Macromolecular amphiphile

The most vibrant development in the field of PAEs is the explosion of their structural features. There are conceptually different ways of how to vary PAE structures. The first approach deals only with PPEs, and the structural modification is introduced by the variation of the side chains. This concept is powerful for introducing macromolecular, amphiphilic, water-soluble, selfassembling, or protective side chains. In most cases, however, the electronic structure of the PPE is untouched. There are exceptions. If the substituent under consideration is conjugated, it will change the electronics of the backbone. Examples of this kind have been prepared by the Bunz and the Swager groups [24,25]. 

Tian L, Hammond PT. Comb-dendritic block copolymers as tree-shaped macromolecular amphiphiles for nanoparticle self-assembly. Chem Mater 2006 18 3976-3984. 

Low-molecular-weight surfactants ( emulsifiers ) are important ingredients in food products. The types of surfactants most commonly studied in food colloids research are phospholipids (lecithin), mono/diglycerides (particularly glycerol monostearate), polysorbates (Tweens), sorbitan monostearate or monooleate (Spans), and sucrose esters. These small lipid-based amphiphiles can typically lower the interfacial tension to a greater extent than the macromolecular amphiphiles such as proteins and certain gums (Bos and van Vliet, 2001). 

Novel Blocked Macromolecular Amphiphiles as Structure-Directing Agents for Silica-Type Materials... 

Block copolymers that consist of hydrophilic and hydrophobic segments are typical amphiphilic polymers, a variety of which have been synthesized by living cationic polymerization. Figure 9 schematically illustrates the structures of some of these amphiphilic polymers thus far obtained though the examples therein are based on poly(vinyl ether) segments, any other appropriate segments may be incorporated. As seen in the illustrations, macromolecular amphiphiles are not necessarily linear AB- and ABA-type block copolymers but may be graft, multiarmed, and network polymers, where the basic components are amphiphilic block copolymers. 

PDMS is an unusual macromolecular amphiphile composed of pendant organic methyl groups along the siloxane backbone. Its surface properties result in a wide variety of applications. Specific examples are listed in Table I (3), which demonstrates the diversity of interfaces at which PDMS-containing materials are active and the apparently contradictory nature of many of the applications adhesion and release, foaming and antifoaming, etc. 

Macromolecular amphiphiles and their aggregates in water are an increasingly important aspect of modem colloidal science. Indeed,... 

The use of proteins as macromolecular amphiphiles was adopted long ago by scientists exploring the stability of multiple emulsions. Gelatin (Zhang et al., 1992), whey proteins (Comec et al, 1998), bovine serum albumin (BSA) (Dickinson et al., 1991 Fredrokumbaradzi and Simov, 1992), human serum albumin (HSA), caseins, and other proteins have been evaluated. In many cases the proteins were used in combination with other monomeric emulsifiers, especially when proteins were used in the internal phase. However, whether the adsorption is competitive or complementary remains a controversial question (Wilde and Clark, 1993 Kerstens et al., 2006). 

W/O/W Under certain conditions some proteins and polysaccharides form hybrids (complexes) with enhanced functional properties compared to the proteins and polysaccharides alone. Conversely, electrostatic complexing between oppositely charged proteins and polysaccharides allows better anchoring of the newly formed macromolecular amphiphile onto the oil-water interfaces. 

The facility to introduce well-defined chain ends has been used to prepare star polymers557 and diblocks via reaction with macromolecular aldehydes.558 The synthesis of amphiphilic star block copolymers has also been described using a cross-linking agent.559 560 A similar strategy has recently... 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

Carbon nanotubes have been also used as a macromolecular scaffold for Gdm complexes. An amphiphilic gadolinium(III) chelate bearing a C16 chain was adsorbed on multiwalled carbon nanotubes (264). The resulting suspensions were stable for several days. Longitudinal water proton relaxivities, r] showed a strong dependence on the GdL concentration, particularly at low field. The relaxivities decreased with increasing field as predicted by the SBM theory. Transverse water proton relaxation times, T2, were practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been... 

Immobilization of the bilayer membranes as thin solid films is required when the bilayer membranes are used as novel functional materials. Casting method is a simple way to immobilize the bilayer membrane on a solid support from an aqueous solution by drying. Polymer film is easily prepared when the cast film of polymerizable bilayer membrane is polymerized. A free standing polymer film prepared by photo polymerization of the cast film of diacetylene amphiphiles was reported by O Brien and co-workers [34]. Composition with macromolecular materials is another way of polymer film preparation. Bilayer membranes are immobilized as polymer composites by the following physical methods ... 

Decher G, Hong JD. Buildup of ultrathin multilayer films by a self-assembly process. 1. Consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces. Makromolekulare Chemie-Macromolecular Symposia 1991a 46 321-327. 

These examples emphasize that not only the macromolecular architecture plays an important role in the determination of the aggregate morphology, but that also interactions between block copolymer segments can strongly influence the final structure of the assemblies formed by these types of amphiphiles as seen for the smaller molecular amphi-philes. 

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... 

Dieckmann et al. in 2003 described an amphiphilic a-helical peptide specifically designed to coat and solubilize CNTs and to control the assembly of the peptide-coated nanotubes into macromolecular structures through peptide-peptide interactions between adjacent peptide-wrapped nanotubes [227]. They claimed that the peptide folds into an amphiphilic a-helix in the presence of carbon nanotubes and disperses them in aqueous solution by noncovalent interactions with the nanotube surface. EM and polarized Raman studies revealed that the peptide-coated nanotubes assemble into fibers with the nanotubes aligned along the fiber axis. The size and morphology of the fibers could be controlled by manipulating the solution conditions that affect peptide-peptide interactions [227]. 

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