Date of Award

Summer 8-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Derek L Patton

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Sergei Nazarenko

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Zhe Qiang

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Yoan Simon

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Xiaodan Gu

Committee Member 5 School

Polymer Science and Engineering

Abstract

Photoinduced thiol-catalyzed hydrogen abstraction and beta-scission of acyclic benzylidene acetals is demonstrated as a new route to “command-destruct” polymer thermosets. Using this approach, we show that poly(thioether acetal) networks synthesized via thiol-ene photopolymerization rapidly degrade to alkyl benzoate byproducts when triggered with light, transitioning from solid to liquid within seconds. The light-driven construction and destruction processes, accessible via distinct differences in kinetics, are readily amendable for photopatterning, additive/subtractive manufacturing, and wavelength-selective applications.

The first chapter of this dissertation details the development of command-destruct poly(thioether acetal) networks via a previously unexplored mechanism for polymer degradation. The degradation mechanism is confirmed via NMR and FTIR spectroscopy and comparison with model compounds. Additionally, this chapter explores the factors required for and influencing degradation, such as thiol:ene stoichiometry, radical photoinitiator concentration, and UV irradiation intensity.

The second chapter explores tuning the network degradation kinetics via exploiting substituent effects in the acetal crosslinkers. Specifically, a library of substituted bis-allyl benzylidene acetals with electronic substituents ranging from highly donating to highly withdrawing were studied in thiol-ene networks and analogous small molecule studies. Relative degradation kinetics were measured using RT-FTIR spectroscopy and fitted to a Hammett linear free energy model to quantify reaction susceptibility to substituent effects. These effects were further quantified in bulk network degradation through real-time photorheology experiments. Furthermore, DFT computational modeling was explored as a tool to study substituent effects on acetal beta-scission in silico.

ORCID ID

https://orcid.org/0000-0002-9352-4940

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