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was carried out in m-
cresol using benzoic acid as catalyst. Polycyclocondensation was carried out at
180°C for 5 h. All the reactions proceeded under homogeneous conditions and
gave rise to the formation of the target phenylated PIs with yields close to the
theoretical values. The polymer viscosities ranged from 0.66 to 2.53 dl/g.
The structures of phenylated PIs were established by FTIR and
1
H and
13
C
NMR spectroscopies. The formation of the
The reaction of
II
with aromatic diamines
IVA-IVG
polymers was confirmed by
the appearance of absorption bands at 1780 and 1730 cm
-1
, which are characteris-
tic of the CO groups of imides [24]. All of the
13
C NMR spectra of phenylated PIs
exhibit an intense signal at 165 ppm, which corresponds to two equivalent car-
bons of the carbonyl of the phthalimide group, and a signal at -200 ppm, which is
characteristic of the C=O group of the benzophenone moiety.
The X-ray diffractrograms of the synthesized PIs show that they are amor-
phous. Possibly, this property of PIs is responsible for their improved solubility.
Most phenylated PIs show good solubility in N-methylpyrrolidone (N-MP), DMF,
and DMSO. They also dissolve rapidly at room temperature in m-cresol, THF,
and chloroform. Upon heating, they show solubility even in pyridine and toluene.
It is pertinent to note that the polyimides
VA-VG
VA
and
VB
containing rigid p-
phenylene and p,p
-diphenylene moieties, respectively, are easily soluble in the
majority of polar solvents. It appears that the high solubility of these polymers is
due to their noncoplanar structure and to the presence of side phenyl groups in the
polymer chains as well.
The thermal properties of the
′
polymers were determined by thermal me-
chanical analysis (TMA) and thermal gravimetric analysis (TGA). The results are
presented in Table 2. As is seen, the T
g
values of these polymers range from 345 to
395°C. As might be expected, the
VA-VG
VA
and
VB
polyimides containing rigid p-
phenylene and p,p
′
-diphenylene moieties have the highest T
g
values. The lower T
g
values of polymers
are apparently due to the introduction of bulky
side trifluoromethyl groups and flexible bonds, respectively, into the polymer chain.
VС
and
VE-VG
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