Synthesis and properties of novel soluble polyimides having an unsymmetricspiro tricyclic dianhydride unit

A novel spiro trialicyclic dianhydride, rel[1S,5R,6R]-3-oxabicyclo[3.2.1]oc tane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione) (DAn) was synthesiz ed from itaconic anhydride (1) and cyclopentadiene via a Diels-Alder reacti on, nitric acid oxidation, and the subsequent dehydration with acetic anhyd ride. The structure of DAn was determined by NMR spectra and single crystal X-ray diffraction. A series of soluble polyimides (PIs) having a spiro ali cyclic unit in the main chain were prepared by the reactions of DAn with se veral diamines through a general two-step polymerization method. Polymeriza tion temperature affected inherent viscosities of poly(amic acid)s. Chemica lly imidized PIs had the inherent viscosities in the range of 0.10-0.49 dL/ g. Due to the unsymmetric spiro alicyclic structure, the PIs showed excelle nt solubility in many organic solvents. Class transition temperatures of PI s ranged from 215 to 279 degreesC and some of them showed no glass transiti on temperature. The 10% weight loss temperatures under nitrogen were in a r ange of 355-430 degreesC. Films of PIs obtained by the thermal imidization were wholly transparent and colorless.