The influence of external mechanical stress on the nematic-isotropic phase transformation of nematic elastomers was investigated. The experimental results of IR-dichroism measurements in the nematic phase and stress-optical measurements in the isotropic phase are in good agreement with the theoretical predicitions of the phenomenological Landau-de Gennes theory. This is for the first time that a significant influence of an external field on the nematic-isotropic phase transformation temperature and on the nematic order parameter S has been proved.

The influence of the spacer length was investigated for the correlation between the network anisotropy and the order parameter of the mesogenic units. Stress-optical measurements show that a closer coupling of the mesogenic moieties to the polymer backbone results in an increased interaction between the mechanical field and the mesogenic groups. The correlation between the phase transformation temperature TNI and the mechanical stress cr is represented using both, our experimental measurements and the derivation from the Landau-de Gennes (LDG) formulation.From our results, it is possible, for the first time, to estimate the cross-coupling coefficient U between the order parameter and the strain of a nematic elastomer. The analysis of the elastic properties of the elastomers suggests that non-linear coefficients might become important to obtain quantitative agreement between theory and experiment.CCC 0025-1 16)

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As a result of an error in the evaluation programme, the values represented in Figs. 5, 6, 7 and 8 for the birefringence and mechanical stress are not correct. The correct values of the measurements are represented in the new Figs. 5 , 6, 7 and 8.The new Fig. 5 shows the plot of birefringence against the applied stress for different temperatures. The theory of Kuhn and Grun predicts for conventional rubbers a linear relation between birefringence and stress. There is no deviation from this linearity until the lowest temperature T = Tn,i + 4K. In Figs. 6 and 7 , no quantitative change is observable. However, the quantitative values for the birefingence and the mechanical stress have changed. The dependence of T* on the applied stress is shown in Fig. 8. This dependence between the hypothetical second-order phase transformation temperature T* and the external field is now linear. In Figs. 2, 3, 9, and 10, the nominal stresses plotted are too high by a factor of two. a r,,,

Three triblock copolymers of nylon-6 (Ny6) and aromatic poly(su1fone ether) (PSuE) were investigated relative to their morphology and their thermal properties. Generally, the nylon blocks of the three Ny6-PSuE-Ny6 samples were very short (between 5 and 16 monomer units). Heterogeneous, microphase-separated morphologies could be observed for all samples, independent of the processing conditions, i.e., solvent casting or melt cooling. However, the process conditions were highly influential on the formation of the supramolecular structures (i.e., spherulites), especially when the crystallizable block was short.