Poly amphiphilic block copolymers

Trialkylsilyl-protected oligo(ethylene glycol)methacrylates, 2- 2- (tert-butyldimethylsilyl)oxy]ethoxy ethyl methacrylate (1), and 2- 2-[2-[(ferf-butyldimethylsilyl)oxy] ethoxy] ethoxy ethyl methacrylate (2) (Scheme 7) were used for the synthesis of amphiphilic block copolymers by anionic poly-... 

Some other degradable (i.e., nonvinyl-type) polymers have been reported as components for amphiphilic block copolymers. For example, Hsiue reported the synthesis of a block copolymer of poly(2-ethyl oxazoline) and PLA by ROP. They reported the use of ABA-type triblock copolymers as pH-responsive polymer... 

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

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],... 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Torchilin et al. synthesized an iodine-containing amphiphilic block-copolymer consisting of iodine-substituted poly-L-lysine which is able to form micelles in aqueous solution [37]. The two components of the block-copolymer were methoxy-poly(ethylene glycol) propionic acid (MPEG-PA) with a molecular weight of 12 kDa and poly[ ,M-(2,3,5-triiodobenzoyl)]-L-lysine. The particle size of the micelles was approx. 80 nm, and the iodine concentration was 20 mg mL . Biodistribution studies in rats showed significant and prolonged enhancement of the aorta, the liver and spleen. 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

Another class of polymers capable of stabilizing Au NPs through physisorption is amphiphilic block copolymers. Initial reports describe the formation of Au NPs in the presence of different amounts of diblock copolymers like PS-P2VP (polystyrene-block -poly-2-vinylpyridine) [111] or PS-PEO (polystyrene-block-polyethyleneoxide) [112]. 

Au NPs have been synthesized in polymeric micelles composed of amphiphilic block copolymers. Poly(styrene)-block-poly(2-vinylpyridine) in toluene has been used as nanocompartments loaded with a defined amount of HAuCl4 and reduced with anhydrous hydrazine. The metal ions can be reduced in such a way that exactly one Au NP is formed in each micelle, where each particle is of equal size between 1 and 15 nm [113]. In another example, the addition of HAuCfi to the triblock copolymer (PS-b-P2VP-b-PEO) (polystyrene-block-poly-2-vinyl pyridine-block-polyethylene oxide) permits the synthesis of Au N Ps using two different routes, such as the reduction of AuC14 by electron irradiation during observation or by addition of an excess of aqueous NaBH4 solution [114]. 

The interfacial properties of an amphiphilic block copolymer have also attracted much attention for potential functions as polymer compatibilizers, adhesives, colloid stabilizers, and so on. However, only a few studies have dealt with the monolayers o well - defined amphiphilic block copolymers formed at the air - water interface. Ikada et al. [124] have studied monolayers of poly(vinyl alcohol)- polystyrene graft and block copolymers at the air - water interface. Bringuier et al. [125] have studied a block copolymer of poly (methyl methacrylate) and poly (vinyl-4-pyridinium bromide) in order to demonstrate the charge effect on the surface monolayer- forming properties. Niwa et al. [126] and Yoshikawa et al. [127] have reported that the poly (styrene-co-oxyethylene) diblock copolymer forms a monolayer at the air - water... 

Amphiphilic block copolymers consisting of a hydrophobic (poly(ethyl ethylene) (PEE) and a hydrophilic polyethylene oxide)(PEO) block form monolayers at the air-water interface. The schematic molecular arrangement of this diblock is shown in Fig. 3.26. 

Amphiphilic block copolymers of SCB and methacrylic acid (and methacrylic acid derivatives) with narrow molecular weight distribution can be synthesized by sequential addition of 1,1-diphenylethylene and methacrylate or its derivatives to living poly(silacyclobutane) in the presence of lithium chloride (Scheme 12) <2001PSA86, 1998PSA2699, 1999MM6088>. 

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

Nolte et al. found that an amphiphilic block copolymer 83 composed of a hydrophobic tail of poly(styrene) and a hydrophilic head group of a charged, right-handed helical poly(isocyanide), which is referred to as a superamphiphile , self-assembles in a hierarchical fashion in water to form left-handed superhelices (Fig. 34) [ 158]. They suggest that this type of copolymer will serve as an experimental model for the theoretical study of the packing of helices due to their versatility and easy accessibility. 

For polymer chemists it is interesting to know how well-known linear polymers can be linked with dendritic architectures and what the supramolecular consequences of this approach might be. Combination of dendrimers with linear polymers in hybrid linear-dendritic block copolymers has been employed to achieve particular self-assembly effects. Block copolymers with a linear polyethylene oxide block and dendritic polybenzylether block form large micellar structures in solution that depend on the size (i.e., the generation) of the dendritic block [10]. Amphiphilic block copolymers have been prepared by the combination of a linear, apolar polystyrene chain with a polar, hydrophilic poly(propylene imine) dendrimer [11] as well as PEO with Boc-substituted poly-a, -L-lysine dendrimers, respectively [12]. Such block copolymers form large spherical and cylindrical micelles in solution and have been described as superamphi-philes and hydra-amphiphiles , respectively. 

Amphiphilic block copolymers consisting of polyethylene glycol and poly-lactide, (I), were prepared by Seo [1] and used as drug delivery agents for Paclitaxel . 

Block copolymers that consist of hydrophilic and hydrophobic segments are typical amphiphilic polymers, a variety of which have been synthesized by living cationic polymerization. Figure 9 schematically illustrates the structures of some of these amphiphilic polymers thus far obtained though the examples therein are based on poly(vinyl ether) segments, any other appropriate segments may be incorporated. As seen in the illustrations, macromolecular amphiphiles are not necessarily linear AB- and ABA-type block copolymers but may be graft, multiarmed, and network polymers, where the basic components are amphiphilic block copolymers. 

By the use of the polymer-linking method with 20a, a variety of starshaped poly(vinyl ethers) have been synthesized (Scheme 12) [208-212]. A focus of these syntheses is to introduce polar functional groups, such as hydroxyl and carboxyl, into the multiarmed architectures. These functionalized star polymers include star block (23a,23b) [209,210], heteroarm (24) [211], and core-functionalized (25) [212] star polymers. Scheme 12 also shows the route for the amphiphilic star block polymers (23b) where each arm consists of an AB-block copolymer of 1BVE and HOVE [209] or a vinyl ether with a pendant carboxyl group [210], Thus, this is an expanded version of triarmed and tetraarmed amphiphilic block copolymers obtained by the multifunctional initiation (Section VI.B.2) and the multifunctional termination (Section VI.B.3). Note that, as in the previously discussed cases, the hydrophilic arm segments may be placed either the inner or the outer layers of the arms. 

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