Amphiphilic Block Copolymer Micelles

Amphiphilic block copolymer Polymer micelle In aqueous media... 

Fullerenes and their derivatives are of broad interest in various fields ranging from ferromagnetism [87] over their application as possible HIV inhibitors [88] to tumor-therapeutic active substance in biological systems [89]. Although C6o is insoluble in water, dissolution may be accomplished by using water-soluble polymers [90] or surfactant solutions containing amphiphilic block-copolymers [91], micelles or liposomes [92, 93]. The immobilization of... 

Cores of Block Copolymer Micelles. In selective solvents (a good solvent only for one block), amphiphilic block copolymers form micelles, the characteristics of which (size and shape) depend on the chemical structure and molecular weight of each block and on the solvent type [27-29]. If the coreforming block contains functional groups, which are able to react with metal... 

Polymersomes, self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles with amphiphilicity similar to lipids constitute a new class of drug carriers. They are spontaneously formed in aqueous media, as unilamellar vesicles up to tens of microns in diameter. Amphiphilic block copolymers form a range of self-assembled aggregates including spherical, rod-like, tubular micelles, lamellae, or vesicles, depending on polymer architectnre and preparation conditions. Polymers having low hydrophobicity (less than 50%) favor the formation of micelles, however, intermediate level of hydrophobicity (50%-80%) favors the formation of vesicles. Polymeric vesicles, which have a liposome-like structure with a hydrophobic polymer membrane and hydrophilic inner cavity, are called polymersomes. 

Li, Z., Zhang, Y, Fullhart, P, and Mirkin, C. A. 2004. Reversible and chemically programmable micelle assembly with DNA block-copolymer amphiphiles. Nano Lett. 4 1055-1058. 

For optimal stealth properties, liposomes would have to be densely covered by a PEO layer. However, PEO liposomes are limited in their ability to integrate high molar ratios of PEO lipid because of shape transitions to micellar structure as a result of the increasing interfacial curvature and lower packing parameter. Poly-mersomes have the advantage that vesicles are entirely composed of PEO-based block copolymer amphiphiles and are not limited by PEO-driven micellization. 

The purpose of this book is to present an up-to-date picture of the dynamics aspects of self-assemblies of surfactants and amphiphilic block copolymers, from micelles to solubilized systems, microemulsions, vesicles, and lyotropic mesophases. It is organized as follows. The first chapter introduces amphiphiles, surfactants, and self-assembhes of surfactants and examines the importance of dynamics of self-assembhes in surfactant science. Chapter 2 briefly reviews the main techniques that have been used to study the dynamics of self- assembhes. Chapters 3 and 4 deal with the dynamics of micelles of surfactants and of amphiphilic block copolymers, respectively. The dynamics of microemulsions comes next, in Chapter 5. Chapters 6 and 7 review the dynamics of vesicles and of transitions between mesophases. The last three chapters deal with topics for which the dynamics of self-assembhes is important for the understanding of the observed behaviors. The dynamics of surfactant adsorption on surfaces are considered in Chapter 8. The rheology of viscoelastic surfactant solutions and its relation to micelle dynamics are reviewed in Chapter 9. The last chapter deals with the kinetics of chemical reactions performed in surfactant self-assembhes used as microreactors. 

To this end, Wang et al have synthesized a series of amphiphilic triblock copolymers of PPE and PGL (PEEP-PGL-PEEP) using Sn(Oct)2 as the catalyst. These amphiphilic block copolymers formed micelles with a hydrophobic core of PGL and a hydrophilic shell of PEEP in aqueous solution. It was found that the size and critical micelle concentration values of the micelles were dependent on both hydrophobic PGL block length and PEEP hydrophilic block length. The in vitro degradation... 

PS CTOss-linked under UV irradiation pyrolyzed at elevated temperatures results in semi-graphitic carbon materials. Both amphiphilic block copolymers that micellize in water (PEO-b-PS) and brushes with PMMA backbones and PS-b-PAA SCs were used to template these nanocarbon stractures.Well-defined nanostractured carbon was prepared by pyrolysis of core cross-linked micelles formed from block copolymers containing PS segments. 

Hickey RJ, Haynes AS, Kikkawa JM, Park SJ (2011) Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers from micelles to vesicles. J Am ChemSoc 133 1517-1525... 

The formation of polymeric capsules can also be achieved by the cross-linking of self-assembled amphiphilic block copolymers [85]. The hydrophobic section of the polymer in an aqueous solution will tend to aggregate on the interior of the micelle, whereas the hydrophilic ends will form the outer shell of the micelle. If the hydrophilic end is appropriately functionalized, it can be cross-linked, giving a polymeric shell. The overarching concept is shown in Figure 5.10. 

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]. 

Meijer et al. [135] further studied aggregation phenomena of amphiphilic copolymers obtained by modifying the termini of the dendrimer units of the above series with carboxylic acid groups (49). TEM experiments indicated that all block copolymers formed large aggregates except third generation copolymer which formed worm-like micelles. 

Kim, J.M., Sakamoto, Y., Hwang, Y.K., Kwon, Y.U., Terasaki, O., Park, S.E. and Stucky, G.D. (2002) Structural design of mesoporous silica by micelle-packing control using blends of amphiphilic block copolymers. Journal of Physical Chemistry B, 106, 2552— 2558. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

Letchford K, Burt H (2007) A review of the formation and classification of amphiphilic block copolymer nanoparticulate structures micelles, nanospheres, nanocapsules and polymersomes. Eur J Pharm Biopharm 65 259-269... 

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

Here, we focus on one class ofblock copolymers synthesized by this method polystyrene-6-poly(vinylperfluorooctanic acid ester) block copolymers (Figure 10.33). After describing the synthesis and characterization, we will treat some properties and the potential applications of this new class ofblock copolymers. The amphiphilicity of the polymers is visualized by the ability to form micelles in diverse solvents that are characterized by dynamic light scattering (DLS). Then the use of these macromolecules for dispersion polymerization in very unpolar media is demonstrated by the polymerization of styrene in 1,1,2-trichlorotrifluoroethane (Freon 113). 

Block copolymers in a selective solvent, ie., a good solvent for one block but a precipitant for the other, behave like typical amphiphiles. The copolymer molecules aggregate reversibly to form micelles in a manner analogous to the aggregation of classical surfactants. Our block copolymers are very amphiphilic in the sense described above and form well-defined micelles in a wide range of selective solvents. In solvents for polystyrene, the polystyrene block is located in the micelle corona, while the modified block is hidden in the micelle core. 

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