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978-3-86853-779-6, Reihe Thermodynamik
Phase- and Interfacial Behaviour of Hyperbranched Polymer Solutions
143 Seiten, Dissertation Technische Universität Berlin (2010), Softcover, A5
Caused by the high application potential of hyperbranched polymers the calculation of the phase- and interfacial properties is essential. In the framework of this work the demixing behaviour of hyperbranched polymer solutions in one or in two solvents was calculated to the first time close to experimental data. This was possible by the application of the Lattice Cluster theory (LCT) to these special types of polymers. This approach permits the study of the influence of architecture on phase separation, without any additional adjustable parameter. The application of LCT leads for the hyperbranched polymer solution to an equation for the Gibbs energy of mixing. It turns out that the mathematical structure of this equation is a simple polynomial equation as function of the polymer concentration, where the coefficients depend on the interaction between different occupied lattice places and the architecture of the polymer.
This theoretical framework was applied to the system water / hyperbranched polymer and n-propanol / hyperbranched polymer. This work was focused on hyperbranched polyester solutions, which are commercially available in different generation numbers and which have OH-endgroups. The most important difference between the two solvents consists in the structure, where water is treated as occupying one lattice place and n-propanol is handled as a short linear chain with three segments. The structure of the solvent has an impact on the polynomial equation describing the excess Helmholtz energy of mixing.
Using the theoretical framework the experimental data given in the literature were modelled qualitatively for aqueous solutions of hyperbranched polyesters, where only one interaction parameter has to be fitted to the maximum of the cloud-point curve. However, also in the experimental data taken from the literature some ambiguity occurs. In order to resolve this problem some experiments were performed. The diluted branch of the measured cloud-point curve was modelled with a high accuracy. The LCT predicts the high-concentrated branch of this curve at too low polymer concentrations. For the solution made from polymer and propanol no experimental data were available in literature. Therefore the cloud-point curve was measured. Also for this system the LCT shows a good performance in modelling the experimental data. In order to improve the theoretical framework the LCT was blended with a special version of the Wertheim association theory. This theory allows the consideration of different association phenomena like self-association of the solvent, self-association of the polymer via the polar end groups and cross-association. Unfortunately, this approach can not be used for the polymer. For this reason the parameters describing the association behaviour of the polymer must be adjusted to the LLE. From the model calculations can be followed that only if all three types of associations were considered physical meaningful results are obtained. If only self-association of the solvent is assumed then the cloud-point curve shifts to unreliable high temperatures. The introduction of the Wertheim theory shifts the binodal branch, connected to the higher polymer concentration, to higher polymer concentrations and hence closer to the experimental data.