Copolymer segments, block Amphiphiles

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. 

They provide an amphiphillic function in blends of dissimilar polymers, where favorable interactions exist between one of the homopolymers and one of the block copolymer segments.Hydrogenated block copolymers which reduce surface tension in polystyrene-polyoletin blends is one example. Another example is the use of a derivatized block copolymer, such as terminally carboxylated styrene-diene di-block copolymers,... 

The same coarse-grained model is used for studying block copolymers with complex architecture, for example, of a comb-tail type. Usually, such copolymers consist of amphiphilic and monophilic (nonamphiphilic) blocks, which have different segmental volume. The top right Panel shows (a) amphiphilic AB monomer unit, (b) conventional (linear) AB diblock copolymer, and (c) amphiphilic comb-tail diblock copolymer. 

Li et al. utilized a solvent-assisted collocation strategy to prepare star-like block copolymers here an amphiphilic diblock copolymer was prepared by sequential monomer addition using a suitably designed RAFT initiator (11), which yielded diblock copolymers with both azide and alkyne groups at the same end of the polymer chain (Scheme 7.27). In this study, they have used either M-isopropylacrylamide (NIPAM) and dimethyl acrylamide (DMA) or styrene and NIPAM to first generate the diblock copolymer the PNIPAM segment in both of them gives the system a temperature-responsive amphiphilic character due the lower critical solution temperature (LCST) behavior of PNIPAM block. 

Fig. 1 Vesicle construct formed from poly(L-lysine)-i)-poly(L-leucme) polypeptides where the poly(L-leucine) block corresponds to the a-helical hydrophobic segments and the poly (L-lysine) block corresponds to the random coil hydrophilic segments. Note that this is one specific example and not all vesicle constructs have a-helical and random coil blocks. Moreover, the amphiphilic copolymer can be comprised of either a pure block copolypeptide or a macromolecule consisting of a polypeptide and another type of polymer. Adapted from [20] with permission. Copyright 2010 American Chemical Society...

Recently, many studies have focused on self-assembled biodegradable nanoparticles for biomedical and pharmaceutical applications. Nanoparticles fabricated by the self-assembly of amphiphilic block copolymers or hydrophobically modified polymers have been explored as drug carrier systems. In general, these amphiphilic copolymers consisting of hydrophilic and hydrophobic segments are capable of forming polymeric structures in aqueous solutions via hydrophobic interactions. These self-assembled nanoparticles are composed of an inner core of hydrophobic moieties and an outer shell of hydrophilic groups [35, 36]. 

PIPAAm-PBMA block copolymers form a micellar structures by selfassociation of the hydrophobic PBMA segments in water, a good solvent for PlPAAm chains below the LCST but a nonsolvent for the PBMA chains. This amphiphilic system produces stable and monodispersed micelles from polymer/A-ethylacetamide (good solvent for the both polymer blocks) solutions dialyzed against water. Hydrophobic dmgs can be physically incorporated into the iimer micelle cores with PBMA chains by hydrophobic interactions between the hydrophobic segments and dmgs. 

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). 

Amphiphilic block copolymers have attracted a great deal of attention in terms of their ability to form nanoparticles. As normally one type of segment, is hy-... 

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