Double hydrophilic block copolymers

Qi, L. Colfen, H. and Antonietti, M. (2001). Synthesis and Characterization of CdS Nanoparticles Stabilised by Double Hydrophilic Block Copolymers. Nano Lett, 1, 61-65. 

Vaterite is thermodynamically most unstable in the three crystal structures. Vaterite, however, is expected to be used in various purposes, because it has some features such as high specific surface area, high solubility, high dispersion, and small specific gravity compared with the other two crystal systems. Spherical vaterite crystals have already been reported in the presence of divalent cations [33], a surfactant [bis(2-ethylhexyl)sodium sulfate (AOT)] [32], poly(styrene-sulfonate) [34], poly(vinylalcohol) [13], and double-hydrophilic block copolymers [31]. The control of the particle size of spherical vaterite should be important for application as pigments, fillers and dentifrice. 

These double hydrophilic block copolymers exhibit stimuli-responsive properties and have potential biotech applications. 

Colfen, H. (2001) Double-hydrophilic block copolymers synthesis and application as novel surfactants and crystal growth modifiers. Macromotecular Rapid Communications, 22, 219-252. 

Double-Hydrophilic Block Copolymers in Aqueous Solution. 94... 

Selected examples of block copolymer micelles in both aqueous and organic media will then be presented in Sects. 3 and 4. Section 4.3 emphasizes stimulus-responsive micellar systems from double-hydrophilic block copolymers. Prediction of the dimensional characteristic features of block copolymer micelles and how it varies with the composition of the copolymers will be shortly outlined in Sect. 5, with a consideration of both the theoretical and experimental approaches. Tuning of micellar morphology and triggering transitions between different morphologies will then be discussed in Sect. 6. 

AB block copolymers containing two water-soluble blocks are often referred to as double-hydrophilic block copolymers. These copolymers have spurred much interest in recent years because they can generally be transformed into amphiphilic copolymers once an adequate stimulus is applied. In other words, one of the hydrophilic water-soluble blocks can be transformed into a hydrophobic block whenever a given property of the aqueous medium is changed. Since these copolymers may contain one or two polyelectrolytic blocks, the typical features of polyelectrolytes described in Sect. 4.2 should also be considered for some double-hydrophilic block copolymers. 

Thermosensitive double-hydrophilic block copolymers micelles have been reported essentially for systems containing blocks exhibiting a LOST in water such as PMVE [189] or PNIPAM. These blocks have been generally associated to PEO blocks. At temperatures below the LOST, both blocks are soluble and... 

Stimulus-reponsive micelles have been intensively investigated during the last 5 years, and further developments could be expected. These micellar systems have been essentially prepared from double-hydrophilic block copolymers and from micelles with noncovalent complexes in the core. The interest related to these micellar systems stems from their potential applications, as briefly discussed in Sect. 4.3. 

Citrate-capped Au NPs have been coated with a layer composed of the double hydrophilic block copolymer polyethylene oxide)-block-poly(2-(dimethylamino)eth-yl methacrylate)-SH (PEO-b-PDMA-SH) leading to core-shell, almost spherical, Au NPs of about 18 nm. The shell cross-linking of these hybrid Au NPs gives rise to high colloidal stability [122]. 

Polyelectrolyte complexes of retinoic acid have been well investigated, they are pharmaceutically active surfactants. In the following, we will therefore discuss the physicochemical properties of drug carriers formed by synthetic polyamino acids, polyethyleneimine, double hydrophilic block copolymers and retinoic acid. 

Antonietti M, Breulmann M, Goltner CG, Colfen H, Wong KKW, Walsh D, Mann S (1998) Inorganic/organic mesostructures with complex architectures precipitation of calcium phosphate in the presence of double-hydrophilic block copolymers. Chem Eur J 4(12) 2493-2500... 

Recent attempts to prepare 26 by RAFT, however, failed [153]. Double hydrophilic block copolymers of NIPAM and 23e [154], as well as of N,N-diethylacrylamide and 23b [155], were prepared with the CTA benzyl dithiobenzoate, and exhibit LCST and UCST behavior in water. The new polymer 51 is also part of amphiphiUc di- and triblock copolymers [152]. Diblock copolymers with poly(ethylene glycol) methyl ether acrylate, dimethylacry-lamide, or 4-vinylstyrene sulfonate are macrosurfactants with a switch-able hydrophobic block. Triblock copolymers containing additionally 4-vinylbenzoic acid differ in the nature of the hydrophilic part [152]. Near-monodisperse block copolymers of N,N-dimethacrylamide and 49a were synthesized in different ways via macro-CTAs of both monomers as the first step. Such sulfobetaine block polymers form aggregates in pure water but are molecularly dissolved after addition of salt [152,156,157]. 

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]. 

Scheme 11 A novel route to double hydrophilic block copolymers...

FIGURE 54.27 Macro-CTAs and schematic representation of the RAFT precipitation polymerization process. (Reprinted with permission from J. Am. Chem. Soc., 129(46), An, Z., Shi, Q., Tang, W., Tsung, C.K., Hawker, C.J., and Stucky, G.D., Facile RAFT precipitation polymerization for the microwave-assisted synthesis of well-defined, double hydrophilic block copolymers and nanostructured hydrogels, 14493. Copyright 2007 American Chemical Society.)... 

PDMAs were either hydrophilic or amphiphilic due to the different R groups of the RAFT agents. When the cross-linker A,A -niethylenebisacrylamide was used, thermosensitive nanogels were produced. When no cross-linker was used, after cooling to room temperature, the nanoparticles dissociated into double hydrophilic block copolymers, which allowed for convenient characterization of the polymers. The use of both types of PDMAs permitted the production of well-defined block copolymers with low values of Mw/Mn, indicating a controlled nature of the RAFT process under precipitation/dispersion conditions. 

In order to prepare core-shell magnetic microspheres for use as an MRI contrast agent, double hydrophilic block copolymers of PEO-Wock-PGA have also been investigated by another research group [106]. 

We have shown that a combination of four simple building blocks (i.e. monomers) and exclusively non-covalent interaction forces, achieved via the co-assembly of fully water-soluble double hydrophilic block copolymers, results in mixed micelles in aqueous solutions. The chemically unlike polymer chains in the micellar corona may give rise to various coronal microstructures, ranging from mixed to segregated, in either the radial or lateral direction, or in both. Hence, co-assembly of charged block copolymers can result in the spontaneous formation of reversible Janus micelles. 

Current Developments in Double Hydrophilic Block Copolymers... 

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