Monodendrons

The main chain of dendronized polymers, due to die large size of the mon-odendrons, is usually forced to take a stretched shape thus the whole molecule exists as a rigid rod architecture both in solution and in the solid state.32d Depending on the backbone stiffness, the degree of monodendron coverage, and the size of die monodendron, the architecture of these macromolecules is no longer a sphere but a cylinder this dictates die properties of the dendronized polymers. 

Given that the presence of three alkoxy chains in the phenyl group produces such a dramatic change in the properties of the material to the point that columnar mesophases are formed at room temperature, the structure of the aryl isocyanide ligand has been further modified to introduce more paraffinic chains, and examples of metallodendrimers containing monodendrons with an isocyanide group in the focal point, and its gold compound 9, have been reported [26]. 

Figure 8.9 Schematic representation of a conical monodendron self-assembled into a supramolecular spherical micellar dendrimer, and then into an fm3m cubic mesophase.

GPC proved to be a method extraordinarily well suited to the analysis and purification of 9-phenylcarbazole monodendrons, naturally branched polymers.12 Monodendrons up to generation four, molecular weight 16.6 kDa, were separated by GPC. Branching, introduced into bacterially produced poly(hydroxy butyrate) by co-polymerization with hydroxyvaleric acid, was analyzed by GPC in chloroform with on-line viscometry.13... 

Zhu, Z. and Moore, J.S., Synthesis and characterization of 9-phenylcarbazole monodendrons an exploration of peripheral groups to facilitate purification, Macromolecules, 33, 801, 2000. 

NOESY and TOCSY experiments. It was noted that while the monodendrons are soluble only in CH3N02 the assemblies readily dissolve in CH2C12 on addition of NPM. 

Percec, V., Cho, W.D., Mosier, P.E., Ungar, G., and Yeardley, D.J.P. (1998) Structural analysis of cylindrical and spherical supramolecular dendrimers quantifies the concept of monodendron shape control by generation number./. Am. Chem. Soc. 120, 11061-11070. 

Figure 14.2 Dependence of intrinsic viscosity, [ /], on generation for PAMAM, PPI and PBzE dendrimers. Data for PBzE monodendrons are included for comparison...

Figure 14.3 Refractive index increment, dn/dc, in THF of PBzE monodendrons and tridendron dendrimers as a function of generation number, (according to ref. [15])...

Fig. 6a,b. Height micrographs obtained by tapping mode SFM from monolayers of a spherical b cylindrical molecules adsorbed on mica [84]. Top self-assembly of monodendron side groups into spherical and cylindrical supramolecular dendrimers. The process depends on the degree of polymerization of the polystyrene main chain... 

Dense substitution of side chains along a main chain gives brush-like macromolecules such as hairy rods [15], worm-like brushes [16-21] or, in the case of the side chains, further branching and monodendron jacketed chains [22-26]. 

Fig. 25a,b. a SFM-micrograph of single 14-ABG-PS molecules on HOPG. b Suggested conformation of monodendron jacketed linear chains [85]... 

To the best of our knowledge, the supercoil conformation of the monoden-dron jacketed polystyrene is one of the first observations of a defined tertiary structure in synthetic polymers. The plectoneme conformation could be caused by underwinding or overwinding of a backbone from its equilibrium state [168]. Quick evaporation of the solvent certainly can cause a residual torsion in the molecule as it contracted in itself. Unlike macroconformations of biomolecules, where the tertiary structures are often stabilized by specific interactions between side groups, the supercoil of the monodendron jacketed polymers is metastable. Eventually, annealing offered a path for the stress relaxation and allowed the structural defects to heal [86]. 

The data demonstrate clearly the importance of the interaction of the subunits of brush like molecules with the substrate. In the case shown in Fig. 31, the structure was formed on a liquid substrate. Detailed studies of the molecular conformation affected by adsorption on a solid substrate have been possible with the monodendron jacketed polymers discussed before [87]. It has been... 

Fig. 33. Monodendron jacketed linear chains adsorbed epitaxially on a HOPG substrate. The solid bar depicts the backbone including benzyl groups, whereas the zig-zag lines correspond to the alkyl side chains...

Fig. 35 a, b. STM micrographs at a low b high resolution of a monolayer of monodendrons obtained by adsorption from a saturated solution in trichlorobenzene. The inserts in (b) show orientation of the molecules relative to the crystalline lattice of HOPG [87]... 

As the desorption is combined with a contraction while the subsequent adsorption involves stretching, the molecule should move in the direction favored by the adsorption pattern. Such a motion was indeed observed in prehminary experiments for monodendron jacketed polymethacrylates with ethylene oxide... 

Percec V, Cho WD, Ungar G. Increasing the diameter of cylindrical and spherical supramolecular dendrimers by decreasing the solid angle of their monodendrons via periphery functionalization. J Am Chem Soc 2000 122 10273-10281. 

Figure 11.38 (Left) Fourth generation monodendron with a hexaethylene glycol tail. (Right) Proposed conformations of poly(benzyl ethyl ether) monodendrons oriented at the air-water interface.

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