Polyimides diamine effect properties

The 6FDA/BDAF polyimide was modified using PPD in an effort to "stiffen" the polymer backbone and improve thermal performance (Tg). A better overall property balance was achieved in several of these 6FDA/BDAF/PPD copolyimides. A series of random copolymers was prepared in which the level of PPD was varied from 0% to 100% based on the total moles of diamine. The incorporation of PPD had little effect on the dielectric constant but did result in improved thermal performance and was accompanied by increased moisture uptake (Figures 1,2, and 3). This behavior is consistent with the overall reduction in the amount of bound fluorine in the polymer backbone however, additional work is required to establish a direct correlation. A reasonable property balance was realized over a range of 40 to 60 mole% PPD which displayed dielectric constants from 2.85 to 2.90, moisture absorption from 1.5% to 2.0%, and Tg from 280°C to 290°C. In addition, the 6FDA/BDAF/PPD copolyimides displayed somewhat less solvent sensitivity than the 6FDA/BDAF homopolymer as described above. 

Jang et al. [85] prepared a highly kinked diamine (3-31 in Table 3.3), a fluorinated diamine (3-32 in Table 3.3), and a biphenyl based-fluorinated diamine (3-33 in Table 3.3) and studied the color intensity and optical properties of the synthesized polyimides. Introduction of kink structures disrupted effective CTC formation, leading to colorless polyimide films with high transmittance. Wang et al. [86] developed meta-diamine, namely 4,4 -/ /s (3-amino-5-trifluoro-methylphenoxy) biphenyl (3-34 in Table 3.3), with the aim of improving the melt processability and solubility of the polyimides. Shao et al. [87] designed a -CF3-substituted unsymmetrical diamine (3-35... 

W. Jang, D. Shin, S. Choi, S. Park, H. Han, Effects of internal linkage groups of fluorinated diamine on the optical and dielectric properties of polyimide thin films. Polymer 48 (7)(2007) 2130-2143. 

Table 12 lists the properties of this PI with those of PMDA-TFDB for comparison. In spite of the presence of electron-withdrawing -CF3 substituents, the maintained reactivity of TFDB is most likely based on the m a-substitution onto benzidine. If the (7r /i(7-substituted diamine counterpart was used, it must be difficult to obtain high molecular weight PAA in the conventional way because of its expected much lower reactivity. The transmission spectra of a series of TFDB-based Pis in Fig. 58 indicate how the 6FDA-TFDB polyimide film is optically transparent. A secondary positive effect of the -CF3 substituents in TFDB on the film transparency is the weakened intermolecular cohesive force due to lower polarizability of the C-F linkage. This functions negatively to interchain CTC formation. 

Significant improvements in condensation polyimide adhesives have been made by chemical modification of the diamine or dianhydride monomers, by use of copolymer composition and by use of a unique ether solvent as the pol3nnerization medium. The effect on adhesive properties was studied and a family of adhesives developed whose bonding pressures (40-200 psi) and use temperature (up to 300°C) can be varied with composition to cover a wide range of practical applications. Alterations in the polymer backbone have also led to imidized films that have sufficient flow for possible use as film adhesives. 

The thermal stability of a polyimide is also dependent upon its molecular structure, but such stability does not necessarily relate to good adhesive properties and previous research has emphasized the former. Further, most commercially available polyimide adhesives are based on particular dianhydride and diamine starting materials because of their availability and low cost, which are major determining factors for production. However, the effect of structure variations on adhesive properties should be the prime concern of research to assess the ultimate capacity of a new resin system. Subsequent development should be directed toward economic factors. 

Polyimide containing poly(ethylene oxide) is a simple and convenient way to improve the gas separation properties. The copolymers are synthesized by the reaction of dianhydride and diamines with/without amine-terminated poly(ethylene oxide). Maya el al. and Munoz et al. reported thermal treatment effect of PEO-Z)-PI copolymer on the gas permeation properties. Phase segregation of the polymer chain at higher treatment temperature to 300 °C contributed to improvement of gas permeability of the membrane. Molecular weight of poly(ethylene oxide) of 6000 was appropriate to induce microphase separation. CO2 permeability was reached from 2.3 to 24 Barrer according to the PEO composition before thermal treatment, while it was enhanced by three to ten times higher permeability after thermal treatment at 300 °C without serious reduction in permselectivity. 

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