Amphiphilic block copolymers water

Absorption is widely used as a raw material and/or product recovery technique in separation and purification of gaseous streams containing high concentrations of VOC, especially water-soluble compounds such as methanol, ethanol, isopropanol, butanol, acetone, and formaldehyde. Hydrophobic VOC can be absorbed using an amphiphilic block copolymer dissolved in water. However, as an emission control... 

For gas absorption, the water or other solvent must be treated to remove the captured pollutant from the solution. The effluent from the column may be recycled into the system and used again. This is usually the case if the solvent is costly (e.g., hydrocarbon oils, caustic solutions, amphiphilic block copolymer). Initially, the recycle stream may go to a treatment system to remove the pollutants or the reaction product. Make-up solvent may then be added before the liquid stream reenters the column. 

Recently, unique vesicle-forming (spherical bUayers that offer a hydrophilic reservoir, suitable for incorporation of water-soluble molecules, as well as hydrophobic wall that protects the loaded molecules from the external solution) setf-assembUng peptide-based amphiphilic block copolymers that mimic biological membranes have attracted great interest as polymersomes or functional polymersomes due to their new and promising applications in dmg delivery and artificial cells [ 122]. However, in all the cases the block copolymers formed are chemically dispersed and are often contaminated with homopolymer. 

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.

A special class ofblock copolymers with blocks of very different polarity is known as amphiphilic (Figure 10.1). In general, the word amphiphile is used to describe molecules that stabilize the oil-water interface (e.g., surfactants). To a certain extent, amphiphilic block copolymers allow the generalization of amphi-philicity. This means that molecules can be designed that stabilize not only the oil-water interface but any interface between different materials with different cohesion energies or surface tensions (e.g., water-gas, oil-gas, polymer-metal, or polymer-polymerinterfaces). This approach is straightforward, since the wide variability of the chemical structure of polymers allows fine and specific adjustment of both polymer parts to any particular stabilization problem. 

Figure 10.1. Schematic drawing of an amphiphilic block copolymer stabilizing the oil-water interface.

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. 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

Similar to micellar assemblies in water, reverse micelles have also been utilized to bring about nonspecific binding interactions in organic solvents. Akiyoshi et al. (2002) have synthesized an amphiphilic block copolymer containing PEO and an amylase chain as receptor for methyl orange (MO Chart 2.2). Amylases are insoluble and methoxy-PEO (MPEO) is soluble in chloroform. Hence, an MPEO-amylase block copolymer forms reverse micelles in chloroform. Akiyoshi et al. established the capability of the buried receptors to extract the complementary analyte by studying the ultraviolet visible (UV-vis) spectra. A solution of polymer was shaken... 

The interfacial properties of an amphiphilic block copolymer have also attracted much attention for potential functions as polymer compatibilizers, adhesives, colloid stabilizers, and so on. However, only a few studies have dealt with the monolayers o well - defined amphiphilic block copolymers formed at the air - water interface. Ikada et al. [124] have studied monolayers of poly(vinyl alcohol)- polystyrene graft and block copolymers at the air - water interface. Bringuier et al. [125] have studied a block copolymer of poly (methyl methacrylate) and poly (vinyl-4-pyridinium bromide) in order to demonstrate the charge effect on the surface monolayer- forming properties. Niwa et al. [126] and Yoshikawa et al. [127] have reported that the poly (styrene-co-oxyethylene) diblock copolymer forms a monolayer at the air - water... 

Amphiphilic block copolymers consisting of a hydrophobic (poly(ethyl ethylene) (PEE) and a hydrophilic polyethylene oxide)(PEO) block form monolayers at the air-water interface. The schematic molecular arrangement of this diblock is shown in Fig. 3.26. 

AFM) as a function of different compression state, they have used a modified approach to interpreted the it - A isotherms of these amphiphilic block copolymers in which they took into account the presence of the surface aggregates at the air -water interface. 

The extremely low CMCs have been advantageous for several applications, since only traces of polymer are required to form micelles. High dilution effects, that are problematic in the case of classical surfactants, do not alter polymeric micelles. The surface activity at the air - water, of the amphiphilic block copolymer or polymeric surfactants must be different from the classical surfactants, because of their much lower diffusion coefficients and their much complex conformations. 

Nolte et al. found that an amphiphilic block copolymer 83 composed of a hydrophobic tail of poly(styrene) and a hydrophilic head group of a charged, right-handed helical poly(isocyanide), which is referred to as a superamphiphile , self-assembles in a hierarchical fashion in water to form left-handed superhelices (Fig. 34) [ 158]. They suggest that this type of copolymer will serve as an experimental model for the theoretical study of the packing of helices due to their versatility and easy accessibility. 

Both functional groups of the initiator 3 simultaneously generate free radicals to initiate the homopolymerization of both types of monomers in their respective phase. As a result of recombination of macroradicals, amphiphilic block copolymers (in low yield) are formed at the oil-water interface. 

In a more conventional approach, Zarka et al. attached a rhodium carbene complex onto an amphiphilic block copolymer [252], The concept is simple and involves the utilisation of a hydroxyalkyl substituted NHC as a ligand for the rhodium(I) catalyst used in hydrofor-mylation of 1-octene. The catalyst is then loaded onto a water-soluble, amphiphilic block copolymer by reacting the alcohol group of the catalyst with a carboxylic acid group of the block copolymer (see Figure 4.81). 

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