CRYSTALLIZATION AND MORPHOLOGY OF SEMICRYSTALLINE POLYIMIDES

Although many semicrystalline polyimides have been synthesized, little work has been done on their solid-state characterization. This is one of the first reports concerning the crystallization behavior and crystal morphology of polyimides. In prticular, this work characterizes a series of polymides consisting of a rigid group [the imide and aromatic rings, 4,4'-oxydiphthalic anhydride (ODPA)] and a flexible linkage (an ethylene glycol sequence of n = 1,2, or 3 repeat units). The overall crystallization behavior of the ODPA (n = 1, 2, and 3) polyimides can be described by the Avrami equation. The overall crystallization rate is dependent upon the chain flexibility and the crystallization conditions. The initial overall crystallization data (at 5% weight fraction crystallinities) show regime II/III transitions as defined by crystallization theory. The crystal morphologies of these polyimides can be observed in the micrometer range through polarized light microscopy, while resolution to a nanometer scale can be reached with transmission electron microscopy. A proposal relating the crystal morphology to the overall crystallization behavior and the crystal/amorphous interfacial structures is presented.