CO2-Responsive Polymer Particles and Gels for Forward Osmosis

Abstract

CO2-responsive polymers are typically amine- or amidine-containing polymers that can be reversibly switched between hydrophobic and hydrophilic forms. The addition or removal of CO2 from water containing the responsive polymer is responsible for its form change. CO2-responsive polymers can be grafted from a surface such as cotton or crosslinked into a particle or gel form. The present research builds an understanding on how to synthesize and utilize these CO2-responsive polymers for industrial applications such as oil-water separation, forward osmosis (FO), and solid phase extraction (SPE). Several polymerization techniques were used in this thesis to create CO2-responsive polymer surfaces and particles. For surfaces, controlled radical polymerization (CRP), specifically atom transfer radical polymerization (ATRP), was used to graft polymers from the surface of cotton. For particles, suspension polymerization was used to create spherical discrete polymer particles that changed shape and size with varying pH. CO2-responsive technology was advanced in the fields of polymer-grafted cotton, SPE, and polymer particles for forward osmosis. Polymer-grafted cotton was synthesized using a unique pre-treatment and ATRP method combination. The cotton surface was shown to change from hydrophobic to hydrophilic and back when exposed to/removed from carbonated water. CO2-responsive silica was used to successfully concentrate selected analytes for the first-time using water and carbonated water as a solution. CO2-responsive particles were used in SPE for their role in reducing organic solvent waste. Silica particles containing pH-responsive functional groups were used to concentrate pH-responsive analytes with water/carbonated water as the main solvent. Finally, CO2-responsive polymer particles were shown to work in a model FO system for the first time to successfully draw water across a cellulose-based membrane.