Synthesis and characterization of homo- and copolyimides prepared from two-step polymerization

Homopolyamic acids and copolyamic acids were prepared from four dianhydrides and three diamines. Copolyimides could be arranged in sequence through different reaction processes, such as alternating, block, and random. Polyamic acids were subsequently converted into corresponding polyimides by the solid-phase imidization. Polyimide derivatives were characterized by viscosity, thermal stability, mechanical properties, and solubility. The extent of polymerization might be influenced by the nucleophilicity of a diamine and the electrophilicity of a dianhydride. In gel permeation chromatography, molecular weight distribution of polymers was 2.5-3.0. The thermal stability of polymers decreased with increasing the ratio of a more flexible component, and alternating copolyimides showed slightly better than corresponding random and block ones. The melting temperatures of all polyimide derivatives did not exist on the differential scanning calorimetry curves, and the results were proof that the X-ray diffraction curves. Polymers derived from bis[4-(3-amino phenoxy)phenyl]sulfone dissolved well in some polar solvents. Alternating copolymers represented a better solubility than the corresponding random and block ones. All polymers had good mechanical properties, both tensile and elongation. The kinetics of imide formation could be also dependent on the structure and reactivity of reagents. The kinetics of cyclodehydration was described by the first-order kinetics up to relatively high conversion but deviated from the first-order kinetics at high conversion followed by the second-order kinetics.