Effects of aromatic regularity on the structure and conductivity of polyimide‐poly(ethylene glycol) materials doped with ionic liquid

Abstract

An understanding of the structure and properties of polymer electrolyte systems can be crucial to a variety of different applications. The current work performs a study of the composition, structure and properties of poly(ethylene glycol) (PEG)-aromatic polyimide systems incorporating ionic liquids that are relevant to several applications especially fuel cell membranes. Composition was varied through using different aromatic dianhydrides, aromatic diamines and in some cases synthesis solvent. Properties were characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltamme-try. By varying solvent, aromatic regularity and expected rigidity can be tuned, impacting average conductivity by 30%. Varying the aromatic diamine can influence the length scale and amount of aromatic regularity, which can ultimately affect the conductivity by a factor of four. The maximum conductivity reached was 83 mS/cm at 80 C and 70 %RH.

Polyimide‐PEG Segmented Block Copolymer Membranes with High Proton Conductivity by Improving Bicontinuous Nanostructure of Ionic Liquid‐Doped Films

“…As a result, the EAN‐doped PI‐PEG membranes can be considered as having two distinctly different phases; one is the rubbery PEG ( T g ≈ –70 °C) domain highly swollen with EAN [PEG+EAN] and the other is the glassy 6FDA‐PDODA PI ( T g ≈ 160 °C; see Figure S2 and the figure caption, Supporting Information) plasticized with EAN. Importantly, there was no evidence of crystalline PEG phase in the copolymer according to the DSC measurements (see Figure S2, Supporting Information for DSC data), as also noted in the previous work . The spatial confinement by covalent bonding to the PI chains seems to prevent the crystallization of PEG segments (see Figure d) …”

“…Recent studies showed that segmented block copolymer (SBC) membranes comprised of aromatic polyimide (PI) and poly(ethylene glycol) (PEG) doped with an ionic liquid (IL) present an atractive potential to develop a new family of PEMs . In the PI‐PEG copolymer membranes, phase‐separated PEG domains swollen with IL act as the ion conducting phase and the PI phase serves as supporting matrix to provide for the required thermo‐mechanical properties.…”

“…In this study, we carried out detailed investgations of the nanoscale structural changes upon thermal annealing of PI‐PEG SBC membranes swollen with an ionic liquid and the accomanying increases of the ionic conductivity of the membranes. A specific copolymer system, prepared from 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) ( Figure a), 4,4′‐(1,3‐phenylenedioxy)dianiline (PDODA) (Figure b), and bis(3‐aminopropyl) terminated poly(ethylene glycol) (PEG1500, M n ≈ 1500) (Figure c), was studied because the resultant PI‐PEG copolymer (Figure d) showed the best performance among several monomer combinations in the previous work on the impact of the monomer structures, PEG contents, and PEG molecular weights on PEM performances . Also, ethylammonium nitrate (EAN) (Figure e) was used as a representative protic ionic liquid with labile protons because the EAN‐doped PI‐PEG membranes showed the highest ionic conductivity among several ionic liquids including propylammonium nitrate (PAN), methylammonium nitrate (MAN), and dimethylammonium nitrate (DMAN)…”

Mechanical, Dielectric, and Thermal Attributes of Polyimides Stemmed Out of 4, 4’–Diaminodiphenyl Ether

“…Therefore, it is necessary to conduct explorations on 2 of 9 their structure-property relationships for practical applications. Although some studies showed that the chain hardness constituted the extremely crucial factor which affects their attributes in a direct way [19][20][21][22][23], the structure-property relationships links PIs are still not well understood.…”

Design and synthesis of high heat-resistant, soluble, and hydrophobic fluorinated polyimides containing pyridine and trifluoromethylthiophenyl units

“…On the other hand, because of the rigid structure of the aromatic polyimide, polymer has high softening temperature and processing temperature, which limits their processability. 6 –10 As we all know, molecular structures have a strong effect on the properties of polymers. To overcome the weakness of the above-mentioned polymers, several efforts have been made worldwide to obtain a class of polyimides, which have good solubility and processability without impairing the performance and extending their technological applications in the industry.…”