Ammonium ionenes are polycations that have quaternary nitrogens in their macromolecular backbone and are synthesized via step-growth polymerization technique. They offer interesting coulombic properties, and the synthetic design provides control over charge density. Non-covalent interactions including nucleobase hydrogen bonding and electrostatics were studied in ammonium ionenes. The non-covalent interactions are expected to increase the effective molecular weight of polymeric precursors and induce microphase separation due to intermolecular associations. The influence of non-covalent interactions on structure-property relationships of ammonium ionenes were studied regarding mechanical (tensile, DMA), thermal (DSC, TGA), and morphological (AFM, SAXS) properties. Hydrogen bonding interaction (10-40 kJ/mol) was introduced using DNA nucleobase pairs such as adenine and thymine. Novel adenine and thymine functionalized segmented and non-segmented ammonium ionenes were successfully synthesized using Michael addition chemistry. In non-segmented systems, we investigated the influence of spacer length on homoassociation and heteroassociation of complementary nucleobase-containing ionenes. Based on DSC analyses, complementary non-segmented ionenes made miscible blends. The Tgs of ionene blends with shorter spacer length (4 bonds between the nucleobase and secondary amine in the polymer backbone) followed the Fox equation, which indicated no intermolecular interactions. The longer alkyl spacer (9 bonds between nucleobase and secondary amine in the polymer backbone) provided efficient flexibility for the self-assembly process to occur. Thus, increasing the spacer length from 4-bonds to 9-bonds, the Tgs of the blends deviated from both Fox and Gordon-Taylor equations and demonstrated the presence of hydrogen bonding interactions. In segmented systems, we investigated the association between nucleobase-containing ionenes and their complementary guest molecules. Job's method revealed a 1:1 stoichiometry for the hydrogen-bonded complexes. These association constants for the 1:1 complexes, based on the Benesi-Hildebrand model were 94 and 130 M-1 respectively, which were in agreement with literature values for adenine and thymine nucleobase pairs (10-100 M-1). DSC thermograms confirmed no macrophase separation for 1:1 [ionene-A/T]:[guest molecule] complexes based on the disappearance of the melting peak of the guest molecule. Morphological studies including atomic force microscopy (AFM) demonstrated a reduced degree of microphase separation for the 1:1 complexes due to the disruption of adenine-adenine or thymine-thymine interactions. Poly(dimethyl siloxane)-based ammonium ionenes having various hard segment contents were synthesized. The charge density or hard segment content was tuned for appropriate application using low molecular weight monomer. The change in hard segment content had a profound effect on thermal, mechanical, rheological, and gas permeability. Microphase separation was confirmed using DSC and DMA in these systems. DMA showed that the rubbery plateau modulus extended to higher temperatures with increasing hard segment content. Tensile analysis demonstrated systematic increase in modulus of PDMS-ionenes with increasing hard segment content. Oxygen transmission rates decreased linearly as the wt% hard segment increased. / Ph. D.

The synthesis and characterization of a variety of ammonium ionenes from water-soluble coatings to high-performance elastomers are discussed. Water-soluble random copolymer ionenes were synthesized using the Menshutkin reaction from 1,12-dibromododecane, N,N,Nâ ²,Nâ ²-tetramethyl-1,6-hexanediamine, and 1,12-bis(N,N-dimethylamino)dodecane. The absolute molecular weights were determined for the first time using a multiangle laser light scattering detector in aqueous size exclusion chromatography and the weight-average molecular weights of these ionenes were in the range of 17,000-20,000 g/mol. Charge density increased with increasing molar ratio of N,N,Nâ ²,Nâ ²-tetramethyl-1,6-hexanediamine and the glass transition temperature (Tg) increased from 69 °C to 90 °C as the charge density increased. Small angle x-ray scattering (SAXS) showed isotropic scattering patterns for these ionenes. A limited study on cytotoxicity of these ionenes showed no direct correlation between charge density and cell viability for human brain microvascular endothelial cell line. A series of low hard segment (HS) content, poly(propylene glycol) (PPG)-based ammonium ionenes were synthesized using a Menshutkin reaction from bromine end-capped PPG oligomers (prepared using acid-chloride reactions) and N,N,Nâ ²,Nâ ²-tetramethyl-1,6-hexanediamine. Matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, titration analyses, and ¹H NMR spectroscopy, confirmed the difunctionality of bromine end-capped PPG oligomers. Thermal analysis revealed Tg's of -60 °C, comparable to pure PPG, using differential scanning calorimetery (DSC), dynamic mechanical analysis (DMA) confirming microphase separation, and an onset of degradation (Td) at 240 °C. Synthesis of a series of random block copolymer ammonium ionenes with an aliphatic 1,12-dibromododecane as part of the hard segment (33 wt% HS) enhanced film formation and supported microphase separation property. The Td and Tg did not change compared to PPG-ionenes with lower HS content. DMA and tensile testing demonstrated the influence of soft segment (SS) molecular weight and hard segment (HS) content on the mechanical properties of segmented ammonium ionenes. DMA showed the onset of flow, ranging from 100-140 ºC for 1K and 2K g/mol PPG-based ionenes respectively. SAXS revealed a Bragg distance scaled with soft segment molecular weight and ranged from 6.6 to 23.4 nm for 1K to 4K g/mol PPG-based ionenes, respectively. An investigation of the salt-responsive solubility property of random block copolymer PPG-ionenes revealed a dependence on PPG molecular weight. The 1K g/mol PPG-based ionenes with a hydrophilic (HPL)/hydrophobic (HPB) value ranging from one to three showed solubility in both water and one wt% NaCl aqueous solutions. The 2K g/mol PPG-based ionenes containing HPL/HPB value of two to 15 showed cloudy dispersions in water and one wt% NaCl solutions. The 4K g/mol PPG-based ionenes possessed the salt-responsive character; 4K g/mol PPG-based ionenes with HPL/HPB values of one to 12 showed milky dispersions in water, suspended particles in one wt% NaCl solutions and film precipitation at a HPL/HPB molar ratio of 19. / Master of Science