Recently, I got PI solution of 6.7wt%, 34cps in NMP+BE+GBL. The MW of PI was around 80k. I tried to synthesize similar PI solution with the MW of 60k -100k, which showed viscosity of 129 - 150 cps at 6.7wt%.
This is not the first time. Whenever I happende to check the viscosity and MW of PI's of other major Companies, they showed reasonable viscosity with proper MW. But my PI's are always too much viscous.
It seems that there is some special technics to control viscosity of known PI mother reaction mixture by dilituion or treatment during synthesis.
Is is just case by case? Please let me know any tips to solve this problem.