Block copolymers, microphase-separated morphologies

Also in bulk block copolymers microphase-separate into ordered liquid crystalline phases. A variety of phase morphologies such as lamellae (LAM), hexagonally ordered cylinders (HEX), arrays of spherical microdomains (BCC, FCC), modulated (MLAM) and perforated layers (FLAM), ordered bicontinuous structures such as the gyroid, as well as the related inverse structures have been documented. The morphology mainly depends on the relative block length. If, for instance, both blocks are of identical length, lamellar structures are preferred. 

Yielding in Biock Copoiymers. While polymer blends show macrophase-separated morphologies, which often lead to a deterioration of mechanical properties because of the immiscibility of the components, in block copolymers microphase-separated structures at the typical size scale 10-100 nm... 

Figure 2. Block copolymer microphase separation with lanthanide complex at the block junction (lamellar morphology shown).

Block copolymers with well-defined segments often show microphase-separated morphologies (such as lamellar layers, hexagonal ordered cylinders, and micelle formation). If we use SCLCP blocks together with non-liquid crystalline segments, the mesophases are formed within one of the separated microdomains. If the non-SCLCP block has a higher Tg than the phase transition temperature of the mesophase, the amorphous block should physically support the SCLCP microdomains, forming a self-supported SCLCP system. 

Cyclic block copolymers with blocks that microphase separate in bulk are expected to form only loops at both sides of the interface, while their linear triblock analogues are able to form loops and bridges. This significant difference is expected to give very interesting morphological properties to the cyclic copolymers. 

For both designs a microphase separated morphology was found with 20-50 nm peptide domains dispersed in a continuous poly(ethylene glycol) phase. Furthermore, a 100-150 nm superstructure was observed in cast films, which was explained to result from the polydispersity and multiblock character of the polymers. The mechanical properties of fibers and films made from these block copolymers could be modulated by manipulating the length and nature of the constituent blocks. Similar work was reported by Shao et al. [47]. 

Much experimental work has been devoted so far to the study of the solid state and melt behavior of nonlinear block copolymers. Most of the studies are concerned with the microphase separation morphology of copolymers with various architectures as well as the phase transition temperature. Other solid state and melt properties have been examined in a few cases. 

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