Polyimide monomers, chemical structures

Table 13.1. Chemical Structures of Dianhydrides from Polyimides Where One or Both Monomer Components Are Fluorinated...

Figure 1. Chemical structure of PMDA/ODA polyimide (PI) monomer unit, benzene (BE), phthalimide (PIM), benzene-phthalimide (BPIM), methyl-phthalimide (MPIM), and malonamid (MAM).

Fig. 5. The chemical structures of some common aromatic dianhydride (a) and aromatic diamine (b) monomers used in the synthesis of electronic-grade polyimides.

Fig. 1. Reaction scheme for polyimide synthesis and chemical structures and abbreviations of monomers, poly(amic acid), and polyimides.

The general methods to synthesize poly(amide imide)s are rather simple and include those monomers and reactions conducting to polyimides or polyamides, consequently, the number and variety of chemical structures reported are countless [174]. The most important ones will be mentioned here. 

Figure 7.8 Chemical structures of other monomers used to make polyimides.

A series of hexafluoro-isopropylidene-containing polyimides were synthesized using solution polycondensation reactions and then chemically imidized [23-25]. Table 7 shows their chemical compositions Fig. 12 shows the monomer structures. The glass transition temperatures, Mw and Mn, of these polyimides are summarized in Table 8. A Perkin-Elmer DSC was used to determine these Tgs with a heating rate of 20 °C/min. All Tgs were measured at the second heating. 

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclodehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability. 

Ma et al. [80] designed a pyridine-based diamine monomer, namely, 4-phenyl-2,6- j5(3-[4 -amino-2 -trifluoromethyl-phenoxy]phenyl)pyridine, to improve the thermal and chemical stability of the polyimides at high temperature. A representative structure of the polyimide with ODPA as a dianhydride unit is shown in 3-73 (in Table 3.4). The Tg of the polyimide was reported to be 187 °C with a Tj 5% as high as 532 °C in air. The TS of the polyimide was recorded at 97 MPa and the EB at 11%, indicating the strong and tough nature of the polyimide. 

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