Block copolymers phase-separated materials

Noguchi, S. Nagano, S. Onuma, Y. Matsushita, Y Seki, X. Optical recording material using amphipathic block copolymer phase-separated monolayer, and its manufacturing method. Jpn. Kokai Xokkyo Kobo JP 2006312253, 2006 Chem. Abstr. 2006, 145, 497726. 

It was pointed out in Section 2.16.9 that anionic living polymerisation can be used to prepare ABA tri>block copolymers suitable for use as thermoplastic elastomers. In such copolymers the A blocks are normally of a homopolymer which is glassy and the B block is of a rubbery homopolymer (e.g. a polydiene such as polybutadiene or polyisoprene). The characteristic properties of these materials stems from the fact that two polymers which contain repeat units of a different chemical type tend to be incompatible on the molecular level. Thus the block copolymers phase separate into domains which are rich in one or the other type of repeat unit. In the case of the polystyrene-polydiene-polystyrene types of tri-block copolymers used for thermoplastic elastomers (with about 25% by weight polystyrene blocks), the structure is phase-separated at ambient temperature into approximately spherical polystyrene-rich domains which are dispersed in a matrix of the polydiene chains. This type of structure is shown schematically in Fig. 4.36 where it can be seen that the polystyrene blocks are anchored in the spherical domains. At ambient temperature the polystyrene is below its Tg whereas the polydiene is above its Tg. Hence the material consists of a rubbery matrix containing a rigid dispersed phase. 

However, one must consider the interactions of each of the four materials in the system with each other. In a neat block copolymer, phase separation is dictated byxAB/ H and/. When swollen with a single solvent, the behavior depends on N, f, and/AB as well as the interaction of the solvent with each block, Xas and /bs- With the two-solvent system (we will call the solvents X and Y), we consider not only the volume fraction/, the degree of polymerization N, and the Flory-Hu ins interaction of the block copolymer /ab< but also the interaction of each solvent with each block (xax- /ay- /bx- and /by) and the interaction of the two solvents, /xy-... 

A copolymer of D2i-DiSiAn, BPADA, and mPD was prepared and examined by DMA. The DMA indicated a distinct transition at 120 corresponding to the siloxane block and a weaker transition at 75 corresponding to the imide hard block. This behavior is consistent with a phase-separated material with short, well-dispersed hard blocks. The physical properties of this copolymer are shown in the following list. The elastoplastic properties of the material are also consistent with this type of microstructure. 

Differences in polarity are carried to the extreme in the ionomers, which feature several percent of salt-containing mers distributed randomly along an otherwise nonpolar, hydrocarbon chain. Although ionomers are actually a subclass of the random copolymers, phase separation and toughening resulting from domains of high salt concentration allow classification of these materials with the block copolymers. In this case, the hard blocks are reduced to but a single mer. 

In the swollen block copolymeric materials, the insoluble block of the polymer aggregates into microphase separated domains that in turn are dispersed in well-defined, spatially periodic supramolecu-lar structures.(18) While the morphologies of these structures are sometimes indistinguishable from textures assumed by thermotropic (and lyotropic) MLCs, these block copolymer phases are frequently more solid-like in their physical properties. Multiple interconnections between microphase separated domains tend to establish static, 3-dimensional, translationally ordered topologies in the materials. These aspects of the mesogenic block copolymers can be emphasized if, for example, multi-block copolymers — chains with several distinct monomer compositions along its contour length — are swollen,(19) Reference 20 provides a current entry to the literature of mesomorphic block copolymers. 

Lastella, S., Jung, Y.J., Yang, H. et al. (2004) Density control of single-waUed carbon nanotubes using patterned iron nanoparticle catalysts derived from phase-separated thin films of a polyferrocene block copolymer. Journal of Materials Chemistry, 14,1791. 

There are a variety of routes currently utilized to fabricate a wide range of hollow capsules of various compositions. Among the more traditional methods are nozzle reactor processes, emnlsion/phase-separation procednres (often combined with sol-gel processing), and sacrificial core techniques [78], Self-assembly is an elegant and attractive approach for the preparation of hollow capsules. Vesicles [79,80], dendrimers [81,82], and block hollow copolymer spheres [83,84] are all examples of self-assembled hollow containers that are promising for the encapsnlation of various materials. 

Triblock copolymers, as shown in Fig. 5.8 d), comprise a central homopolymer block of one type, the ends of which are attached to homopolymer chains of another type. As with other block copolymers, the components of triblocks may be compatible or incompatible, which will strongly influence their properties. Of particular interest are triblocks with incompatible sequences, the middle block of which is rubbery, and the end blocks of which are glassy and form the minor phase. When such polymers phase-segregate, it is possible for the end blocks of a single molecule to be incorporated into separate domains. Thus, a number of rubbery mid-block chains connect the glassy phases to one another. These materials display rubber-like properties, with the glassy domains acting as physical crosslinks. Examples of such materials are polystyrene/isoprene/polystyrene and polystyrene/polybutadiene/polystyrene triblock copolymers. 

---