| Abstract |
The present thesis is investigating the structure and dynamics of nanocomposites based on
hyperbranched polymers. Nanocomposites consisting of polymers and layered silicates are
considered as a new generation of composite materials due to their unique properties. In
recent years, these nanocomposites have attracted scientific and technological interest, mainly
due to their special properties such as enhanced strength and thermal resistance, reduced gas
permeability, reduced flammability etc, which render them candidates for numerous
applications. Furthermore, intercalated nanohybrids offer a unique avenue to study the
behavior of macromolecules in nanoscopic confinement.
On the other hand, nanosized hyperbranched polymers have received much attention lately.
The advantage that distinguishes them is the extremely large number of functional groups
available, allowing multiple applications. Together with their cost-effective synthesis, as
compared to dendrimers, they can be used in industrial applications, such as coatings,
membranes and batteries, as well as for the encapsulation of substances in the pharmaceutical
industry and medicine. Therefore the investigation of the structure and the dynamics, for
hyperbranched polymers in the bulk and under severe confinement, is attempted.
During the present thesis, three different generations of the hyperbranched polyester Boltorn
were mixed with natural hydrophilic sodium montmorillonite, to synthesize hybrids with a
broad range of compositions between pure polymer and pure clay. The nanocomposites were
synthesized via a solution-intercalation method utilizing DI water and methanol as solvents.
Τhe structure for the three generations of the polymer and the corresponding nanocomposites
in various compositions was investigated, and the effect of the different solvent on the final
structure of the nanohybrids was examined. The investigation was performed utilizing X-ray
diffraction and infrared spectroscopy, whereas differential scanning calorimetry was used for
the study of the materials thermal properties. In the case of the nanohybrids, the formation of
polymer monolayers or bilayers inside the clay galleries was examined, depending on the
polymer concentration whereas the thermal annealing of the hybrids, in order to obtain
equilibrium structures, was studied,. The glass transition temperature, Tg, of the pure
polymers was determined by differential scanning calorimetry and a Tg dependence on
generation was observed. The effect of the severe confinement of macromolecules on the
glass transition was studied, as well.
Apart from the nanocomposites structure, the dynamics of the polymer chains was studied in
the bulk as well as under confinement. The aim of this study is to investigate the relaxation
processes of the three different generations, for both segmental motions and local sub-Tg
processes. At the same time, the behavior of polymers close to interfaces can be very
different from that in the bulk, especially when the molecules are confined to nanometric
dimensions. The intercalated structures in particular, are ideal systems for studing the
properties of macromolecules under strong confinement (comparable to their sizes) by
utilizing macroscopic samples and conventional analytical techniques.
In order to study the hyperbranched polymer dynamics for the three generations under
confinement, the nanocomposites with ~50wt% polymer, where all chains are confined in the
galleries of the clay, were utilized. The dynamics investigation was performed by broadband
dielectric relaxation spectroscopy experiments that were performed at the Institute for
Chemical and Physical Processes, IPCF-CNR, in Pisa, Italy.
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Δομή και Δυναμική Νανοσύνθετων Υλικών Βασισμένων σε Υπερδιακλαδισμένα Πολυμερή
