Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemistry

Major Professor

Julie P. Harmon, Ph.D.

Committee Member

Shengqian Ma, Ph.D.

Committee Member

Abdul Malik, Ph.D.

Committee Member

Sylvia Thomas, Ph.D.

Keywords

Polyetherdiamine, Hydrogen Bonding, Polyurea, Ureidopyrimidone

Abstract

In this work, Polyimides were synthesized by incorporating an aromatic diamine monomer with a methylene linker, 4,4'-methylenebis(2,6-dimethylaniline) (MBDMA), to make a robust main chain along with aliphatic polyetherdiamine backbone linkers to reduce rigidity. The polymers were designed to exhibit thermal properties in between those of conventional aromatic polyimides and polymers with wholly aliphatic ether diamine links. Through dynamic mechanical analysis and differential scanning calorimetry, it is shown that control of the molar ratios of the aromatic MBDMA and the composition and size of the aliphatic polyetherdiamine can be used to tune the glass transition temperature. The materials were characterized and further improved by exploring the interaction of the polymer chains.

First, we explored the behavior of the hydrogen-bonding between the polymer chains and then the packing order of the polymer strands. Hydrogen-bonding was provided by the incorporation of a urea linkage connected to a UPy unit as a terminal monomer and the introduction of a diisocyanate for some internal bonding sites. Through dynamic mechanical analysis and differential scanning calorimetry, it is shown that the addition of 1,6 Hexamethylene Diisocyanate and the 2-amino-4-hydroxy-6-methyl-pyrimidine increase hydrogen bonds content and improved the thermal and mechanical properties of the polyimide. Furthermore, the imide ring is an important component to maintain the physical and thermal stability of the polyimide-UPy and the polyimide-polyurea hybrids.

Secondly, we investigated the behavior of crystalline regions provided by the organized packing of polyethylene glycol into the formerly characterized polymers. Through dynamic mechanical analysis and differential scanning calorimetry, it is shown that the incorporation of polyethylene oxide diamine and the removal of methyl pending groups can be used to improve the organized packing of the chains, which ameliorates thermal and mechanical properties of the polyimide.

Furthermore, the crystalline regions, the terminal, and internal hydrogen bonding are important components to maintain the temperature and mechanical stability while maintaining the processability. The polymers were characterized by FTIR, NMR, GPC, WAXS, thermomechanical and calorimetric analysis (DSC, DMA, and Rheology), microhardness, and tensile testing.

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