Doctor of Philosophy
Chemical and Biochemical Engineering
Incorporating the binding chemistry of catechol functionality with RAFT chemistry offers a facile and simplified approach for developing a suite of new 2D and 3D hybrid materials with tailored morphologies. Leveraging both chemistries by synthesizing catechol-end functionalized RAFT agents and catechol-containing monomeric species for RAFT (co)polymerization, this dissertation examined a new series of advanced materials that were designed for water-based applications including model flocculants, thermoresponsive hydrogels, adsorbents and underwater adhesives.
To prepare the RAFT agents, novel trithiocarbonates with several catechol end R groups (as postpolymerization anchors) were synthesized that differ in their carbonyl α-substituents (Dopa-CTAs). These materials were evaluated for their livingness characteristics in the polymerization of acrylamido-based monomers, as well as their chain transfer activity. Apparent chain transfer coefficients for the Dopa-CTAs were found to vary within one order of magnitude. Catechol end-functionalized polyacrylamides were RAFT synthesized and their subsequent anchoring via catechol induced linkage to γ-alumina nanoparticles (grafting to) was successful, giving PAM-inorganic nanocomposites with thermally stable tethering.
Reactivity ratios of the acrylamido-based comonomer pair (NIPAM and DMAm) RAFT copolymerized with the Dopa-CTAs were determined using in situ 1H-NMR technique via non-linear least square methods and found to be rDMAm = 1.28 – 1.31 and rNIPAM = 0.48 – 0.51. Concomitantly, a series of low MW poly(DMAm-co-NIPAM) samples (MWs ≤ 26 KDa, Ð < 1.08) were prepared in batch mode by varying the comonomer ratios to achieve tunable lower critical solution temperature (LCST) behavior (LCST values: 31 – 92 oC). Since the versatility of catechol chemistry allows for post-polymerization linking, the samples were further assessed for their LCST behavior under pH conditions necessary for maintaining the trithiocarbonates’ integrity and promoting catechol-induced linkages. This resulted in the LCST values varying within 3 oC for all the poly(DMAm-co-NIPAM) samples.
With N-[3,4-dihydroxyphenethyl]methacrylamide (DHPMA) being a catechol containing monomer, the combined strategies were explored in the preparation of graphene oxide (GO)-poly(styrene-co-DHMPA) assemblies as adsorbent materials. RAFT synthesized poly(styrene-co-DHPMA) samples characterized by uniform dispersity were morphological transformed into nanospheres, whose cores were styrene rich and corona, catechol rich. The nanospheres were then linked to GO via the catechol functionalities, resulting in assemblies integrating a variety of molecular separation interactions. Adsorption tests carried out with the assemblies on methylene blue and tebuconazole contaminated water (5ppm initial concentration), showing over 99.8 % and 72.5 % removal respectively, both following pseudo second-order kinetics.
Bio-inspired by the adhesive properties of marine sessile organisms, a series of poly[N-(3,4-dihydroxy aryl) acrylamide]-co-styrene samples were prepared via RAFT synthesis and Lewis-acid deprotection approaches for underwater adhesion of plastic substrates. Adhesion testing in DI water and seawater indicated that there is a threshold copolymer hydrophobicity beyond which the optimal mole fraction of catechol in a copolymer required for the maximum bonding strength is similar for both media.
Through controlled macromolecular systems design under RAFT regime and catechol binding chemistry, coupled with a fundamental understanding on the structures and properties of these new materials, this thesis affords a new methodology for preparing materials as flocculants, thermoresponsive hydrogels, adsorbents or underwater adhesives for large-scale water-based applications.
Oyeneye, Olabode, "Adaption of Catechol and Reversible Addition-Fragmentation Chain-Transfer (RAFT) Chemistries for Water-Based Applications" (2017). Electronic Thesis and Dissertation Repository. 5129.
Available for download on Monday, November 19, 2018