Amphiphilic block copolymers nonionic

Nonionic Amphiphilic Block Copolymers in Aqueous Solution. 89... 

Nonionic amphiphilic block copolymers in aqueous solution are typically formed of a water-soluble hydrophilic block, e.g., PEO, PMVE, PNIPAM, linked to a hydrophobic block, e.g., PPO, PBO, PS, PMMA. 

In the case of inverse systems, hydrophilic monomers such as hydroxyethyl acrylate, acrylamide, and acrylic acid were miniemulsified in non-polar media, e.g., cyclohexane or hexadecane [45,46]. Rather small and narrow distributed latexes in a size range between 50 nmsynthesized with nonionic amphiphilic block copolymers. Depending on the system, the surfactant loads can be as low as 1.5 wt% per monomer, which is very low for an inverse heterophase polymerization reaction and clearly underlines the advantages of the miniemulsion technique. 

P-12 - Mesostructure design using mixture of nonionic amphiphilic block copolymers... 

The impact of different surfactants (SDS, DOSS, CTAB and hexadimethrine bromide, bile salts °), nonionic and mixed micelles, and additives (neutral and anionic CDs," " tetraalkylammonium salts, organic solvents in EKC separations has been demonstrated with phenol test mixtures. In addition, phenols have been chosen to introduce the applicability of more exotic EKC secondary phases such as SDS modified by bovine serum albumin, water-soluble calixarene, " starburstdendrimers, " " cationic replaceable polymeric phases, ionenes, amphiphilic block copolymers,polyelectrolye complexes,and liposome-coated capillaries. The separation of phenols of environmental interest as well as the sources and transformations of chlorophenols in the natural environment have been revised. Examples of the investigation of phenols by EKC methodologies in aquatic systems, soil," " and gas phase are compiled in Table 31.3. Figure 31.3 illustrates the electromigration separation of phenols by both CZE and EKC modes. 

Self-assembly of block copolymers that are made of poly(ethylene oxide), PEO, as the hydrophilic non-ionic block, has been extensively explored. The research interest in PEO-containing block copolymers was motivated, to a great extent, by potential biomedical applications, which rely on the finding that PEO moieties are biocompatible. Because amphiphilic block copolymers of PEO and poly(propylene oxide) PPO (pluronics) are produced on an industrial scale, research on these nonionic polymeric surfactants resulted in many technological applications. Both PPO and PEO are thermoresponsive, having a low solution critical temperature (LSCT),... 

Since Bangham s 1960s description of lipid vesicles as liposomes (4), many other somes have been created such as virosomes by integrating a cell-binding HIV protein into liposomes (5), niosomes made from nonionic amphiphiles similar in size to lipids (6), polymersomes formed hy amphiphilic block copolymers (7), pep-tosomes made of block copol5uners containing polypeptide chains (8,9), and nova-somes, multilamellar niosomes developed for topical and cosmetic application (10). 

As already mentioned, there has been an extensive amount of studies on the self-assembly of amphiphilic block copolymers in selective solvents over the years. In this section, we will try to give representative examples of these studies divided into two main categories regarding the solvation medium, i.e. amphiphilic copolymers in organic solvents or in aqueous solutions. The latter can be further distinguished in nonionic or ionic containing copolymers. These examples will be limited to the more commonly studied di- and triblock linear copolymers, but concise reviews on the self-assembly of amphiphilic copolymers with more complex non-linear chain architectures can be found elsewhere [98-100]. 

The self-assembly of amphiphilic block copolymers in aqueous solutions has attracted considerable interest not only because of their unique properties but also due to their widespread application possibilities in technical and especially biomedical areas. As far as representative examples of such systems are concerned, a categorisation into nonionic and ionic containing copolymers is feasible. 

Scheme 15 Synthesis of nonionic amphiphilic block copolymers via living CROP of ROZO monomers giving a hydrophilic segment at 1st stage and a hydrophobic segment at 2nd stage.

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

Recently, a new class of inhibitors (nonionic polymer surfactants) was identified as promising agents for drug formulations. These compounds are two- or three-block copolymers arranged in a linear ABA or AB structure. The A block is a hydrophilic polyethylene oxide) chain. The B block can be a hydrophobic lipid (in copolymers BRIJs, MYRJs, Tritons, Tweens, and Chremophor) or a poly(propylene oxide) chain (in copolymers Pluronics [BASF Corp., N.J., USA] and CRL-1606). Pluronic block copolymers with various numbers of hydrophilic EO (,n) and hydrophobic PO (in) units are characterized by distinct hydrophilic-lipophilic balance (HLB). Due to their amphiphilic character these copolymers display surfactant properties including ability to interact with hydrophobic surfaces and biological membranes. In aqueous solutions with concentrations above the CMC, these copolymers self-assemble into micelles. 

Some of the most widely used surfactant templates are nonionic amphiphilic triblock copolymers composed of poly(ethylene oxide)-poly(propylene oxide)-poly (ethylene oxide) blocks. These templates are nontoxic. 

In the case of ordered mesoporous oxides, the templating relies on supramolecular arrays micellar systems formed by surfactants or block copolymers. Surfactants consist of a hydrophihc part, for example, ionic, nonionic, zwitterionic or polymeric groups, often called the head, and a hydrophobic part, the tail, for example, alkyl or polymeric chains. This amphiphiUc character enables surfactant molecules to associate in supramolecular micellar arrays. Single amphiphile molecules tend to associate into aggregates in aqueous solution due to hydrophobic effects. Above a given critical concentration of amphiphiles, called the critical micelle concentration (CMC), formation of an assembly, such as a spherical micelle, is favored. These micellar nanometric aggregates may be structured with different shapes (spherical or cylindrical micelles, layered structures, etc. Fig. 9.8 Reference 70). The formation of micelles. 

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