Copolyimides

Copoly(amide-imides) comprise an important class of copolyimides that have been developed into a commercial product. Incorporating the amide linkage into the PI makes the polymer more tractable than simple Pis, but involves a loss in thermal stabiUty. However, copoly(amide—imides) still possess quite good thermal stabiUties, intermediate between those of polyamides and Pis (12). They are relatively inexpensive to synthesize. 

A number of phosphorus containing polyimides were synthesized by Varma and coworkers and their properties were studied [137-141]. Polyimides have also been synthesized by the reaction of benzophenonetetra-carboxylic dianhydride (BTDA) and bis(3-aminophen-yl)methylphosphine oxide [142]. Copolyimides were... 

From a mechanistic point of view, the polyimide synthesis via the polyamic acid is not a convenient method of preparing the block copolyimide for two main... 

Figure 5.15 Naphthalenic copolyimides with sulfonated block.

This method is being increasingly used for the preparation of soluble polyimides, and the rate is faster than in aprotic solvents. This method allows for preparation of block copolyimides.78... 

Figure 22. Six-membered ring copolyimide prepared with bulky unsulfonated diamine.

Kaneda et al. synthesized [61] a series of high molecular weight extended chain copolyimides (XV) by the reaction of PMDA and 3,3, 4,4 -biphenyltetra-carboxylic dianhydride (PPDA) with 3,3 -dimethyl-4,4 -diaminobiphenyl. Solvents used for the one-step synthesis to the fully cyclized imide structure were phenol, p-chlorophenol, m-cresol, p-cresol and 2,4-dicholorophenol. The polycondensations were performed at 180°C for 2h with a monomer concentration of 6% by weight and p-hydroxybenzoic acid used as a catalytic accelerator. A maximum of 50 mol % of PMDA could be used before the copolymer precipitated from solution. Reconstituted copolymers as isotropic dopes (8-10% by weight) in p-chlorophenol were dry-jet wet spun between 80 and 100 °C [62]. 

Table 3 shows the mechanical properties obtained on the as-spun and heat treated (450 °C) fibers as a function of dianhydride composition. The results summarized in the table reveal an amazing effect of heat treatment on the mechanical properties of the copolyimide fibers. 

Blend systems with significantly improved thermo-oxidative performance can be achieved through incorporation of carefully designed polyimide molecules. As shown in Table 1, a copolyimide containing the sulfone and 6F moieties which exhibits a Tg above 300 °C (see Fig. 5), as well as extraordinary short-term thermo-oxidative stability can be synthesized. 

The fluorinated copolyimides (including homopolyimides) are all more transparent than the nonfluorinated PMDA/ODA. The color of 10-pm-thick films changes gradually from bright yellow to colorless as the 6FDA/TFDB content increases. All these copolyimide films are also homogeneous compared with polyimide blends of 6FDA/TFDB and PMDA/TFDB. 

For example, the fluorinated copoly imide with 10 mol% 6FDA/TFDB has almost the same CTE as a Si substrate. Figure 15.8 shows the TMA curves, temperature vs. elongation, of the fluorinated copolyimides with 10 mol%... 

Figure 15.7. Coefficient of thermal expansion of fluorinated copolyimides.

Figure 15.8. TMA curves of copolyimides containing 10 and 100 mol% 6FDA/TFDB.

Figure 15.9. Decomposition temperature of fluorinated copolyimides (heating rate—10°C/min).

FDA/TFDB and PMDA/TFDB homopolyimides have Tg s of 335 and over 400°C (it is not observed below 400°C by differential scanning calorimetry), respectively, and the Tg s of all that have been investigated copolyimides are above 335°C. ... 

It is also possible for these copolyimides to control the refractive index because 6FDA/TFDB and PMDA/TFDB have largely different values. The refractive index and birefringence of the fluorinated copolyimides are described in detail in the next section. 

The fluorinated polyimides PMDA/TFDB and 6FDA/TFDB and the copolyimides have the high optical transparency, controllable refractive index. 

Low-loss, heat-resistant single-mode optical waveguides were fabricated using the fluorinated copolyimides with a high optical transparency and refractive index controllability. The high thermal stability of these waveguide materials... 

Yoshino, M., Nakamura, S., Kita, H., Okamoto, K.-i., Tanihara, N. and Kusuki, Y. (2003) Olefin/paraffin separation performance of asymmetric hollow fiber membrane of 6FDA/BPDA-DDBT copolyimide. Journal of Membrane Science, 212, 13-27. 

For the preparation of these segmented polyimides or block copolyimides, diamines rather than dianhydrides are preferred as the monomer bearing the flexible segment. Some of these monomers have been listed in Table 1. 

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