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Aromatic-Alicyclic Polyimides: From Basic Aspects Toward High Technologies
Published in Andreea Irina Barzic, Neha Kanwar Rawat, A. K. Haghi, Imidic Polymers and Green Polymer Chemistry, 2021
Camelia Hulubei, Elena Hamciuc, Corneliu Hamciuc
Doddamani and its group60 have also used a green chemistry approach to manufacture nonlinear optical PI materials. Their idea relied on coupling N-methyl-N-(2-hydroxyethyl)-4-amino benzaldehyde with barbituric acid, 1,3-indanedione, and 1,3-diethyl-2-thiobarbituric acid with the role of acceptors through stilbene linkage. The main advantage of this concept was that the synthesis reactions were performed in less than 10 min at room temperature and required no other solvents but water. The reaction of poly(hydroxy-imide)s with chromophores through Mitsunobu procedure led to two different side-chain PIs. The imidic polymers were mainly developed based on aromatic dianhydrides (4,4′-(hexafluoroisopropylidene) diphthalic anhydride or pyromellitic dianhydride) and 4,4′-diamino-4″-hydroxytriphenylmethane. The resulting materials have good solubility in polar aprotic solvents, being easy to process. The samples display different molecular orientations after electrical poling. The Maker fringe method allowed determining the second harmonic generation coefficients of the corona-poled PI foils, indicating values that vary between 59.33 and 77.82 pm/V. Raised thermal endurance was noticed for the PIs as a result of the extensive hydrogen bonds in the matrix. The reported materials present no decay in second harmonic generation signals under 110°C, revealing their suitability for nonlinear optical devices.
Macromolecules of Polyamic Acids and Polyimides
Published in Michael I. Bessonov, Vladimir A. Zubkov, Polyamic Acids and Polyimides, 2020
Aprotic solvents have a rather high dielectric constant and do not contain acidic hydrogens. Therefore, when dissolving ionic compounds these solvents solvate mainly cations, leaving anions relatively free. As a result of electrolytic dissociation of the polyamic acid macromolecule, uncompensated negative charges appear in the carboxylic groups. Interaction between adjoining similarly charged groups along the macromolecule chain (short-range interaction) leads to its local “straightening”, i.e., to an increase in the chain rigidity. Naturally, the drawing closer of chain sections lying at a distance from one another gets more difficult (long-range interaction increases) if they are charged similarly. An increase in the short-range interaction is the most important of these two consequences of polyamic acid macromolecule ionization. However, it is rather small since polyamic acids are weak polyelectrolytes.34, 35 Only a small part of the carboxylic groups dissociate in polyamic acid solution. Correspondingly, the number of counterions (H+ cations) being formed is also small. Dilution of the solution up to the concentration required to determine the intrinsic viscosity does not effectively change the solution ionic strength (quasi-isoionic dilution). As a result ηsp/c vs. c dependence has a “normal” shape. This is frequently taken for the absence of a polyelectrolytic effect. However, the absence of deviation of this dependence from the straight line does not always mean the absence of a polyelectrolytic effect.
Theoretical Consideration Of Solubility
Published in A. L. Horvath, Halogenated Hydrocarbons, 2020
The line that is usually drawn between polar and nonpolar solvents is at dielectric constants having a value of 30. In this division, CH3OH belongs to the polar group of compounds, whereas C2H5OH is a nonpolar solvent (μ = 24). Furthermore, both polar and nonpolar classes can be subdivided into protic and aprotic subclasses, (i.e., hydrogen-bonded and nonhydrogen-bonded solvents). The molecules of aprotic solvents are more polar than are those of protic solvents. Therefore, the ion-dipole and molecule-dipole solute-solvent interactions are stronger in dipolar aprotic solvents. These molecules are more polarizable than the molecules of protic solvents, and the London dispersion forces are also more pronounced in dipolar aprotic solvents (Symons, 1977).
Effect of aprotic solvent on characteristics of Al2O3 ceramic hollow fiber substrates prepared by phase inversion for hydrogen permeation applications
Published in Journal of Asian Ceramic Societies, 2022
Edoardo Magnone, Seung Hwan Lee, Min Chang Shin, Xuelong Zhuang, Jae Yeon Hwang, Jeong In Lee, Jung Hoon Park
In this work, a two-step process involving phase inversion and high-temperature sintering was used to prepare α-Al2O3 hollow fiber substrates [24]. In particular, to prepare the AlCHFS we used a mixture in equal parts of two different particle sizes of Al2O3 powders i.e. about 0.3 μm (99.9%, Kceracell Co., Korea) and 0.5 μm (99.9%, Kceracell Co., Korea) in diameter [25]. Polyethersulfone (PES, Ultrason® E6020P, BASF, Germany) as a polymer binder was used for preparing the starting solution. Polyvinylpyrrolidone (PVP, Sigma Aldrich, USAA) was used as an additive with surfactant properties. In all preparations, the weight ratio of 0.3 μm Al2O3, 0.5 μm Al2O3, PES, and PVP on the dope solution is constantly equal to 30, 30, 5.75, and 0.75 wt.%. To determine the composition of the dope solution, we use the results obtained in previous literature [26–28]. The remaining 33.5% of the dope solution is made up of aprotic solvent. We investigated three different types of aprotic solvents in this study: (1) Dimethyl sulfoxide (DMSO, 99.5%, Samchun Pure Chemical Co., Ltd, Korea), (2) N,N-Dimethylacetamide (DMAC, 99.5%, Samchun Pure Chemical Co., Ltd, Korea), and (3) 1-Methyl-2-pyrrolidone (NMP, 99.5%, Samchun Pure Chemical Co., Ltd, Korea). The DMSO, DMAC, and NMP solvents were selected to cover a wide range of Hansen solubility parameters like dispersion force component (δd), polar bonding component (δp), and hydrogen bonding component (δh) [29]. The total Hildebrand solubility parameter (δt) of aprotic solvents used in this work are calculated as follows: