Properties of Aromatic Polyimides

The relationship between the structures and properties of polyimides must be clarified in order to design the polyimides suitable for application of some fields. In this section, the properties of characteristic polyimides are introduced. 

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The synthesis as well as the structure and properties of aromatic polyimides has been reviewed.This combination of synthesis, structure, and properties is a general characteristic of papers in this field. For example, the preparation of polyimides from di-isocyanates, poly(o-amino-o-carbonyl)amides, maleimides, and Af-(4-substituted phenyl)itaconimides, all follow this pattern. The preparation of polyimide fibres, wet spun from solution, has also been given. ... 

Key properties of aromatic polyimides are their outstanding thermooxidative stability and high resistance to radiation and to deformation under load at elevated temperatures. This section discusses the properties of polyimides in general. 

Sava I., Chisca S., Wolinska-Grabczyk A., et al. Synthesis and thermal, mechanical and gas permeation properties of aromatic polyimides containing different linkage groups. Polym. Int. 64 no. 1 (2015) 154-164. 

Hsiao S-H, Chen W-T. Syntheses and Properties of Aromatic Polyimides Based on 1,1-Bis[4-(4-aminophenoxy)phenyl]-l-phenyl-2,2,2-trifluoroethane and l,l-Bis[4-(4-aminophenoxy) phenyl]- -phenylethane. J. Pol)mi. Res. 2003 10 95-103... 

The outstanding property of aromatic polyimides is their thermal stability. Films of the polyimide prepared from pyromellitic dianhydride and 4,4 -diaminophenyl ether are stable in air up to about 420 C above this temperature volatilization occurs. Mechanical and electrical insulation properties are maintained after prolonged exposure to elevated temperatures for example, after 1000 hours in air at 300°C the polymer retains 90% of its initial tensile strength and 90% of its initial dielectric strength. At room temperature the physical and electrical properties of the polyimide film are comparable to those of poly(ethylene terephthalate) film. The resistance of the polyimide to most... 

The outstanding property of aromatic polyimides is their thermal stability. Films of the polyimide prepared from pyromellitic dianhydride and 4,4 -diaminophenyl ether are stable in air up to about 420°C above this tempera-... 

Optical properties, of colorless polyimides, 277-279 Optical rotation, 490 Opto-electronic targets, 271-272 Organic phase-soluble aromatic polyesters, 77... 

Recently much effort has been made to induce liquid crystallinity in polyimides. Kricheldorf et al., Chen et al., and Sato et al. have suggested that an aromatic im-ide ring may be an excellent mesogen through their studies on thermotropic liquid-crystalline polyimide-esters [41-54] and polyimide-carbonates [55, 56]. Some thermotropic properties of aromatic polyether-imides have also been reported by Asanuma et al. [57]. 

Kim TH, Koros WJ, Husk GR, and O Brien KC. Relationship between gas separation properties and chemical-stmcture in a series of aromatic polyimides. J. Membr. Sci. 1988 37 45-62. 

We have previously reported that polyimides obtained by one-step high-temperature polycondensc on of diaminotrif nylmethane (DA-TPM) and aromatic dianhydrictes yield flexible and tou films with good mechanical properties. (5-7) Properties of these polyimides, named PI-TPMs, are mainly due to the homogeneity of the repeating units in the polymer backbone, which was demonstrated by UV-visible spectroscopy, CP-MAS C-NMR and WAXD analysis. 7,8)... 

Aromatic poly(amide-imide) (PAI) has an outstanding resistance not only to the thermal operations but also mechanical, electrical, and chemical operations. Although the properties of PAI are inferior to those of aromatic polyimide (PI), which is one of the most heat-resistant polymers, PAI has been widely utilized as a high performance heat resistant polymer as well as PI, because PAI is superior to PI in its workability in industry. ... 

Many research groups have been systematically studied the effect of the structure-property relationship on gas transport properties of fluorinated polyimides. In this connection, Kim et al. investigated the effect of incorporating fluorinated alkyl side groups into polyimide membranes in terms of their physical and gas permeation properties (Table 3.5) [61]. They demonstrated four polyimides with fluorinated side groups and another four without side groups by polycondensation of 2-(perfluorohexyl)ethyl-3,5-diamino benzoate (PFDAB) and m-PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively (Scheme 3.12). 

C.P. Yang, J.H. Lin, Syntheses and properties of aromatic polyamides and polyimides based on 3,3-( w[4-(4-aminophenoxy)phenyl]-phthalimi-dine. Polymer 36 (13) (1995) 2607-2614. 

Cosutchi AI, Nica S-L, Hulubei C, Homocianu M, loan S. Effects of the aliphatic/aromatic stmcture on the miscibility, thermal, optical and rheological properties of some polyimide blends. Polym. Eng. Sd. 2012 52(7) 1429-1439. 

The properties of the polyimides from APAB are summarized in Table 7.9. Like the pol5nmides ftom TAHQ, these pol)dmides showed low water absorption, and the CTE values were lower than those of the polyimides from TAHQ. The low CTE values were explained by the imidation-induced in-plane orientation induced by the p-aromatic ester linkage. 

Table III lists the properties of perfluorinated polyimides, along with those of partially fluorinated and unfluorinated polyimides. The structure of PMDA/ODA is the same as that of Dupont s Kapton. Because of the direct introduction of fluorines into the aromatic rings and the flexible structure of the lOFEDA component, the polymer decomposition temperatures and Tg s of perfluorinated polyimides are slightly lower than those of conventional poly imides. The thermal stability of these films is nonetheless high enough to withstand the manufacturing process for IC s and muitichip modules.

Design of the reactions via long-lived active intermediate was found to be important for developing photosensitive polyimide tystems, and this concept is especially effective for the reactions in solid state 11), because the solid-state reactions are controlled by the molecular motions 12). In addition, change in the electronic state in polymer solid was found to affect the efficient of their photoreactions. Charge-transfer structure is one of the characteristic nature of aromatic polyimides, which is affected by the change in their physical properties, and which in turn controls their photoreactivities. 

This procedure is not well suited for aromatic diamines, because their basicity is 5-6 orders of magnitude lower than that of aliphatic diamines. This problem prompted the elaboration of a new approach which became the standard procedure for the technical production of polyimides (see Formula 6.2, bottom). At first the diamine is directly reacted with the dianhydride yielding a polyamic acid which in most cases is soluble in the reaction medium (e.g., dimethyl acetamide or NMP) [43, 47, 48]. This solution which is useful for casting films, may be stored at — 10 °C for several months. Heating of poly(amic acid)s to 200 °C or better to 250-300 °C promotes the inmidization process the progress of which increases with time and temperature. Stmcture and thermal properties of several polyimides prepared by the DuPont group before 1964 are compiled in Table 6.3. 

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