Synthesis and characterization of dendritic architectures

University dissertation from Stockholm : KTH

Abstract: The goal of this work was to synthesize different dendritic architectures and evaluate the effect from the dendrons on the material properties. The work presented in this licentiate thesis, Synthesis and Characterization of Dendritic Architectures, is divided into major parts. The first part deals with the synthesis and characterization of two sets of dendritic porphyrins based on 2,2-bis(methylol)propionic acid (bis-MPA). The second part deals with the synthesis and characterization of a series of dendronized polymers based on bis-MPA.Both free-base and zinc containing dendritic porphyrins were synthesized up to the fifth generation utilizing the acetonide protected anhydride of bis-MPA. The resulting dendrimers were characterized by SEC, NMR, and MALDI-TOF. The dendrimers were found to be well-defined, virtually monodisperse, molecules up to the fourth generation. In the case of the fifth generation dendrimers, some structural defects were observed. The hydrodynamic volume (in THF) of these molecules was calculated using the rotational correlation time, and they were found to be more compact than the corresponding Fréchet-type dendrimers of the same generation.Macromonomers of the first and second generation were also synthesized utilizing the acetonide protected anhydride of bis-MPA and subsequently polymerized by atom transfer radical polymerization, using a system of N-propyl-2-pyridylmethanamine, Cu(I)Br, and Cu(I)Br2. This system resulted in well-controlled polymerizations with low polydispersity polymers. By adopting a divergent ‘graft-to’ approach, welldefined dendronized polymers with acetonide, hydroxyl, acetate, and hexadecyl functionality respectively, were obtained.The bulk properties of the dendronized polymers were investigated by differential scanning calorimetry, dynamic-mechanical measurements, and 1H-NMR selfdiffusion. It was found that that increasing the size of the pendant dendron increased the glass transition temperature of the materials. The degree of crystallization of the hexadecyl functional materials was found to decrease with dendron size, most likely due to the reduced flexibility of the backbone prohibiting effective crystallization. The dynamic mechanical measurements revealed that the behavior of the complex viscosity as a function of frequency was independent of functionality. The second and third generation materials were found to have a Newtonian plateau up to a frequency where they become shear-thinning. The fourth generation materials were found to be shearthinning in the frequency range. 1H-NMR self-diffusion measurements revealed that the shape of the acetonide functional dendronized polymers in solution was best described by using a rod-like or prolated ellipsoid model.

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