very small e g on the order of microns or tens of microns between components and the requirements for uniformity are high the formability of the gel so prepared varies with the cross link density of the gel the higher the cross link density the more difficult it is to form the gel into a shaped article a slow to gel composition can be formed into a shaped article at a given state of gelation followed by additional gelation to higher cross link density it is found in the practice of the invention that the rate of gelation is very sensitive to the solids content of the combined solution for example it was found that a solution of 11 solids gelled completely in approximately 18 minutes while a 15 solids solution of the exact same composition gelled in about 8 minutes the viscosity of the gel can be reduced to improve formability by employing part of the anhydride containing polymer in acid or ester form this reduces the cross linking reaction between the free amines ends in the oligomeric amic acid and the anhydride containing polymer in one embodiment it is contemplated to solution cast a sheet on a moving belt or other substrate by combining the two solutions in situ from two independent feed streams in such embodiment high concentrations can be employed to achieve gel times on the order of seconds to minutes in a preferred embodiment the combined solution is cast into film or sheet on a suitable substrate prior to gelation after gelation and removal of excess solvent the resulting gel sheet is a freestanding sheet which can be formed into more complex structures by the application of the appropriate molding forces and heat one particularly preferred method of forming the sheet is vacuum forming thermoforming.