High-performance polymer films. III. Preparation and characterization

A series of polyimide and copolyimide films were prepared by film casting, drying, and thermal imidization from the respective precursor poly(amic aci d) (PAA) and copoly(amic acid) solutions derived from two dianhydrides, pyr omellitic dianhydride (PMDA) and 3,3 ' ,4,4 ' -benzophenonetetracarboxylic dianhydride (BTDA), and two diamines, 4,4 ' -oxydianiline (ODA) and a propr ietary aromatic diamine (PD) as monomers. Depending on the solution's inher ent viscosity value (molecular weight) and the nature of the polymer chains (derived from rigid or flexible monomers), precursor poly(amic acid) and c opoly(amic acid) solution concentrations of 8-12% (w/w) were found to be su itable for the preparation of good quality polyimide/copolyimide films. The recovery of film toughness and creasability from the brittleness at the in termediate temperature of the cure cycle depended not only on the molecular weight of the precursor poly(amic acids)/copoly(amic acids) but also on th eir chain flexibility. The poly(amic acid) derived from both rigid dianhydr ide and diamine practically gave rise to a brittle film of polyimide even a fter curing to 360 degreesC. The resulting polyimide and copolyimide films were compared with Du Pont's Kapton H film. The density of the films was in the range 1.39-1.42 g/cm(3). The thickness of most of the films was in the range 20-30 mum. The HPF 3 film, based on PMDA-PD, appeared to be highly c olored (reddish brown), and the HPF 2 film, based on BTDA-ODA, had the ligh test yellow coloring among the films in this investigation, including Kapto n H film. HPF 2, HPF 6, and HPF 8 films were more amorphous than the other films. (C) 2001 John Wiley & Sons, Inc.