Controlled molecular weight, thermoplastic polyimides have been
prepared via poly(amic
acid) salt precursors.
2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane
dianhydride and m-phenylenediamine (the Ultem monomers), together with calculated amounts of phthalic
anhydride were reacted in
N-methylpyrrolidinone as well as in tetrahydrofuran to form
poly(amic acid)s with controlled molecular
weights. Poly(amic acid) salts were prepared in heterogeneous
reactions of the poly(amic acid)s with
quaternary ammonium bases or triethylamine dissolved in methanol or
water, to yield soluble salts. The
poly(amic acid) salts were then melt imidized in air at 250 or 300
°C for 30 min. Results suggest that
the poly(amic acid) salt counterion controls the mechanism by
which the salt imidizes, which in turn
controls the properties of the final polyimide. The
triethylammonium poly(amic acid) salts yielded
linear,
thermoplastic, molecular weight controlled polyimides upon melt
imidization. The polyimides prepared
from the poly(amic acid) salts containing the triethylammonium,
tetraethylammonium, and tetrapropylammonium counterions showed dynamic weight loss profiles comparable to
the polyimide produced directly
from the control poly(amic acid).
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