Willman, Jeremy Aaron (2020-12). Calixarenes, Cavitands, and Organic Cages Utilized to Construct Polymer Networks with Varied Porosities. Doctoral Dissertation.
Thesis
Calixarenes are a class of "cup-shaped" macrocyclic molecules which are notable for their modularity which permits the synthesis of many derivatives and their ability to bind small molecules which allows for their use in a range of applications such as sensing, catalysis, supramolecular assembly, host-guest chemistry, and separations. Several classes of these macrocyclic molecules were utilized to construct Porous Polymer Networks (PPNs), based on the hypothesis that the monomers' structures would modify the porosity of the resulting sorbents. One series of phenol-aldehyde PPNs was constructed with "pre-structured" calixarene monomers and systematically compared to chemically similar "unstructured" porous Novalac resins. The pre-structured calixarene-derived polymers were found to be more microporous than their unstructured Novalac resin counterparts. Additional differences were observed between the PPNs pairs in morphology, dependence on linking aldehyde equivalents, zeta potentials, dye affinities, and resistance to chemical fouling. Another series of PPNs derived from rigid bridged-calixarene cavitands were compared to flexible calixarene-derived polymers. The porosity of cavitand polymers were found to differ greatly from their flexible calixarene pairs, exhibiting a regular decrease in porosity with the length of the monomers' alkyl "feet" groups. The observations indicate that porosity of these PPNs was predominately defined by the rigid macrocyclic region of the cavitand while the attached functional groups occupied pore volume. The cavitand bridging groups are suspected to labilize during the thermoset synthesis, acting as templates to the polymer network structures. Finally, polymers were constructed from calixarenes that were pre-assembled into molecular capsules or "organic cages." It was hypothesized that the polymers derived from organic cages would have porosities modified by the monomers' molecular pores. While polymers were successfully derived from the organic cages through several different approaches, the products were found to be nonporous. The utilized organic cages may be unsuitable monomers for porous network formation due to steric considerations, and larger cages may have been more successful in this approach. While this work focused on exploring synthesis and porosity PPNs constructed from calixarenes, their potential for easy modification and functionalization should allow for the targeted application of these materials with further investigation.
