I made a polyurethane polymer with MW around 17k. And I dissolved them in 30% methnol/ 70% DCM solution with a concentration of 24mg polymer/ mL solution. And then I added the solution to the area around by the tape. After around 10 mins, the solution evaporated, and film couldn't form and it seems like the polymer precipitate out. Is it the MW of my polymer too small, making it difficult to form a film? could I know whether there is better protocol to make a film by solvent cast method?