Synthesis and Characterization of New Soluble Polyimides from 3,3′,4,4′-Benzhydrol Tetracarboxylic Dianhydride and Various Diamines

New soluble polyimides were prepared from a series of diamines and a tetracarboxylic dianhydride with a benzhydrol unit, 3,3′,4,4′-benzhydrol tetracarboxylic dianhydride (BHTDA), by one-step method polymerization. The diamines containing flexible units, bulky substituents, and/or noncoplanar conformation unit were prepared by the reaction of the corresponding bisphenol precursors and p-chloronitrobenzene, followed by catalytic reduction of the dinitro compounds. The polyimides obtained were soluble in various solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, pyridine, γ-butyrolactone, m-cresol, and even tetrahydrofuran except for polymer PId. The polymers were amorphous and had number-average molecular weight (M_n) in the range (3.0-10.2) × 10⁴. The glass transition temperatures (T_g) of the polymers ranged from 268 to 341 °C. These polymers exhibited good thermal stability without significant weight loss up to 420 °C. The temperatures at 10% weight loss range from 457 to 524 °C in nitrogen and 449 to 519 °C in air, respectively. The polyimide films were found to be transparent, flexible, and tough. The films had a tensile strength range 72-105 MPa, an elongation range at break of 4-7%, and a Young's modulus range of 2.18-2.85 GPa.