Date of Award

Summer 7-14-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Christopher N. Bowman

Second Advisor

Wei Zhang

Third Advisor

David M. Walba

Abstract

This thesis is focused on understanding and implementation of the thiol-Michael addition reaction for controlling polymer structures and properties. The thiol-Michael addition `click' reaction has numerous advantageous characteristics for polymerization reactions, such as having a high reaction rate and yield under mild reaction conditions without the formation of byproducts, starting from a large selection of easily accessible monomers. Firstly, control of the onset of the thiol-Michael addition reaction was achieved by development of two different initiator systems, i.e., a latent initiator (nucleophilic initiator and acid inhibitor) and a photoinitiator (sensitizer, base-tetraphenylborate complex and radical inhibitor). Both initiator systems provided excellent control of the onset of the reaction and provided facile methods to form crosslinked polymer networks. Secondly, selectivities of various functional groups toward the thiol-Michael addition reaction were assessed, and it was demonstrated that multiple functional group combinations present over 99% selectivity of one functional group over the other. This concept of kinetically selective thiol-Michael addition reactions are implemented to control polymer structural evolution, and eventually led to dendrimer synthesis and multiphase network polymer formation. In dendrimer synthesis, a 5th generation dendrimer or dendritic-linear polymer conjugate were synthesized in less than a half day, and in the case of dendritic-linear polymer conjugate, the reactions were all in one-pot with just one purification step for the whole procedure. Multiphase network polymer formation was demonstrated by sequential, selective thiol-Michael addition reactions of multicomponent monomer mixtures, and it was shown that the material exhibits two distinct glass transition temperatures (10 and 55 °C). Thus, triple shape memory behavior was achieved with a stable intermediate shape. Lastly, spatiotemporal control of both the thiol-ene reaction and thiol-Michael addition reaction were utilized to form a material with patterned functionalities and material properties, starting from a mixture of multifunctional thiols and an excess of multifunctional acrylates. This approach is based on the difference in the thiol-vinyl reaction mechanisms between the radical pathway and the anionic pathway, in which the former consumes more acrylates via homopolymerization and the latter consumes both thiols and acrylates in a stoichiometric ratio

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