Doctor of Philosophy (PhD)
This dissertation focuses on the development and synthesis of model system for the investigation of the morphology, interactions, and dynamics in linear and branched polymers and polymer nanocomposites. The materials are designed to reduce the number of uncontrolled parameters and to be ideally suitable for neutron scattering studies. Hereby, two main objectives are defined:
The first project is to develop model nanocomposites based on the grafting of poly(dimethylsiloxane) (PDMS) to primary particles and well-defined aggregates. For that purpose, the functionalization of silica nanoparticles with a chlorosilane and the influence of moisture on the reaction was studied. Higher grafting densities than previously accessible for PDMS could be accomplished for the tethering of living, anionic PDMS to the functionalized silica particles. Hereby, the particle concentration could be identified as an additional parameter for the phase stability of grafted nanoparticles. The model systems permitted to study the relaxation rate and diffusion coefficient of the grafted polymer and its influence on the interacting polymer matrix. With the model aggregates a first step to bridge the gap between academic and industrial nanocomposites was taken, showing the similarity of the phase behavior of primary particles and aggregates.
The second objective is the origin of the different properties of bottlebrush polymers with the model of a PDMS homopolymer bottlebrush. In the course of this work three different chlorination methods for silanes were applied for the functionalization of poly(methylhydrosiloxane), resulting in the synthesis of poly(methylchlorosiloxane) (PMClS). The grafting of living and silanol end functional PDMS onto the PMClS was studied towards the synthesis of PDMS bottlebrushes of spherical and elongated nature. The spherical bottlebrushes were identified as shell-only particles and thus an ideal model for the study of the polymer shell dependent dispersibility in linear PDMS. This allowed to confirm the influence of concentration on the phase stability and a possible origin of instability. Pairs of protonated and deuterated bottlebrushes in solution and melt allowed to identify the melt behavior of bottlebrush as polymeric questioning the picturization as thick filaments.
Jakobi, Bruno, "Silica and Siloxane Model Systems" (2019). LSU Doctoral Dissertations. 5054.
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