High performance shape memory polyimides based on π–π interactions†
A series of polyimides (PIs) with different chain structures were synthesized by a two-step method. The influences of chain conformations on their thermal and mechanical properties were investigated by dynamic mechanical analysis, thermogravimetric analysis, as well as by a universal testing machine. All PIs exhibited high glass transition temperature (>240 °C) and thermal decomposition temperature (>480 °C). Moreover, all these PIs could show shape memory properties more or less, especially ODA–BPDA with a shape recovery ratio (Rr) greater than 93%. The high value of Rr was mainly due to the existence of π–π interaction, a type of non-covalent interaction. The dependence of Rr on π–π interaction was investigated in detail by UV-vis spectroscopy. Finally, atomic oxygen (AO) exposure experiments showed that the shape memory properties of ODA–BPDA were affected little by the erosion due to AO.