Micellization process, amphiphilic copolymers

Polymeric micelle formation occurs as a result of two forces. One is an attractive force that leads to the association of molecules while the other one, is a repulsive force, preventing unlimited growth of the micelles to a distinct macroscopic phase (Price, 1983 AstaLeva et al., 1993 Jones and Leroux, 1999). Amphiphilic copolymers form micellar structures through self-association of the insoluble segments when placed in a solvent that is selective for the other monomer (Kataoka et al., 1993 Jones and Leroux, 1999). The process of micellization for amphiphilic copolymers is similar to the process described for conventional hydrocarbon chain-based surfactants as described in the Lrst part of this chapter. 

The self-assembly process of non-ionic surfactants in aqueous media differs in several aspects from the micellization of amphiphilic copolymers ... 

Detailed overviews on the micellisation of amphiphilic copolymers in organic solvents are provided in the reviews of Riess [1], Gohy [2], Hamley [7] and Chu et al. [101]. Apparently, a wide range of styrene, acrylate or methacrylate and diene-based block copolymers have been investigated, while AB diblock and ABA triblock architectures have been systematically compared. One of the main conclusions is that the formation of micelles in organic solvents can generally be considered as an entropy-driven process. 

Similarly to surfactant micelles, amphiphilic block copolymer micelles are not frozen objects, at least when the copolymer molecular weight is relatively low. The same processes as those discussed in Chapter 3 — that is, exchange of surfactants between micelles and bulk phase and micelle formation/break-down — also occur in micellar solutions of copolymers. In view of the structure of amphiphilic copolymers, it is readily realized... 

Guo et al. synthesized a series of block-type amphiphilic copolymers via copolymerization of methacrylate end-capped oligo-urethane and MPS via the sol-gel process [167]. After hydrolysis and condensation of the copolymer precursors (self-assembled in the form of spherical micelles), polyurethane-silica hybrid materials with excellent thermal stability and mechanical properties were obtained. Etmimi et al. synthesized PS-GO nanocomposites via surface RAFT-mediated miniemulsion polymerization [155]. The molar mass and dispersity of PS in the nanocomposites were dependent on the amount of RAFT-grafted GO in the system. The PS-GO nanocomposites were of exfoliated morphology, and their thermal stability and mechanical properties were dependent on the modified GO content and better than those of neat PS polymer. Salami-Kalajahi et al. studied the effect of pristine nanoparticle loading on the properties of PMMA-silica nanocomposites prepared... 

The vesicles made from lipid bilayers are analogous to polymersomes, which are vesicles formed from high molecular weight amphiphilic block copolymers [94—96], Unlike the micelles discussed earlier from the similar copolymer components, the presence of bilayer walls formed from the aggregation of hydrophobic domains provides new properties. They can be designed to respond, for example, by opening or by disassembly, to external stimuli such as pH, heat, light, and redox processes [97]. This makes them usable as scaffolds for cascade reactions, even those with combinations of enzymes [98, 99]. 

Whenever amphiphilic block copolymer chains are dissolved at a fixed temperature and in a selective solvent for one of the blocks, they self-associate through a closed association process to form micelles similarly to low-MW surfactants. 

By covalent linkage of different types of molecules it is possible to obtain materials with novel properties that are different from those of the parent compounds. Examples of such materials are block-copolymers, soaps, or lipids which can self-assemble into periodic geometries with long-range order. Due to their amphiphilic character, these molecules tend to micellize and to phase-separate on the nanometer scale. By this self-assembly process the fabrication of new na-noscopic devices is possible, such as the micellization of diblock-co-polymers for the organization of nanometer-sized particles of metals or semiconductors [72 - 74]. The micelle formation is a dynamic process, which depends on a number of factors like solvent, temperature, and concentration. Synthesis of micelles which are independent of all of these factors via appropriately functionalized dendrimers which form unimolecular micelles is a straightforward strategy. In... 

In this review we summarize and discuss the amphiphilic properties of polyoxyethylene (PEO) macromonomers and PEO graft copolymer molecules, the aggregation of amphiphilic PEO macromonomers into micelles, the effect of organized aggregation of macromonomers on the polymerization process, and the kinetics of radical polymerization and copolymerization of PEO macromonomer in disperse (dispersion, emulsion, miniemulsion, microemulsion, etc.) systems [1-5]. 

Kim and coworkers observed the formation of micelles in aqueous solutions by synthesizing a amphiphilic linear-dendritic diblock copolymer based on poly(ethylene oxide) (PEO) (Figure 5)50,62. In this case, the PEO can be considered as the core upon which the dendrimer was synthesized via a divergent process. In an aqueous phase, the hydrophilic... 

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