Rotational conformational energetics of stiff aromatic polyimides: Effects of exchange repulsions, dipole-moiety interactions, and pi-conjugations

被引:11
作者
Cui, CZ
Cho, SJ
Kim, KS
Baehr, C
Jung, JC
机构
[1] POHANG UNIV SCI & TECHNOL,CTR BIOFUNCT MOL,DEPT CHEM,POHANG 790784,SOUTH KOREA
[2] POHANG UNIV SCI & TECHNOL,DEPT MAT SCI & MET ENGN,POHANG 790784,SOUTH KOREA
关键词
D O I
10.1063/1.474156
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
To study the conformational stability of aromatic polyimides which are highly thermally stable and retain their useful physical and electrical properties over 200 degrees C, we investigated four pristine compounds (N-phenyl-1,8 -naphthalenedicarboximide, N-phenylmaleimide, N-2-pyrrolyl maleimide, and N-3-pyrrolylmaleimide) using ab initio calculations. Among these, the polyimides having the last two pristine compounds have not been synthesized yet. The four compounds representing the aromatic polyimides were comprised of two adjoining rings of, respectively, 6-6, 5-6, 5-5, and 5-5', where each number denotes the number of atoms in each ring-skeleton, and 5' represents a ring having an N-H group (instead of a C-H group in 5) to interact with the C=O group of the imide ring. The (internal rotation) angles (phi) between two rings of the global minimum energy conformers for the systems of 6-6, 5-6, 5-5, and 5-5' are predicted to be 90 degrees (perpendicular), 46 degrees, 0 degrees (coplanar), and 0 degrees, respectively. The conformational energetics are governed mainly by the competition between the exchange repulsions, dipole-moiety interactions, and pi conjugations. For rings/6-6 and rings/5-6, the dipole interactions and pi conjugation effects in favor of coplanar structures are overwhelmed by the exchange repulsions which make the coplanar structures unstable. On the other hand, for rings/5-5 and rings/5-5', the dipole-moiety interactions just overcome the exchange repulsions, hence the rr conjugation effects would become relevant in accounting for the statibility of the coplanar conformation. It is worthwhile investigating these new types of coplanar polyimides for possible developments of new types of polyimides with useful electrical, optical, and physical properties. (C) 1997 American Institute of Physics. [S0021 -9606(97)50747-1].
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页码:10201 / 10206
页数:6
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