Date of Award
Campus Access Dissertation
Chemistry and Biochemistry
Ken D. Shimizu
Solvent programmable polymers (SPPs) were developed based on restricted rotation with the ability to respond and remember the stimuli-induced properties. The SPP was prepared via Ring Opening Metathesis Polymerization (ROMP). The recognition properties of SPPs can be modulated by heating in different solvents. At elevated temperatures, the carboxylic acid recognition groups have free rotation and can switch their relative orientations in response to the solvent. On cooling to room temperature, these solvent-induced changes were saved due to restricted rotation about the Caryl-Nimide bonds. Thus, the orientation of the carboxylic acid groups were maintained even when the imprinting solvent is removed or exchanged. The solvent-induced changes are also reversible, and the binding properties can be modulated by cycling between heating the polymer in a polar and nonpolar solvent. The solvent responsive behavior will fall off with <50% crosslinking. Thermodynamic studies showed large enthalpic terms and very small entropic terms which is consistent with the bond rotation mechanism.
The second aspect of the work presented involves examining the influence of functional monomer dimerization and aggregation on the efficiency of the molecular imprinting process. Specifically, the dimerization of the commonly utilized methacrylic acid (MAA) via hydrogen bonding in the prepolymerization complex and its influence on the binding properties of the resulting molecularly imprinted polymers (MIPs) was studied. MAA dimerization was found to be able to suppress the formation of background binding sites which made "observed" imprinting effect looked much larger. The equilibrium processes in the prepolymerization mixture were modeled using a computer simulation with the program COPASI. The simulation results were consistent with the experimental data. In another MIP system, the influence of functional monomer aggregation upon the binding properties of MIPs was also investigated. This study of tetrabutylammonium diphenyl phosphate (TBA-DPP) imprinted urea MIPs and non-imprinted polymers (NIPs) shows that functional monomer aggregation can greatly reduce the number of background sites by self-blocking recognition groups that are not bonded to template molecules. The studies of MAA dimerization and urea monomers aggregation showed that common method for characterizing the imprinting effect can lead to misidentification and overestimation of the imprinting effect with functional monomers that are able to dimerize or aggregate. We predict that functional monomers that can dimerize or aggregate and can form strong interaction with prospective template can improve the imprinting efficiencies by suppressing the formation of the background binding sites.
Zhang, Y.(2010). Molecularly Imprinted Polymers--New Insights and Strategies. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/299