Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Christopher N. Bowman

Second Advisor

Jeffrey W. Stansbury

Third Advisor

Charles Musgrave

Fourth Advisor

Mark Stoykovich

Fifth Advisor

Marianela Trujillo-Lemon

Abstract

We explored formation-structure-property relationships in thiol-ene functionalized oligosiloxanes to create crosslinked networks. Specifically, nine oligomers were synthesized, three with thiol-functional silane repeats and three with allyl-functional silane repeats. Structural variations in each oligomer were systematically induced through the incorporation of non-reactive repeats bearing either diphenyl or di-n-octyl moieties, and the oligomer molecular weight was limited by the presence of monofunctional silane condensation species. The molecular weights and chain compositions of all oligomers were ascertained and subsequently used in the evaluation of network properties formed upon photopolymerization of thiol- and ene-functional reactants. Polymerization kinetics of the thiol-ene functionalized siloxanes were also investigated using photoinitiation owing to the spatial and temporal control afforded by this technique. In particular, the effects of the viscosity of the ene-functionalized oligomer and the degree of thiol functionalization on the observed polymerization rate were determined. Results showed that the speed of polymerization varied with changes to the rate-limiting step, which was heavily influenced by neighboring non-reactive functionalities. Moreover, the thiol-ene reaction was found to exhibity unimolecular termination exclusively in siloxane-based systems. Proposed use of the thiol-ene functionalized siloxane system as a dental impression material necessitated the development of a redox initiation scheme. Evaluation of the benzoylperoxide/dimethyl-p-toluidine redox pair in traditional systems showed bulk thiol-ene polymerizations comparable to photoinitiation with the added advantage of uninhibited depth control, as also demonstrated in small molecule thiol-ene coupling reactions initiated by this same redox system. Application of the redox pair to the siloxane system allowed for the viscoelastic properties as well as the feature replication abilities to be compared against commercial impression materials. The siloxane system was found to match the commercial material for strain recovery and stress relaxation and exceed its replication properties though it would require greater overall strength to function adequately in the clinical setting.

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