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Degradation of aromatic polymers—II. The crosslinking during thermal and thermo-oxidative degradation of a polyimide

✍ Scribed by Shin-ichi Kuroda; Itaru Mita

Publisher
Elsevier Science
Year
1989
Tongue
English
Weight
696 KB
Volume
25
Category
Article
ISSN
0014-3057

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✦ Synopsis

A soluble polyimide (PI2080) was thermally and thermo-oxidatively degraded. Crosslinking was found to proceed under both conditions. Crosslinking densities of degraded samples were estimated before and after the gel point by gel permeation chromatography and by a new method using thermomechanical analysis. It was suggested by i.r. study that crosslinking occurs by recombination and addition to benzene rings of on-chain radicals formed in a chain reaction initiated by the cleavage of C 6 H4---CH2C 6 H 4 linkage. Crosslinking during thermal degradation is affected by the mobility of polymer chains and ceases when the glass transition temperature (Tg) of the crosslinked sample reaches the degrading temperature. On the other hand, in thermo-oxidative degradation crosslinking due to oxygen seems to proceed without large motion of polymer chains and it continues even after the T s of the degraded sample exceeds the degrading temperature. It was shown by the relation between T, and crosslinking density that the crosslinking structure depends on the degradation conditions, i.e. in vacuum or in air, and that thermo-oxidative degradation gives more restricted crosslinking than pure thermal degradation.

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