Star block copolymers multiarm

In this case, chlorosilane reagents (XVIII, XIX), halomethyl benzene reagents (XX), and 1,1-diphenylethylene (DPE) derivatives (XXI) carrying aUsyUialide functions are typical coupling agents used to deactivate anionically derived polymers, mostly PS, PB, and PI. A variety of star-like polymers of precise functionality, including multiarm stars, star-block copolymers, asymmetric and miktoarm stars, and other branched architectures, are accessible in this way [1, 12-14, 35]. This... 

Multiarm star-block copolymer can be prepared by incorporation of a small amount of divinylbenzene. 

ROP and RAFT polymerization techniques were combined to synthesize multiarm star-block copolymers having PeCL inner blocks and PDMAEMA outer blocks. A hyperbranched polyester core was used as a multifunctional initiator. It was calculated that the functionality of the star-blocks was equal to 19. Temperature and pH-responsive micelles were obtained in aqueous solutions. Equilibrium between unimolecular and mulrimolecular micelles was observed at pH 6.58 by dynamic LS and TEM measurements. In low-pH solutions, the PDMAEMA chains were fully protonated and therefore highly stretched, leading to maximum Rh values. When the pH was increased, the micellar Rh decreased as a result of the deprotonation of the dimethylamine groups. PDMAEMA is also a temperature-sensitive polymer, as it exhibits lower critical solution temperature (LCST) behavior. It precipitates from neutral or basic solutions between 32 and 58 °C. At pH 6.58, the Rh values were found to decrease with increasing temperature, due to the gradual collapse of the PDMAEMA outer blocks. 

Antioxidants are usually employed to prevent oxidation of the double bond in either of the polydienes. Specialty grades are available where the polydiene has been hydrogenated, which gives much better chemical stability and uv resistance. Multiarm and star-block copolymers are some examples of specialty copolymers that can be used to modify the performance of block copolymer adhesives (19). 

More complex architectures such as multiarm star-block copolymers were reported by Isono and co-workers [100] and by Dumas and co-workers [ 101,102] who used as a starting point 1,1-diphenyl end-capped macromonomers. The application of 1,1-diphenyl ethylene chemistry in anionic synthesis of block copolymers with controlled structures was extensively developed by Quirk eta/. [78] as well as by Dumas and co-workers [103]. 

As an alternative the multifunctional initiators developed by Sogah and co-workers [ 104] appeared to be as one of the most efficient routes for the synthesis of multiarm star-block copolymers. 

Li, Y. and Kissel, T. (1998) Synthesis, characterization and in-vitro degradation of star-block copolymers consisting L-lactide, glycolide and branched multiarm poly(ethylene oxide). Polymer, 39,4421-4427. 

Dag, A., Durmaz, H., Thnca, U., and Hizal, G. (2009) Multiarm star block copolymers via Diels-Alder click reaction. Journal of Polymer Science Part A-Polymer Chemistry, XI, 178. 

Meyer, N., Delaite, C., Hurtrez, G., and Dumas, P. (2002) A common route to A2B and A3B multiarm star block copolymers. Polymer, 43,7133-7139. 

Another approach to synthesize multiarm star block copolymers is based on a combination of CuAAC and the arm-first method (Durmaz et al, 2010). Protected alkyne PS polymers were prepared via ATRP and subsequently crosslinked by a divinyl containing compound. The formed 27-arm star-shaped polymers containing a protected alkyne periphery, was deprotected and subsequently coupled with azide-end-functionalized PEG and PtBuA to form star block or mixed block copolymers. The CuAAC reactions occurred at room temperature for 24 h, surprisingly leading to a full click efficiency. The quantitative character of the latter click reaction at ambient temperatures for such dense polymer structures is in contrast to those obtained by other research groups, as mentioned in previous paragraphs. 

The same group also reported on the synthesis of multiarm star block copolymers by using Diels-Alder cycloaddition reactions (Dag et al., 2009). First, an a-anthracene-end functionalized PS (PS-anthr) and furan-protected maleimide-end-functionaUzed polymers, including PMMA and PtBuA, were prepared via ATRP. The maleimide functionalities were protected as they can contribute to the copolymerization with MMA or tBuA. Moreover, the polymerization temperature was kept below 60 °C to prevent deprotection during the polymerization. In the next step, a 33-arm anthracene-end functionalized (PS) star polymer was obtained using PS-anthr as macroinitiator and divinyl benzene as crosslinker. These star polymers were then reacted with the unprotected maleimide end-functionalized PMMA or PtBuA to give multiarm star block copolymers via Diels-Alder click reaction. The efficiencies were foimd to be 96 and 88%, respectively. 

