Handbook of Solvents - George Wypych - ChemTech - Ventech!

842 Norio Tsubokawa
[13.4.2]
PAI is supposed to be a linear polymer containing equivalent amounts of amide and
imide bonds. Therefore, PAI is soluble in polar solvents such as NMP, DMAc, and
N,N-dimethylformamide (DMF). However, it is well known that PAI becomes insoluble
and infusible when it is heated over 200°C. We have pointed out that some remaining carboxyl
groups of PAI play an important role in the curing of PAI by heating. 4,5 Because of
such a thermosetting property, PAI solution is used as a heat resistant temperature coating
or an insulating enamel of magnet wire.
In the following section, the effect of polymerization solvent, DMAc and mixed solvent
of methyl ethyl ketone (MEK) with water, 6 on the chemical structure and curing of
PAIs prepared by diamine process will be summarized. 7
13.4.2 EFFECT OF SOLVENT ON THE CHEMICAL STRUCTURE OF PAI
13.4.2.1 Imide and amide bond content of PAI
Four kinds of PAAA, as precursor of PAI, were prepared by the polycondensation of
TMAH-Cl with DDE or DDM in DMAc and MEK/water mixed solvent (MEK containing
30 vol% of water) at room temperature. The results are shown in Table 13.4.1. It was found
that the conversions reached 78-96% within 2hatroom temperature and the rate of the
polycondensation of TMAHCl with diamine in MEK/water mixed solvent was much larger
than that in DMAc.
Table 13.4.1. Polymerization conditions and conversion of samples [Data from
reference 7]
Sample No. Solvent Diamine Time, h Conversion, %
PAAA-1 MEK/H2O DDE 0.5 90.3
PAAA-2 DMAc DDE 2.0 89.6
PAAA-3 MEK/H2O DDM 0.5 78.4
PAAA-4 DMAc DDM 2.0 96.8
TMAH-Cl=diamine=0.06 mol ; solvent, 172 ml; TEA, 5.0 ml; room temp.
These PAAAs, PAAA-1, PAAA-2, PAAA-3, and PAAA-4, were heated at 180°C for
2 h to give PAI-1, PAI-2, PAI-3, and PAI-4, respectively. Figure 13.4.1 shows the infrared
spectra of (A) PAAA-1, (B) PAI-1, and (C) PAI-3.