Page 297 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology En012c-604 July 26, 2001 16:2

806 Polymers, Thermally Stable

FIGURE 14 Strength retention of Nomex, PBI, and BBB fibers in air at various temperatures. [Reprinted with permis-
sion from Preston, J., Black, W., and De-Winter, W. (1969). Appl. Polym. Symp. 9, 145. Copyright 1969 John Wiley &
Sons, Inc.]

TABLE X Flexural Properties of a Polyimidazo-
quinazoline/Carbon Fiber Laminate at Elevated
Temperature a
Retention
Flexural Flexural of RT
Heat aging strength modulus strength
conditions (MPa) (GPa) (%)
RT 1540 119 —
◦
200 hr at 316 C 1249 115 81
◦
500 hr at 316 C 1252 126 81
1000 hr at 316 C 598 81 39
◦
RT 1939 119 —
◦
1hrat371 C 1181 126 61
◦
50 hr at 371 C 1187 117 61
◦
100 hr at 371 C 992 100 51
RT 1617 116 —
◦
1hrat426 C 1497 113 93
5hrat426 C 987 102 61
◦
10 hr at 426 C 331 98 20
◦
1hrat481 C 1181 110 73
◦
1hrat536 C 629 63 39
◦
3. Polyimidazoquinazolines (PIQs) a Reprinted with permission from Gosnell, R. B.,
Fitzgerald, W. P., and Milligan, R. J. (1973). Appl. Polym.
Fused-ring PIQs (LXVI) are the only heteroaromatic
Symp. 22, 21. Copyright 1973 John Wiley & Sons, Inc.
ladder-type competitors to pyrrone—and BBB/BBL—
systems as applicational high-temperature materials. Sev-
of flexural properties at elevated temperature (>500 C)
◦
eral synthetic routes based on aromatic tetraamines have
have been observed for the PIQ resins (Table X).
been used; the most practically useful is reminiscent of
PBI manufacture, involving the melt-polycondensation of
1
2, 2 -bis(O-aminophenyl)bibenzimidazole with aromatic SEE ALSO THE FOLLOWING ARTICLES
dicarboxylic acids.
Like the PBIs, evolution of volatiles is a problem in pro- COMPOSITE MATERIALS • HETEROCYCLIC CHEMISTRY
cessing but carbon fiber laminates with excellent retention • MATERIALS CHEMISTRY • POLYMER PROCESSING •