Polyimide copolymers and membranes, preparation methods and uses thereof as well as systems and methods for purifying helium gas

A polyimide random copolymer, characterized in that the copolymer has a structure represented by formula (I):

• in formula (I), m and n are each independently an integer from 10 to 2000;
• X is any one selected from the group consisting of formulas (X3) and (X4);
• in formula (X3) and formula (X4), R5, R6, R9 and R10 are each independently H, an optionally substituted C1-C4 alkyl group, or an optionally substituted C6-C10 aryl group;
• Y is any one selected from the group consisting of formulas (Y1), (Y3), (Y4) and iptycene-based structures;
• in formulas (Y1) and (Y3), R7, R8, R11, R12, R13, and R14 are each independently H, an optionally substituted C1-C4 alkyl, or an optionally substituted C6-C10 aryl group;
• Z and Z′ are each independently selected from the group consisting of iptycene-based structures and an optionally substituted formula (Z1);