Amphiphilic alternating copolymers

The present work Illustrates the wide range of phenomena that are exhibited by amphiphilic alternating copolymers. It remains to be seen how large a range of chromophores can be polymerized in this manner and what kind of solution properties - photophysical behavior relations will be found. 

Dautzenberg et al. reported on an alternative method to produce cationic amphiphilic block copolymers starting from a poly(vinylbenzyl) precursor block, which was then converted into a cationic polyelectrolyte by reaction with tertiary amines [162],... 

A polymer is considered to be a copolymer when more than one type of repeat unit is present within the chain. There are a variety of copolymers, depending on the relative placement of the different types of repeat units. These are broadly classified as random, block, graft, and alternating copolymers (see Fig. 2.1 for structural details Cheremisinoff 1997 Ravve 2000 Odian 2004). Among these stmctures, block copolymers have attracted particular attention, because of their versatility to form well-defined supramolecular assemblies. When a block copolymer contains two blocks (hydrophobic and hydrophilic), it is called an amphiphilic diblock copolymer. The immiscibility of the hydrophilic and lipophilic blocks in the polymers provides the ability to form a variety of assemblies, the stmctures and morphologies of which can be controlled by tuning the overall molecular weight and molar ratios of the different blocks (Alexandridis et al. 2000). 

Single hydrophobic-amphiphilic (HA) copolymers with the same HA composition but with different distribution of H and A units along the main hydrophobic chain were also simulated [212]. In particular, regular copolymers comprising H and A units in alternating sequence, regular multiblock copolymers composed of H and A blocks of equal lengths, and the quasirandom protein-like copolymers with a quenched primary structure were studied. These copolymers are schematically depicted in Fig. 24b,c, and d. 

These are stable micelles that are formed with polymeric surfactants. Amphiphilic block copolymers such as the pluronics (polyoxyethylene-polyoxypropylene block copolymers) are able to self-assemble into polymeric micelles and hydrophobic drugs may be solubilized within the core of the micelle or, alternatively, conjugated to the micelle-forming polymer. Although micelles are rather dynamic systems that continuously exchange units between the micelle structure and the free units in solution, those composed of polyoxyethylene - poly(aspartic acid) have been found sufficiently... 

In the second approach, metal-ion/complex was first attached to one of the polymer blocks. A thin film of the resulting polymer metal complex was then obtained by spin coating/solution casting. Alternatively, the polymer metal complex may also be dissolved in a suitable solvent system that selectively dissolves one of the blocks. Micelles or nanosized aggregates formed in this case. The micellization of amphiphilic block copolymers and their use in the formation of metal nanoparticles has been discussed previously.44 A monolayer of micelles was introduced on a substrate surface by dipping or electrostatic attraction. The substrate was then subjected to further chemical or physical treatments as mentioned earlier. The third approach involves the formation of micelles from the metal-free block copolymer in a suitable solvent system. The micelle solution was then added with metal ion, which was selectively coordinated to one of the blocks. These micelle-metal complexes can also be processed by a procedures similar to the second approach. 

Not only small molecular facial amphiphiles have been described but also polymeric facial amphiphiles. Amphiphilicity can be induced in polymers by using hydrophilic and hydrophobic blocks. Self-assembly of such head-tail amphiphilic block copolymers has extensively been described and is controlled by phase separation of the hydrophilic and hydrophobic blocks and their volume fractions. On the contrary, facial amphiphilic polymers can be obtained from alternating copolymers of hydrophilic and hydrophobic monomers, or by polymerization of facial amphiphilic monomers. 

An alternative strategy, which utilizes micelle-forming amphiphilic block copolymers in the stabilization of metal nanoparticles, has been extensively studied and can be described as nanoreactors as the metal colloids are synthesized within their interior. This has enabled the formation of nanosized (l-2nm) metal colliods or clusters within polystyrene-Z -polyvinylpyridine (PS- -PVP) micellar assemblies, with diameters around 30 mn, and these... 

ABA amphiphilic triblock copolymers have been accomphshed by grafting poly(ethylene glycol) into polyffluorine vinylene)s [169]. Multiblock copolymers of alternating 9,9-dihexylfluorene and methylene segments have also been prepared via ADMET [170]. 

We have reported examples for the formation of tubular structures with the help of block copolymers, in most cases with amphiphilic blocks or alternating copolymers. They have all been engineered in such a way that they self-assemble into vesicles, fibers, or tubes. The mechanism for the formation of those tubes, with hollow insides in some cases, was described through two possible routes, which shows how powerful block copolymers can be. Furthermore, the field of applications is very broad material sciences, catalysis, smaller electronic devices, strong nanocomposites, sensors, ion transport, and many others. Creating helical structures or tubes is also interesting in order to mimic nature and to try to understand the way they are created in biological systems. 

Supra-molecular self-assembly provide routes for the synthesis of ordered mesoporous carbon molecular sieves via a soft-template route as recently reported by Meng et al. (2006), Huang et al. (2007), Wan et al. (2007) and Xue et al. (2008). As an alternative to hard-template methods, researchers have focused on the synthesis of OMC by a single-step (soft-template) method, which can eliminate the pre-formed silica (hard) template and tedious infiltration steps. In this regard, commercially available amphiphilic triblock copolymers such as pluronics or symper-onics are used for the preparation of OMCs. The synthesis procedure involves the preparation... 

Another route toward potentially amphiphilic copolymers is the copolymerization of styrene with maleic anhydride, which has the particularity to lead to poly(styrene-co-maleic anhydride) alternate copolymers and ultimately to poly (styrene-co-maleic anhydtide)-b-polystyrene block copolymers after complete depletion in maleic anhydride. Maleimide comonomers were similarly copolymetized with styrene such... 

PIB with pendant functionalities could be prepared by copolymerization of IB with a functional monomer such as bromomethylstyrene or chloromethylstyrene in CH2CI2 at -80 °C with BCI3. An alternate method to obtain initiating sites along a PIB backbone involves the copolymerization with p-MeS followed by selective halogenation. In subsequent initiation of 2-methyl-2-oxazoline, water-soluble amphiphilic graft copolymers have been obtained. ... 

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