Preparation of Polyimide Films from A-BPDA/ODA by One-Pot and Two-Step Imidization Methods

Polyimide films were prepared from 2, 3, 3′, 4′-biphenyl tetracarboxylic dianhydride (a-BPDA) and 4, 4′-oxydianiline (ODA) by a two-step method (thermal and chemical imidization) and a one-pot method. In the case of the polyimide films prepared from polyamic acid solution by the two-step method, the molecular weight of the films decreased before achieving its final value. In the case of polyimide films prepared by the one-pot method, the molecular weight increased smoothly to its final molecular weight during cure. The inflection point in the viscosity curve was observed between 215 and 250 °C in the polyimide prepared by the two-step method, and the range of the inflection temperature was very different from the T g of the polyimide (340 °C). So, this inflection of molecular weight was considered to be independent of the T g of the polyimide. The films prepared from three methods had almost the same molecular weight and properties in spite of the different preparation processes. For this reason it is thought that the polyimide from a-BPDA/ODA has less crystallinity and less phase orientation.