A bundle assembly for vertical, gravity flow driven polymerization reactors for combinations of high viscosity, high throughput, and thin polymer films is provided. The bundle assembly includes static internal components that provide large areas of free liquid surfaces in contact with the atmosphere of the reactor while still attaining sufficient liquid holdup times for polymerization to take place. The bundle assembly includes one or more stationary film generators. The bundle assembly further includes one or more stationary arrays of film support structures. Each of the film support structures has a first side and a second side. Both sides of the film support structure are coated with flowing polymer. The vertical arrangement of components in the bundle assembly cause the polymeric melt to cascade down the vertical length of a reaction vessel interior that incorporates the bundle assembly. The present invention also provides a polymerization reactor that incorporates the assembly of the invention and a method of increasing the degree of polymerization of a polymer melt by using the assembly of the invention.