Synthesis of novel biphenyl-fused alicyclic tetracarboxylic dianhydride and its performance in thermostable and transparent colorless polyimides

Biphenyl fused alicyclic tetracarboxylic dianhydride, 6,6 ',7,7 '-tetracarboxylic dianhydride-5,5 ',6,6 ',7,7 ',8,8 '-octahydro-2,2 '-binaphthalene (OHBNDA) was successfully synthesized from biphenyltetracarboxylic dianhydride (BPDA) through hydrolysis, reduction, bromination, and Diels-Alder reaction. Three OHBNDA-based polyimides (PIs) were synthesized by one-step polycondensation at high temperature with 9,9-bis(4-aminophenyl)fluorene (BAFL), 2,2 '-bis(trifluoromethyl)-4,4 '-diaminobiphenyl (TFMB), and 4,4 '-diamino-2,2 '-dimethyl-1,1 '-biphenyl (m-TolDA) diamines, respectively. These PIs have moderate molecular weights and good solubility in polar organic solvents, such as N,N-dimethylformamide, dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). OHBNDA-TFMB, OHBNDA-m-TolDA, and OHBNDA-BAFL display glass transition temperatures (T(g)s) of 309, 329, and 377 degrees C from differential scanning calorimetry (DSC) curves, and the decomposition temperatures at 5% weight loss (T-d5) of as high as 522, 507, and 548 degrees C under nitrogen, respectively. Meanwhile, these PI films also show good optical transparency with the cut-off wavelength <315 nm and the transmittance >75% at 400 nm. These results confirm that aryl-fused alicyclic tetracarboxylic dianhydrides can afford transparent/colorless PIs with high thermal stability, especially the higher decomposition temperatures than the wholly alicyclic dianhydrides.