Novel Non-Coplanar and Tertbutyl-Substituted Polyimides: Solubility, Optical, Thermal and Dielectric Properties

A novel aromatic diamine monomer bearing tertbutyl and 4-tertbutylphenyl groups, 3,3-ditertbutyl-4,4-diaminodiphenyl-4-tertbutylphenylmethane (TADBP), was prepared and characterized. A series of non-coplanar polyimides (PIs) were synthesized via a conventional one-step polycondensation from TADBP and various aromatic dianhydrides including pyromellitic dianhydride (PMDA), 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA), 4,4-oxydiphthalic anhydride (OPDA), 3,3,4,4-benzophenone tetracarboxylic dianhydride (BTDA) and 4,4-(hexafluoroisopropylidene)dipthalic anhydride (6FDA). All PIs exhibit excellent solubility in common organic solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), chloroform (CHCl3), tetrahydrofuran (THF), and so on. Furthermore, the obtained transparent, strong and flexible polyimide films present good thermal stability and outstanding optical properties. Their glass transition temperatures (T(g)s) are in the range of 298 to 347 degrees C, and 10% weight loss temperatures are in excess of 490 degrees C with more than 53% char yield at 800 degrees C in nitrogen. All the polyimides can be cast into transparent and flexible films with tensile strength of 80.5-101 MPa, elongation at break of 8.4%-10.5%, and Young's modulus of 2.3-2.8 GPa. Meanwhile, the PIs show the cutoff wavelengths of 302-356 nm, as well as low moisture absorption (0.30% -0.55%) and low dielectric constant (2.78-3.12 at 1 MHz).