Micelles schizophrenic

Exploiting ATRP as an enabling technology, we have recently synthesised a wide range of new, controlled-structure copolymers. These include (1) branched analogues of Pluronic non-ionic surfactants (2) schizophrenic polymeric surfactants which can form two types of micelles in aqueous solution (3) novel sulfate-based copolymers for use as crystal habit modifiers (4) zwitterionic diblock copolymers, which may prove to be interesting pigment dispersants. Each of these systems is discussed in turn below. 

The PPO block is temperature-sensitive, with an LCST (cloud point) of around 15 °C, whereas the DEA block is pH-responsive. At pH 6.5 and 5°C, both blocks are solvated and the copolymer is molecularly dissolved in aqueous solution. On adjusting the solution pH to pH 8.5, the DEA block becomes deprotonated and hence hydrophobic, leading to the formation of DEA-core micelles at 5 °C. On the other hand, if the pH is held constant at pH 6.5 and the temperature is raised above the LCST of the PPO block, PPO-core micelles are obtained with the weakly cationic DEA chains forming the micelle coronas. Since these new diblock copolymers can exist in two micellar states we have christened them schizophrenic copolymers. ... 

The idea in Fig. 6.12 is to prepare a light-responsive schizophrenic diblock (AB) copolymer micelle using azobenzene that is, the core- and shell-forming blocks can be reversed upon illumination at two different wavelengths. Ames et al. first... 

Figure 6.12. A possible design of light-responsive schizophrenic micelle based on azobenzene-containing diblock copolymers.

Liu et al. reported the preparation of two types of shell-cross-linked (SCL) micelles with inverted structures via click chemistry starting from a well-defined schizophrenic water-soluble triblock copolymer in purely aqueous solution. They present an efficient synthesis of two types of SCL micelles with either pH- or temperature-sensitive cores from a novel poly(2-(2-methoxyethoxy) ethyl methacrylate)-ft-poly(2-(dimethylamino) ethyl methacrylate)-Z -poly(2-(diethylamino) ethyl methacrylate) [PME02MA-ft-P(DMA-co-QDMA)- -PDEA] triblock copolymer. First, PMEO2MA- -PDMA- -PDEA was prepared and the DMA blocks were partially converted to a quaternized DMA (QDMA) block with click-cross-linkable moieties to form novel schizophrenic water-soluble triblock copolymers. The pH- or temperature-induced micellization and subsequent shell cross-linking of the P(DMA-co-QDMA) inner shell with the tetra-(ethylene glycol) diazide via click chemistry resulted in nanogel networks (Figure 54.14). 

Jiang, X. Zhang, G. Narain, R. Liu, S.H. Fabrication of two types of shell-cross-linked micelles with Inverted structures in aqueous solution from schizophrenic water-soluble ABC triblock copolymer via click chemistry. Langmuir 2009, 25 (4), 2046-2054. 

Schizophrenic solution behavior has been also observed in a PMAA-PDEAEMA DHBC. The particular copolymer formed core-shell micelles at extreme pH ranges, i.e. pH < 5.5 or pH > 9.2, while it was phase separated at intermediate pH values. Micelles having PMAA cores were formed in acidic solutions, while micelles with PDEAEMA cores were formed in alkaline solutions [15]. 

Figure 11. Schizophrenic micellization behavior of a PVBA-b-PDEAEMA DHBC. Reproduced from [13] by permission of Wiley.

Another example of schizophrenic behavior has been observed in the case of A-b-(B-co-C) DHBCs. The copolymers P(EGMA-co-MMA)-PDEA (with various contents of MAA) associated in water either at elevated temperature and low pH values or at low temperature and increased pH values [28], Inverse micelles were observed in each case. Moreover, both the solution salinity and the content of MAA had a great influence on the critical micellization temperature, as was revealed by the experimental observations. 

Synthesis macrosurfactants, polysoaps, polyelectrolytes as building blocks preparation of spherical, cylindrical, multicompartment, and schizophrenic micelles, polymer vesicles, polyion complexes bottom-up self-assembly stimuli-sensitive colloids... 

So-called schizophrenic block copolymers containing tertiary amine methacrylic sequences were developed in the recent years by Armes and co-workers [57, 93, 193,194] and Liu and Armes [191]. They offer interesting combinations of solubility properties versus pH, temperature and electrolytes that make them very attractive for micellization studies. These authors investigated essentially the combination of four types of tertiary amine ethylmethacrylates blocks with the following structures ... 

Amphiphilic diblock copolymers undergo a self-assembly micellar process in solvents that are selective for one of the blocks [100]. By choosing selective conditions for each block, conventional micelles and so-called inverse micelles can be formed. Examples of the so-called schizophrenic micelles were reported [101]. In this case hydrophilic AB diblock copolymers can form micelles in an aqueous solution, in which the A block forms the inner core and inverted micelles (with the B block forming the iimer core) [102]. A diblock copolymer with two weak polybases, (poly-[2-(N-morphoUno)ethyl methacrylate-i)Iock-2- and (diethyl amino)ethyl methacrylate) (PMEMA-block-DEAEMA), forms stable micelles with DEAEMA cores by adjusting the pH value of the solution. The formation of inverted micelles (MEMA core) was achieved by a salting out effect by adding electrolytes to the aqueous solution. 

Rao J, Luo F, Ge Z, Liu H, Liu S (2007) Schizophrenic micellization associated with coil-to-helix transitions based on polypeptide hybrid double hydrophilic rod-coil diblock copolymer. Biomacromolecules 8 3871-3878... 

Smith AE, Xu X, Kirkland-York SE, Savin DA, McCormick CL (2010) Schizophrenic self-assembly of block copolymers synthesized via aqueous RAFT polymerization from micelles to vesicles. Macromolecules 43 1210-1217... 

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