Date of Award
Summer 8-28-2022
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
Sarah Morgan
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Sergei Nazarenko
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Derek Patton
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
Xiaodan Gu
Committee Member 5 School
Polymer Science and Engineering
Abstract
This dissertation aims to elucidate different aspects of network formation in different thermosetting polybenzoxazines and the implications on the final morphology, free volume, solvent ingress, and thermomechanical properties. This research is divided into five distinct fragments 1) benzoxazine monomer synthesis, 2) implications of the meta-substitution of the aniline species in the cured benzoxazine network, 3) effect of the cure protocol on meta-substituted aniline based benzoxazine matrices, 4) investigation of the utilization of different bisphenol species for the formation of novel and known benzoxazine networks, and 5) the elucidation of the cure-induced shrinkage of benzoxazine networks utilizing an improved method developed within this research. A total of five highly pure benzoxazine monomers are synthesized from three different meta-substituted anilines –aniline, m-toluidine, and 3,5-dimethylaniline and two different bisphenol species –bisphenol A and bisphenol F-. The structure and purity of these benzoxazine species were proved through 1H NMR, 13C NMR, COSY (1H-1H), HSQC (1H-13C), and HMBC (1H-13C) experiments.The effects of the meta-substitution in aniline of the benzoxazine species on the final network and the importance of the central group of the bisphenol species on the processing properties were characterized taking several approaches (Chapter IV and VI). Kinetics and rheological studies characterized the polymerization of the meta-substituted aniline-based benzoxazine monomers. Then, the network and free volume of the cured polybenzoxazine matrices were analyzed through PALS and solvent submersion experiments. The thermal and mechanical properties were reported after DMA, TMA, and compression testing were performed on the final polybenzoxazine networks. iiiNext, the cure path dependency of meta-substituted aniline base benzoxazine and its effects on the morphology and performance of the fully cured networks was studied (Chapter V). First, DSC studies along with the DiBenedetto model are performed to elucidate the evolution of Tgand conversion. Rheological studies revealed the impact of the different ramp rates used on the gel point of each sample. TGA, DMA and PALS were used to elucidate the relationship between different cure pathways and the thermal stability, thermomechanical performance and network free volume.Finally, the cure-induced shrinkage of polybenzoxazines after a frequency-independent point of gelation was investigated herein (Chapter VII). Different benzoxazine samples were subjected to different isothermal cure cycles and their volumetric shrinkage was measured before and after the cool down through an improved method with the utilization of a rheometer
ORCID ID
0000-0002-6652-0207
Copyright
Bernardo Barea Lopez, 2022.
Recommended Citation
Barea-López, Bernardo L., "Importance of Alkyl Substitution on the Molecular Architecture and Thermomechanical Performance of Glassy Polybenzoxazine Networks" (2022). Dissertations. 2073.
https://aquila.usm.edu/dissertations/2073