Amphiphilic hyperbranched polymer

Hydrophilic pEG or pentaerythritol ethoxylate cores with hyperbranched polystyrene arms were prepared by reacting PEG or pentaerythritol ethoxylate with 2-bromopropionyl bromide followed by the ATRP of the macroinitiator and chloromethylstyrene to produce the amphiphilic hyperbranched polymer. Depending on the functionality of the macroinitiator, the products have either a dumbbell or 4-arm starburst structure. The dumbbell polymers tend to have... 

Zhou, Y. and Yan, D. (2009) Supramolecular self-assembly of amphiphilic hyperbranched polymers at all scales and dimensions progress, characteristics and perspectives. Chemical Communications, 1172-1188. 

Peleshanko S, Gunawidjaja R, Petrash S, Tsukruk W (2006) Synthesis and interfacial behavior of amphiphilic hyperbranched polymers poly(ethylene oxide)-polystyrene hyperbranches. Macromoleeules 39 4756-4766... 

Amphiphilic Star Polymers with a Hyperbranched Core... 

More recently, the scope of using hyperbranched polymers as soluble supports in catalysis has been extended by the synthesis of amphiphilic star polymers bearing a hyperbranched core and amphiphilic diblock graft arms. This approach is based on previous work, where the authors reported the synthesis of a hyperbranched macroinitiator and its successful application in a cationic grafting-from reaction of 2-methyl-2-oxazoline to obtain water-soluble, amphiphilic star polymers [73]. Based on this approach, Nuyken et al. prepared catalyticaUy active star polymers where the transition metal catalysts are located at the core-shell interface. The synthesis is outlined in Scheme 6.10. 

Scheme 6.10 Synthesis of the amphiphilic star polymers with a hyperbranched core and amphiphilic diblock graft arms [59].

By modifying the functional groups they can be used,for example, as crosslinkers in high solid or powder coatings and in thermosets. Because of their good miscibility and low melt viscosity, they find applications as melt modifiers and as blend components. Modified hyperbranched polymers, like alkyl chain substituted poiy(ether)s and po-ly(ester)s sometimes exhibit amphiphilic behavior.They can, therefore, be used as carriers for smaller molecules,for example, dyestuff into polypropylene. 

In spite of an irregular polymer architecture, some amphiphilic, hyperbranched polyphenylene derivatives were found to assemble, forming quite uniform Langmuir monolayers at the water/air interface. For example, 3J assembled into a monolayer at the water/air interface and provided a surface similar to the Langmuir film of fatty acids in the nucleating of mineral crystallization on the water/air interface. 

The structure of these amphiphiles is radically different from that of conventional Langmuir film-forming amphiphiles, where segregation of the hydrophobic and hydrophilic parts of molecules at the air/water interface is a prerequisite. This is the first example of a Langmuir-Blodgett film that is fabricated with a micellelike substance. It is intriguing that amphiphilicity is still required to form a stable monolayer film of hyperbranched polymers, in spite of their fundamental structural differences from conventional amphiphiles. 

Figure 2.2 An amphiphilic hyperbranched core-shell polymer. Reproduced with permission from S. Chen, X-Z. Zhang, S-X. Cheng, R-X. Zhuo and Z-W. Gu, Biomacromolecules, 2008, 9, 10, 2578. 2008, American Chemical Society [10]...

The topology of molecules can drastically influence their supramolecular chemistries and properties in general. For example, dendrimers or hyperbranched polymers show dramatically different properties when compared with their linear counterparts. To take a recent example, hyperbranched polyglycerols with a core-shell amphiphile structure encapsulate guests and thereby act as phase-transfer agents, while their strictly linear countei-parts do not.f i... 

The group of Yan developed another method for self-assembly using an amphiphilic hyperbranched multiarm copolymer.After addition to a selective solvent like acetone, macroscopic tubes with centimeter-scale length and millimeter-scale diameter were formed. The star polymer was composed of a hyperbranched poly(3-ethyl-3-oxetanemethanol) (HBPO) core and hydrophilic poly(ethylene glycol) (PEO) arms and self-assembled into a multi-walled tube. 

Lianwei Li, Xu Wang, Chen He, and Weidong He, Association, Emulsifying and Solubilization Properties of Amphiphilic Hyperbranched Poly(acrylic acid) Grafted with Polystyrene (HB-PAA-g-PS) , J. Polym. ScL, Polym. Chem. 2013, 52, 128. 

Hyperbranched polymers and dendrimers have been used as the key starting materials for the preparation of a globular amphiphile with a unimolecular micellar property. However, recent research has indicated that some of the amphiphilic dendritic polymers do not become a... 

Many micellar catalytic applications using low molecular weight amphiphiles have already been discussed in reviews and books and will not be the subject of this chapter [1]. We will rather focus on the use of different polymeric amphiphiles, that form micelles or micellar analogous structures and will summarize recent advances and new trends of using such systems for the catalytic synthesis of low molecular weight compounds and polymers, particularly in aqueous solution. The polymeric amphiphiles discussed herein are block copolymers, star-like polymers with a hyperbranched core, and polysoaps (Fig. 6.3). 

Fig. 6.3 Different types of micelles and micelle analogous structures a) amphiphilic block copolymers, b) star-like polymers with a hyperbranched core, c) polysoaps.

Real-time monitoring of fusion and fission has been reported for polymer vesicles generated from an amphiphilic multiarm copolymer with a hyperbranched poly(3-ethyl-3-oxetanemethanol) core and many oligo(ethylene oxide) arms (HBPO-star-PEO) [152,153], Sonication could partly break the hydrogen bonds and give rise to molecular packing defects on the membrane, which triggers the membrane fusion. 

Figure 2 Schematic representation of various modes of attachment of catalyticaUy active complexes to soluble polymers covalent binding to a PPI dendrimer (upper left) electrostatic binding to linear poly(diallyldimethyl-ammonium chloride) (upper right) physisorption in a unimolecular micelle of amphiphillically modified hyperbranched polyglycerol (lower left) specific hydrogen-bonding to a urea functionalized PPI dendrimer.

L. Zhang, C.-H. Hu, S.-X. Cheng, R.-X. Zhuo, Hyperbranched amphiphilic polymer with folate mediated targeting property, Colloids Surf. B 79 (2010) 427 33. 

Wang DL, Chen HY, Su Y, Qiu F, Zhu LJ, Huan XY, Zhu BS, Yan DY, Guo FL, Zhu XY (2013) Supramolecular amphiphilic multiarm hyperbranched copolymer synthesis, self-assembly and drug delivery applications. Polym Chem 4(l) 85-94... 

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]. 

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