Synthesis and characterization of fully deuterated Upilex type polyimides

Polyimide films are materials of choice as membrane shutters of the hohlraum that contains a plastic microshell in which nuclear products are located to carry out Inertial Confinement Fusion experiments. In addition to high mechanical properties, polymer membranes must exhibit a high transparency in the infrared (IR) wavelengths range between 2.86 and 4 mu m (3500 and 2500 cm(-1)) to allow the IR assisted deuterium-tritium ice layer redistribution. Upilex (TM) type polyimides exhibit the desired mechanical properties but are not transparent in this wavelengths range due to the aromatic C-H stretching bands. In order to provide the required optical properties, the hydrogen atoms must be substituted by deuterium atoms. In the present contribution, we wish to report the first synthesis of a fully deuterated Upilex (TM) type polyimide. Optimized ways of synthesis. and purification for the two deuterated monomers 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA-d6) and p-phenylene diamine (PDA-d4) have been developed. These monomers have been used to prepare deuterated poly(amic-acid) solutions in NMP Thermal treatment of films obtained from these solutions gives rise to deuterated Upilex type polyimide films. These films show a high transparency in the 2.86-4 mu m region. The synthesis and the characterization of this new deuterated polymer will be discussed.