Molecular orientation of polypyromellitimide by using swollen drawing of homo-poly(amic acid) and copoly(amic acid) films

Poly(amic acid)s were synthesized from pyromellitic dianhydride (PMDA) or 3 ,'3,4,4'-biphenyltetracarboxylic dianhydride (BPDA) with p-phenylenediamine (PDA) in N,N-dimethylacetamide (DMAc). Copoly(amic acid)s were synthesized from prepolymer of PMDA with PDA in DMAc with BPDA at room temperature. Un iaxially drawn poly(amic acid) (PAA) films which were obtained by using a l aboratory-made drawing machine in a swelling solvent such as ethylene glyco l (EG) or EG/DMAc were thermally imidized and annealed. The mechanical prop erties, WAXD patterns, TMA, and density changes of these polyimide (PI) fil ms were measured. The results were as follows. (1) The orientation of these PI films depends on the state of swollen PAAs in solvents. For homo-polyme r PI(PMDA/PDA) films, the maximum modulus of 112 GPa was attained at a draw ratio of 300%. (2) Compared to the PI blend of PI(PMDA/PDA)/PI(BPDA/PDA), the corresponding copolyimides are homogeneously swollen. (3) Drawing of th e swollen PAA of the wholly aromatic rigid-rod polypyromellitimide with p-p henylene and its copolymer with semi-rod. polybiphenylimide provided films with a high tensile property. (4) The molecular orientation of copoly(amic acid) films was enhanced at a relatively low draw ratio, resulting in the i ncrease of modulus up to 146 GPa at 200% draw ratio with 20 mu m. The tensi le strength of the copolyimide films was much increased compared with those of the homo-polyimide.