Synthesis and characterization of new organosoluble poly(ether imide)s derived from various novel bis(ether anhydride)s - Polyimides and Other High Temperature Polymers - page 56

the eluent. The eluents were monitored with a UV detector (Gilson model 116) at
254 nm. Polystyrene was used as the standard. Thermogravimetric data were ob-
tained on a DuPont 2100 equipment in flowing nitrogen or air (60 cm 3 . min -1 ) at a
heating rate of 20 C . min -1 . Differential scanning calorimetry (DSC) analysis was

performed on a DuPont 2000 differential scanning calorimeter.

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3. RESULTS AND DISCUSSION

3.1. Monomer synthesis
As shown in Scheme II, all the bis(ether anhydride)s were prepared by a three-
stage synthesis procedure starting from the nucleophilic nitrodisplacement reac-
tion of diols (1A-1F) and 4-nitrophthalonitrile in dry DMF in the presence of po-
tassium carbonate at room temperature. It was preferable to carry out the nitrodis-
placement reaction at low temperature (at room temperature) than at higher
temperature (higher than 100 C) since the products (2A-2B) always showed dark

color when they were obtained at high temperature. After the nitrodisplacement
reaction of diols (1A-1F) and 4-nitrophthalonitrile, a series of new bis(ether ni-
trile)s (2A-2F) were obtained. The resulting bis(ether dinitrile)s (2A-2F) were
then hydrolyzed in an alkaline solution in the presence of hydrogen peroxide to
obtain the corresponding bis(ether diacid)s (3A-3F). Nitriles can be hydrolyzed to
give either amides or carboxylic acids. Although the amide is being formed ini-
tially, carboxylic acid is the most common product since amides are hydrolyzed
with an acid or base. When carboxylic acid is desired, the reagent of choice is
aqueous KOH containing about 6 to 12% hydrogen peroxide, although acid-
catalyzed hydrolysis is also carried out frequently. The hydrolysis of 2A-2F (ex-
cept 2B) was performed in two days. However, the hydrolysis of bis(ether dini-
trile) 2B needed longer time due to the poorer solubility of 2B than 2A. After
complete hydrolysis, the solution became clear. Before acidification by aqueous
HCl, the removal of the residual ethanol was necessary. The presence of the re-
sidual ethanol in the aqueous solution always resulted in viscous product during
acidification. The bis(ether diacid)s were then cyclodehydrated to bis(ether anhy-
dride)s (4A-4F) using dehydrating agent such as a mixture of acetic anhydride
and glacial acetic anhydride. The structures of these compounds were confirmed
by elemental analysis, IR and NMR. For instance, the cyano group (C N) of
compound 2A was evident from the peak at 2222 cm -1 in the IR spectrum. How-
ever, in the IR spectrum of 3A, the cyano stretching vibration was absent, al-

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though a broad C(O)O-H absorption appeared in the region 2500-3600 cm -1 and a
C=O stretching absorption appeared at 1690 cm -1 . Furthermore, the IR spectrum
of the bis(ether anhydride) 4A shows characteristic cyclic anhydride absorptions
at 1837 and 1767 cm -1 attributed to the asymmetrical and symmetrical stretching
vibrations, respectively, of the carbonyl group. The NMR spectra data are listed in
Tables 1-3. The NMR spectra agree satisfactorily with the proposed structure.