Higher-order unimer micelles

Dynamic Properties of Higher-Order Unimer Micelles. 

The extent of the restriction on the mobility of an azobenzene moiety covalently incorporated into higher-order unimer micelles, monitored by photoisomerization and thermal back isomerization rates, is much more pronounced in cyclododecyl domains than in dodecyl domains, which can be related to a difference in the mobility of these aliphatic hydrophobes in the microdomains (52). Cyclododecane is a rigid molecule with much less conformational freedom than dodecane because of its cyclic structure. The latter is a flexible chain that can adopt a variety of conformations. Therefore, cyclododecyl groups may be more tightly associated than dodecyl groups and form a more rigid hydrophobic microdomain. 

Hydrophobic functional-molecules can be incorporated into the higher-order unimer micelles either via chemical bonding of the functional molecules to amphiphilic polymers or by physically solubilizing tiie mol ules into the unimer micelle. For example, when an AMPS-DodMAm copolymer and a hydrophobic small-molecule are dissolved together in ethanol, and the ethanol solution is poured into excess water, then the hydrophobic molecules can be entrapped in a hydrophobic microdomain during the process of the hydrophobic self-association of polymer-bound dodecyl groups. However, it is practically difficult to precisely control the number of the sm l... 

Janus micelles are non-centrosymmetric, surface-compartmentalized nanoparticles, in which a cross-linked core is surrounded by two different corona hemispheres. Their intrinsic amphiphilicity leads to the collapse of one hemisphere in a selective solvent, followed by self-assembly into higher ordered superstructures. Recently, the synthesis of such structures was achieved by crosslinking of the center block of ABC triblock copolymers in the bulk state, using a morphology where the B block forms spheres between lamellae of the A and C blocks [95, 96]. In solution, Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) half-coronas around a crosslinked polybutadiene (PB) core aggregate to larger entities with a sharp size distribution, which can be considered as supermicelles (Fig. 20). They coexist with single Janus micelles (unimers) both in THF solution and on silicon and water surfaces [95, 97]. 

Not only the copolymers of AMPS and DodMAm but also the copolymers of AMPS and a methactylamide A -substituted with cyclododecyl, adamantyl, or naphthylmethyl groups (Chart 3) form either a unimolecular flower-like or higher-order micelle (i.e., tertiary structure) depending on the hydrophobe content in die copolymer. An important feature for these copolymers is that such unimer micelles are formed even at hi polymer concentrations in water. Some of the requiate structures for polymers to form unimer micelles are (i) the hydrophobes should be sufficiently bulky, (ii) the sequence distribution of hydrophobic and electrolyte monomer units should be random, and (iii) the hydrophobes should be linked to the polymer main chain via amide spacer Ending (22). 

This chapter deals with a recently developed unimer micelle, a novel intramolecular assembly with a higher-order structure, formed from tailored amphiphilic random copolymers bearing charge and bulky hydrophobes. The first half of this chapter will be devoted to the synthesis of such amphiphilic poly electrolytes and characterization of the unimer micelle. The functionalization of the unimer micelles with chromophoric molecules and some functional properties of these functionalized unimer micelles will be described in some detail in the second half of this chapter. 

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