Amphiphilic monomers

The Larson model and Larson-type models have been widely used to study micelles [37,111,114-120], amphiphiles at oil/water interfaces [121,122] bilayers [117,123] and various other problems [125-128]. The models differ from each other in the range of the interactions and in the treatment of the amphiphile monomers. Other than in Larson s original model, most authors include only nearest-neighbor interactions, sometimes in combination with a... 

Amphiphilic monomers and dimers (Gl, G2) Abundant in mammalian brain, muscles and intestine for both ChEs. 

Although numerous amphiphilic monomers have been polymerized and a great number of amphiphilic polymers have been investigated, only some hints in the literature indicate mesomorphic behavior of concentrated polymer solutions 105.106.121>. Nearly all measurements were carried out "at low concentrations, in order to characterize the properties of these polysoaps in view of applications as surfactants. For these applications high polymer concentrations are, of course, not of interest. 

In the case of more water-soluble monomers and (amphiphilic) macromonomers, the Smith-Ewart [16] expression does not satisfactorily describe the particle nucleation. The HUFT [9,10] theory, however, satisfactorily describes the polymerization behavior or the particle nucleation of such unsaturated hydrophilic and amphiphilic monomers. The HUFT approach implies that primary particles are formed in the aqueous phase by precipitation of oligomer radicals above a critical chain length. The basic principals of the HUFT theory is that formation of primary particles will take place up to a point where the rate of formation of radicals in the aqueous phase is equal to the rate of disappearance of radicals by capture of radicals by particles already formed. Stabilization of primary particles in emulsifier-free emulsion polymerization may be achieved if the monomer (or macromonomer) contains surface active groups. Besides, the charged radical fragments of initiator increases the colloidal stability of the polymer particles. 

From the picture presented in Fig. 7, one can expect that the sequential hydrophobization of a polymer coil should lead to a copolymer with a non-random sequence distribution. This is indeed the case. As an example, let us consider the average number fractions of blocks consisting of l neighboring amphiphilic monomers, /a( ), occurring in a copolymer chain. Some results are shown in Fig. 8 on a semilogarithmic scale. 

Fig. 8 Average number fraction of blocks consisting of l neighboring amphiphilic monomers occurring in a 256-unit copolymer chain hydrophobically modified in a solvent having different selectivity for modifying agent. Adapted from [25]...

Fig. 15 a Schematic representation of the distribution of hydrophobic and amphiphilic monomers polymerizing in micelle and b the reaction between the monomers... 

Selb and Gallot [214] have demonstrated that poly(styrene)-gra/f-poly(4-vinyl-N-ethylpyridium bromide) forms unimolecular micelles in water/ methanol mixtures. These experimental data can be treated as an indirect confirmation of the simulation result [97] that sufficiently long regular copolymers with amphiphilic monomer units do form intramolecular aniso-metric micellar structures in a poor solvent. 

Abstract A concept of amphiphilicity in application to monomer units of water-soluble polymers is presented. Molecular simulation and experimental studies of polymers consisting of amphiphilic monomers units are reviewed. Those polymers reveal unusual conformational behavior in aqueous solutions forming nanostructures of nonspherical shape. Self-association of amphiphilic thermosensitive polymers in water solutions is discussed. Possibilities for the use of thermosensitive copolymers as catalysts are described. The sharp water-organic boundaries formed by polymer associates in water solutions are shown to be a prospective medium for catalysis owing to adsorption of interfacially active substrates at the interface. 

Keywords Amphiphilic monomers Interfaces Polymer catalysts ... 

Scheme 1 Amphiphilic monomer units of synthetic and natural polymers...

The present review has the following structure. In Sect. 2, the properties of amphiphilic monomers are discussed and a special classification of monomer units according to interfacial and partition properties is described. Also, the possibility of nanostructure formation in polymers composed of amphiphilic monomers is touched upon. This topic is more broadly treated in Sect. 3, where conformational properties of a key class of water-soluble polymers are... 

Fig. 6 Typical cylinder-shaped globules of polymers containing amphiphilic monomer units. Darker spots denote hydrophobic backbone nodes inside the core, lighter spots are hydrophilic side groups comprising the shell of the globule. (Adapted from Ref. [24])...

The properties associated with the amphiphilic monomer units are strongly exemplified in thermosensitive water-soluble polymers, typical examples of which are shown in Scheme 5. Thermosensitive polymers possess a lower critical solution temperature (LCST) in water solutions. Due to their sharp response to temperature variation, they are widely used in various scientific and technological applications. Drug and gene delivery [1-3], chromatographic [9,10], membrane technology [11,12], and catalyst immobiliza-... 

The analogous considerations are valid for polymer systems as well. Indeed, amphiphilic monomer units also tend to occupy interfacial areas of macromolecular associates as it is normal for low molecular weight surfactants to adsorb at polymer-poor solvent boundaries. And, if such interfacial groups of the polymer associate catalyze chemical transformation of a compound which tends to adsorb at the associate interfaces, this can result in unusual kinetics effects. Okhapkin et al. [18] studied the influence of temperature-induced aggregation on the catalytic activity of thermosensitive... 

Fig. 13 Constitutional adaptation to the environment in the hydrophobically-driven component selection on formation of a rigid rod dynamer from amphiphilic monomers. Polycondensation occurs in aqueous solution with preferential incorporation of the monomer presenting the largest hydrophobic area. Selectivity is progressively lost in solutions containing increasing amounts of organic solvent, acetonitrile...

For low molecular mass amphiphiles, hydrophobic interactions and surface effects determine the critical concentration at which micellar aggregates are favored over the molecularly dispersed amphiphilic solutes. For polysurfactants, however, the amphiphiles are linked together and the dynamic exchange of associated and non-associated amphiphilic monomer units is prevented. Consequently the micelle formation does not only depends on the hydrophilic/ hydrophobic balance of the monomer... 

The intention of this brief survey has been to demonstrate that besides the "classical" aspects of isotropic polymer solutions and the amorphous or partially crystalline state of polymers, a broad variety of anisotropic structures exist, which can be induced by definable primary structures of the macromolecules. Rigid rod-like macromolecules give rise to nematic or smectic organization, while amphiphilic monomer units or amphiphilic and incompatible chain segments cause ordered micellar-like aggregation in solution or bulk. The outstanding features of these systems are determined by their super-molecular structure rather than by the chemistry of the macromolecules. The anisotropic phase structures or ordered incompatible microphases offer new properties and aspects for application. 

Cosnier, S. (1997) Electropolymerization of amphiphilic monomers for designing amperometric biosensors. Electroanalysis, 9 (12), 894-902. 

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