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PhD Thesis

Untersuchungen zum Orientierungsverhalten von Zwei- und Dreiblockcopolymeren in oszillierenden Scherfeldern

Stefan Stangler (01/2002-01/2002)

Support: Volker Abetz

Summary

In this work the orientation behavior of AB and ABC block copolymers under shear was discussed. Chapter 1 explained structure development by microphase separation and macroscopic orientation behavior of block copolymers. In chapter 2 synthesis of polymers by living anionic polymerization and polymer characterization by gel permeation chromatography, 1H-NMR and membrane osmometry was described. An overview of several characterization methods for orientation and structure was given in chapter 3. The next chapter, 4, contained a discussion of the results of other workgroups on the topic of shear alignment of block copolymers. Two additional methods for the in situ characterization of alignment kinetics, FT-rheology and rheooptics, were presented in chapter 5. In chapter 6 the results of these experiments with five different block copolymer systems were shown and discussed. - S50I5020: With this lamellar SI polymer it was demonstrated that the SI system used in this work allows the reproduction and confirmation of the results of other groups. Additionally, the new experimental setup was tested successfully. Characterization of the resulting orientation via small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) was explained on one example. The results of the orientation experiments with in situ birefringence were in good agreement with the literature. Slight deviations could be explained by small differences in the used polymers. - I45S45V1022: In this lamellar ISV block copolymer analogous orientation behavior to that of the lamellar SI system was found. At low frequencies and amplitudes of shear perpendicular orientation resulted, whereas high frequencies and amplitudes of shear induced parallel orientation. As the prealignment due to preparation methods could not be erased, it was not possible to get reproducible orientation kinetics by birefringence experiments. Nevertheless, 2D-SAXS and TEM could characterize the resulting end orientation. - S50I5020+DOP: Dilution of the polymers was required to lower the ODT of the system, so that the prealignment could be erased without destroying the polymer. Results from dynamic mechanical analysis and birefringence measurements were reported. Large amplitude oscillatory shear (LAOS) experiments at several frequencies and strain amplitudes followed. The dependence of shear alignment on the strain amplitude was examined and compared to the literature on non-dilute AB systems. The tendency of frequency and amplitude dependence of the orientation behavior was similar in both systems: low frequencies and small strain amplitudes lead to perpendicular orientation (regime 1), higher frequencies or amplitudes resulted in parallel orientation. In the latter case there were two different pathways: parallel orientation could be reached via a previous built perpendicular (regime 2) or transverse (regime 3) orientation. - I45S45V1022+DOP: The TOOT of this system was 80 °C. Therefore extinction of the prealignment could easily be achieved by heating over TOOT. LAOS experiments were performed at 60 and 70 °C at several frequencies and strain amplitudes. From the birefringence data an apparent orientation behavior like regime 1, 2 and 3 could be assumed. However, 2D-SAXS clearly indicated that the orientation process is not uniaxial. A distribution of all three alignment directions could be verified. Under all tested shear conditions parallel orientation was always dominating. Due to non-uniaxial orientation distribution it was impossible to determine the dependence of alignment kinetics on strain amplitude. It was noticeable that the orientation mechanism stayed the same over a broader frequency and strain amplitude regime when compared to the diluted AB system. - S40I40M2025: The orientation behavior of the non-lamellar SIM system differed from that of the lamellar systems. A long induction time and independence of end orientation from shear conditions were found. The induction phase could be explained by growth of domains, improving microphase separation and the eventually resulting change of morphology. Analysis of the end orientation showed perpendicular oriented lamellae connected by PMMA cylinders in the lamellar PI phase. Because of this anchoring with PMMA the PS phase was unable to slide over the low viscosity PI phase (as it did in SI), and there was no advantage in parallel orientation. Therefore parallel orientation was not formed. Consequently it can be concluded that birefringence measurements combined with 2D-SAXS and TEM are suitable for the characterization of alignment behavior of block copolymers, whereas FT-rheology was of little help.

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