Formation of spherical nanoparticles in poly(amic acid) films

We found for the first time the formation of spherical nanoparticles in poly(amic acid) (PAA) derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline films after pre-baking. Several factors influencing the formation of spherical nanoparticles have been investigated. The molecular weights of PAA and the pre-bake temperature are important and effective parameters influencing the particle morphology. On the other hand, spherical nanoparticle formation does not depend on the film casting method. The particle size distribution after pre-baking at 100–150 °C for 5 min is rather narrow in the range of 25–45 nm and the mean particle diameter is 33 nm, which means that the resulting film is transparent and can be used as a photoresist. This observation is very important for developing photosensitive polyimides providing a deeper insight into a development process using organic solvents or aqueous base solutions.