High modulus and high strength ultra-thin polyimide films with hot-stretch induced molecular orientation

This paper concerns uniaxially stretched ultra-thin polyimide (PI) films containing ether and ketone moieties. The stretched PI films exhibited remarkable high modulus (4.9 GPa) and high strength (258 MPa) in the stretch direction compared with commercial polyimides because of their high degree of molecular orientation induced by uniaxial hot stretch. The tensile strength of the stretched PI films is about 2.4 times of that of undrawn films and the coefficients of thermal expansion decreased by as much as 84%. Studies of birefringence and wide-angle X-ray diffraction all proved a high degree of molecular orientation and crystallization induced during the drawing process. The thickness of stretched PI films was reduced at least 75% as compared to unstretched PI films and the thinnest film is only 7 μm.