Microstructure Control in Block and Graft Copolymers, and Polymer Blends

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Abstract
Block and graft copolymers with incompatible sequences exhibit characteristic morphological behavior and interesting properties, owing to microdomain formation in the solid state. The thermodynamic approach to the problem of microdomain formation for block copolymers has been worked out [1–5] by demonstrating that the morphology of the domain structure-such as equilibrium size, shape, and interfacial thickness-can be described in terms of a balance of physical factors. It has been established, especially by electron microscopy, small-angle X-ray scattering, and X-ray diffraction, that segregated microphases can be spheres, cylinders, or lamellae. The type of morphology adopted by the copolymer essentially depends on its composition [6]. The morphological changes on AB block copolymer will be observed also by changing the selectivity of the casting solvent for the A component in solution-cast films or in ordered solutions [7–9], simply because selectivity changes the ratio between the effective radii or gyration of A- and B-block chains. More recently, a new morphology named “tetrapod-network” structures were found in a block copolymer [10], a three-component pentablock copolymer [11], and in star- block polymers [12–14]. Generally, physical properties of these multicomponent polymer systems depend strongly on the morphology of domain structure. According to the foregoing results, thc establishment of a synthesis method for well-defined block and graft copolymers will be important in the design of the desired morphology of the domain structure (domain spacing and shape).