The Synthesis of Anionic and Amine Containing Polymers for Potential Gas Separations
With the growth of industry, the need for gas separation has increased. In the last few decades, various types of polymeric gas separation membranes have been developed due to their advantages of energy-efficiency, easy operation processes, and low cost on assembly and maintenance. While it is crucial to develop high performance membranes that have high permeability and selectivity, it is also necessary for membranes to have good mechanical strength and thermal stability to withstand applications at various operation pressures. The objective of this research is to develop new synthetic routes to polymers for potential uses in gas separation applications. Initial efforts focused on the synthesis of sulfonyl polyimide ionomers (SPI). A novel SPI with tertiary amine cations (SPI[DIPEA]) was synthesized via a condensation polymerization. With the anionic charges on the pendant groups of SPI, ionic liquids can be combined with SPI polymers by simple cation exchanges. In this study, four different imidazolium species (i.e., 1-n-butyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium bromide, 1,3-dibutylimidazolium bromide, and 1-butyl-2,3,4,5-tetramethyl imidazolium bromide) were successfully embedded in SPI forming SPI[C4mim], SPI[C4dmim], SPI[C4bim], and SPI[C4m4im]. SPI[DIPEA] and SPI[C4mim] showed higher CO2 solubility than other gases (H2, N2, CH4) and this resulted in better CO2/ N2 and CO2/ CH4 ideal selectivities in comparison with SPI[Na]. Cationic imidazolium polymers (e.g., [PMDA-API-pXy][Tf2N] and [6FDA-API-pXy][Tf2N]) were also combined SPI[DIPEA] and SPI[C4mim] yielding binary polymer mixtures (i.e. SPI/[PMDA-API-pXy][Tf2N], SPI[C4mim]/ [PMDA-API-pXy][Tf2N], and SPI[C4mim]/ [6FDA-API-pXy][Tf2N]). However, attempts at preparing solution-casted membranes from these binary polymer mixtures failed due their poor processability. Next, the synthesis and characterization of anionic sulfonated polyimide and polyamide ionenes with negative charges on the polymer backbone were studied. In this study, the monomer amino-N-(4-aminophenyl)sulfonylbenzenesulfonamide was synthesized and reacted with dianhydrides (PMDA, 6FDA) and dichloride containing comonomers (1,3-benzenedicarbonyl dichloride and 1,4-benzenedicarbonyl dichloride, and adipoyl dichloride). The sulfonamide monomer had poor solubility in all common organic solvents. Different polymerization conditions (e.g., solvents, bases, and temperatures) were applied to combat the poor solubility of the reagents and produced polymers. However, the resulting polyimide and polyamide ionenes were found to be insoluble in all tested solvents and attempts to characterize these ionene polymers were challenging. The last chapter of this dissertation focuses on the polymerization of N-tert-butylcarboxy-2-methylaziridine (BOCMeAz) via anionic ring opening polymerization to form poly(BOCMeAz). The N-substitute BOC protecting group can be removed from the resulting polymer to form linear polypropyleneimine (PPI). The high amine density allows PPI to be used for CO2 capture. High molecular weight samples of poly(BOCMeAz) could not be achieved due to possible chain transfer to the DMSO solvent during the polymerization. Evidence for transfer to DMSO is shown by MALDI-TOF mass spectra and the H-D exchange in 1H NMR spectra. The rate of AROP of BOCMeAz is first-order with respect to the propagating polymer chain ends.
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