Figure 8.15 Synthesis of a PiBA-PS multiarm star block copolymers by the combination of RAFT-hetero-Diels-Alder and ATRP. (Reprinted from S. Sinn well, M. Lammens, M.H. Stenzel et al., Efficient access to multi-arm star block copolymers by a combination of ATRP and RAFT-HDA click chemistry, Journal of Polymer Science, Part A Polymer Chemistry, 47, 8, 2207-2213 (Figure 3), 2009, with the permission of John Wiley Sons, Inc.)...

Kreutzer, G., Ternat, C., Nguyen, T.Q. et al. (2006) Water-soluble, unimolecular containers based on amphiphilic multiarm star block copolymers. Macmmolecules, 39,4507. 

Linking reaction of living polymers has been employed as an alternative way to prepare star-block copolymers. The synthesis of poly(St-b-IB) multiarm star-block copolymers was reported using divinylbenzene (DVB), as a linking... 

Kreutzer G, Temat C, Nguyen TQ, Plummer CJG, Manson JAE, Castelletto V, Hamley IW, Sun F, Sheiko SS, Herrmaim A, Ouali L, Sommer H, Fieber W, Velazco MI, BQok HA (2006) water-soluble unimolecular containers based on amphiphilic multiarm star block copolymers. Macromolecules 39 4507 516... 

More recent examples include end-functionalized multiarmed poly(vinyl ether) (44), MVE/styrene block copolymers (45), and star-shaped polymers (46—48). With this remarkable control over polymer architecture, the growth of future commercial appHcations seems entirely likely. 

Puskas, J.E., Pattern, W.E., Wetmore, P.M., and Krukonis, A. Multiarm-star polyisobutylene-polystyrene thermoplastic elastomers from a novel multifunctional initiator, Polym. Mater. Set Eng., 82,42 3, 1999. Brister, L.B., Puskas, J.E., and Tzaras, E. Star-branched PIB/poly(p-t-bu-Styrene) block copolymers from a novel epoxide initiator, Polym. Prepr., 40, 141-142, 1999. 

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. 

Well-characterized systems. This depends on the appropriate chemistry and subsequent characterization (typical issues here are the polydispersity, control of grafting density, reproducibility of procedure to obtain identical particles). One frequent problem here is that the price one pays for such systems is tlie availability of small amounts (sometimes only fractions of 1 g) of material. For example, multiarm star polymers are in many ways unique, clean, soft colloids [ 19,23], but their nontrivial synthesis makes them not readily available. On the other hand, recent developments witli block copolymer micelles from anionically synthesized polymers [54-58] and arborescent graft copolymer synthesis [40] appear to have adequately addressed this issue for making available different alternative star-like systems. 

Multiarm star polymers have recently emerged as ideal model polymer-colloids, with properties interpolating between those of polymers and hard spheres [62-64]. They are representatives of a large class of soft colloids encompassing grafted particles and block copolymer micelles. Star polymers consist of f polymer chains attached to a solid core, which plays the role of a topological constraint (Fig. Ic). When fire functionality f is large, stars are virtually spherical objects, and for f = oo the hard sphere limit is recovered. A considerable literature describes the synthesis, structure, and dynamics of star polymers both in melt and in solution (for a review see [2]). 

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. 

With the significant progress in the living polymerization techniques , in the design of multifunctional initiators and the control in coupling reactions a large variety of block copolymers with sophisticated architecture became available such as cyclic, H and star shaped, multiarm and pahn-tree or dumbell structures, dendritic blocks linked to linear blocks, etc. 

This result proves that well-defined structures with low degree of heterogeneity of the multiarm star-shaped polymers can be synthesized. Moreover, the method reported herein can also provide a synthetic pathway for the introduction of block copolymers synthesized via different polymerization routes (RAFT, ROP, etc.) onto the anthracene-end-functionalized multiarm star-shaped polymers. Although the Diels-Alder cycloaddition between anthracene and maleimide derivatives has proven to provide good results in the formation of complex architectures, the major drawback of this method remains the requirement of high temperature and relatively long reaction times. 

Motivated by the preparation of wdl-defined hyperbranched polyglyddols, a variety of polyglyddol-based complex polymer architectures were synthesized. These include linear-dendritic block copolymers,random copolymers, and multiarm star copolymers. ... 

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