Morphology zigzag

Various types of morphologies and crystalline modifications of s-PS have been reported [44], One of these modifications has an orthorhombic form (space group = P2i2i2i) with a planar zigzag conformation of back-bone chain. This form corresponds to the a-phase found by Kobayashi et al. [35] and to the P-phase named by Guerra et al. [36], The crystal structure of this form was analyzed and the plane of phenyl rings within this form is normal to the chain axis (c-axis) [37-39],... 

The potential for novel phase behaviour in rod-coil block copolymers is illustrated by the recent work of Thomas and co-workers on poly(hexyl iso-cyanate)(PHIC)-PS rod-coil diblock copolymers (Chen etal. 1996). PHIC, which adopts a helical conformation in the solid state, has a long persistence length (50-60 A) (Bur and Fetters 1976) and can form lyotropic liquid crystal phases in solution (Aharoni 1980). The polymer studied by Thomas and co-workers has a short PS block attached to a long PHIC block. A number of morphologies were reported—wavy lamellar, zigzag and arrowhead structures—where the rod block is tilted with respect to the layers, and there are different alternations of tilt between domains (Chen et al. 1996) (Fig. 2.37). These structures are analogous to tilted smectic thermotropic liquid crystalline phases (Chen et al. 1996). 

Figure 5. Schematic representation of (a) interdigitated model and (b) bilayer model in the zigzag morphology.

Figure 6. TEM images for (a) zigzag lamellar morphology of rod-coil copolymer with Toa = 0.90 and (b) arrowhead morphology of rod-coil copolymer with Tod = 0.98. (Reprinted with permission from ref 52. Copyright 1996 American Association for the Advancement of Science).

Rod-coil diblock copolymers with a relatively short rod segment self-assembled into a wavy-lamellar morphology, while increasing the rod fraction resulted in the formation of a zigzag lamellar phase. At rod fractions/phic of 0-96 and 0.98, the PS coils were found to organize into arrowhead-shaped domains embedded in a PHIC matrix. Unlike the self-assembly of the PPP-17-PS and PPQ-b-PS diblock copolymers, the unconventional morphologies discovered for the PHIC-I7-PS rod-coils are related to their macromolecular architecture and are... 

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