Ph-responsive micelles

An early illustration of pH-responsive micellization can be found in P2VP-PEO copolymers that exist as unimers at pH < 5 and form micelles at higher pH values, as demonstrated by Webber et al. [165]. Recently, we investigated a P2VP-PEO copolymer with a larger P2VP block [ 166]. Although this copoly-... 

As introduced previously, type 2 ABC triblock copolymer micelles are formed by triblock copolymers containing an insoluble A block while the B and C blocks are soluble in the considered solvent. The insoluble blocks can be located either between the two soluble blocks (BAC structure) or at one end of the triblock (ABC or ACB structures). Micelles of the latter type were discussed above for, e.g., PS-P2VP-PEO pH-responsive micelles and are indeed considered as core-shell-corona, onion, or three-layer structures since the heterogeneity in the micellar corona is observed in the radial direction (Fig. 18). Micelles formed by BAC triblock copolymers are different from the previous case because they can give rise in principle to a heterogenous corona in the lateral dimension (Fig. 18). This could induce the formation of noncentrosymmetric micelles as discussed in Sect. 7.3. 

Ma et al. (78) recently reported the pH-responsive micelle and physical gel formation of ABA-type triblock copolymers. They prepared ABA-tjqje triblock copolymers... 

Some pH-responsive micelle formulations have been developed. A simple example is a triblock copolymer of PEG-Z)-PDMAEMA-f)-PDEAEMA which... 

ROP and RAFT polymerization techniques were combined to synthesize multiarm star-block copolymers having PeCL inner blocks and PDMAEMA outer blocks. A hyperbranched polyester core was used as a multifunctional initiator. It was calculated that the functionality of the star-blocks was equal to 19. Temperature and pH-responsive micelles were obtained in aqueous solutions. Equilibrium between unimolecular and mulrimolecular micelles was observed at pH 6.58 by dynamic LS and TEM measurements. In low-pH solutions, the PDMAEMA chains were fully protonated and therefore highly stretched, leading to maximum Rh values. When the pH was increased, the micellar Rh decreased as a result of the deprotonation of the dimethylamine groups. PDMAEMA is also a temperature-sensitive polymer, as it exhibits lower critical solution temperature (LCST) behavior. It precipitates from neutral or basic solutions between 32 and 58 °C. At pH 6.58, the Rh values were found to decrease with increasing temperature, due to the gradual collapse of the PDMAEMA outer blocks. 

Similar to the pH-responsive micelles, the pH responsive vesicles are also made from amphiphilic polymers consisting of pH-responsive blocks. The pH-responsive blocks usually form the wall of the vesicle. For example, Du et al reported a vesicle prepared from a zwitterionic diblock copolymer from monomers 2-(methacryloyloxy) ethylphosphorylcholine (MFC) and 2-(diisopropylamino) ethylmethacrylate (DPA) by atomic transfer radical polymerization. The structure of the block polymer and the formed vesicle is shown in Figure 17. The PDPA block dissolves in water below pH 6 as a weak cationic polyelectrolyte, but becomes insoluble above approximately pH 6 due to deprotonation of its tertiary amine groups (its p (a is around 6.3). Therefore, the PDPA blocks form the... 

Yusa S-I, Shimada Y, Mitsukami Y, Yamamoto T, MorishimaY. pH-responsive micellization of amphiphihc diblock copolymers synthesized via reversible addition fragmentation chain transfer polymerization. Macromolecules 2003 36 4208-4215. 

Checot F, Rodiiguez-Hemandez J, Gnanou Y, Lecommandoux S. pH-responsive micelles and vesicles nanocapsules based on polypeptide diblock copolymers. Biomol Eng 2007 24 81-85. 

Liang, J., Wu, W.-L., Xu, X.-D., Zhuo, R.-X., Zhang, X.-Z., 2014. pH Responsive micelle self-assembled from a new amphiphilic peptide as anti-tumor drug carrier. Colloids Surf. B Biointerfaces 114, 398 03. 

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