Block copolymers amphiphilicity

In spite of the fact that block-copolymer amphiphiles have only been more recently developed, many applications in the field of material sciences have already emerged since their unique properties impart many desired characteristics such as functionality and stability.281,282. Numerous functional polymer materials are still waiting in the wings to be incorporated in to this family of super-amphiphiles . Once a more comprehensive knowledge of the factors governing their aggregation behaviour is gained, a plethora of polymer based architectures with valuable nanoscience applications can be anticipated. 

Polymersomes, self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles with amphiphilicity similar to lipids constitute a new class of drug carriers. They are spontaneously formed in aqueous media, as unilamellar vesicles up to tens of microns in diameter. Amphiphilic block copolymers form a range of self-assembled aggregates including spherical, rod-like, tubular micelles, lamellae, or vesicles, depending on polymer architectnre and preparation conditions. Polymers having low hydrophobicity (less than 50%) favor the formation of micelles, however, intermediate level of hydrophobicity (50%-80%) favors the formation of vesicles. Polymeric vesicles, which have a liposome-like structure with a hydrophobic polymer membrane and hydrophilic inner cavity, are called polymersomes. 

Carlsen A, Lecommandoux S (2009) Self-assembly of polypeptide-based block copolymer amphiphiles. Curr Opin Colloid Interface Sci 14 329-339... 

Figure 39 Chemical structures of (a) PS-6-P4VP block copolymer/amphiphile complexes " and (b) Li s cationic biock copoiymer/anionic poiymer...

Li, Z., Zhang, Y, Fullhart, P, and Mirkin, C. A. 2004. Reversible and chemically programmable micelle assembly with DNA block-copolymer amphiphiles. Nano Lett. 4 1055-1058. 

For optimal stealth properties, liposomes would have to be densely covered by a PEO layer. However, PEO liposomes are limited in their ability to integrate high molar ratios of PEO lipid because of shape transitions to micellar structure as a result of the increasing interfacial curvature and lower packing parameter. Poly-mersomes have the advantage that vesicles are entirely composed of PEO-based block copolymer amphiphiles and are not limited by PEO-driven micellization. 

In addihon, there is a whole series of nonionic emulsifiers and protective colloids, which are frequently used in combination with ionic emulsifiers. Ethylene oxide-propylene oxide block copolymers, amphiphilic 2- and 3-block copolymers, polyvinyl alcohols, polyvinyl-pyrroHdone, aUcylpolyglycol ethers, etc. 

---