Double Hydrophilic Block Copolymers DHBCs

Using the DHBC design, not only the required lowering of the crystal-water interface energy by polymer adsorption is obtained, but it is also possible to create a high specificity to distinct crystaUine surfaces by adjustment of the functional polymer pattern [280]. 

Particle stabilization when In contact with crystal 

Various DHBCs have successfully been used as a stabilizer for the purely steric or combined steric/electrosteric stabilization of ceramic precursor particles like AI2O3 [308,309], BaTiOs [310-314] colloidal silica [315-320] alumina coated Ti02 [321], Ce02 [322], o -Fe203 (hematite) [281,323-325], and various pigments [327] in aqueous solution. The solid amoimt can be stabilized to extremely high concentrations (up to 80 wt % [327]) showing the stabilization capabilities of optimized DHBCs. 

Recently, DHBCs have been used as a good stabilizer for the in-situ formation of various metal nanocolloids and semiconductor nanocrystals such as Pd, Pt [328-330], Au [280,328-330], Ag [331], CdS [332], and lanthanum hydroxide [333]. PAA-fe-PAM and PAA-fc-PHEA were used as stabihzer for the formation of hairy needle-Uke colloidal lanthanum hydroxide through the complexation of lanthanum ions in water and subsequent micelhzation and reaction [333]. The polyacrylate blocks induced the formation of starshaped micelles stabilized by the PAM or PHEA blocks. The size of the sterically stabilized colloids was controlled by simply adjusting the polymer-to-metal ratio, a very easy and versatile synthesis strategy for stable colloids in aqueous environment [333]. The concept of induced micelhzation of anionic DHBCs by cations was also apphed in a systematic study of the direct synthesis of highly stable metal hydrous oxide colloids of AP+, La +, Ni +, Zn , Ca , or Cu via hydrolysis and inorganic polycondensation in the micelle core [334,335]. The AP+ colloids were characterized in detail by TEM [336], and the intermediate species in the hydrolysis process by SANS, DLS, and cryo-TEM [337]. 

The stabilization of specific crystal planes by face-selective polymer adsorption is a powerful tool for modifying the crystal morphology and for deriving low dimensional crystal morphologies like plates or fibers. Recent reports show that the DHBCs can also be used for stabilization of specific planes of some crystals for their oriented growth, e.g., Au [280], ZnO [300-302], calcium oxalate [299], PbCOa [291], and BaS04 [295]. 

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Amphiphilic block copolymers containing a cationic block may carry as the second block a hydrophilic or a hydrophobic one. Those containing a hydrophilic second block belong to the so called double-hydrophilic block copolymers (DHBC), which have recently been reviewed [60]. This promising class of polymers has potential applications in drug-carrier systems, gene therapy, desalination membranes, as switchable amphiphiles, and others [45, 60, 77]. 

Double hydrophilic block copolymers (DHBCs) are a class of polymers that combine the self assembly ability of block copolymers with the water solubility of hydrophilic macromolecular chains. Numerous sophisticated works have been already described in the literature, indicating the potential of this class of copolymers in emerging technologies. The synthesis of novel DHBCs, using either new monomers or post polymerization functionalization schemes, is the subject of intense investigation during the current years. 

Polyelectrolytes Linear polyelectrolytes in solution can provide a scaffold for the adsorption of metal ions with opposite charges. Thereafter, the ion-absorbed polyelectrolyte templates can transform to ID metal or semiconductor-NP assemblies either by a reduction reaction or by chemical combination of ion pairs. Minko and co-workers explored this strategy to prepare ID Pd NP assemblies. Colfen and co-workers adopted double-hydrophilic block copolymers (DHBCs) with more complex stractures, in which one hydrophilic block interacted strongly with appropriate inorganic materials and the other hydrophilic block mainly promoted solubility in water, to synthesize ID NP assemblies of materials such as CaC03, CdW04. 

The use of double hydrophilic block copolymers in biomimetic mineralization processes has been investigated in recent years. In contrast to rigid templates (like carbon nanotubes and porous aluminum templates which predefine the final structure) water soluble polymers could be used as soluble species at various hierarchy levels. Usually, in the case of DHBCs, one of the block acts as scaffold for the development of the crystal, while the other acts as a soluble-stabilizing matrix. Therefore, both of the blocks play a crucial role on the development of the crystals. There is a plethora of reports on the emerging bio-inspired mineralization field. Various crystal structures have been presented during the last years, following versatile synthetic routes. A very detailed and illustrious review has been recently given by Colfen [3]. The above review describes in detail all aspects of the specific field. Herein, we present just a few selected examples. 

The synthesis of a miktoarm star copolymer of the type AnBn has been also demonstrated. The synthesis was performed via ATRP using divinylbenzene, as the core cross-liking agent. PEO macroinitiator chains were utilized for the polymerization of divinylbenzene forming a star polymer, with a random number of branches. The above star polymer was used as a multi-functional initiator for the polymerization of methacrylate monomers. Therefore, the synthesis of an amphiphilic miktoarm star copolymer was realized [54]. Finally, the hydrolysis of the protected methacrylate block led to the preparation of the desired DHBCs, namely the PEOn-PMAA stars. SEC analysis of the preeursor PEOn-PMMA copolymer revealed a relatively broad molecular weight distribution. Nevertheless, this is a good example for the synthesis of A Bn double hydrophilic star copolymers. 

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