Synthesis and Characterization of Organo-Soluble Polyimides Derived from Alicyclic Dianhydrides and a Dihydroxyl-Functionalized Spirobisindane Diamine

Two organo-soluble polyimides were synthesized by reaction of alicyclic bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BC) or 1,4,7,8-tetrabromobicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic anhydride (BCBr4) with 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′-diamino-6,6′-diol (SBIDA). BC–SBIDA and BCBr4–SBIDA showed thermal stability of up to ∼420 and 352 °C and displayed microporosity as indicated by Brunauer–Emmett–Teller surface areas of 191 and 243 m2 g–1, respectively. The polyimides were solution-processable in polar organic solvents and exhibited strong mechanical properties with tensile modulus of 1.15–1.4 GPa, tensile strength of 27–28 MPa, and elongation at break of 2–4%. Introducing alicyclic moieties disturbs the delocalization of π-electrons across the polyimide backbone that reduces formation of charge transfer complexes (CTCs) leading to formation of colorless and transparent polyimide films. A fresh film sample of the bromine substituted BCBr4–SBIDA showed oxygen permeability of 31 barrer and oxygen/nitrogen selectivity of 5.9. Long-term physical aging of BCBr4–SBIDA over 365 days resulted in decrease of O2 permeability to 17 barrer with a simultaneous boost in O2/N2 selectivity to 6.6, which demonstrated highly competitive performance compared to commercially available polymers for air separation.