Chemistry Reference
In-Depth Information
cured in a vacuum oven by heating to 50°C for 1 h, 150°C for 1 h, 250°C for 1 h,
and finally 290°C for 1 h. After cooling to room temperature, the coatings on
glass were soaked in water and carefully lifted from the glass to give free-
standing films.
2.2. Methods
The intrinsic viscosity,
η
inh
for the poly(amic acid)s was measured at a concentra-
tion of 0.5 g/dL in NMP at 30°C using an Ubbelohde viscometer. The thermal de-
composition temperature for the polyimides was determined under nitrogen on a
TA Instruments Model 2950 thermogravimetric analyzer with the heating rate of
10°C/min. The decomposition temperatures were taken when the weight loss re-
duced by either 5 or 10% of the original weight. The glass transition temperature
was measured on a TA Instruments model 2920 differential scanning calorimeter
under nitrogen. The samples were heated to 350°C in nitrogen and cooled to room
temperature, and then heated to 400°C. The glass transition temperatures were de-
termined from the second heating. The tensile properties of the polymer films
were measured on an Instron Model 4465-STANDARD with 100 N load cell. The
samples for the test were prepared by the ASTM method [15] and the crosshead
speed was 10 mm/min. Five replicate samples were tested for each polymer and
the reported values were the average of the five. The moisture absorption was de-
termined by drying the polyimide films under vacuum at 80°C for 24 hours. The
films were weighed and then exposed to 85°C and 85% relative humidity in a
Tenney model TH Jr temperature humidity chamber for one week. After exposure
the films were weighed again to determine the percent moisture uptake.
3. RESULTS AND DISCUSSION
The viscosity data, Table 1, for the poly(amic acid)s showed that the polymers
had very similar molecular weights. The thermal stability of amine-quinone poly-
imides was determined by measuring the temperature of 5% weight loss (T
5%
) and
percent char yield at 800°C by thermogravimetric analysis under nitrogen, Table
2. All amine-quinone polyimides showed the excellent thermal stability one
would expect for polyimides. The polymers exhibited T
5%
weight loss temperature
ranging from 440 to 479°C. The char yields, residual weight % at 800°C, ranged
from 60 to 69%. The thermal stability did not depend on the choice of monomers
and all amine-quinone polyimides showed excellent thermal stability. The glass
transition temperatures of amine-quinone polyimides were measured by differen-
tial scanning calorimetry, Table 2. All polymers showed a glass transition tem-
perature between 279 and 310°C.
Most of the amine-quinone polyimides gave transparent, flexible and tough
films suitable for measurements of tensile properties, Table 3. Free-standing films
could not be made from AQPI-5, because the poly(amic acid) was always ob-
tained as a gel. In the case of AQPI-4, the film was not very uniform and gave
Search WWH ::
Custom Search