Semicrystalline DABP-BTDA polyimide modified by fullerenes for wear protection - Polyimides and Other High Temperature Polymers - page 499

2. EXPERIMENTAL
2.1. Synthesis
BTDA (with T m =225-226°) recrystallized from dry acetic anhydride and 3,3 ′
DABP were used as monomers [11]. Poly(amic acid) (PAA) was synthesized by
introducing a stoichiometric quantity of the dianhydride into the diamine solution
of N,N-dimethyl acetamide (DMAc) with stirring at 50°C. The concentration of
the PAA solution was 25% (by wt.) and the time of synthesis in DMAc was 4 h.
Powdered PI samples were prepared by chemical imidization in DMAc as de-
scribed earlier [11].
To obtain fullerene-containing semi-crystalline BTDA-DABP PI, several
methods of fullerene introduction into the polymer were employed. A mixture of
C 60 -C 70 fullerenes in the weight ratio of 78:22% was used. Fullerene was dis-
solved in a solution of an aromatic diamine (3,3′-diaminobenzophenone - one of
the monomers), which was used in the preparation of the poly(amic acid), a pre-
cursor of polyimide. We proceeded from the fact that it was possible to distribute
fullerene homogeneously and to immobilize it in the polymer bulk by binding its
molecules to terminal amino groups of the monomer because fullerene molecules
are known to interact actively with amines. In the first experiment (the first
method), fullerene was dissolved in DMAc (solution concentration 0.05 mg/ml)
and the diamine was introduced into the solution. In the second experiment (the
second method), a diamine solution in DMAc was prepared and then fullerene so-
lution in o-dichlorobenzene (solution concentration 20 mg/ml) was introduced
into this diamine solution, because fullerene solubility in o-dichlorobenzene is
much higher than in DMAc. Therefore, the use of o-dichlorobenzene favored the
introduction of a greater amount of fullerene into the polymer than in the case of
fullerene solution in DMAc. When o-dichlorobenzene was used, 0.1% of
fullerene based on dry polymer weight was introduced. When only DMAc was
used as solvent, 0.015% of fullerene was introduced. The mixture of fullerene and
3,3′-DABP in a mixture of solvents, DMAc and o-dichlorobenzene (solvents
weight ratio 1:5) was kept for 1 h at room temperature. After this, PAA was syn-
thesized by introducing BTDA, the second monomer, into this solution. Powdered
samples of BTDA-DABP PI were subsequently obtained by chemical imidization
in solution.
The third way (the third method) of fullerene introduction was to add fullerene
solution in o-dichlorobenzene (solution concentration 20 mg/ml) to the solution of
the prepared PAA (25 wt.%). The resulting mixture was kept at room temperature
for 2 h. Subsequently, just as in the previous cases, PAA chemical imidization in
solution was carried out by exposing to the imidizing mixture (consisting of acetic
anhydride and triethylamine) for 24 h at room temperature. During imidization,
the polymer became insoluble and was precipitated from the reaction mixture in
the form of powder.