Crystallization and phase behavior in nylon 6/aromatic polyimide triblock copolymers

Several series of new b-nylon 6-b-polyimide-b-nylon 6 triblock copolymers were synthesized via a condensation polymerization of polyimide segments and anionic polymerization of the nylon 6 components. Crystallization and phase behavior of these triblock copolymers have been studied with varying polyimide block molecular weights and copolymer compositions as well as chemical structures (and therefore, different solubility parameters) of the polyimide components. Furthermore, in-situ and solution blends have also been prepared in order to compare the phase behaviors of the triblock copolymers. Wide angle X-ray diffraction experiments indicate that in these triblock copolymers, only nylon 6 components crystallize and polyimides do not take part in the crystals. From isothermal crystallization kinetics studies carried out in differential scanning calorimetry experiments, the miscibility of the polyimide components with nylon 6 critically affects the crystallization rate of these triblock copolymers. When the polyimide composition is low and its solubility parameter is similar to that of the nylon 6 components, the polyimides mix with the amorphous part of the nylon 6 components and are located in the inter-lamellar region. This can be identified by monitoring the change of α-relaxation temperature and activation energy measured using a dynamic mechanical method and by examining the crystalline lamellar morphology under small angle X-ray scattering experiments. Microphase separation can also be recognized by transmission electron microscopy using an OsO₄ vapor staining technique. As the difference of solubility parameters between these two components as well as the block molecular weight of the polyimides increase, microphase separation between the two components in the triblock copolymers can be found.