Star copolymers amphiphilic

Gitsov 1, Frechet JMJ. Stimuli-responsive hybrid macromolecules novel amphiphilic star copolymers with dendritic groups at the periphery. J Am Chem Soc 1996 118 3785-3786. 

Tsitsilianis and coworkers [41] presented results on the micellization behavior of anionically synthesized amphiphilic miktoarm star copolymers with PS... 

Starblock (or radial star) copolymers form another kind of amphiphilic nanoparticles which can be regarded as unimolecular micelles. Alternatively, cylindrical core-shell brushes can be regarded as unimolecular cylinder micelles. Due to the covalent attachment of the block copolymers at one end, frustrated micellar structures can be made which would never form spontaneously. The cylindrical systems will be reviewed in Sect. 4.2. 

Fig. 6 Plot of membrane tension t as a function of dilation for a wide range of copolymer amphiphiles as extracted from MD simulations. The computational models, derived from systematic coarse-graining (black symbols), show nearly the same dilational behavior marked by the solid line. The slope of the line, ka, is very close to experimental measurements performed on giant vesicles 0colored symbols). Experimental data for a dimyristoyl phosphatidylcholine lipid membrane are also shown. The point of membrane lysis as observed experimentally for selected lipid and polymersome systems is also shown in the plot with green and red stars, respectively. Reprinted by permission from Macmillan Publishers Ltd Nature Materials, Ref. [85], copyright (2004)...

Tsitsilianis et al. recently published [245] preliminary results on the micelliza-tion behavior of anionically synthesized amphiphilic heteroarm star copolymers with polystyrene and poly(ethylene oxide) branches in THF and water. The former solvent is not very selective for one of the segments whereas the latter is strongly selective for PEO. The apparent molecular weights found for the micelles in THF were two orders of magnitude larger than the ones measured for the unimers. By increasing concentration an increase in the depolarization ratio was observed supporting the conclusion that multimolecular micelles are formed by this kind of miktoarm star copolymer. 

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. 

Amphiphilic (PsCL)i4(PAA)7 miktoarm star copolymers having a p-cyclodextrine core were prepared by ROP and ATRP techniques. Thermodynamically stable micelles were obtained in aqueous solutions. A variety of stmaures, such as spherical micelles, clusters, and wormlike aggregates, were observed by dynamic LS and AFM measurements. Both the copolymer architecture and the composition affea the morphology and the dimensions of the aggregates. 

Double hydrophilic and amphiphilic AB2 miktoarm star copolymers were prepared by ATRP techniques and their micellar stmctures were studied in aqueous solutions showing pH and thermal sensitivity. For example, the PPO(PDMAEMA)2... 

The self-assembly behavior of amphiphilic PEO(PLLA)2 mik-toarm star copolymers was examined in aqueous solutions. " Using a variety of LS and miaoscopy techniques, it was shown that vesicular stmctures were formed in a much broader range of PEO volume fractions (0.2-0.7) compared to the corresponding linear block copolymers (Figure 12). Taking advantage of this behavior, the efBdent encapsulation of the anticancer dmg doxorubicin hydrochloride was achieved. 

Similarly, stable macroanions obtained by the subsequent metalation of the proper end groups such as diphenylvinyl and diphenylmethoxy were used in the living polymerization of tBMA yielding PIB-l7-PtBMA block copolymers with almost quantitative efficiency (Scheme 35). Moreover, amphiphilic polymeric materials can be prepared by hydrolysis of ester moieties of the polymers obtained by this method for instance, amphiphilic PIB-I7-PMAA diblock was prepared by the hydrolysis of the acrylate segment of the suitable precursor copolymer. A series of linear and star copolymers consisting of PIB and PMMA were also prepared. ... 

FIGURE 2.1.2 Polymer self-assemblies based on amphiphilic polymers with different architectures, (a) Diblock copolymer, (b) triblock copolymer, (c) graft copolymer, (d) star copolymer, and (e) hyperbranched copolymer [38]. 

A variety of amphiphilic random, block and star copolymers of 2-methyl-2-oxazoline with 2-oxazoline-beaiing pendant hydrophobic moieties (LCST behaviour was not studied) [371,481-484]... 

A special case of a miktoarm star copolymer with many arms are so-called Janus Micelles, which are formed by cross-linking the short middle block of a triblock terpolymer in the microphase separated bulk state, in which the center block self-assembles in spherical [ 189,190] or cylindrical domains [191]. By this procedure the two different outer blocks are oriented to the two opposite hemicoronas around the center block domain and subsequent dissolution leads to amphiphilic particles (Figure 14). While spherical Janus Micelles form superstructures in solution, the cylindrically shaped Janus Micelles seem to have a lower tendency of self-aggregation to higher superstructures. 

