Organo-soluble and transparent polyimides containing phenylphosphine oxide and trifluoromethyl moiety: Synthesis and characterization

A series of aromatic polyimides (PI-IIa-d) containing lateral phenylphosphine oxide (PPO) and trifluoromethyl (-CF3) moiety were prepared from an aromatic diamine, 2,5-bis[(4-amino-2-trifluoromethylphenoxy)phenyl]diphenyl-phosphine oxide (BATFDPO) and various aromatic dianhydrides via a two-step chemical imidization procedure. In parallel, for comparison, another series of polyimides (PI-Ia-d) without trifluoromethyl were synthesized from a diamine, 2,5-bis[(4-aminophenoxy)-phenyl]diphenylphosphine oxide (BAD-PO) and the same dianhydrides. It was found that both of the two series of polyimides (Pis) were soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and the solubility of PI-IIa-d was highly enhanced by the introduction of the bulky -CF3 group. Flexible and tough PI films with tensile strengths higher than 70 MPa were cast from the PI solution. The introduction of -CF3 moiety slightly sacrificed the thermal stability and mechanical properties of the PI films. For example. PI-IIa-d showed 5% weight loss at 472-476 degrees C, which was about 50 degrees C lower than those of their PI-Ia-d analogues. However, -CF3 group apparently improved the optical transparency and decreased the refractive indices of the PI films. PI-IId derived from BATFDPO and 4,4'-hexafluoroisopropylidenediphthalic anhydride (6FDA) exhibited the highest optical transparency with the transmittance of 90% at 400 nm and the refractive index as low as 1.5511 at 1310 nm. (C) 2009 Elsevier Ltd. All rights reserved.