Unimer micelle

Size-exclusion chromatography (SEC) has been used to characterize the unimer-micelle distribution. However, SEC is not an absolute method and thus requires calibration. Since it is practically impossible to calibrate a SEC apparatus for the unimers and micelles formed by a block copolymer, only indicative MW values can be obtained. Moreover, several authors have noted a strong perturbation of the unimer-micelle equilibrium during SEC experiments even when interaction of the material with the SEC column was minimized [4,61,62],... 

The dynamics of micellar systems is a very important concern that is relevant at several levels. In this respect, the dynamics required for the establishment of the unimer-micelle equilibrium is one aspect. The so-called problem of micelle hybridization that deals with the exchange rate of unimers between different micelles is closely related. Finally, the chain dynamics of polymer blocks in either the core or the corona is another concern that can, however, be linked to some extent to the first two mentioned concepts. These different aspects have been scarcely studied and reviewed by Tuzar and Kratochvil [6,41], and... 

Stop-flow experiments have been performed in order to study the kinetics of micellization, as illustrated by the work of Tuzar and coworkers on PS-PB diblocks and the parent PS-PB-PS triblocks [63]. In these experiments, the block copolymers are initially dissolved as unimers in a nonselective mixed solvent. The composition of the mixed solvent is then changed in order to trigger micellization, and the scattered light intensity is recorded as a function of time. The experiment is repeated in the reverse order, i.e., starting from the block copolymer micelles that are then disassembled by a change in the mixed solvent composition. The analysis of the experimental results revealed two distinct processes assigned as unimer-micelle equilibration at constant micelle concentration (fast process) and association-dissociation equilibration, accompanied by changes in micellar concentration (slow process). 

Tuzar and coworkers [305] studied the micellization of a poly(isoprene-g-styrene) copolymer in solvent mixtures selective either for the backbone or for the grafts. Their results from static and dynamic light scattering and sedimentation velocity experiments favor the closed association model for the description of the unimers-micelles equilibrium. The graft copolymer micelles were found to have lower aggregation numbers and to be less compact than the micelles formed by linear diblocks. 

Using this difference in transition temperatures, a dynamic unimer-micelle transition under the conditions of the BZ reaction was demonstrated. By adding the BZ substrates (HNO3, NaBr03, andMA) into the block copolymer solution, the oscillating behavior of the block copolymer under the constant conditions was analyzed. The scattering intensity and... 

A great number of experimental and theoretical studies have been published concerning the surface modification of biomedical devices by block copolymers in order to promote-spe-cific characteristics, for example wetting, improved biocompatibility, etc. For the surface modification by block and graft copolymers, it is important to determine not only the conformation and the surfaces density of the adsorbed chains in form of a brush, but also the kinetics of this phenomenon which in fact will depend on the unimer-micelle equilibrium. 

As/bod is further increased to 50 mol % or higher, the polymers form compact unimer micelles where polymer chains are highly collapsed, arising from secondary association between the surfaces of hydrophobic microdomains within the same... 

Dynamic Properties of Higher-Order Unimer Micelles. 

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). 

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