Διαμορφωτικές ιδιότητες δενδριτικών πολυμερών

Abstract

This thesis deals with the conformational properties of dendritic polymers in dilute solutions, which are the key to a variety of potential uses of these hyperbranched macromolecular structures. On the basis of the Gaussian model of polymer chain we have developed coarse-grained theoretical models in order to describe analytically the dependence of the conformational properties on the structural characteristics as well as on the quality of the solvent. First, the case of dendritic homopolymers of first generation has been studied. The analytical equations describe the dependence of the mean square end-to-end distances of various parts of the macromolecule as a function of the branch length, functionality and solvent quality. The results were compared with the respective properties of the corresponding star polymers. A comparison of the analytical results and those of existing Monte Carlo simulations is also given. Next, we have proposed a new theoretical model in order to describe the conformational properties of dendritic homopolymers with a larger number of generations by taking only the interactions between the numerous branching points into account. The description was based on the dependence on the number of generations, the molecular weight of each branch, the functionalities of the branching points and of the core as well as on the quality of the solvent. A comparison between the analytical results and the results from existing Monte Carlo simulations of trifunctional dendritic polymers with interacting branching points up to four generations is given. Three mean square end-to-end distances were calculated which determine the extension of the each shell from the origin, the sizes of the branches in each generation and the average distance between symmetrical points on different dendrons. On the basis of these distances, the dependence on the microscopic characteristics of the dendritic polymer of the positions of the terminal groups and the size of the branches in each generation was analyzed. Effective angles between symmetrical points on different dendrons were used to describe the degree of segregation of different dendrons, the possibility of entrances into the matrix of the polymer as well as the amount of the vacancies in its interior. The given model was able to reproduce all known regularities of the conformational properties of dendrimers. Finally, the previous model was extended to include the case of the dendronized polymers, which are composed of a linear polymeric backbone and grafted dendrons made of units of different chemical nature. The ways that the molecular weights of dendron branches and backbone segments, the number of dendrons, their number of generations and the functionality of their branching points affect the size of the backbone and the dendrons, but also the overall shape of these macromolecules, were given in detail. Special emphasis was given on the important role that the quality of the solvent (which is capable to be different for the dendrons and the backbone) plays on the conformations of the dendronized polymers.