Hello respected researchers,

I am suffering to make a colourless polyimide (PI) film, so I want to ask for some help or tips.

My background is not about polymer, so this problem comes quite a burden to me.

To help comprehension, a method (Ref. Chio et al.) is explained below:

I dissolved 4,4′-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′-diaminodiphenyl sulfone (APS) powders in nitrogen-purged N,N-dimethylformamide (DMF) at room temperature (25 oC(Celsius degree)) by stirring.

The homogeneous precursor solution (transparent brown colour) was coated onto the glass substrate with tens of micrometres by blade coating. The coated area was 4 cm^2. No air bubbles were observed.

The main problem appeared in the following heat procedure.

At first, the film was heated at 100 oC for 1 hour, and the temperature was increased to 200 oC subsequently. However, when the temperature approaches about 150 oC, gas bubbles appeared from boiling DMF, messing the morphology of the film with the holes.

If the film was heated only at 100 oC for many hours, an unexpected brownish brittle film was formed.

What I want to get is a colourless and flexible PI film. (could be used as the substrate for a semiconductor device)

Could anyone inform any tips for me?

I am also trying to search for other papers more.

Thank you.

[Ref: Choi et al. NPG Asia Mater. 2016, 8]