A monomer is selected to produce a polymeric film having desirable characteristics for a particular application. The monomer is ppolymerized under controlled conditions to produce a solid oligomer having those characteristics at a molecular weight suitable for evaporation under vacuum at a temperature lower than its thermal decomposition temperature. The process of polymerization to produce the oligomer is carried out under conditions that yield a finite molecular-chain length with no residual reactive groups. The solid oligomer so produced is extruded as a film onto a revolving drum (38) in the evaporation section (40) of a vapor deposition chamber, and then cryocondensed on a cold substrate (44) to form a solid film having the same characteristic selected in the solid oligomer constituting the starting material. As a result of the initial complete reaction to produce the oligomer, the thin-film product does not contain unreacted groups and all attendant disadvantages are avoided.