9-Alkylated fluorene-based poly(ether imide)s and their gas transport properties

Monomer Dependence of Colorless and Transparent Polyimide Films: Thermomechanical Properties, Optical Transparency, and Solubility

Six poly(amic acid)s (PAAs) were synthesized by reacting bis(3-aminophenyl) sulfone with various dianhydride monomers such as pyromellitic dianhydride, 4,4'-biphthalic anhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, 4,4'-oxidiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride. These PAAs were then converted to polyimide (PI) films by thermal imidization at various temperatures. To obtain colorless and transparent PI (CPI), the dianhydride monomer used in this study had an overall bent structure, a structure containing a strong electron-withdrawing -CF3 substituent or an alicyclic ring. In addition, some monomers contained ether or ketone functional groups in their bent structures. The thermomechanical properties, optical transparency, and solubility of CPI films with six different dianhydride monomer structures were investigated, and the correlation between the monomer structure and CPI film properties was clarified. Overall, CPI with an aromatic main chain structure or a linear structure had excellent thermal and mechanical properties. In contrast, CPI with a bent structure containing functional groups or substituents in the main chain exhibited excellent optical transparency and solubility.

Cellulose-based thermosensitive supramolecular hydrogel for phenol removal from polluted water

Pollution of phenolic effluent from spice and plastics factories has become increasingly serious. Thus, developing a green and highly efficient adsorbent to remove phenolic compounds from wastewater is of urgent need. In this study, cellulose graft copolymer was synthesized through grafting 4-vinylpyridine monomer and polyethylene glycol methacrylate to a molecular skeleton of cellulose by free radical polymerization. The supramolecular hydrogel was successfully synthesized by physical cross-linking of cellulose graft copolymer and α-cyclodextrin. These supramolecular hydrogels were thoroughly characterized and the adsorption performance (adsorption isotherms and adsorption kinetics) of phenol on the supramolecular hydrogel were investigated in batch operation. The supramolecular hydrogel not only exhibited excellent adsorption of phenol, but also demonstrated increased mechanical strength due to the introduction of a modified cellulose base material. The adsorption kinetics of phenol on the supramolecular hydrogel followed a quasi-second-order reaction, with a correlation coefficient of 0.9909. The adsorption isotherm conformed to the Langmuir adsorption isotherm, and the maximum adsorption capacity of phenol can reach 80.71 mg g^-1, which was 2-3 times higher than traditional carbon-based materials. The results demonstrate the great promise of the waste-derived supramolecular hydrogel to be used as an efficient adsorbent in wastewater treatment.

Macromolecular Design for Oxygen/Nitrogen Permselective Membranes-Top-Performing Polymers in 2020

Oxygen/nitrogen permselective membranes play particularly important roles in fundamental scientific studies and in a number of applications in industrial chemistry, but have not yet fulfilled their full potential. Organic polymers are the main materials used for such membranes because of the possibility of using sophisticated techniques of precise molecular design and their ready processability for making thin and large self-supporting membranes. However, since the difference in the properties of oxygen and nitrogen gas molecules is quite small, for example, their kinetic diameters are 3.46 Å and 3.64 Å, respectively, the architectures of the membrane macromolecules should be designed precisely. It has been reported often that oxygen permeability (PO2) and oxygen permselectivity (α = PO2/PN2) have trade-off relationships for symmetric membranes made from pure polymers. Some empirical upper bound lines have been reported in (ln α - ln PO2) plots since Robeson reported an upper bound line in 1991 for the first time. The main purpose of this review is to discuss suitable macromolecular structures that produce excellent oxygen/nitrogen permselective membranes. For this purpose, we first searched extensively and intensively for papers which had reported α and PO2 values through symmetric dense membranes from pure polymers. Then, we examined the chemical structures of the polymers showing the top performances in (ln α - ln PO2) plots, using their aged performances. Furthermore, we also explored progress in the molecular design in this field by comparing the best polymers reported by 2013 and those subsequently found up to now (2020) because of the rapid outstanding growth in this period. Finally, we discussed how to improve α and PO2 simultaneously on the basis of reported results using not only symmetric membranes of pure organic polymers but also composite asymmetric membranes containing various additives.

Aromatic polyamide nonporous membranes for gas separation application

Polymer membrane-based gas separation is a superior economical and energy-efficient separation technique over other conventional separation methods. Over the years, different classes of polymers are investigated for their membrane-based applications. The need to search for new polymers for membrane-based applications has been a continuous research challenge. Aromatic polyamides (PAs), a type of high-performance materials, are known for their high thermal and mechanical stability and excellent film-forming ability. However, their insolubility and processing difficulty impede their growth in membrane-based applications. In this review, we will focus on the PAs that are investigated for membrane-based gas separations applications. We will also address the polymer design principal and its effects on the polymer solubility and its gas separation properties. Accordingly, some of the aromatic PAs developed in the authors’ laboratory that showed significant improvement in the gas separation efficiency and placed them in the 2008 Robeson upper bound are also included in this review. This review will serve as a guide to the future design of PA membranes for gas separations.

