed: a -relaxation is detected for polymers containing azobenzene moieties. The temperature dependence of the reaction rate of the thermal Z/E isomerization process measured by optical spectroscopy seems to correlate with the values of the b 9 -process. A correspondence between dielectric and photochemical behavior is discussed.