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Trapping dendrimers in inorganic matrices: Formation of silica xerogels with spherical cavities and dendrimer /zinc arsenate lamellar composites
This work explores the use of spheroidal polymer molecules called dendrimers in the preparation of dendrimer/inorganic composites that, in one case, yielded silica xerogels with spherical cavities (after template removal), and in a second approach produced lamellar dendrimer/zinc-arsenate composites with long range layered structures. These unique materials are expected to open the door to synthetic pathways of even more sophisticated nanostructured composites that will ultimately exploit the full potential of dendrimer templates. ^ The first part of this dissertation involves the use of dendrimers with amine terminal groups as templates in the formation of spherical cavities in silica xerogels prepared through a sol-gel route. Two families of dendrimers are represented in this part: poly-amidoamine generation 4 (PAMAM) dendrimer, and poly propyleneimine generation 4 and 5 (PPI Gn) dendrimers. The former rendered only microporous silicas (after thermal treatment) with two systems of micropores. The other set of materials produced a microporous solid (with PPI G4), and a mesoporous xerogel (with PPI G5). Both porous structures showed narrow pore size distributions and their pore diameters correlated well with the dimensions of the template molecules as measured by argon adsorption. Transmission electron microscopy (TEM) of platinum stained samples corroborated that the symmetry of the cavities was indeed spherical. ^ The second part deals with the study of a synthetic route to lamellar dendrimer/zinc-arsenate composites. All commercially available generations of the PPI Gn family of dendrimers were included in these composites as it was shown by X-ray diffraction (XRD) measurements and chemical analysis. However, calculation of interlayer distances indicated that the spacing in between inorganic lamellae changes more slowly with dendrimer generation than was expected, compared to reported free dendrimer diameters in solution. This suggests that the dendrimers tend to adopt compressed, or oblate conformations in the interlayer. Images of these composites, obtained by TEM, showed that the zinc-arsenate sheets displayed some degree of flexibility and occasional branching defects. ^
Lotero, Edgar, "Trapping dendrimers in inorganic matrices: Formation of silica xerogels with spherical cavities and dendrimer /zinc arsenate lamellar composites" (2001). ETD collection for University of Nebraska - Lincoln. AAI3028658.