Interfacial activity, block copolymer

Figure 7 compares the water/toluene interfacial tensions measured in the presence of various commercial surfactants and P0/PS based diblock (8) and star-shaped copolymers the higher activity of the star-shaped block copolymers over a broad range of concentrations is clearly put in evidence. 

In the field of thermoplastic immiscible blends, the emulsifying activity of block copolymers has been widely used to solve the usual problem of large immiscibility associated with high interfacial tension, poor adhesion and resulting in poor mechanical properties. An immiscible thermoplastic blend A/B can actually be compatibilised by adding a diblock copolymer, poly(A-b-B) whose segments are chemically identical to the dissimilar homopolymers, or poly(X-b-Y) in which each block is chemically different but thermodynamically miscible with one of the blend component. Theoretical... 

Figure 16 shows that the best retardation effect is obtained with R22f5 among repulsive block copolymers investigated in this study. Thus, the competitive interactions of the blocks with different homopolymers are shown to promote the retardation. In other words, as the relative repulsion between block C and homopolymer B and between block D and homopolymer A increases, i.e., if the interaction of block C (D) with homopolymer B (A) is more repulsive than that of block C (D) with homopolymer A (B),the rate of phase separation is retarded more effectively. Vilgis and Noolandi [81] also predicted strong interfacial activity of block copolymers with such interactions. Therefore, it can be concluded that the interaction energy between blocks also has an important effect on the phase separation of immiscible blends. 

Not only molecular weight influences the interfacial activity of the PS-hPBD diblock copolymers but also the internal structure. Instead of a single covalent bond between PS and hPBD, a more or less random copolymer sequence can form the transition between the two blocks resulting in the so-called tapered diblock copolymers. The effect of the tapered structure (12,22) and its superiority over the pure diblock (18) have been documented elsewhere and discussed in terms of a change in the interface itself and the melt viscosity of the interfacial agent. 

Adedeji A, Hudson SD, Jamieson AM. Effect of exothermic interfacial mixing on interfacial activity of a block copolymer. Macromolecules 1996 29 2449— 2456. 

Regardless of the application, the placement (i.e., terminal or internal, isolated or in block sequences) of the hydrophobe-modified monomer in the macromolecular chain is important to the performance of the polymer. The difficulties encountered in determining the sequence structure of hydrophobe-modified acrylamide (water-insoluble) monomers in acrylamide copolymers are discussed in Chapter 20. In this respect, the bicontinuous nature of microemulsions may prove an advantageous method of synthesis. The surfactants used in such a process, however, are significantly more interfacially active than the surfactants used in most application formulations and may detract from the performance of RAM copolymers. The most recent patent (20) in the RAM area discusses the synthesis of RAM copolymers by a microemulsion process, but complexities due to surfactant differences in formulations are not addressed. 

Simple melt blending reactions can also be applied to preparations of block copolyamides, similarly to the process for polyesters, th time, total equilibrium conditions also are gradually achieved in the melt. Interfacial polycondensation is also useful in preparation of block copolymers. When mixed diacid chlorides and/or mixed diamines are reacted, the more active diacid chlorides and/or diamines react preferentially and blocks form. In addition, it is possible to carry out the growth of one of the segments first, to a fairly large size, and follow it by addition of the other comonomers. ... 

An experiment that clearly shows the interfacial activity of block copolymers at polymer/polymer interfaces may be done by making a bilayer sample of two incompatible polymers, which we shall refer to as A and B, and incorporating in one of the polymers some AB block copolymer that has been labelled in... 

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