Star-block copolymers amphiphilic

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... 

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). 

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. 

Three arm amphiphilic star block copolymers of IBVE and 2-hydroxyethyl vinyl ether (HOVE) were prepared using the trifunctional initiator 8 with sequential cationic polymerization of two hydrophobic monomers, IBVE and AcOVE. Subsequent hydrolysis of the acetates led to the hydrophilic poly(HOVE) segments [38]. Two types of stars were prepared depending on which monomer was polymerized first three arm star poly(IBVE-h-HOVE), with the hydrophobic part inside and three arm star poly(HOVE-h-IBVE), with the hydrophobic part outside. When IBVE was polymerized first, the experimental conditions were the same as described in Sect. 2.2.1. After reaching quantitative monomer conversion, AcOVE was added and temperature was raised from 0 to 40 °C to accelerate the reaction since this monomer is less reactive than IBVE. When starting with AcOVE as a first block, both polymerizations were carried out at 40 °C. SEC analysis showed that MWDs were narrow for the two steps whatever the se-... 

Hedrick, J. L., et al. (1998), Dendrimer-like star block and amphiphilic copolymers by combination of ring-opening and atom transfer radical polymerization, Macromolecules, 31,8691-8705. 

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. 

For example, amphiphilic star block copolymers (Scheme 12) may be characterized by its high accumulation of hydrophilic alcohol groups... 

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]. 

Living cationic polymerization techniques are also capable of producing well defined star-block copolymers. An approach similar to the DVB method described above for the case of anionic polymerization was employed in order to prepare amphiphilic star-block copolymers [20]. In one case, living diblock copolymers of vinyl ethers and ester-containing vinyl ethers, prepared by the initiating system Hl/Znh in toluene, were reacted with a small amount of a difunctional vinyl ether to produce star shaped block copolymers (Scheme 5). 

Three arm amphiphilic star-block copolymers of isobutyl vinyl ether (IBVE) and 2-hydroxyethyl vinyl ethers were also prepared by Higashimura et al. [23]. The synthetic strategy involved the sequential living cationic polymerization of IBVE and 2-acetoxyethyl vinyl ether, initiated by the trifunctional initiator system composed of tris(trifluoroacetate) and ethylaluminum dichloride, with excess of 1,4-dioxane as a carbocation-stabilizing Lewis base (Scheme 8). 

Ring-opening metathesis polymerization was also used recently for the preparation of amphiphilic star-block copolymers [25]. Mo (CH-f-Bu) (NAr) (0-f-Bu)2 was used as the initiator for sequential polymerization of norbornene-type, unfunctionalized and functionalized, monomers. The living diblocks were reacted with endo-ris-endo-hexacyclo- [ 10.2.1.1.3/115>8.02>l 1. O 1-9] heptadeca-6,13-diene, a difunctional monomer in a scheme analogous to the use of DVB in anionic polymerization, to form the central core of the star (Scheme 10). 

The carboxylic moieties of the functional monomers, protected with trimethylsilyl groups during the polymerization reaction, were deprotected by hydrolysis, resulting in amphiphilic star-block copolymers. Molecular weight distributions of the stars were usually higher than 1.2, as determined by SEC, and only in one case was 1.06, although the polydispersities of the Unear diblocks were lower than 1.05. 

Amphiphilic star-block copolymers can be readily prepared by the use of a suitable polycyclic diene such as 4 or the more readily available 5. For example, monomer 6 is first added to the initiator Mo-2 (Table 14.1), followed by norbomene... 

FIGURE 2.1 Various possible architectures for amphiphilic copolymer (a) linear block copolymers with different numbers of A and B blocks, (b) cyclic block copolymers, (c) star block copolymers, (d) graft block copolymers, (e) block copolymers with dendritic or hyper-branched blocks, and (f) semitelechelic polymer (upper), telechelic polymer (middle), and asymmetrical telechelic polymer with different hydrophobic chain ends [9]. 

As a proof of the concept, an amphiphilic A2B2 star-block copolymer (A = PIB and B = PMeVE) has been prepared by the living coupling reaction of living PIB followed by the chain ramification polymerization of MeVE at the junction of the living coupled PIB as shown in Scheme 26.5 [136]. 

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... 

In the following typical examples of these new amphiphilic structures will be outlined, by considering at first block copolymers with poly A/polyB sequences and then those comprising poly A/poly B/poly C blocks. In both cases only copolymers having at least one water-soluble block will be considered. Further details and informations especially on star-block copolymers can be found in the excellent review articles recently published by Hadjichristidis etal. [13], Hirao etal. [77] and Quirk etal. [78]. 

Hydrophilic aminoethyl methacrylate blocks can therefore be combined with various hydrophobic blocks as shown also by J6r6me and co-workers [195]. PDMAEMA-PMMA diblock and star-block copolymers, quaternized on the PDMAEMA block with different alkyl halides were synthesized by these authors who could demonstrate that with short alkyl halides the diblock copolymers behave like classical amphiphiles on micellization, whereas their behavior becomes similar to polysoaps in the case of long alkyl halides. 

Yun etal. [238] investigated the aqueous solution properties of amphiphilic linear and star-block copolymers AjEj, A2B2, A3B3 and (AB)3, where A is PIB and B is PVME. The CMC measured by fluorescence spectroscopy at 20 C increased in the order ... 

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