Chemistry Reference
In-Depth Information
Table 1 shows the results of bending tests obtained on BTDA-DABP PI mold-
ings. These data show that for a polymer obtained by thermal imidization the
bending strength is very low and the sample is brittle. These characteristics of
moldings, obtained by thermal imidization, are probably due to the low flowabil-
ity of melt at T=320°C. As a result, it does not possess the homogeneous struc-
ture. Hence, the moldings obtained by chemical imidization, in contrast to its ana-
logs obtained by thermal imidization, can be processed into a molded product at
relatively low temperatures, 300-330°C, which are much lower than the PI ther-
mal degradation start temperature 450°C. The BTDA-DABP PI moldings ob-
tained by chemical imidization exhibit relatively high mechanical characteristics,
which are comparable to the BTDA-DABP PI amorphous films, obtained by
thermal imidization. The mechanical characteristics of this amorphous film at
room temperature are as follows: bending strength 100-120 MPa, Young's
modulus 3000-3300 MPa, and failure strain 5-6%.
It is for this reason that BTDA-DABP PI obtained by chemical imidization was
chosen for fullerene incorporation.
The samples were studied and compared with the samples of semi-crystalline
BTDA-DABP PI without fullerene by thermogravimetry (determination of ther-
mal degradation range and thermal stability indices τ
o
, τ
5
and τ
10
, where τ
o
is the
temperature of beginning of weight loss, τ
5
and τ
10
- temperatures of 5% and 10%
weight loss respectively) and differential scanning calorimetry (temperature and
enthalpies of melting).
The data in Table 2 show that the introduction of fullerene into the reaction so-
lution influenced the process of polymer structure formation. In most cases, the
degree of polymer crystallinity decreased, as indicated by decreased melting en-
thalpy. However, in all cases fullerene-containing polymer has a melting tempera-
ture close to that of semi-crystalline BTDA-DABP PI (without fullerene) obtained
by chemical imidization. Consequently, it can be processed into a composite ma-
trix or a molding at temperatures of 300-350°C.
A comparison of thermal stability of the samples shows (Table 3) that fullerene
introduction into PI increases the thermal stability of BTDA-DABP PI (τ
0
- tem-
perature of the beginning of weight loss): τ
5
and τ
10
- temperatures of 5% and
10% of weight loss also increase considerably.
Moldings based on BTDA-DABP PI-fullerene compositions were tested for
friction behavior. Fig. 2 shows the coefficient of sliding friction vs. pressure in
tribocontact for moldings based on polyimide-fullerene compositions and for a
molding based on pure BTDA-DABP PI. It should be noted that up to a pressure
of 5 MPa the friction coefficient for all moldings (based on polyimide-fullerene
compositions, obtained by methods 1-4) remains almost unchanged and is in the
range of 0.15-0.2. At contact pressures above 5 MPa, the coefficient of friction
stays nearly constant only for the moldings based on polyimide-fullerene compo-
sitions obtained by method 2. Hence it is promising for application at contact
pressure up to 8 MPa. Moldings, based on polyimide-fullerene compositions, ob-
tained by other methods, are stable only up to 5 MPa.
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