Polymeric surfactants poly

Cholesterol is one of the main components of cell membranes and has several functions in the body, including the synthesis of certain hormones such as vitamin D and bile acid. Over the years, gas chromatography has been used to characterize cholesterol and its derivatives. Thiam et al. [123] developed an isocratic CEC method that allows baseline separation of a complex mixture of cholesterol and 12 ester derivatives in less than 40 min. The use of a polymeric surfactant, poly(sodium N-undecanoyl-L-glycinate), in the CEC buffer reduced migration time and improved resolution of the analytes. 

The use of bilayer coatings was reported from Kapnissi et al. [31], where a permanently adsorbed coating of a cationic polymer salt [poly(diaIlymethylammo-nium chloride)] was covered with a dynamically adsorbed polymeric surfactant [poly (sodium undecylenic sulfate)]. In contrast to the stable coatings, the adsorbed layers can be easily prepared. Traditionally, polymeric surfactants have been used in MEKC [38] and the separation principle can therefore be transferred to o-CEC. However, several other types of dynamically attached pseudo-stationary phases (PSPs) exist, such as cyclodextrins [39], dendrimers [40], proteins [41], liposomes [42], ionenes [43], siloxanes [44] micelles [3, 38] and microemulsions [45]. Comparisons between MEEKC and MEKC are often made, as their separation basis is similar [46-48]. In MEKC, surfactant molecules form micelles and solutes dissolve in them, which facilitates separation. Solutes can penetrate a microemulsion droplet more easily than a more rigid micelle and the loadability of a droplet compared with a micelle is much higher. 

Long-chain alcohols, such as are obtained by the hydrogenation of coconut oil, polymerization of ethylene, or the 0x0 process (qv), are sulfated on a large scale with sulfur thoxide or chlorosulfuhc acid to acid sulfates the alkaU salts are commercially important as surface-active agents (see Surfactants). Poly(vinyl alcohol) can be sulfated in pyhdine with chlorosulfuhc acid to the hydrogen sulfate (84). 

Y. Sela, Y. Magdassi, and N. Garti Polymeric Surfactants Based on PolysUoxanes-Graft-Poly(Oxyethylene) for Stabilization of Multiple Emulsions. Colloids Surfaces 83, 143 (1993). 

Poly(alkylene oxide)-based (PEO-PPO-PEO) triblock and diblock copolymers are commercially successful, linear non-ionic surfactants which are manufactured by BASF and ICI. Over the last four decades, these block copolymers have been used as stabilisers, emulsifiers and dispersants in a wide range of applications. With the development of ATRP, it is now possible to synthesise semi-branched analogues of these polymeric surfactants. In this approach, the hydro-phobic PPO block remains linear and the terminal hydroxyl group(s) are esteri-fied using an excess of 2-bromoisobutyryl bromide to produce either a monofunctional or a bifunctional macro-initiator. These macro-initiators are then used to polymerise OEGMA, which acts as the branched analogue of the PEO block (see Figures 2 and 3). 

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.,... 

In addition, two end-tethered delaminated hybrid systems prepared by in-situ polymerization - (a) Poly( -caprolactone)-montmorillonite (PCLC) and (b) nylon-6-montmorillonite (NCH) - wherein the polymer chains are end-tethered to the silicate surface via cationic surfactants [54] (Fig. 20), were also studied. 

Polymerization of the alkoxyallene with macromonomers having a poly (ethyleneglycol) group by [(7r-allyl)Ni(OCOCF3)]2/PPh3 produces a graft copolymer with narrow molecular weight distribution [129]. The products serve as polymeric surfactants in the polymer blend system of polystyrene and poly(methyl methacrylate). 

These are stable micelles that are formed with polymeric surfactants. Amphiphilic block copolymers such as the pluronics (polyoxyethylene-polyoxypropylene block copolymers) are able to self-assemble into polymeric micelles and hydrophobic drugs may be solubilized within the core of the micelle or, alternatively, conjugated to the micelle-forming polymer. Although micelles are rather dynamic systems that continuously exchange units between the micelle structure and the free units in solution, those composed of polyoxyethylene - poly(aspartic acid) have been found sufficiently... 