To realize the long-term hydrophilicity of the blend polymer membranes, the key point is to improve the stability of the hydrophilic component on the membrane surface and matrix. To this end, amphiphilic polymers have been adopted to replace linear hydrophilic PEG and PVP in membrane preparation. Theoretically, improved interactions among the hydrophobic segments in amphiphilic polymers and the fluoropolymer can improve the compatibility of the blend, and thus enhance the stability of amphiphilic polymer in the membrane matrix. Three kinds of amphiphilic polymers, viz., triblock copolymer of poly(ethylene oxide)-( -poly(propylene oxide)-ft-poly(ethylene oxide) (EPE), comb-like copolymer of polysiloxane with poly(ethylene oxide) and poly(propylene oxide) side chains (ACPS), and the hyperbranched star copolymer of polyester-g-methoxyl poly(ethylene glycol) (HPE-g-MPEG), have been... 

The most common pH-sensitive polymer structures described in the literature are linear homopolymers or copolymers, amphiphilic block copolymers which form micelles, grafted copolymers, polymer brushes, star and dendritic polymers, NPs, vesicles or HGs (Fig. 3.4). Some of these examples are explained in this section. 

Lambert, O., Dumas, P., Hurtrez, G., and Riess, G. (1997) Synthesis of an amphiphilic triarm star copolymer based on polystyrene, poly(ethylene oxide) andpoly( -caprolactone). Macromolecular Rapid Communications, 18,343-351. 

Babin, J., Leroy, C., Lecommandoux, S. et al. (2005) Towards an easy access to amphiphilic rod-coil miktoarm star copolymers. Chemical Communications, 15,1993-1995. 

Amphiphilic star-shaped copolymers with a cholic acid core comprising PCL tethered on the OH sites and linear PEO or PNIPAM tethered on the COOH site have been prepared by combination of ROP and COOH-NH2 coupling reaction (Scheme 19) [127, 129]. The polymerization of s-caprolactone in these cases was catalyzed by Sn(Oct)2. The star-shaped amphiphilic or thermo-responsive copolymers were studied to assess their micellization behavior and degradation rate, for potential use as smart drug-release systems. 

Scheme 96 Star-shaped, amphiphilic block copolymers prepared by the polymerizations of TMC initiated with a three-armed PEG-based surfactant.

Wang et repotted the synthesis of a series of initiators characterized by the presence of one, two, three, or four thioa-cetates, which, when deprotected with sodium methanolate, produce the corresponding number of thiolates. These initiating systems were rrsed to produce linear monofunctional or difiincdonal growing polymers and three-arm or four-arm star-shaped thiol-terminated PMTs. In the same paper, the synthesis (and some properties) of star-shaped amphiphilic block copolymers based on PMT and PEG are described. In a subsequent paper by the same group, the role of disulfides in MT polymerization and the methods to minimize their presence and their effect on the final polymer stmctures are described. ... 

The term amphiphile implies an affinity to two different media. Familiar amphiphilic molecules incorporate two incompatible components that give rise to this behavior. Similarly, in AB and ABA block copolymers there are two incompatible blocks of different solubility. However, ABC triblock copolymers incorporate three chemically different blocks. When the three blocks are mutually incompatible and of different solubilities the ABC surfactants can exhibit affinity to three different media rather than two. The consequences of this higher functionality have not been explored in detail. For example, little attention has been given to their behavior at interfaces. Linear ABC triblock copolymers or the corresponding star copolymers may be able to form two-dimensional mesophases [56], This can occur at the interface between two fluids I and II such that the B block is selectively solubilized in I while A and C are only soluble in II. In this situation, the A and C blocks are constrained to the surface and bound to each other. A two-dimensional amphiphile is obtained when the A and C blocks are incompatible. A dense monolayer of this type should undergo microphase separation leading to the formation of circular and striped mesophases. Note that cylindrical and lamellar mesophases are indistinguishable in this case. A mixed monolayer comprised of BC, BA, and ABC block copolymers will mimic the behavior of amphiphiles in the presence of two two-dimensional and incompatible fluids. When the ABC copolymers are a minority component, they should straddle the boundary line between the two-dimensional A and C phases. 

Star copolymers are also attainable by using a well-defined R(I) alkyl iodide as CTA. Thus, 1,1,1-ttimethylolpropane tri (2-iodoisobutyrate) was synthesized and used as an R(I)3 CTA for the polymerization of styrene in benzene initiated by AIBN at 65 °C, yielding R(PS)s. Then, polymerization of butyl acrylate afforded R(polystyrene-b-poly( ert-butyl acrylate))3. Finally, an amphiphilic star-block copolymer R(polystyrene-b-poly(acrylic add))3 was obtained by acidic hydrolysis in dichloromethane with trifluoroacetic acid (Scheme 25). 

Rezaei SJT, Nabid MR, Niknejad H, Entezami AA. Folate-decorated thermoresponsive micelles based on star-shaped amphiphilic block copolymers for efficient intracellular release of anticancer drugs. Int J Pharm 2012 437 70-9. 

The facility to introduce well-defined chain ends has been used to prepare star polymers557 and diblocks via reaction with macromolecular aldehydes.558 The synthesis of amphiphilic star block copolymers has also been described using a cross-linking agent.559 560 A similar strategy has recently... 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

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