Date of Award

Fall 12-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Dr. Jeffrey Wiggins

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Dr. James Rawlins

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Dr. Sergei Nazarenko

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Dr. Derek Patton

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Dr. Zhe Qiang

Committee Member 5 School

Polymer Science and Engineering

Abstract

High-performance polymers can retain functional properties when exposed to long-term or short-term durations of harsh conditions, such as mechanical action, at elevated temperatures (>177 °C). A mixture of intramolecular and intermolecular forces of and between polymer chains provide excellent property retention at elevated temperatures. Specifically, the highly aromatic nature of high-performance polymer backbones provides outstanding thermal stability, which is typically attributed to π-π stacking. However, the interrelationship between thermal stability and high aromaticity creates a challenging structure-processing relationship paradigm, which causes poor polymer processability in most high-performance polymers. Herein, it was demonstrated that rationally designing a crosslinking phenylethynyl imide oligomer with hydroxyl functionalities (oHIOs) greatly improved their solubility in common polar protic solvents, such as EtOH. The oHIOs were further capable of undergoing TR at similar temperatures to phenylethynyl crosslinking (350-450 °C), which greatly improved thermal stability of the final TR-PBOx network (Td5: 533 °C, Td10: 553 °C, char yield: 61% in N2), which was directly related to the TR conversion. Specifically, the highest thermal stability was observed in oHIOs that achieved the highest TR conversion (75%), which was observed in oHIOs that incorporated asymmetric monomers. TR conversion ultimately became diffusion limited in all oHIOs as Tg increased from both network formation and TR.

TR could be further leveraged in crosslinking co-ortho hydroxyl imide oligomers (Co-oHIOs) to manipulate the thermomechanical properties of TR-PBOIx networks, which led to a wide range of Tgs (248-443 °C, peak of Tan δ), CTEs (27-58 ppm/K), and water contact angles (71.3-90.9 °). Additionally, oHIOs could also be pyrolyzed to form polymer-derived carbons, which are another form of high-performance materials. The structural change in the oHIO backbone when preparing TR-PBOx networks resulted in well-defined, slit micropores between 6-7 Å with large BET surface areas (558-839 m2/g) and volumes (0.195-0.298 cm3/g), which was dependent on the carbonization time and temperature.

All studies remained focused on the utilization of TR for preparing high-performance materials. Evaluation of oHIO structure-processing-property relationships led to a wide range of polymer network and carbon matrix properties. TR provides a platform chemistry that can be broadly applied to a wide range of high-temperature applications.

ORCID ID

0000-0002-6309-4601

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