Elastic and optical properties of oriented polyimide and other polymer films

The optical and elastic properties of uniaxially oriented films of polyimides and other polymers are studied. A sharp increase in birefringence, Young's modulus, and elasticity nonlinearity characteristics is observed with all the polyimides at low elongations, the limit being attained at about 100% elongation. This indicates rapid transition of the polyimides into the highly oriented state, and a change in the nature of the forces affecting the elasticity from intermolecular to intramolecular forces.