Rod-coil systems

If indeed supramolecular dusters are formed spontaneously in bulk films of appropriately designed rod-coil systems, by inclusion of appropriate reactive units it should be possible to convert these into molecular objects by crosslinking, while maintaining the predse size and shape of the cluster. In order to test this hypothesis, rod-coil triblock copolymers, with structures similar to those described previously, but with a few modifications to enable crosslinking, were prepared. Stupp and coworkers replaced the poly(isoprene) block with a poly( butadiene) (PB) block (which contains both 1,2- and 1,4-linked repeat units), which is known to undergo thermal crosslinking at high temperatures [70]. Additionally, the phenolic OH... 

Lee et al. also reported on small rod—coil systems with a mesogenic rod segment. Their molecules are based on flexible polyethylene oxide) or polypropylene oxide) as a coil block.62-63 The rod—coil molecule based on poly(ethylene oxide) coil (8) exhibits a... 

This chapter will present an overview of recent work in designing rod-coil systems, demonstrating their self-organization capability into a variety of liquid crystalline phases. 

A strategy to manipulate supramolecular structures assembled from rod segments may be accessible by the alteration of the coil architecture (linear (5) versus branched (6)) in the rod-coil system [36]. On the basis of SAXS and TEM results, rod-coil molecules (5) with a linear PPO coil showed a honeycomb-like lamellar rod assembly with hexagonally arrayed PPO coil perforations, while the rod-coil molecules (6) with a dibranched PPO coil self-organized into rod-bundles with a body-centered tetragonal symmetry surrounded by a PPO coil matrix (Fig. 3). The notable feature is that a sim-... 

Copolymeric systems with amylose are therefore systems in which at least one component is based on a conformationally rigid segment, which are generally referred to as rod-coil systems." By combining rod-like and coillike polymers a novel class of self-assembling materials can be produced since the molecules share certain general characteristics typical of diblock molecules and thermotropic calamitic molecules. The difference in chain rigidity of rod-... 

Scheme 1. Microphase separation process for LC-BCPs. Solvents have the same effect as raising temperature due to a reduced x=Xiii- Path 1 and 2 for SGLC-coil systems (e.g. SICN5 systems, see Scheme 9 for structures) path 3 for rod-coil systems (e.g. po-ly(styrene-h-n-hexyl isocyanate)).

Although polypeptide rod-coil block copolymers [9, 10, 59] are very interesting materials, the study of a true rod-coil system requires a simpler model material because polypeptides have so many possible... 

These materials represent the first observation of the SmC (zig-zag) and SmO (arrow head) structure in rod-coil diblock copolymers [41] in contrast to the homopolymer of poly( -hexyl isocyanate) which only form a nematic mesophase (both lyotropic [65] and thermotropic [66]). This confirms the idea by Halperin [60, 69] that rod-coil systems are a microscopic model for smectic liquid crystals in general. Although the SHIC rod-coil system has a relatively broad polydispersity, a smectic mesophase over a size scale of as much as 10 xm has been observed (Fig. 4B). This indicates that microphase separation plays a very important role in determining the self-assembly of the liquid crystalline process of these blocks. The existence of only a nematic phase in the rod homopolymer system is probably due to its broad polydispersity in contrast to the fact that a smectic meso-... 

Due to the conformation asymmetry in rod-coil diblock copolymer systems, the packing is expected to be totally different from conformationally symmetric coil - coil block copolymers. Semenov and Vasilenko [71] have predicted that a N-SmA transition can be either a first-order transition (in the case of large coil fraction) or a second-order transition (in the case of small coil fraction) and a SmC phase in a rod-coil system is also expected for f <036. 

All the above theories are based on geometric considerations. By applying self-consistent field theory, Miiller and Schick [74] have predicted that the only thermodynamically stable morphologies for rod-coil systems are those with the coils on the convex side of the interface. Very recently Gurovich [75] developed a statistical theory which treats the microphase separation in LC block copolymer melts near the spino-dal and predicts orientational and reorienta-tional phase transitions driven by the configurational separation and four different phases. 

The study of the SHIC rod-coil system offers an excellent model system for testing existing theories and opens routes to a new world of materials which combine aspects of liquid crystals, statistical physics, and. solid-state physics. 

In protdn-based rod-coil systems, changes in pH can be used to tri er helix-to-coil hansitions that result in changes in aggregate size. Poly(butadiene- -L-glutamic add) (PB- -PLGA) block copolymers in water, a sdective solvent for the rod. 

Block co-polymer which use reversible supramolecular interactions like hydrogen bonding can form materials with interesting properties. As the interactions are reversible, more control can be exercised and the properties can be minutely controlled. Meijer and coworkers have designed an ureidotriazine (UTr) based systems, which on combination with poly (ethylene/butylenes) give rise to rod-coil systems [14]. 

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