An apparatus for the constrained drying and/or heat treating of a continuous or roll of, web stock of film. This apparatus includes a mechanism which grasps a film by its edges and moves said film through a drying zone, with said mechanism holding said film taut without substantial stretching of said film in the drying zone, and a means to remove the evaporated solvent from said apparatus. The apparatus is particularly useful for drying film of polybenzoxazole, polybenzothiazole and copolymers thereof, as well as molecular composite films. A method of drying/heat treating film is also disclosed.