Rod-coil co-polymers

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). 

The potential of block copolymers in forming supramolecular structures on surfaces has been studied in great detail by Stupp and co-workers [36]. Their studies have concentrated on the supramolecular properties of diblock and triblock rod-coil polymers which consist of one or two components that are conformationally flexible and one component with a more rod-like character at one of the ends of the polymer chain ( c in Figure 4.25). This latter component can be crystallized and is expected to yield well-defined structural arrangements. The Stupp-type copolymers are based on diblock styrene-b-isoprene coils combined with various rod-like components. The synthesis of such materials is carried out in two stages. In the first step, the diblock coil part is produced, as shown in Figure 4.26. The... 

Some recent examples demonstrating the molecular dispersion of rod polymer molecules in coil polymer matrices due to ionic interactions were given by Parker et al. (1996). These systems were based on three types of ionic PPTA s (Figure 5.4) and polar polymers, such as poly(4-vinylpyridine) (PVP), poly(vinyl chloride) (PVC), poly(ethylene oxide) (PEO), and poly(styrene-co-acrylonitrile) (S-AN). Due to the ionic-dipole interactions the rod-coil polymer pairs formed molecular composites as revealed by optical clarity, polarized microscopy, Tg measurements, as well as TEM observations. More significantly the molecular composites based on amorphous matrix polymers (e.g., PVP) were all transparent and showed no phase separation upon heating. Therefore they are melt-processible. As would expected, the mechanical properties of the molecular composites were... 

I, 4-phenylenebenzobisthiazole-co-decamethylene - benzobisthiazole) (HPBT-co-PBTCIO, 5). The molecular structures and compositions of all the rod-coil copolymers 1-5 (Chart 1) were established primarily by NMR and FTIR spectroscopies, thermal analysis (TGA, DSC), intrinsic viscosity and various other spectroscopic measurements, as previously done for related polymers (10,... 

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]. 

Perhaps some of the most exciting work using one-component dendritic gelators has been performed by Stupp and co-workers. They have investigated the assembly properties of so-called dendron rod-coil molecules (Fig. 18) [59]. These dendron rod-coils are effectively tri-block copolymers, which have a flexible (coil) polymer unit attached to a well-defined linear rigid rod unit, which is, in turn, grafted to a dendritic head unit. The synthesis of... 

Figure 19.6 AFM topography images obtained from a drop of copolymer solutions in water deposed on a mica surface (a) low concentration and (b) high concentration, (c) Schematic representation of the concentration effect on the morphology. (Reproduced with permission from A. de Cuendias, E. Ibarboure, S. Lecommandoux et al., Synthesis and self-assembly in water of coil-rod-coil amphiphilic block copolymers with central 7i-conjugated sequence, Journal of Polymer Science Part A Polymer Chemistry, 2008, 46, 4602-4616. Wiley-VCH Verlag GmbH Co. KGaA.)...

For two series of rod-coil copolymers [95] poly(l,4-phenylenebenzobisthi-azole-co-decamethylenebenzobisthiazole) (see Fig. 29b) and poly[(l,4-phen-ylenedivinylene)benzobisthiazole-co-decamethylenebenzobisthiazole] (see Fig. 29c) the authors also investigated the photophysical properties with varying composition. In these cases the photoluminescence quantum yield reached over seven fold higher values than for a pure conjugated homo polymer. Furthermore the emission color was tunable in the visible region by varying rod fraction. 

For adjusting interfacial interactions in fullerene-polymer composite materials, in addition to changing the miscibility of C-60, novel block copolymers have also been prepared, in which one of the blocks contains C-60 grafts. For example, Richard and co-workers synthesized novel rod-coil block copolymers of P3HT and PS-graft-fullerene, observing significant... 

Figure 9 Schematic representation of a tube nanostructure formed by PE0z21-/ PBLG68 in benzyl alcohol. The PEOz chains are depicted as coils, and the PBLG units as dark helical rods. Reproduced with permission from Kuo, S. W. Lee, H. F. Huang, C. F. etal. J. Polym. ScL, Part A Polym. Chem. 2008, 46, 3108-3119, Copyright Wiley-VCH Verlag GmbH Co. KGaA. ° ...

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