Investigation of solid state imidization reactions of the vapour deposited azo-polyimide thin films by FTIR spectroscopy

• Experimental parameters for Azo-PI films preparation by solid state reactions have been established.
• The structure of Azo-PI films has been determined by FTIR spectroscopy.
• The kinetic of imidization has been investigated by FTIR spectroscopy at different temperatures.
• The appropriate temperature for solid state imidization is 300 °C for 1 h.

In this paper solid state imidization reactions of azo-polyimide thin films prepared at different temperatures have been investigated by FTIR spectroscopy. The starting precursors DAAB (4,4′-diaminoazobenzene) and PMDA (pyromellitic dianhydride) were vacuum deposited as thin films. It was estimated that the necessity of the following thermal treatment 1 h at 300 °C are appropriate conditions for imidization of the initial PMDA–DAAB mix to Azo-PI (azo-polyimide) film. The parameters have been selected experimentally (temperatures, deposition rates, mode of substrates, etc.), for the vapour deposition of the precursors in view to prepare layers with a high imidization degree, reproducible composition and structure, which determined the film properties. Due to their magnetic anisotropy and cis–trans–cis isomerization cycle the azo-polymer films are promising material for application in optics, optoelectronics, sensors, etc. For this reason a study of the kinetics of solid state imidization reactions at different temperatures is carried out. It is identified and discussed that the imide III band intensity at 1363–1381 cm−1 characterizing imide ring is different at three temperatures.