A study on the effect of spirocyclic structures in the main chain on the physical properties of copolyimides

A series of copolyimides were prepared from two alicyclic dianhydrides havi ng the common molecular formula C10H8O6, rel-[1S,5R,6R]-3-oxabicyclo[3.2.1] octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',-5'dione) (DAn) and c-3-car boxymethyl-r-1,c-2,c-4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride ( TCAAH), with p-phenylenediamine (PPD) by a conventional two-step procedure. With increasing DAn fractions in the backbones, the copolyimides showed be tter film formability, enhanced solubility, increased glass transition temp eratures and birefringences, and decreased average refractive indices. The unsymmetric spiroalicyclic structure of DAn might be responsible for these results. Films of copolyimides obtained by both thermal and chemical imidiz ation were fully transparent and were colorless or pale yellow depending on the film thickness.