Polymer blends containing block copolymers

Block copolymers represent a special class of polymer blends characterized by covalent bonding between the individual molecules comprising the blocks. The molecular structure (monodisperse molecular weights) achieved with anionic polymerization has allowed for styrene-diene and diene-diene AB and ABA block copolymers, offering well-defined morphologies. The phase separation morphology and properties of block copolymers have been well-covered in many references [656-660] and wiU not be detailed here. Blends of block copolymers with their homopolymer constituents as well as in other polymer blends will be discussed. Cases where minor amounts of block copolymers are included in polymer blends as compatibihzers have been noted in Section 3.7. 

One of the imique features of phase separated block copolymers involves their ordered morphologies which can include spheres, cylinders, lamellae, bicontinuous as well as ordered bicontinuous doubled diamond and gyroid structures (see Figs. 4.17 and 4.18). Gyroid struc- 

Spontak permission obtained from reference Jinnai, H., Mishikawa, Y., Spontak, R. J., Smith, S. D., Agard, D. A. and Hashimoto.T., Rhys. Rev. Lett. (2000) 84, p. 518) copyright (2000) by the American Physical Society) 

The morphology changes of block copolymers with addition of one or both of the homopolymers has thus been a subject of interest. When a homopolymer A (with lower molecular weight than block A) is mixed with block copolymer AB, the homopolymer A dissolves in the block A domain and expands the A domain size. For lamellar morphology, the interfacial curvature 

Theories of the phase behavior and morphology predictions of homopolymer blends with block copolymers are beyond the scope of this book. Several of the many studies related to this subject are foimd in [684—690]. 

In blends of two or more homopolymers with block copolymer, there is an interplay between macrophase separation of the homopolymers and microphase separation of the block copolymer. Which effect predominates depends on the relative lengths of the polymers, and on the composition of the blend. 

One of the most important applications of block copolymers is as compatibi-lizers of otherwise immiscible homopolymers. This compatibilization results from the reduction of interfacial tension due to segregation of copolymer to the interface between homopolymers. Experiments and theory concerned with the understanding of the thermodynamics of these ternary blends are discussed in this chapter. 

Binary blends of block copolymers can also macrophase separate if the mismatch in molecular weights is sufficient. In the other limit, blends of diblocks of 

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A number of classes of polymer blends containing block copolymers have been studied. Namely, binary blends of a block copolymer with a homopolymer, ternary mixtures of a block copolymer with two homopolymers and blends of two block copolymers. Experimental and theoretical studies of all these mixtures are the subject of Chapter 6. 

A crucial aspect on polymer blends containing block copolymers concerns the concentration of block copolymer both in bulk and at the surface. The former can be controlled in the design of the initial blend and the latter depends not only on the amount initially introduced in the blend but also on the eventual surface segregation. In Fig. 5.18 is schematically illustrated the block copolymer arrangement of binary blends with variable amount of block copolymer. At low concentrations (a, b) the block copolymer can reside either in the bulk or at the interface and the amount of block copolymer segregated at the interface is directly related to the... 

Micro-/nanostructured polymer blends containing block copolymers... 

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