Crystalline microdomain structure

It is clear from many experimental results that crystalline blocks confined in isolated nanodomains surrounded by glassy (or hard) matrices show unique crystal orientations as compared with those by soft matrices (Section 10.3.3.). However, the physical properties of such block copolymers with crystalline microdomain structures have scarcely been investigated up to now. 

When of crystalline-amorphous diblock copolymers is sufficiently large, the soft microdomain structure is stable against the subsequent crystallization. Therefore, this structure is preserved through the crystalUzation process, that is, constituent blocks crystallize within the soft microdomain stmcture, to yield a crystalline microdomain structure (lower route in Fig. 10.7). Amorphous domains in the crystalline microdomain structure are not hard in this case, so that crystalline domains can deform moderately during crystalUzation in order to get a larger crystalUnity and/or favorable crystal orientation, which is criticaUy different from the crystallization of block copolymers with high-T amorphous blocks, as described in Section 10.3.2. 

The basic research on the crystallization in more complicated systems started recently to find ouf unique morphologies formed in polymer systems. The crystallization of block copolymers is a striking example of such crystallization, which is intimately dependent on the molecular characteristics of crystalline block copolymers. For example, the crystallization of crystalline-amorphous diblock copolymers yields the lamellar morphology or crystalline microdomain structure depending on xN of block copolymers, Tg of amorphous blocks, crystallization conditions, and so on. These kinds of crystallization have the possibility of developing new crystalline polymer materials. Therefore, we strongly anticipate future advances in this research field. 

Yui et al. [86-89] have previously reported another type of microdomain-structured polymer, po y(propylene oxide) (PPO)-segmented nylon 610, which has a crystalline-amorphous microdomain structure ... 

According to Asano and Seto [259], the monoclinic structure of PET would be paracrystalline in the sense that the monoclinic symmetry would describe, on average (in the long range), a mosaic-like structure formed by the assembly of crystalline microdomains in the normal triclinic form of PET (in the short range) with different inclination. 

It is widely recognized that amorphous-amorphous diblock copolymers form a variety of microdomain structures when the segregation strength between different blocks is moderately large. When one block is crystalline and the other is amorphous (i.e., crystalline-amorphous diblock copolymers), it is easily supposed that the morphology formation at low temperatures is driven by a close interplay between... 

Figure 10.7 Schematic illustration showing the possible morphology formation in crystalline-amorphous diblock copolymers by the crystallization of constituent blocks. The upper route represents break-out crystallization, that is, the microdomain structure is completely replaced with the lamellar morphology, whereas the lower route shows confined crystallization, where the microdomain structure is preserved after crystallization, a-d indicate driving factors for the morphology formation.

The crystalline morphology formed in crystalline-crystalline diblock copolymers is more complicated as compared with that in crystalline-amorphous diblock copolymers, because two kinds of crystallization start from some microdomain structure existing in the melt. It is useful to classify this crystallization into two cases in terms of the crystallizable temperature of both blocks (Fig. 10.8) two-step crystallization when of one block is significantly higher than that of the other, and simultaneous crystallization when both values are sufficiently close. 

The crystallization of homopolymers yields a hierarchical structure in polymer materials, which substantially controls their physical properties. Therefore, the crystalline morphology of homopolymers has been one of the important research subjects in polymer science. In addition, the crystallization of homopolymers spatially confined in various nanodomains, such as micelles, AAO, or microdomain structures, may bring new information on crystallization mechanisms of homopolymers, because it will be possible to highlight a specific crystallization mechanism (e.g., nucleation or crystal growth) in the overall crystallization process consisting of several combined mechanisms. Furthermore, the crystallization in nanodomains has the possibility of providing new polymer materials, and their physical properties should be unique as compared with usual polymer materials. This is because the substantial control of nano-ordered structures formed in polymer materials will be possible by this crystallization, which is never achieved by the crystallization of neat homopolymers. 

This chapter deals primarily with examples in the semidilute concentration range, corresponding to overlapped chainlike aggregates of isotropic gels." As mentioned, the heterogeneity of the networks makes possible the existence of more concentrated microdomains, where chains are somewhat ordered in crystalline or lyotropic structures (corresponding to anisotropic gels). 

Rod—coil block copolymers have both rigid rod and block copolymer characteristics. The formation of liquid crystalline nematic phase is characteristic of rigid rod, and the formation of various nanosized structures is a block copolymer characteristic. A theory for the nematic ordering of rigid rods in a solution has been initiated by Onsager and Flory,28-29 and the fundamentals of liquid crystals have been reviewed in books.30 31 The theoretical study of coil-coil block copolymer was initiated by Meier,32 and the various geometries of microdomains and micro phase transitions are now fully understood. A phase diagram for a structurally symmetric coil—coil block copolymer has been theoretically predicted as a... 

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