Surfactants have also been used to overcome the solubility limitation of synthetic polymers in CO2 (most common synthetic polymers would be considered to be C02-phobic). For example, surfactants have been used to aid in the dispersion polymerization of poly(methylmethacrylate) (PMMA) in CO2 (58-60). The surfactants used in the polymerizations of PMMA are more accurately referred to as stabilizers. The C02-phobic region acts as anchor to the growing polymer, either by physical adsorption or by chemical grafting. The C02-philic region sterically stabilizes the growing polymer particles, preventing flocculation and precipitation. When a biopolymer is not soluble in CO2, specific surfactants may be designed to aid in the solubilization of the polymer into CO2. 

The condensation method begins with molecular units, and the particles are built-up by a process of nucleation typical example is the preparation of polymer lattices, in which case the monomer (e.g., styrene or methylmethacrylate) is emulsified in water using an anionic or nonionic surfactant (e.g., sodium dodecyl sulphate or alcohol ethoxylate). A polymeric surfactant is also added to ensure the long-term colloid stabiHty of the resulting latex. An initiator such as potassium persulphate is then added and, when the temperature of the system has increased, initiation occurs that results in formation of the latex [polystyrene or poly(methylmethacrylate)]. 

Perhaps the simplest type of a polymeric surfactant is a homopolymer, that is formed from the same repeating units, such as PEO or poly(vinyl pyrrolidone). These homopolymers have minimal surface activity at the O/W interface, as the homopolymer segments (e.g., ethylene oxide or vinylpyrroUdone) are highly water-soluble and have little affinity to the interface. However, such homopolymers may adsorb significantly at the solid/liquid (S/L) interface. Even if the adsorption energy per monomer segment to the surface is small (fraction of kT, where k is the Boltzmann constant and T is absolute temperature), the total adsorption energy per molecule may be sufficient to overcome the unfavourable entropy loss of the molecule at the S/L interface. 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

As discussed above, the incorporation of an oil-soluble polymeric surfactant that adsorbs strongly at the O/W interface would be expected to cause a reduction in the Ostwald ripening rate. To test this hypothesis, an A-B-A block copolymer of poly(hydroxystearic acid) (PHS, the A chains) and PEO (the B chain) PHS-PEO-PHS (Arlacel P135) was incorporated in the oil phase at low concentrations (the ratio of surfactant to Arlacel was varied between 99 1 and 92 8). For the hexadecane system, the Ostwald ripening rate showed a decrease with the addition of Arlacel PI 35 surfactant at ratios lower than 94 6. Although similar results were... 

Leemans L, Fayt R, Teyssie Ph, de Jaeger NC. Poly(alkyl methacrylate-fe-sulfonated glycidyl methacrylate). A new amphiphilic polymeric surfactant for the preparation and stabilization of polymer acrylic latices in aqueous medium. Macromolecules 1991 24 5922-5925. 

Typical polymeric pseudostationary phases include micelle polymers, polymeric surfactants, water-soluble anionic siloxanes and dendrimers [223-231]. Micelle polymers [e.g. poly(sodium 10-undecylenate), poly (sodium 10-undecenylsulfate), poly(sodium undeconylvalinate), etc.] are synthesized from polymerizable surfactant monomers at a concentration above their critical micelle concentration. These polymers have similar structures to micelles without the dynamic nature of the micelle structure. Polymeric surfactants are polymers with surfactant properties [e.g. acrylate copolymers, such as 2-acrylamide-2-methyl-l-propanesulfonic acid and alkyl methacrylamide, alkyl methacrylate or alkyl acrylate, poly (ally lamine)-supported phases, poly(ethyleneimine), etc]. Water-soluble anionic siloxane polymers are copolymers of alkylmethylsiloxane... 

Elemental analysis (EA) is a convenient method for determination of copolymer and blend composition if one homopolymer contains an element not present in the second one. For example, EA can be properly used to quantify nitrogen in copolymers containing acrylonitrile units and oxygen in polymeric surfactants such as poly(oxy-alkylene). Therefore, for a binary system, every element can be balanced according to the following equation ... 

The separation of PCB congeners has been addressed by SDS/neutral CD containing electrolytes, modified by organic solvents or urea and mixtures of bile salts. CD-EKC and CDCD-EKC modes with a large assortment of ionic CDs and modifiers are often employed for the chiral discrimination of PCB racemates. The use of polymeric surfactants such as polysodium undecyl sulfate (poly-SUS), in acetonitrile and its valinate form (poly-D-SUV) in combination with hydroxypropyl-y-CD, methanol, and urea has also been reported. 

The second group of surfactants that can be used in dynamic coatings are polymeric surfactants. The most common polymers include PEO, poly(ethylene glycol) (PEG), poly(propylene oxide)... 

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