Sean M. Ramirez

Incompletely Condensed Fluoroalkyl Silsesquioxanes and Derivatives: Precursors for Low Surface Energy Materials

A novel synthetic method was developed for the controlled functionalization of fluorinated polyhedral oligomeric silsesquioxanes (F-POSS), which are useful as low surface energy materials for superhydrophobic and superoleophobic materials. Utilizing triflic acid, open-cage compounds were created and then reacted with a variety of dichlorosilanes to produce functional F-POSS structures possessing alkyl-, aryl-, and acrylate-based moieties. The crystal structure for an endo,endo-disilanol F-POSS compound was determined by single-crystal X-ray diffraction. The chemical structures were confirmed using multinuclear NMR spectroscopy ((1)H, (13)C, (19)F, and (29)Si), FT-IR, and combustion analysis. Dynamic contact angle measurements of these compounds were taken with water and hexadecane. These novel structures were found to possess excellent wetting-resistant behavior, similar to that of the parent F-POSS compound. They are the first well-defined fluorinated nano-building blocks with a controlled level of reactive functionality for the development of new superhydrophobic and superoleophobic materials.

Reversible addition–fragmentation chain transfer (RAFT) copolymerization of fluoroalkyl polyhedral oligomeric silsesquioxane (F-POSS) macromers

Reversible addition–fragmentation chain transfer (RAFT) polymerization techniques were used to copolymerize an F-POSS macromer with methyl methacrylate (MMA) to produce novel copolymers that possess excellent wetting-resistant behaviour and are the first examples of covalently bound F-POSS nanocomposites for improved surface robustness. These F-POSS/MMA copolymers have also been used to coat cotton fabrics, resulting in both superhydrophobic and oleophobic behaviour.

Synthesis of Aromatic Polyhedral Oligomeric SilSesquioxane (POSS) Dianilines for Use in High-Temperature Polyimides

A series of novel aromatic Polyhedral Oligomeric SilSesquioxane (POSS) dianiline molecules has been synthesized for use in the preparation of high temperature aromatic polyimides. A general synthetic strategy was devised to improve the structure, yield, and utility of POSS dianilines over those currently available. Peripheral aromatic functionality was specifically incorporated in order to improve thermal properties and to increase compatibility with aromatic polymers. Silyloxy and/or aromatic functional groups were used to link the aniline groups to the POSS cage in order to ensure that this linkage was not a thermal weak point. Additionally, the stereochemistry of the aniline functionality has been varied to produce both meta- and para- isomers. The new dianiline monomers can be used to produce high molecular weight polyimide polymers. These dianilines have been incorporated both as pendants to the polymer backbone, and in a “bead-on-a-string” fashion by insertion into the polymer main-chain. In addition to producing POSS polyimides with superior thermal stability, these new monomers will allow full characterization and comparison of POSS-polyimides with differing structures in order to delineate the structure-property relationships of POSS and polymer architectures.

Crystallographic analysis of analogous silicon- and carbon-containing di(cyanate ester)s and tri(cyanate ester)s

Cyanate esters are versatile, thermosetting monomers that are commercially important due to their outstanding physical properties such as fire and heat resistivity. This class of molecules also possesses relatively low melting points, allowing for improved processability and manufacturing. While studies of this class of polymers are prominent, the monomers tend to shy away from focus. In an effort to understand organic crystal engineering of these compounds, four structures of siliconand carbon-containing di(cyanate ester)s and tri(cyanate ester)s are presented and analyzed using single-crystal X-ray diffraction. This data, in concert with extensive thermodynamic and computational studies, assist in understanding how a subtle change, such as exchanging quaternary central carbon for a silicon, affects the molecular degrees of freedom. From a crystallographic standpoint, this affects the packing efficiency and intermolecular interactions.