A new synthesis of hyperbranched polymers through proton transfer polymerization of thiol and epoxide groups is presented. For this, an AB 2 monomer bearing two epoxides and a thiol groups is synthesized. Base-catalyzed proton transfer polymerization of this monomer led to the formation of a polythioether-based hyperbranched polymer with a 65−69% degree of branching and carrying about 2% of disulfide-based structural defects. This polymer contained two reactive sites, a hydroxyl group and an epoxide unit, distributed throughout the branched scaffold. The epoxide groups could be employed in anchoring an alkyl, aryl, or ethylene oxide chain through a thiol−epoxy reaction, while the hydroxyl groups produced during the polymerization and the first functionalization reactions could be engaged in attaching positively charged primary ammonium groups to the branched backbone. These sequential postpolymerization modifications transformed the general dual-reactive scaffold into dual-functionalized hyperbranched materials with potential utility in the arena of gene delivery applications.

A synthetic route is developed for the preparation of an AB-type of monomer carrying an epoxy and a thiol group. Base-catalyzed thiol-epoxy polymerization of this monomer gave rise to poly(b-hydroxythio-ether)s. A systematic variation in the reaction conditions suggested that tetrabutyl ammonium fluoride, lithium hydroxide, and 1,8-diazabicycloundecene (DBU) were good polymerization catalysts. Triethylamine, in contrast, required higher temperatures and excess amounts to yield polymers. THF and water could be used as polymerization mediums. However, the best results were obtained in bulk conditions. This required the use of a mechanical stirrer due to the high viscosity of the polymerization mixture. The polymers obtained from the AB monomer route exhibited significantly higher molecular weights (M w 5 47,700, M n 5 23,200 g/mol) than the materials prepared from an AA/BB type of the monomer system (M w 5 10,000, M n 5 5400 g/mol). The prepared reactive polymers could be transformed into a fluorescent or a cationic structure through postpolymerization modification of the reactive hydroxyl sites present along the polymer backbone.

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Microstructures of yttria-stabilized zirconia (YSZ) thin fi lms deposited by spray pyrolysis at 370 ° C on sapphire are investigated. The as-deposited fi lms are predominantly amorphous and crystallize upon heating at temperatures above 370 ° C, developing grains in the range of 5 nm to several 100 nm. During post-deposition heat treatment up to 800 ° C, ∼ 50 vol% porosity develops in the center of the fi lms with gradients towards almost dense interfaces to the air and substrate. The reason for this porosity is the decomposition of residues from the precursor and the free volume liberated due to crystallization. Dense YSZ thin fi lms consisting of one monolayer of grains are obtained with annealing temperatures exceeding 1200 ° C. In gadoliniumdoped-ceria (CGO) thin fi lms similar microstructures and porosity are found after low-temperature heat treatments indicating that the precursor residues due to the deposition method are the main cause of the porosity. Grain growth stagnation in annealed thin fi lms is observed in both the YSZ and in CGO thin fi lms. Stagnating grain growth in the thin fi lms is rather caused by reduced grain boundary mobility, here predominately due to a "secondary phase", i.e., pores, than to other effects. The stagnation ceases at higher annealing temperatures after densifi cation has taken place.sapphire substrate and the obtained powder was measured in a Pt crucible up to 1300 ° C at 3 ° C min − 1 . Buoyancy and heat fl ow corrections were performed with the data from a second run using fully crystallized YSZ spray-pyrolyzed powder of the same mass.

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