New transparent and thermally stable cardo poly(ether imide)s derived from 10,10-bis[4-(4-amino-2-pyridinoxy)phenyl]-9(10H)-anthrone

A new diamine bearing flexible ether, rigid pyridine, and bulky anthrone pendent group, 10,10-bis[4-(4-amino-2-pyridinoxy)phenyl]-9(10 H)-anthrone (BAPPA), was prepared in three steps from anthrone. BAPPA was reacted with six conventional aromatic dianhydrides in N, N-dimethylacetamide (DMAc) to form the corresponding new poly(ether imide)s (PEIs) via the poly(ether amic acid) (PEAA) precursors with inherent viscosities ranging from 0.85 dL g−1 to 1.26 dL g−1 and thermal imidization. All the PEAAs could be cast from DMAc solution and thermally converted into transparent, flexible, and tough PEI films with tensile strength of 72.2–112.4 MPa, tensile modulus of 1.8–2.1 GPa, and elongation at break of 10–18%. These PEIs were predominantly amorphous and displayed excellent thermal stability with the glass transition temperature of 290–388°C, the 5% weight loss temperature of 480–514°C, and the residue of 68–43% at 800°C in nitrogen. The PEIs derived from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 4,4′-hexafluoroisopropylidenediphathalic anhydride exhibited excellent solubility in organic solvents such as N-methyl-2-pyrrolidinone, DMAc, N, N-dimethylformamide, pyridine, and even in tetrahydrofuran. Meanwhile, these PEIs also exhibited high optical transparency with the ultraviolet cutoff wavelength in the 374–427 nm range and the wavelength of 80% transparency in the range of 468–493 nm.

Fluorine in the structure of polymers: influence on the gas separation properties

Results of studies on the separation of gases and vapours using fluorine-containing polymers are integrated and analyzed. Methods for the synthesis of these polymers are considered, including direct gas-phase fluorination, plasma polymerization of fluorine-containing precursors and modification of organic polymers, as well as diverse syntheses of monomers containing C−F and C−CF3 bonds and their subsequent polymerization. Structure – property relationships for these polymers are elucidated and their actual and potential applications as membrane materials are discussed.

The bibliography includes 165 references.

Polyimides Containing Phosphaphenanthrene Skeleton: Gas-Transport Properties and Molecular Dynamics Simulations

A series of new semifluorinated polyimide (PI) films with phosphaphenanthrene skeleton were prepared by thermal imidization of poly(amic acid)s derived from a diamine monomer: 1,1-bis[2'-trifluoromethyl-4'-(4″-aminophenyl)phenoxy]-1-(6-oxido-6H-dibenz⟨c,e⟩⟨1,2⟩oxaphosphorin-6-yl)ethane on reaction with four structurally different aromatic dianhydrides. The chemical structures of the polymers were established by Fourier transform infrared and 1H NMR spectroscopy techniques. The polymers showed a good combination of thermal and mechanical properties (T d10 up to 416 °C under synthetic air and tensile strength up to 91 MPa), low dielectric constant (2.10-2.55 at 1 MHz), and T g values as high as 261 °C. Gas permeabilities of these films were investigated for four different gases CO2, O2, N2, and CH4. The PI films showed high gas permeability (P CO2 up to 175 and P O2 up to 64 barrer) with high permselectivity (P CO2 /P CH4 up to 51 and P O2 /P N2 up to 7.1), and the values are better than those of many other similar polymers reported earlier. For the O2/N2 gas pair, the PIs (PI A) surpassed the present upper boundary limit drawn by Robeson. A detailed molecular dynamics (MD) simulation study has been conducted to understand better the gas-transport properties. The effect of phosphaphenanthrene skeleton, its spatial arrangement, and size distribution function of the free volume were studied using molecular dynamics (MD) simulation and the results are correlated with the experimental data.

Aromatic polyamides and copolyamides containing fluorene group

A series of new aromatic polyamides (PAs) and copolyamides (CPAs) containing fluorene group have been synthesized through polycondensation reaction. The chemical structure was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR). PAs and CPAs exhibited the higher thermal stability ( Td15 > 378°C in nitrogen), the higher glass transition temperature ( Tg > 345°C), and excellent solubility in polar solvent. Gas transport properties of the PA and CPA membranes were investigated using different single gases (hydrogen (H2), carbon dioxide (CO2), oxygen (O2), methane (CH4), and nitrogen (N2)). We discussed the effect of chemical structure and operating temperature on gas transport properties. The results show that PA-1 containing a hexafluoroisopropylidene moiety exhibited the highest gas permeability ( PH2 = 12.71 Barrer, PCO2 = 12.26 Barrer, and PO2 = 2.62 Barrer) and reasonably good selectivity ( α(H2/N2) = 27.63, α(CO2/N2) = 26.65, and α(O2/N2) = 5.70) at 25°C and 1 atm. For all the membranes, gas permeability gradually increased with the increase in operating temperature, while the selectivity gradually decreased. These gas permeation results were well correlated with fractional free volume, interchain d-spacing ( dsp), and intermolecular interaction.

Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations

Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations.