Block polymers, chemically incompatible components

Block Copolymers. The chemically stabilized permanent two phase systems which are obtained by block-copolymerlzatlon of incompatible chains exhibit the rather unexpected gas solubility characteristics shown on Figure 11. Tentatively this peculiar behavior has been ascribed to the special properties of the "interfacial" region between the two polymer phases (19). If the reality of the special properties of such an Interfacial region is validated by independent experiments, we can speak of a component phase. Given the early development stage of this field, a definitive theory must be based on far more experimental work than has been produced so far. 

The chief reason for the interest in graft copolymers originates from the incompatibility between polymer chains of different chemical nature. Intramolecular phase separation results, because grafts and backbone repell each other, and these compounds exhibit a marked tendency to form mesomorphic phases like block copolymers and soaps do. When these species are mixed with a solvent that exhibits a preferential affinity for one of the components (grafts or backbone) the incompatibility may be enhanced. This intramolecular phase separation has led to a number of applications. If small amounts of a graft copolymer are included into a homopolymer of the same nature as the grafts (or the backbone), surface modifications can result as described below. 

In most cases the different constituent blocks are incompatible, giving rise to intramolecular phase separation, but the chemical connectivity restricts the special dimension of phase segregation to the nanoscale. As a result, at sufficiently high molecular weight, monodisperse block copolymers form a rich variety of self-assembled structures or an array of periodic nanostructures with a periodicity of 10-100 nm, commonly referred to as microphase-separated structures. By changing the relative composition, the compatibility between the component polymers, and the architecture of the copolymer molecules, the size and type of nanostructures can be precisely controlled [1-6]. 

An immiscible polymer blend that exhibits macroscopically uniform physical properties is called compatible. Compatibility means the capability of individual component substances in either an immiscible polymer blend or a polymer composite to show interfacial adhesion that in which interfaces between phases or components are maintained by intermolecular forces, chain entanglements, or both, across the interfaces. In the case of block copolymers, if their parent s homopolymers A and B are incompatible, the copolymer may show segregation, i.e., the A-segments and the B-segments are then located in separate domain [6]. The term domain may be used for an entity of a material system that is uniform in chemical composition and physical state. 

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