Copolymers, diblock containing

Figure 2. Schematic three-dimensional plot showing various planes of AB polymer/polymer composition. From left to right homopolymer blends blends containing 50 weight percent diblock copolymer diblock copolymers. 

Fig. 2.54 Neutron reflectivity profile for a symmetric PS-dPMMA diblock (Mw 30 kg moP1) as a function of incident wavevector (Russell 1990). The inset shows the scattering length density (b/V, the neutron scattering length per unit volume) profile normal to the film surface that was used to calculate the reflectivity profile shown as the solid line, This is typical of a block copolymer film containing a multilayer stack, with lamellae parallel to the surface.

In this chapter, structure formation in semicrystalline diblocks containing PE, PEO and other crystalline blocks is discussed in Section 5.2. Section 5.3 is concerned with theories for the equilibrium crystallization of block copolymers, whilst Section 5.4 summarizes recent experimental work on the kinetics of crystallization. There have been few studies of crystallization in thin block copolymer films, and consequently Section 5.5 is correspondingly short. Finally, structure formation in glassy diblocks is considered in Section 5,6. 

Wu et al. reported on a rod—coil diblock copolymers based on mesogen-jacketed liquid crystalline polymer as the rod block and polystyrene as the coil block (Scheme 6).82 Styrene was polymerized by TEMPO mediated radical polymerization, followed by sequential polymerization of 2,5-bis[4-methoxyphenyl]oxy-carbonylstyrene (MPCS) to produce the rod—coil diblock copolymer (20) containing 520 styrene and 119 MPCS repeating units. The rod—coil copolymer was observed to self-assemble into a core—shell nanostructure in a selective solvent for polystyrene... 

The l(Mig period of the regularly packed microdomains, as illustrated in Fig. 9.12, can be determined by the small-angle X-ray scattering. One may make a scaling analysis on the equilibrium domain sizes from the calculation of free energy changes as follows. In comparison to the macrophase-separated polymer blends, the microphase-separated diblock copolymer system contains mainly two... 

Also, it is interesting to note that in a diblock copolymer that contains azobenzene groups... 

Saunders, R. S., Cohen, R. E., and Schrock. R. R., Synthesis and characterization of diblock copolymer films containing self-assembled polyacetylene structures. Macromolecules, 24, 5599-.5605 (1991). 

In addition, polymer micelles have been demonstrated to be more stable and also have a significantly lower cmc than surfactant micelles. Further discussion of surfactant micelles is beyond the scope of this review, and, instead, the reader is directed to a recent review article by Armes. In fact, the polymer building blocks need not be amphiphilic and such phase-separated nanostructures can be formed from completely hydrophobic or lipophilic diblock copolymers that contain two segments with differing solubility (such as polystyrene- -polyisoprene) and hence can undergo phase separation in selective solvents. One example of such completely hydrophobic phase-separated micelles are those reported by Wooley and coworkers, which can be obtained from toluene and acetone solutions of a [polystyrene-a/f-poly(maleic anhydride)]-fc-polyisoprene Iriblock. Conversely, inverse structures are also accessible and are known as reverse micelles. These can be formed by adding a nonsolvent for the hydrophilic block to afford the opposite of a conventional micelle, for which the hydrophilic core is surrounded by a hydrophobic shell in a hydrophobic surrounding media. There have been a handful of reports on the application of these reverse micelles, for example, as nanoreactors and for the extraction of water-soluble molecules. ... 

All growing polymer chains remain unterminated (or active) and consequently can continue to grow if more monomer (either the same monomer or a comonomer) is added. If a second type of monomer is added, then the result is the formation of a diblock copolymer that contains a block of one polymer covalently linked to a block of second polymer (Scheme 7.2). 

Figure B3.6.5. Phase diagram of a ternary polymer blend consisting of two homopolymers, A and B, and a synnnetric AB diblock copolymer as calculated by self-consistent field theory. All species have the same chain length A and the figure displays a cut tlirough the phase prism at%N= 11 (which corresponds to weak segregation). The phase diagram contains two homopolymer-rich phases A and B, a synnnetric lamellar phase L and asynnnetric lamellar phases, which are rich in the A component or rich in the B component ig, respectively. From Janert and Schick [68].

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

Vinyl copolymers contain mers from two or more vinyl monomers. Most common are random copolymers that are formed when the monomers polymerize simultaneously. They can be made by most polymerization mechanisms. Block copolymers are formed by reacting one monomer to completion and then replacing it with a different monomer that continues to add to the same polymer chain. The polymerization of a diblock copolymer stops at this point. Triblock and multiblock polymers continue the polymerization with additional monomer depletion and replenishment steps. The polymer chain must retain its ability to grow throughout the process. This is possible for a few polymerization mechanisms that give living polymers. 

---