High Strength and High Modulus Aromatic Polyimide. Effect of Introducing Copoly (amic acid) on Molecular Orientation and Tensile Properties of the Rigid-rod Polyimides Obtained by Swollen Drawing of Poly (amic acid) Copolymer Films.

Copoly (amic acid) s have been synthesized from pyromellitic dianhydride (PMDA) and 3, 3', 4, 4'-biphenyltetracarboxylic dianhydride (BPDA) with p-phenylene-diamine (PDA) at room temperature. Uniaxial drawn Copoly (amic acid) (PAA) films which were obtained by swollen drawing in ethylene glycol were thermally imidized and annealed. The mechanical properties, WAXD patterns, TMA, and density changes of these polyimide (PI) films were measured. The main results were as follows; 1) The orientation of these PI films depends on the state of swollen PAAs in solvents. 2) In respect to effect of flexible BPDA content in the units, the maximum values of tensile modulus and strength of PI films are 163.2GPa and 2.63GPa, respectively for 2:1 copolymer of PI (PMDA; BPDA/PDA); (PMDA33%). 3) WAXD results showed that, polymer chain molecules which are both BPDA/PDA and PMDA/PDA component in this copolymer are preferentially oriented to the drawing direction. 4) The introduction of the semi-rigid BPDA/PDA molecules in PMDA/PDA polymer chain units could improve the tensile, mechanical properties for rigid-rod PI (PMDA/PDA) films.