Patent ID: 8772417

Claim:
A method for preparing a polyimide membrane comprising: providing a solution containing a solvent and grafted polyimides, the grafted polyimides having molecular weights of 10,000-300,000 and containing monomers A and, optionally, also containing monomers B; each of the monomers A, which are the same or different, having the following formula: and each of the monomers B, which are the same or different, having the following formula: in which each of the Ar 1 moieties, independently, is each of the Z moieties, independently, being C(CF 3 ) 2 , C(═O), O, S, S(O 2 ), C(CH 3 ) 2 , CH 2 , or O(-Ph-)O; each of the Ar 2 moieties, independently, is each of the X, X 1 , X 2 , and X 3 , independently, being H, C 1 -C 5 alkyl, C 1 -0 5 alkoxyl, phenyl, and phenyoxyl; and each of the Y moieties, independently, being C(CF 3 ) 2 , C(═O), O, S, S(O 2 ), C(CH 3 ) 2 , CH 2 , or O(-Ph-)O; each of the Ar 3 moieties, independently, is each of the R moieties, independently, being C(CF 3 ) 2 , C(═O), O, S, S(O 2 ), C(CH 3 ) 2 , CH 2 , or O(-Ph-)O; each of the R 1 moieties, independently, being H, C 1 -C 5 alkyl, C 1 -C 5 alkoxyl, phenyl, and phenyoxyl; each of the n values, independently, being 0, 1, 2, or 3; and each of the T moieties, independently, is a thermal labile side chain containing a —O— group linked to the carbonyl group in the Ar 3 moiety in a monomer A, and also containing at least one hydroxyl group; evaporating the solvent to form a membrane; cross-linking Ar 3 moieties via T moieties by covalent bonding therebetween to form a cross-linked membrane, the covalent bonding resulting from reaction between the hydroxyl group in a T moiety and the carbonyl group in an Ar 3 moiety; and heating the cross-linked membrane so as to both decompose the T moieties and form covalent bonds between aryl rings in the Ar 1 , Ar 2 , and Ar 3 moieties, wherein, if the grafted polyimides also contain the monomers B, the molar ratio of the monomers B to the monomers A is 0.11 to 99, and a monomer A and a monomer B are linked as follows: