Polymer blends nano-organized morphology

The case of block copolymers is peculiar and deserves a specific development. In such a structure, the A and B blocks are connected to one another by a covalent bond, and their respective molar mass and composition can be varied independently. Being incompatible, A and B blocks tend to minimize their surface of contact but, contrary to the mere blends of two polymers they cannot phase separate to a macroscopic scale due to the bond which links them. Classical composition-temperature phase diagrams cannot be constructed for block copolymers as for the corresponding blends. Indeed the A and B blocks are forced to self-organize in domains of more reduced nano- or mesoscopic size. The transition from a homogeneous blend to a system composed of ordered phases as well as the size and the morphology of these ordered phases depend on two elements the product Xab " (X = total degree of polymerization) and the dissymmetry in size of the two blocks. 

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