Amphiphilic polystyrene-poly

An amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-support has been used successfully as a suitable support for asymmetric catalysts in aqueous media. A polymeric (R]-2-(diphenylphosphino) binaphthyl (MOP) ligand 205 anchored onto the PS-PEG resin was shown to be an effective chiral ligand for the enantioselective p-allyhc substitution under aqueous condihons (Scheme 3.67) [130]. 

Suzuki couplings of aryl halides (eight varieties) and aryl- or vinylboronic adds (12 varieties) have been reported in water in the presence of a palladitmi complex of an amphiphilic polystyrene-poly(ethylene glycol) copolymer resin-supported N-an-chored 2-aza-l,3-bis(diphenylphosphino)propane ligand and potassium carbonate to give uniform and quantitative yields of the corresponding biaryls products (96 combinations) (Equation 75) [104]. 

Amphiphilic resin supported ruthenium(II) complexes similar to those displayed in structure 1 were employed as recyclable catalysts for dimethylformamide production from supercritical C02 itself [96]. Tertiary phosphines were attached to crosslinked polystyrene-poly(ethyleneglycol) graft copolymers (PS-PEG resin) with amino groups to form an immobilized chelating phosphine. In this case recycling was not particularly effective as catalytic activity declined with each subsequent cycle, probably due to oxidation of the phosphines and metal leaching. 

An interesting molecular approach using the hydrophobic effect to assemble gold nanoparticles was taken by Zubarev and coworkers who attached V-shaped (twin-tailed) amphiphilic polystyrene- Zock-poly(ethylene oxide) with a central carboxylic acid moiety (which binds to the gold nanoparticle), effectively giving biphasic, Janus-type characteristics [39]. Self-assembly led to wormlike aggregates (see Fig. 6). 

The use of more complex systems such as ternary blends allows the functionalization of the surfaces with varies chemical functionalities. For instance a PS matrix was mixed with two block copolymers, a hydrophobic (PS-b-P5FS) and an amphiphilic polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-6-P(PEGMA)) copolymer [96], The chemical distribution of the resultant surface pattern implies an enrichment of the holes in the amphiphilic copolymer with an external surface mainly functionalized in the fluorinated copolymer with low surface energy (Scheme lO.lg). Other ternary blends combining incompatible copolymers and homopolymers have been reported leading to more complex topographies and chemical distributions [148],... 

Block copolymers in solution can be self-assembled into a variety of architectures. Micelles are common self-assembled stmctures formed by block copolymers when dissolved in a selective solvent , which is a good solvent for one of the polymer blocks but a poor solvent for the blocks of the other polymer. Binding one of the copolymer blocks with inorganic moieties leads to the formation of nucelles. The inorganic moieties are localized within the core of the micelles and coated with a thin shell of the other copolymer blocks. For example, Taton s group prepared a unidirectional structure of hybrid nucelles based on amphiphilic polystyrene-Wock-poly(acrylic acid) (PS-h-PAA) and gold nanoparticles (AuNPs) (Fig. 1) [25]. 

As polymers that contain both hydrophilic and hydrophobic components aroused keen interest from theoretical and practical points of view over the past years, synthesis of amphiphilic branched copolymers by ring-opening metathesis polymerization of miscellaneous macromonomers is an important goal of the actual research. Thus, in order to obtain globular shape macromolecules that would present the same features as those exhibited by certain assemblies of molecules such as the micelles or the latices, with a bulk part different from the external surface, polymerization of norbornyl polystyrene-poly(ethylene oxide) macromonomer has been conducted in the presence of Schrock-type catalyst Mo(NAr)(CH/Bu)(OC(CH3)(CF3)2)2 in toluene at room temperature to produce poly-norbornene-polystyrene-poly(ethylene oxide) block copolymers (120) [88] [Eq. (52)]. 

To study the solution property of novel amphiphilic hyperbranched graft copolymer chains, we further prepared amphiphilic hyperbranched poly(acrylic acid) grafted with short polystyrene copolymer (HB-PAA- -PS) with a large hydro-phihc hyperbranched PAA core and short hydrophobic PS grafted chains. The copolymer chains with different branching degrees of PAA core were carefully prepared and well confirmed by SEC, H NMR, and FT-IR. As well, the... 

Fig. 4.15 Schematic of synthesis of amphiphilic hyperbranched poly(acrylic acid) grafted with short polystyrene copolymer chains (HB-PAA-g-PS) and their linear triblock PS-PAA-PS...

Lianwei Li, Xu Wang, Chen He, and Weidong He, Association, Emulsifying and Solubilization Properties of Amphiphilic Hyperbranched Poly(acrylic acid) Grafted with Polystyrene (HB-PAA-g-PS) , J. Polym. ScL, Polym. Chem. 2013, 52, 128. 

Lambert, O., Dumas, P., Hurtrez, G., and Riess, G. (1997) Synthesis of an amphiphilic triarm star copolymer based on polystyrene, poly(ethylene oxide) andpoly( -caprolactone). Macromolecular Rapid Communications, 18,343-351. 

Fig. 3 a-c. Summary of data from different laboratories, obtained by surface force measurement, on the average layer thickness L as a function of tethered chain length for flat, tethered layers constructed by adsorption of amphiphilic polymers on mica. Adapted from Ref. 21. (a) Data of reference 20 on poly-tert-butylstyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (b) Data of references 11 and 12 on polystyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (c) Data of references 13 and 14 on polystyrene chains anchored by adsorbing zwitterionic groups [13] or by small adsorbing blocks of polyethyleneoxide [14]... 

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). 

Another class of polymers capable of stabilizing Au NPs through physisorption is amphiphilic block copolymers. Initial reports describe the formation of Au NPs in the presence of different amounts of diblock copolymers like PS-P2VP (polystyrene-block -poly-2-vinylpyridine) [111] or PS-PEO (polystyrene-block-polyethyleneoxide) [112]. 

Au NPs have been synthesized in polymeric micelles composed of amphiphilic block copolymers. Poly(styrene)-block-poly(2-vinylpyridine) in toluene has been used as nanocompartments loaded with a defined amount of HAuCl4 and reduced with anhydrous hydrazine. The metal ions can be reduced in such a way that exactly one Au NP is formed in each micelle, where each particle is of equal size between 1 and 15 nm [113]. In another example, the addition of HAuCfi to the triblock copolymer (PS-b-P2VP-b-PEO) (polystyrene-block-poly-2-vinyl pyridine-block-polyethylene oxide) permits the synthesis of Au N Ps using two different routes, such as the reduction of AuC14 by electron irradiation during observation or by addition of an excess of aqueous NaBH4 solution [114]. 

Another beneLt of polymeric surfactants over traditional surfactants is the potential for much lower CMCs. Amphiphiles with a high CMC may not be suitable as drug-targeting devices since they are unstable in an aqueous environment and easily dissociate upon dilution (Jones and Ler-oux, 1999). It must be noted that while some polymers exhibit very low CMCs, for instance, the CMC of poly -benzyl-L-aspartate) (PEO-PBLA), poly(N-isopropylacrylamide-polystyrene (PNIPA-PST), and poly(caprolactone) (PEO-PCL) are between 0.00005% and 0.002% (La etal.,... 

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