Synthesis of aromatic benzoxazole polymers for high T, low dielectric properties/Title> - Polyimides and Other High Temperature Polymers - page 211

Figure 1. DSC trace of 50/50 6FPBO-OH-co-12FPBO (polymer 6) showing T g onset at 354°C and
an inflection point at 361°C.

the polymer T g . This can be ascertained from the data in Table 1 by comparing
sample groups . The T g en-

hancement is clearly borne out to be a function of the number of consecutive
fused rings in the hydroxy 6F-benzoxazole systems as envisaged in Scheme 2.
Thermogravimetric analysis (TGA) showed that the onset temperature of deg-
radation of sample

7-10 , 3-6 , 1-2 , and by comparison among samples 3-6

C in helium (Figure 2). This
high onset degradation temperature is representative of all the polymers listed in
Table 1.

6 occurred at approximately 533 °

3.2. Dynamic mechanical analysis
A comparison of the tensile storage moduli among different compositions are
shown in Figure 3, for polymers , revealing the impact of the hy-

droxyl functionality on the mechanical behavior of the polymers. It is observed
that while the tensile moduli are all in the range of 1.5 to 2 GPa (for temperatures
near room temperature), the fall-off in tensile modulus with temperatures near T g
shows sensitivity to the copolymer composition. In particular, it should be noted
that the hydroxyl content of polymers in Figure 3 ranges from polymer

2 , 4 , 5 , and 6

2 with no

hydroxyl content, to polymer with 90% content of the hydroxyl-bearing repeat

unit. The glass transition temperature increases substantially while the negative
slope of log (modulus) versus temperature decreases. Intermediate levels of hy-
droxyl content in the polymers, i.e. polymers

4

, lead to mechanical behavior
intermediate between the two extremes in hydroxyl content.

5 and 6