Polymer micelles self-assembly

Keywords Aliphatic polyesters Amphiphilic polymers Polymer micelles Self-assembly Smart materials... 

Gheybi, H. and Entezami, AA. (2013) Nanosized micelles self-assembled from amphiphilic poly(citric acid)—poly(e-caprolactone)—poly(citric acid) copolymers. Polym. Bull, 70, 1875. 

Milk is a natural colloidal dispersion that contains casein micelles, self-assembled protein associates with a diameter of about 200 nm [20]. The casein micelles are protected against flocculation by an assembly of dense hairs (often called a brush ) at their surfaces. Polymer brushes can thus provide steric stabilization of colloids. For millennia, man used the fact that milk flocculates and gels when it is acidified, as in yogurt production. Below pH = 5 macroscopic flocculation of the casein micelles in milk is observed [21]. This means that the interactions between casein micelles change from repulsive to attractive. The explanation is that acidification leads to collapse of the casein brushes [22]. In cheese-making the steric stabilization is removed by enzymes, which induce gelation into cheese curd. 

In a previous study, our group synthesized a new temperature and pH-sensitive poly(2-(dimethylamino) ethylmethacrylate-fe-vinylcaprolactam-fc-(2-(dimethylamino) ethyl methacrylate)), PDMAEMA- i-PVCL-fc-PDMAEMA, triblock copolymer by RAFT polymerization. PDMAEMA is dual sensitive (pH and temperature) and its LCST was around 50 °C, while PVCL is a thermo-responsive polymer and its LCST was around 32 °C. By modifying the structure and adjusting the composition of these polymers it is possible reduce the LSCT and pK values in order to ensure compatibility with physiological temperature and pH (see Table 9.1, Triblock 1). The results showed that these polymers can self-assemble into micelles in different environments [60]. 

Chen, C., Liu, G., Liu, X., Pang, S., Zhu, C., Lv, L., Ji, J. (2011). Photo-responsive, biocompatible potymeric micelles self-assembled from hyperbranched polyphosphate-based polymers, Polym. Chem., 2, 1389-1397. 

Well-defined mono end-capped C o-containing alkali-soluble PMAA (PMAA-fe-C o) polymer also self-assembled into nanoscale aggregates in aqueous solution [82]. PMAA-fe-Cso was soluble at high pH and showed pH-responsive properties. In dilute solution, the micelles coexisted with large secondary aggregates. These secondary aggregates consist of individual micelles that possess a microstructure similar to LCMs. Both the micelles and LCMs were formed via the closed association mechanism. The Rj, of the micelles increased from 6 to 10 nm with increasing... 

The formation of polymeric capsules can also be achieved by the cross-linking of self-assembled amphiphilic block copolymers [85]. The hydrophobic section of the polymer in an aqueous solution will tend to aggregate on the interior of the micelle, whereas the hydrophilic ends will form the outer shell of the micelle. If the hydrophilic end is appropriately functionalized, it can be cross-linked, giving a polymeric shell. The overarching concept is shown in Figure 5.10. 

Examples. 2D SAXS/WAXS experiments on highly anisotropic polymer materials during melting and crystallization can be used to visualize and understand the evolution of nanostructure [56,57], Transformations of biopolymers in solution, e.g., virus crystallization can be studied in situ [58], It is possible to study solidification mechanisms of spider silk [59], or the self-assembly of micelles on a time-scale of milliseconds [60],... 

Recently, biodegradable polymers have been used to fabricate macro- and nanometer scale self-assembled systems such as microspheres (MSs), nanospheres (NSs), polymer micelles, nanogels, and polymersomes (Fig. 1). These have attracted growing interest because of their potential utility for drug delivery systems (DDS), tissue engineering, and other applications. To construct these self-assembled systems... 

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

Block copolymer micelles in which the core-forming polymer blocks are able to crystallize are relatively similar to rod-coil copolymers. A significant part of these crystalline-core micelles is actually resulting from the self-assembly of rod-coil block copolymers. 

Fig. 17 Formation of rodlike micelles with diameter of 25 nm from self-assembly of a protein (lipase enzyme)-polymer (PS) hybrid in THF. Reprinted with permission from [264]. Copyright (2003) American Chemical Society... 

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