Free-radical polymerization and its application for nanocomposite synthesis

High-temperature free-radical polymerization is an environmental-friendly method for the synthesis of acrylate resins. Polymers synthesized by this method have lower average molecular weights partly due to secondary reactions that happen at high temperatures, T>140 °C. [Beta]-scission and depropagation are two of these secondary reactions that significantly lower average molecular weights. Resins with lower molecular weights need less organic solvents to be sprayable and brushable. Less amount of organic solvents in a resin leads to the release of less volatile organic compounds (VOCs) into the atmosphere after applying the resin to a substrate if the vapor is not collected. High-temperature free-radical homopolymerization involves a large set of more than 40 different reactions. Some of these reactions have not been studied well yet, and their reaction rate coefficients are not available. By accounting for these reactions, macroscopic-scale modeling allows for predicting resin properties and estimating unavailable reaction rate coefficients. In this Ph. D. project, a macroscopic-scale model based on the method of moments was developed to investigate high-temperature free-radical polymerization of acrylates. Batch homopolymerization of n-butyl acrylate and methyl acrylate was carried out in both bulk and solution media, and monomer conversion and average molecular weights of polymer samples were measured. Unavailable reaction kinetic parameters such as monomer self-initiation, [beta]-scission, and backbiting rate coefficients as well as gel-effect parameters were estimated from the measurements. As high-temperature free-radical polymerization produces polymers with low average molecular weights and consequently low viscosities, this method lets in-situ fabrication of polymer nanocomposites without using a large amount of organic solvents. Using this polymerization technique, polymer nanocomposites containing silica and Ti₃C₂ MXene nanoparticles were synthesized. Three different grades of hydrophobic silica were used as the filler in high-temperature free-radical polymerization of isobornyl acrylate to develop hydrophobic coatings. Ti₃C₂ MXene/polymer nanocomposites were also synthesized to investigate the properties of polymer resins embedded with Ti₃C₂. As Ti₃C₂ inherently has hydroxyl, oxygen and fluorine on its surface, its surface was modified with silane coupling agents. The surface modification allows Ti₃C₂ to participate in a variety of chemical reactions such as those of free-radical polymerization.