Amphiphilic star polymers

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].

Amphiphilic star polymers were also prepared using this approach via the post modification of miktoarm star polymers containing PtBA arms. The subsequent hydrolysis of PtBA with trifluoroacetic acid (TFA) afforded three-miktoarm stars that each included one hydrophobic arm and two hydrophilic poly(acryUc acid) arms (Scheme 30.13). 

Scheme 30.13 Synthesis of well-defined three-miktoarm star polymers using a combination of ATRP and CuAAC click" coupling. Amphiphilic star polymers were prepared that contain one hydrophobic arm and two hydrophilic poly(acrylic acid) arms. Reproduced with permission from Ref. [108] 2006, American Chemical Society.

Although currently under extensive study, supercritical fluids are the only example of an alternative solvent under investigation for Green Chemistry. Hatton (67) at MIT has reported early results of the use of amphiphilic star polymers as solvents in synthesis. In addition to their innocuous nature, due in part to their size, they also have the advantage of minimizing the need for intensive separations that can require additional solvent use. 

Amphiphilic star-block copolymers can be prepared by adding a polycyclic diene such as 238 to a living diblock copolymer made by sequential ROMP of (i) the monomer in Table 9 with R = COOSiMe3, and (ii) norbomene. The trimethylsilyl ester groups are then converted to carboxylic acids by soaking the cast film of the polymer in water for 2-3 days to give a product with a hydrophobic core of polynorbomene and a hydrophilic outer layer126,502. 

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. 

Similar host-guest interactions are found not only with the amphiphilic star block copolymers [210,220] but also with the corresponding heteroarm [211] and core-functionalized [212] versions. Overall, these starshaped polymers induce the interaction more efficiently than their linear counterparts [220],... 

The macromonomer method (C) has also been adopted in cationic polymerization. For instance, amphiphilic graft polymers of vinyl ethers are synthesized by the cationic polymerization of a vinyl ether-capped macromonomer (26) with a block copolymer chain consisting of IBVE and AcOVE segments, followed by alkaline hydrolysis of the latter part into the HOVE units [165], This graft polymer also undergoes a host-guest interaction similar to those with amphiphilic star block copolymers [220]. 

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. 

Another difiinctional monomer, endo-cis-endo-hexacydo-[10.2.l.l .l .0 .0 ]heptadeca-6,13-diene was also used for the synthesis of star polymers. Using the arm-first approach, star polymers of norbomene, 5,6-bis (methox3methyl)norbomene (DMNBE) and 5,6-bis(dicarbotri-methylsilyloxy) norbomene (TMSNBE) were obtained. Amphiphilic star-block copolymers were prepared by reacting... 

Three-layered nanoparticles containing an hbPG core and cross-linked block copolymers based on N-isopropyl acrylate and N,N-dimethylaminoethyl acrylate as the respective arms were synthesized and proved to be thermoresponsive. ° Chu and co-workers" reported electrically conductive core-shell nanoparticles based on poly(n-butylacrylate-b-polystyrene) multiarm star polymers. The PS segments were converted to poly(p-styrenesulfonate) (PSS), thus generating amphiphilic tmimolecular micelles. Then the oxidative propagation of 3,4-ethylenedioxythiophene (EDOT) on the PSS chains was carried out by counterion-induced polymerization to produce a stable aqueous dispersion of the respective PEDOT complex. 

LIB Libera, M., Trzebicka, B., Kowalczuk, A., Walach, W., and Dworak, A., Synthesis and thermoresponsive properties of four arm, amphiphilic poly(terf-butyl glycidylether)-6/oc -polyglycidol stars, Polymer, 52, 250, 2011. 

Soga, M. Tatekawa, M. Matsno, H. Ink for ink-jet recording containing an amphiphilic star block polymer, and ink cartridge and recording apparatus including the same. U.S. Pat. Appl. Publ. US 2004087679, 2004 Chem. Abstr. 2004,140, 376700. 

B. S. Lele and J. C. Leroux, Synthesis of novel amphiphilic star-shaped poly(e-caprolactone)-Wocfc-poly(N-(2-hydrox)rpropyl) methacrylamide) by combination of ring-opening and chain transfer polymerization. Polymer, 43,5595-5606 (2002). 

It is desired to synthesize (a) AA -type triarm asymmetric polystyrene (PSt) stars with asymmetry in the molar mass of their branches, (b) AB2-type miktoarm star polymer core-(PSt)(PtBA)2 (where PtBA = poly(ten-butyl acrylate)), and (c) amphiphilic core-(PSt)(PAA)2 (where PAA = poly(acrylic acid)). Suggest a methodology to synthesize these polymers entirely by ATRP processes. 

Keywords Click reaction Crosslinked hydrogels Smart polymers Amphiphilic polysaccharides Supramolecular hydrogels Star polymers Ordered polysaccharides Interpenetrating polymer networks Antibiofilm... 

Fig. 15 a Synthesis procedures and the structures of ot-CD-OEI star polymers, b Schematic representation of skirt- (left) and jellyfish-type (right) polycationic amphiphilic CDs (paCDs)... 

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. 

Scheme 29.10 Synthetic strategy to synthesizing amphiphilic ferrocene-containing block copolymers (PVFc-BGE-PEO) and ABj miktoarm star polymers (PVFc-(PEO)2).

Peleshanko, S., Jeong, J., Gunawidjaja, R. and Tsukruk, V.V. (2004) Amphiphilic heteroarm PEO-b-PS, star polymers at the air-water interface aggregation and surface morphology. Macromolecules, 37,6511 522. 

Gou, P.F., Zhu, W.P., Zhu, N., and Shen, Z.Q., (2009) Synthesis and characterization of novel resorcinarene-centered amphiphilic star-block copolymers consisting of eight ABA triblock arms by combination of ROP, ATRP, and click chemistry. Journal of Polymer Science Part A-Polymer Chemistry, 47,2905. 

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