Synthesis of novel polyimides from dianhydrides with flexible side chains - Polyimides and Other High Temperature Polymers - page 78

Table 4.
Thermal properties of polyimides from C m -OADA
Thermal stability in N 2

Polymer
code

T g (°C) (a) T o (°C) (b) T d1 (°C) (c) T d2 (°C) (d) T 10 (°C) (e) R 900 (%) (f)
C 4 -PDA 292 439 472 702 459 47.58
C 8 -PDA 176 422 497 680 440 40.76
C 12 PDA 138 408 447 661 418 36.02
C 4 -ODA 259 449 452 643 443 50.15
C 8 -ODA 163 435 466 664 447 45.83
C 12 -ODA 124 413 463 656 434 42.34
C 4 -MDA 232 441 479 678 470 45.86
C 8 -MDA 134 431 466 653 451 40.01
C 12 -MDA 111 413 453 643 426 37.06
C 4 -FDA 294 453 477 610 477 45.64
C 8 -FDA 160(267) (g) 432 472 619 453 38.61
C 12 -FDA 116 406 443 579 425 36.78
C 4 -TOL 298 436 464 669 468 52.77
C 8 -TOL 202 422 459 669 442 43.30
C 12 -TOL 165 412 455 657 427 40.57
(a) From the second heating traces in DSC measurements conducted at a heating rate of 20°C/min
in N 2 atmosphere; (b) Onset temperature of degradation; (c) 1st, (d) 2nd decomposition temperatures
measured by TGA at a heating rate of 20°C/min under N 2 ; (e) 10% weight loss temperatures meas-
ured by TGA at a heating rate of 20°C/min under N 2 ; (f) Residual weight % at 900°C measured by
TGA at a heating rate of 20°C/min under N 2 ; (g) Melting transition measured by DSC

From Table 3, it is obvious that with increasing side chain length, the T d1
greatly decreases, indicating that thermal stability of the polyimides is greatly af-
fected by the presence of the side chains. On the other hand, T d2 changed only
slightly, which means that entire side chains had already degraded in the low-
temperature range.
In case of polyimides having an alicyclic unit as well as an alkyloxy side chain,
they were thermally stable to about 420°C, and then began to degrade drastically
in the range of 443~497°C, followed by second slight degradation occurring in
the 579~702°C range. Thus the degradation shows a two-step weight loss behav-
ior. As shown in Table 4, the residual weight percent determined at 900°C varies
with backbone structure of each polymer. When these values are compared with
the theoretically calculated side chain content values, the coincidence falls within
a 4% range. These results indicate that the first drastic degradation originates

mainly from the degradation of the side chains, while the second degradation
arises from that of the polymer backbone containing alicyclic unit. All the resid-
ual weights showed higher values than 36.02% calculated on the basis of the
structures of polyimides.

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