The out-of-plane elastic moduli of two polyimides, such as Poly(4,4'-o
xydiphenylene pyromellitimide) (PMDA-ODA) with flexible chains and pol
y(p-phenylene biphenyl tetracarboximide) (BPDA-PDA) with rigid-rod-lik
e chains, ranging from 4 to 20 mu m have been investigated using a pre
cision capacitance dilatometry with a loading-unloading technique. It
is found that the elastic moduli of both polyimides in the out-of-plan
e direction are smaller than in the in-plane direction and they are de
pendent on the film thickness. In addition, PMDA-ODA is less anisotrop
ic than BPDA-PDA. It indicates that the anisotropy in modulus is depen
dent on the molecular structure of polyimide. Experimental results sho
w that the out-of-plane elastic modulus is correlated to the in-plane
molecular orientation and the main chain structure of polyimide. (C) 1
998 Elsevier Science S.A. All rights reserved.