Title

Covalently Functionalized Clay and New POSS Derivatives for Nanocomposite and Nanomaterials Applications

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Lon J. Mathias

Advisor Department

Polymers and High Performance Materials

Abstract

This dissertation relates to nanocomposites and nanomaterials, particularly polymer-clay and polyhedral oligomeric silsesquioxane (POSS) systems. Most of the dissertation involves new methods to functionalize clays, with applications in both polymer-clay nanocomposites and reactive nanomaterials. Covalent functionalization of clay was achieved through reaction of the clay's silanol groups, which are on the edge of the clay sheets. Laponite, a synthetic clay, was chosen for these studies because of its high edge-to-surface area ratio. Chapter 2 introduces the concept and describes the procedures for reacting the silanol groups of clay with silane coupling agents. The functionalities bound to clay include methacrylate, benzophenone, amine; and tertiary bromine. Chapter 3 describes atom transfer radical polymerization (ATRP) from covalently attached initiators on clay. These covalently-linked polymer-clay materials contain up to 80 wt-% PMMA, are dispersible in organic solvents and can be cast into transparent films. Chapter 4 explores the compatibility and dispersibility of PMMA-modified clays in commercial poly(methyl methacrylate). PMMA nanocomposites were synthesized and characterized, resulting in transparent films of up to 10 wt-% clay with modulus improvement of up to 50%. Chapter 5 explores an observation that occurred during polymer/clay studies, in which polymer/clay attachment occurs in the absence of any functional group on the clay during in situ free radical polymerization. This chapter explores the mechanism of polymer/clay binding and the polymer properties of unbound versus bound polymer. It was found that polymerization within the clay interlayer forms very high molecular weight polymer, 1000 kDa, which is physically entangled with the clay. Chapter 6 describes the synthesis of a new class of siloxy-imidazolium salts and their potential uses as clay surfactants and ionic liquids. Hydrophobic siloxy-containing moieties were attached to imidazolium compounds to create clay surfactants for enhancing clay dispersion and exfoliation. These compounds are also ionic liquids, and have potential applications as low viscosity media. Chapter 7 covers incorporating POSS into commercial dental resins. A variety of POSS compounds were incorporated into commercial dental resins to improve mechanical properties. One system demonstrated a modulus improvement of 80% at room temperature, while many other formulations showed significant modulus improvement after T g .