Premium
The origin of β relaxations in segmented rigid‐rod polyimide and copolyimide films
Author(s) -
Arnold Fred E.,
Bruno Katie R.,
Shen Dexing,
Eashoo Mark,
Lee Chul Joo,
Harris Frank W.,
Cheng Stephen Z. D.
Publication year - 1993
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760332102
Subject(s) - polyimide , crystallinity , materials science , relaxation (psychology) , diamine , dielectric , polymer , composite material , polymer chemistry , polymer science , chemical physics , optoelectronics , chemistry , psychology , social psychology , layer (electronics)
Most aromatic polyimides and copolyimides show a β relaxation process below their α relaxation processes in dynamic mechanical and dielectric measurements. The origin of this β relaxation has been under active discussion. In order to gain a better understanding of the origin of the β relaxation process, the dynamic mechanical behavior of a series of segmented rigid‐rod polyimide and copolyimide films with different dianhydrides and diamines has been systematically studied. For some of the polymers, crystallinity and orientation effects on the β relaxation process were also investigated. It is found that the β relaxation process in the unoriented films can mainly be attributed to a relatively noncooperative motion in uncrystallized diamines. However, this noncooperative nature may be gradually lost by increasing the crystallinity and orientation. Molecular modeling and computation have led to a discussion of possible diamine motion in the β relaxation process.