Date of Award

Fall 9-24-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Yoan C. Simon

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Derek L. Patton

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Jeffrey S. Wiggins

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Sergei Nazarenko

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Xiaodan Gu

Committee Member 5 School

Polymer Science and Engineering

Abstract

Stimuli-responsive polymers respond to changes in their environment by altering their physical and chemical properties. Their responsiveness allows them to be used as sensors, mechanical actuators, delivery systems, and can yield either elongated lifetimes through healing mechanisms or shortened lifetimes through triggered degradation. Still a growing field in polymer science, researchers seek to expand the capabilities of these materials by improving their specificity, range, and mechanisms of both the stimuli and the response. The work presented explores stimuli-responsive materials, focusing on mechanical and light stimuli, and how to gain control of the response by specific changes in the polymeric material.

After a broad introduction in CHAPTER I (which includes peripheral work performed by the author), CHAPTER II focuses on how photodegradation catalyst dispersion can affect photodegradation rate in immiscible polyester blends. Blends of poly(ε-caprolactone) and poly(lactic acid) with either no additives; only compatibilizer; only photodegradation catalyst; or both compatibilizer and catalyst, are compared to their pristine polymers in terms of thermomechanical properties and aging. Improvement in flexural modulus is seen in blends with catalyst and with increased improvement in the compatibilized blend with catalyst. We then demonstrate that the blends with photodegradation catalyst degrade rapidly compared to blends without as expected, but that compatibilization did not positively affect photodegradation rate. This indicates that the mobility of the reactive oxygen species produced by the catalyst and responsible for degradation was not improved by compatibilization.

In CHAPTER III, we seek to gain better understanding of how polymer solution properties affect their degradation during ultrasonication, a method widely used to test mechanically responsive materials. In this chapter, we compare isotactic and syndiotactic poly(methyl methacrylate), allowing examination of scission rate in the absence of chemical alteration. The solution properties of both stereoregular polymers are investigated and the polymers exposed to ultrasonic irradiation. Using an a priori approach, we discuss the cause of the faster scission rate seen in isotactic poly(methyl methacrylate) as opposed to the syndiotactic polymer.

In CHAPTER IV, we give a summary of the work presented herein, offer guidance for improvement of the ultrasonication testing facilities, and detail two projects for future exploration.

ORCID ID

0000-0002-1097-340X

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