Free amino Silane monomers, of course, is easily removed from the polymer film by extraction, using a proper solvent. Monomers can be dissolved instantly in solvent, while polymers only slowly diffuse into the solvent--its a slow process. Furthermore, if the polymer has been crosslinked, it will never dissolved in any solvent,
The way to find a proper solvent for amino silane monomer can be tested one by one according the polarity of different solvents. Only a test tube and several solvents are good enough.
Aminopropyltri(m)ethoxysilane is soluble in (nearly) all organic solvents from hexane to methanol (but not in water). I do not know a solvent in which it is not soluble. Interestingly aminopropyltris(methoxyethoxy)silane is not only soluble in all organic solvents, including hexane, but also in water. I do not know another substance which is mixable in every proportion in hexane and in water.