Linear poly(ethylenimine), [LPEI], is a synthetically versatile polymer host compared to poly(ethylene oxide), in that various groups can be attached to the backbone nitrogen atoms. The interactions of LPEI with sodium cations are modeled by solutions of N,N'-dimethylethylenediamine, DMEDA, containing dissolved sodium triflate [NaTf]. During these studies, the crystalline compound (DMEDA)(2)(NaTf)(5) was discovered and characterized by X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, and Raman spectroscopy. The compound crystallizes in polymeric chains in a triclinic unit cell of the P $(1) over bar $ space group. In the crystal, the sodium ions are both five- and six-coordinate. A spectroscopic comparison of DMEDA, the (DMEDA)2(NaTf)5 crystal, and (DMEDA),NaTf solutions over a composition range of 7.5:1 to 1.5:1 [DMEDA:NaTf, molar ratio] was conducted using infrared and Raman spectroscopy. In (DMEDA)(2)(NaTf)(5), the triflate ions vibrate as either [Na2Tf](2+) or [Na3Tf](2+) species due to the coordination of the triflate ion by sodium ions. However, in solution, only the [Na2Tf](+) species is present at high NaTf compositions. At a 7.5:1 DMEDA/NaTf composition, contact ion pairs [NaTf] are the dominant species.

Linear poly(N-methylethylenimine), LPMEI, a methylated derivative of linear poly(ethylenimine), shows potential as a polymer electrolyte host. The interactions of LPMEI with lithium and sodium cations are modeled by solutions of N,N,N',N',N"-pentamethyldiethylenetriamine, PMDETA, containing either dissolved LiCF3SO3 (LiTf) or NaCF3SO3 (NaTf). During these studies, crystalline compounds were discovered and characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy (IR), and Raman spectroscopy. Crystals of the NaTf complex, (PMDETA)NaTf, were of sufficient size to allow a structure determination by X-ray diffraction. The (PMDETA)NaTf crystallizes as two dimers with different symmetries in a monoclinic unit cell in the P2(1)/c space group. A spectroscopic comparison of PMDETA, the crystalline complex PMDETA-LiTf, crystalline (PMDETA)NaTf, and their corresponding salt solutions over a composition range of 1.7:1 to 6.7:1 (PMDETA:MTf molar ratio, M = Li+, Na+) was carried out with IR and Raman spectroscopy. The dominant species in the (PMDETA),NaTf solutions is the triple cation [Na2Tf](+), even at a 6.7:1 PMDETA:NaTf molar composition.

Linear poly(ethylenimine) (LPEI) is an NH-containing analog of poly(ethylene oxide) (PEO). Various groups (e.g. CH3) can be attached to the nitrogen atoms in order to decrease the crystallinity and eliminate hydrogen bonding of the host polymer. This paper focuses on linear poly(N-methylethylenimine), LPMEI, with dissolved lithium triflate (LiTf) and sodium triflate (NaTf). These electrolytes were investigated using infrared spectroscopy, differential scanning calorimetry (DSC), and impedance measurements of the conductivity. A spectroscopic comparison of LPMEI containing LiTf and NaTf over a composition range of 5:1 to 20:1 (nitrogen:cation) shows that contact ion pairs are the predominant species in both systems except for the 5:1 NaTf sample, where the “free” triflate ions are the predominant species. Furthermore, there is an increase in the degree of ionic association with increasing salt concentration in the LiTf systems. The effect of salt concentration on the glass transition temperature (Tg) of the polymer host was examined using DSC. In LPMEI, Tg occurs at −91°C and increases to 3°C at a 5:1 (N:Li) composition. Conductivity measurements of the LPMEI:LiTf system over a composition range of 5:1 to 20:1 are compared with the LPEI:LiTf systems for temperatures between 25 and 60°C. In addition, X-ray powder diffraction (XRD) show a significant presence of crystalline domains in the LPMEI:NaTf samples.

Linear poly(ethylenimine) (LPEI) has been modified by reductive alkylation to form linear poly(N-(2-(2-methoxyethoxy)ethyl)ethylenimine) (LPEI-G2) as verified by nuclear magnetic resonance spectroscopy (NMR). The resulting LPEI-G2 has short methyl-capped oligo(ethylene oxide) side-chains attached to the LPEI backbone. Characterization of pure LPEI-G2 and LPEI-G2 complexed with lithium triflate (LiTf) was carried out over a variety of concentrations using infrared (IR), differential scanning calorimetry (DSC), and impedance techniques. Initial spectroscopic studies indicated that at a 20:1 oxygen atom to lithium ion ratio, “free” ions are the dominant triflate species present. At the same composition, the electrolyte has a Tg of −60°C and a conductivity 7×10−5 S cm−1 at 60°C. The vibrational spectra and conductivity values of samples at O:Li compositions of 20:1 and 5:1 will be discussed.

Linear poly(N-methylethylenimine) (LPMEI), a methylated derivative of linear poly(ethylenimine) (LPEI), shows potential as a polymer electrolyte host. The interactions of LPMEI with lithium and sodium cations are modeled by solutions of N,N,N',N'-tetramethylethylenediamine, TMEDA, containing either dissolved lithium triflate (LiTf) or sodium triflate (NaTf). During these studies, crystalline compounds were discovered and characterized by X-ray diffraction, differential scanning calotimetry, and Fourier transform infrared spectroscopy (FT-IR). The TMEDA:LiTf crystallizes as dimers in an orthorhombic unit cell in the Pccn space group; however, the TMEDA:NaTf crystallizes as tetramers in a triclinic unit cell in the P (1) over bar space group. A spectroscopic comparison of TMEDA, TMEDA:LiTf crystal, TMEDA:NaTf crystal, and their corresponding salt solutions over a composition range of 5:1 to 20:1 (nitrogen: cation, molar ratio) is carried out using FTIR and Raman spectroscopy. The triple cation species [Li2Tf](+) is the dominant species in the TMEDA:LiTf solution and exclusively present in the crystal. However, the dominant species in the TMEDA:NaTf samples is the aggregate [Na3Tf](2+). The N-C-C-N dihedral angle, which appears to be a mixture of gauche minus and trans in both LiTf and NaTf solutions, changes to gauche minus upon crystallization. Finally, the vibrations of individual TMEDA molecules appear to be completely decoupled in the TMEDA:LiTf crystal, although each dimeric unit contains two TMEDA molecules.