The relaxation of holographic phase gratings was examined to obtain some information about the involved photochemically induced changes. The studies were performed with statistical liquidcrystalline side group copolymers having different concentrations of the azobenzene dye. The formation of mesophases, which normally exist in the thermodynamic equilibrium, was prevented during the sample preparation by quenching the polymer films. Two relaxation processes were found in this glassy state of the polymers. The faster one could be described by a dispersive stretched exponential function and was attributed to relaxation processes which are related to the amorphous phase of the sample, while the slower one, corresponding to a single exponential process, correlates with the formation of light-induced liquid-crystalline microstructures. The latter are believed to be the main cause for the modulation of the refractive index.
Broad-band dielectric spectroscopy in the frequency range from lo-' Hz to lo6 Hz and in a temperature range from 170 K to 430 K was employed to study the molecular dynamics in polymethacrylates with novel calamitic side groups. As mesogenic units, derivatives of pmethoxyphenyl benzoate were used where the hydrogen in the meru position of the benzoate ring is substituted by a methoxy group or by bromine. The substituted samples do not show any mesophases. The following results were obtained: (i) The S-relaxation which corresponds to a rotational fluctuation of the mesogen around its long axis is drastically suppressed by the lateral substitution. Moreover the activation parameter of this process depends strongly on the actual mesophase structure of the material under study. (ii)) The a-relaxation is related to the dynamic glass transition of the system. It is shown that the value of the glass transition temperature of the liquid-crystalline polymethacrylate can be understood as competition of internal plasticization and molecular ordering. (iii) The &-relaxation corresponds to a rotational fluctuation of the side group around its short axis. From comparison of the relaxation rates of the a-and &relaxation, the temperature dependence of the order parameter of the liquid-crystalline polymethacrylate is estimated by dielectric spectroscopy.
Bei der Umlagerung von 0-Alkyl-bzw. 0-Arylsulfonyl-N-benzoyl-N-phenylhydroxylaminen 3 in Aminophenole 4 wird durch "0-Indizierung gezeigt, daB die Beweglichkeit in den intermediar gebildeten Ionenpaaren durch groBe Alkylreste sowie durch Wechselwirkung mit einem protischen Losungsmittel in typischer Weise verandert wird.
Internal Mobility in the Ion Pairs during Aromatic Rearrangement of 0-Sulfonyl-N-phenylhydroxylaminesIn the rearrangement of 0-alkyl-or 0-arylsulfonyl-N-benzoyl-N-phenylhydroxylamines 3 to aminophenols 4, the internal mobility in the ion pair intermediates depends both on the size of the alkyl groups and on the interaction with the protic solvent, as was shown by "0 labeled educts.Die aromatische Umlagerung von 0-Arylsulfonyl-N-benzoyl-N-phenylhydroxylaminen (3, R = Aryl), die intermediar bei der Umsetzung von Sulfonylchloriden 2 mit der Hydroxamsaure 1 entstehen, fiihrt zu den Aminophenolen 4l).
Ph-CO-N-OHWir konnten friiher an "0-indizierten Substanzen zeigen, daB die Beweglichkeit der Ionen im intermediaren Ionenpaar von der Substitution im Arylrest und besonders von der Polaritat des Losungsmittels abhangt. Dies entspricht einem ionischen Ablauf iiber enge sowie losungsmittelgetrennte Ionenpaare, wobei erstere vor der Bildung von 4 keine, letztere freie Rotation in den Arensulfonat-Ionen zeigen2).Um die Deutung iiber einen ausschlieBlich ionischen 3, Ablauf zu sichern, haben wir die Eigenschaften des Ionenpaares weiter untersucht. a) Einerseits wurden verschiedene Alkansulfonylchloride 2 mit 1 umgesetzt. In Abhangigkeit von der GroBe des Alkylrestes wurde eine unterschiedliche Beweglichkeit der Ionen erwartets).
The copolymerization behaviour of methacrylate monomers with several decoupled side groups was studied depending on the structure of the linked mesogen. Some units (-N=N--, -CO-NH-)in the rnesogen influence the copolymerization reaction in spite of the strong decoupling by a C6-spacer group and lead to retarding effects and to the preferred insertion of monomers with weaker mesogenic interactions. The liquid-crystalline behaviour of the copolymers was not affected due to the relatively small differences in the copolymerization parameters.
The phase behaviour of lateral substituted side group copolymethacrylates was investigated. With structural changes it is possible to influence the phase behaviour of the polymers. The lateral substituents have a stronger influence in side group polymers then in low molecular systems because of the coupling of the mesogens via the main chain. According to simulations, the possibility of rotational motions of the side groups around their long axis is hampered by a lateral substitution.With the described structural changes in the mesogen we have synthesized side group copolymethacrylates on the border between the liquid crystalline and the amorphous state.In some further papers we will discuss the consequences of a lateral substitution in the mesogen in the described materials for the dielectrical and photochemical behaviour.
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