Abstract
A series of polyimide and copolyimide films were prepared by film casting, drying, and thermal imidization from the respective precursor poly(amic acid) (PAA) and copoly(amic acid) solutions derived from two dianhydrides, pyromellitic dianhydride (PMDA) and 3,3β²,4,4β²βbenzophenonetetracarboxylic dianhydride (BTDA), and two diamines, 4,4β²βoxydianiline (ODA) and a proprietary aromatic diamine (PD) as monomers. Depending on the solution's inherent viscosity value (molecular weight) and the nature of the polymer chains (derived from rigid or flexible monomers), precursor poly(amic acid) and copoly(amic acid) solution concentrations of 8β12% (w/w) were found to be suitable for the preparation of good quality polyimide/copolyimide films. The recovery of film toughness and creasability from the brittleness at the intermediate temperature of the cure cycle depended not only on the molecular weight of the precursor poly(amic acids)/copoly(amic acids) but also on their chain flexibility. The poly(amic acid) derived from both rigid dianhydride and diamine practically gave rise to a brittle film of polyimide even after curing to 360Β°C. The resulting polyimide and copolyimide films were compared with Du Pont's Kapton H film. The density of the films was in the range 1.39β1.42 g/cm^3^. The thickness of most of the films was in the range 20β30 ΞΌm. The HPF 3 film, based on PMDAβPD, appeared to be highly colored (reddish brown), and the HPF 2 film, based on BTDAβODA, had the lightest yellow coloring among the films in this investigation, including Kapton H film. HPF 2, HPF 6, and HPF 8 films were more amorphous than the other films. Β© 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 976β988, 2001