Synthesis and Characterization of Highly Soluble and Oxygen Permeable New Polyimides Bearing a Noncoplanar Twisted Biphenyl Unit Containing tert-Butylphenyl or Trimethylsilyl Phenyl Groups

The two new dianhydrides, 2,2‘-bis(4‘ ‘-tert-butylphenyl)-4,4‘,5,5‘-biphenyltetracarboxylic dianhydride (BBBPAn) and 2,2‘-bis(4‘ ‘-trimethylsilylphenyl)-4,4‘,5,5‘-biphenyltetracarboxylic dianhydride (BTSBPAn), composed of a noncoplanar twisted biphenyl unit containing tert-butylphenyl or trimethylsilylphenyl groups were prepared. Two series of new organosoluble polyimides were prepared from the dianhydride and aromatic diamines by the conventional polyamide acid reaction followed by chemical imidization as well as high-temperature one-step polymerization. The structures of polymers were confirmed by various spectroscopic techniques. The weight-average molecular weight and polydispersities of resulting polymers were in the ranges 60 400−332 400 and 1.87−3.51, respectively. The polyimides showed good solubility in various organic solvents such as chloroform and THF. The polyimides exhibited 5% weight loss at 540−550 °C in nitrogen as measured by thermogravimetric analysis. The polyimides showed high T g's and good mechanical properties. The oxygen permeability coefficient (P O 2 ) and permselectivity of oxygen to nitrogen (P O 2 /P N 2 ) of the films were in the ranges 31−110 barrer and 2.8−4.3, respectively.