Date of Award
Spring 4-21-2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
School
Polymer Science and Engineering
Committee Chair
Jeffrey Wiggins
Committee Chair School
Polymer Science and Engineering
Committee Member 2
Derek Patton
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Sergei Nazarenko
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Zhe Qiang
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
James Rawlins
Committee Member 5 School
Polymer Science and Engineering
Abstract
Phthalonitrile monomers undergo diamine-promoted polymerization by a complex reaction mechanism involving two competitive cure pathways, forming two primary network architectures: linear polyisoindoline chains and branched triazine crosslinks. The influence of the diamine curing additive on the polymerization pathway, and the influence of the resulting network architectures on cured network properties, have not been adequately explored within the phthalonitrile field. Two structurally different diamine curing additives, bis[4-(3-aminophenoxy)phenyl] sulfone (mBAPS) and 1,3-phenylenebis((4-(4-aminophenoxy)phenyl)methanone) (AEK-134), were studied for the polymerization of resorcinol phenylphosphate phthalonitrile (RPPhPN), where the influence of diamine structure and concentration on the polymerization behavior, network architecture, and bulk thermal and thermomechanical properties of RPPhPN were elucidated.
Methods of synthesizing the RPPhPN monomer and its synthetic precursor, 3-(3,4-dicyanophenoxy)phenol (ResPN), were optimized, enabling increased reaction throughput and improved product purity while employing methods more relevant for high-throughput industrial manufacturing. Baseline phthalonitrile networks were prepared by curing RPPhPN with the industrial standard diamine curing additive mBAPS; the effects of diamine nucleophilicity and concentration on polymerization behavior and cured network architecture were evaluated through comparisons to a novel diamine curing additive, AEK-134. The previously established consensus within the phthalonitrile field attributing higher diamine reactivity to a reduction in the polymerization temperature was refuted, as no correlation between diamine nucleophilicity and polymerization onset temperature was observed. mBAPS-RPPhPN networks contained a greater relative abundance of triazine compared to networks cured with AEK-134. Additionally, relative triazine content was observed to decrease with increased AEK-134 concentration, indicating a preference towards the polyisoindoline cure pathway. This phenomenon was attributed to the ketone functional groups within the AEK-134 diamine backbone which promoted proton-transfer events, thereby lowering the activation energy of polyisoindoline formation.
Thermal stability and char yield of RPPhPN networks increased with increased triazine content due to the more rigid, crosslinked structure of the triazine architecture. Alternatively, increased polyisoindoline content within cured RPPhPN networks correlated with increased glassy modulus, decreased rubbery modulus, and increased dampening factor in the rubbery state. This was attributed to polyisoindoline chain flexibility and linearity, which facilitated segmental packing in the glassy state and energy-dissipating molecular relaxations in the rubbery state. Our evaluation of structurally dissimilar diamines aimed to deepen the understanding in the phthalonitrile field regarding diamine curing additives, which can direct polymerization pathways and alter the properties of cured RPPhPN networks.
Recommended Citation
Richardson, Tyler J., "The Influence of Diamine Curing Additives on the Network Architecture of Phthalonitrile Thermosetting Polymers" (2023). Dissertations. 2160.
https://aquila.usm.edu/dissertations/2160