Block copolymer solution self-assembly

Roy, D., Cambre, J.N., and Sumerlin, B.S. (2009) Triply-responsive boronic acid block copolymers solution self-assembly induced by changes in temperature, pH, or sugar concentration. Chem. Commun., 16, 2106-2108. 

A diblock copolymer made from a soluble and a nonsoluble monomer has an amphiphilic character. The nonsoluble blocks aggregate and the soluble parts dangle out in the solution. In an aqueous environment, such block copolymers thus self-assemble to form polymer micelles that consist of a nonaqueous densely... 

Block copolymers spontaneously self-assemble into interesting microstructures in dilute solution, in the bulk, and in the presence of surfaces and interfaces. Monte Carlo simulations of coarse-grained block copolymers on simple lattices have been used in the last few years to investigate the generic properties of block copolymers [1,2]. Since the coarse-grained chains are not atomistic, it is diflBcult to make a one-to-one comparison of a simulation and a spe-... 

Micellar-drug formulation is another delivery system based on hydrophilic-hydrophobic block copolymers that self-assemble in aqueous solution into micellar particles with a hydrophobic core and a hydrophilic shell. NK012 is an example of micellar formulation of SN 38 (11) developed by Nippon Kayaku which is in Phase 1 clinical trial [287-289]. 

The stractural and functional complexity of biomembranes has ehal-lenged researehers to develop simpler artificial models to mimie their properties. Amphiphilic block copolymers are of particular interest, beeause of the dual environmental affinity that is associated with covalently bound hydrophobie and hydrophilic blocks. These strive to minimize their eontaet, and therefore drive self-assembly into assemblies with different arehi-teetures. Based on their chemical specificity, as for example the hydrophilie-to hydrophobie ratio, amphiphilic block copolymers can self-assemble in dilute aqueous solutions into micelles, vesicles, tubes, wire-like structures, nanopartieles, or planar membranes at water-air interfaces. Synthetic membranes have greater mechanical stability than phospholipids because of the higher moleeular weight (Mw) of amphiphilic block copolymers, and thus are thicker and stiffer than lipid bilayers. 

As already described in the previous sections, the classical approach for preparation of polymeric nano-size aggregates from amphiphilic block copolymers by self-assembly in a selective solvent involves several steps. The first step is synthesis of an amphiphilic copolymer with a narrow molar mass distribution, followed by purification and characterization. Then, the self-assembly is performed by adding a non-solvent of one block into dilute copolymer solution or by direct dissolution of the copolymer in a selective solvent. Usually, the copolymer concentration varies between 1 and 10 g (0.1-1 wt%). 

Hamley IW, Ansari A, Castelletto V et al (2005) Solution self-assembly of hybrid block copolymers containing poly(ethylene glycol) and amphiphilic beta-strand peptide sequences. 

Malmsten, M Lindman, B, Self-Assembly in Aqueous Block Copolymer Solutions, Macromolecules 25, 5440, 1992. 

The cosolvent method, also known as solvent injection method permits vesicle formation for glassy or crystalline block copolymers. As a rule, the amphiphilic copolymer is dissolved in an appropriate organic solvent or solvent mixture, the role of which is to lower the Tg below room temperature next the solution is added dropwise to an aqueous buffer under vigorous stirring. Originally this method has been employed for PS-PAA and PS-PEO copolymers that self-assembled in vesicular structures by adding water to DMF or dioxane polymer solution [61,105] and then further applied to many other polymer systems [165],... 

Additionally, McCormick et al. utilized imine bonds for the preparation of reversible imine SCL micelles. They synthesized a temperature-responsive triblock copolymer, a-methoxypoly(elhylene oxide)- -poly(A-(3-aminopropyl) methacryIamide)-fc-poly((V-isopropyIaCTyIamide) (mPEO-PAPMA-PNIPAM), via aqneons RAFT polymerization. By inCTeasing the solution temperature above the LCST of the PNIPAM block, the polymers self-assembled into micelles. Subsequently, the PAPMA shell was cross-linked with terephthaldicarboxaldehyde to generate SCL micelles with cleavable imine linkages (Figure 54.16). 

Malmsten, M. and Lindman, B., Self-assembly in aqueous block copolymer solutions. Macromolecules, 25, 5440-5445 (1992). 

The self-assembly of polymer chains in aqueous solution can also take place due to a micellization process. Amphiphilic block copolymers (e.g., diblock or triblock copolymers) can self-assemble in aqueous solution and further be cross-linked... 

---