Date of Award

5-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Bin Zhao

Committee Members

Mark D. Dadmun, Charles S. Feigerle, Wei He

Abstract

This dissertation presents the synthesis of stimuli-responsive hydrophilic diblock copolymers and the study of their behavior in water under various conditions. The polymers were made by “living”/controlled radical polymerization. Chapter 1 presents a background of this dissertation. Chapters 2-4 describe a family of doubly thermosensitive diblock copolymers with a small amount of carboxylic acid groups incorporated into either one or both blocks. The lower critical solution temperature (LCST) of the weak acid-containing block increases with increasing pH due to the ionization of carboxylic acid. Chapter 5 presents the preparation of pH-sensitive diblock copolymer micelle-embedded agarose hydrogels.

Chapter 2 describes the synthesis and solution behavior of poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate) (P(TEGMA-co-AA)-b-PDEGEA)). PTEGMA and PDEGEA are thermosensitive polymers with LCSTs of 58 and 9 °C [degree Celsius], respectively, in water. A 20 wt% aqueous solution of P(TEGMA-co-AA)-b-PDEGEA with pH of 3.11 underwent transitions from a free-flowing liquid, to a free-standing gel, to a hot liquid, and to a cloudy mixture upon heating. The Tsol-gel [sol-to-gel transition temperature] and Tgel-sol [gel-to-sol transition temperature] are closely related to the LCSTs of the two blocks. Upon raising pH, the Tgel-sol increased, while the Tsol-gel remained the same. Accordingly, only the upper boundary of the sol-gel phase diagram shifted upward.

Chapter 3 presents the tuning of Tsol-gel of moderately concentrated aqueous solutions of doubly thermosensitive diblock copolymers by incorporating a small amount of AA groups into the lower LCST block and changing the solution pH. The AA content had a significant effect on the pH dependence of Tsol-gel. Chapter 4 shows that by incorporating a small amount of carboxylic acid groups into both blocks of a doubly thermosensitive diblock copolymer, the C-shaped sol-gel phase diagram can be readily and reversibly shifted by changing the solution pH.

Chapter 5 presents the fabrication of pH-sensitive diblock copolymer micelle-embedded agarose hydrogels. The gel properties were not significantly affected by the incorporation of the micelles even when the polymer concentration reached 5 mg/g. The pH-induced release of the payload from the core of micelles in a hybrid gel was studied. Chapter 6 presents conclusions and future work.

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