Star polyethers

Star polyethers have been synthesized by a core-first method. AB2- and A2B-type mikto-arm star copolymers consisting of aromatic polyether arms as the A segment and polystyrene arms as the B segment were synthesized by using orthogonal trifunctional initiators (Scheme 32) [73]. 

The composition of the star-shaped block copolymer is easily determined by proton NMR analysis from this and the mean number average molecular weight (Mn) of the sequence PA, Mn of the polyether component can be calculated. The later is very similar to the value from membrane osometry. Hydroxyl end group of PA(P0)2 star-shaped block copolymers have been titrated and their mean number per copolymer (1.85) agrees with the presence of two polyoxirane branches. On the average, the polydispersity of the star-shaped block copolymers varies between 1.2 and 1.3 (Figure 6). 

Fig. 29. Computer simulated molecular graphics (wireframe) using POLYGRAF for STAR-BURST (polyether) dendrimers of generations 1-4...

If trifunctional initiators such as glycerol or trimethylolpropane are used as starters for the alkylene oxides polymerisation, star-like polyether triols are formed [1-13, 15-17, 54, 60, 69, 75] ... 

Yu, D., Vladimirov, N., and Frechet, J.M.J., MALDl-TOF in the Characterization of dendridic linear Block Copolymers and Stars, Macromolecules, 32,5186 (1999). Leon, J.W., Frechet, J.M.J., Analysis of Aromatic Polyether Dendrimer and Dendrimer-Linear Block Copolymers by MALDl-MS, Polym. Bullett., 35, 449 (1995). 

These indude polyethers, polythioethers, and polyamines [82-85]. In addition to linear materials, star-shaped polymers such as 4.39 have been reported [86]. These materials are redox-active as a result of the presence of the cationic ArFe(i/ -CsHs) moieties, which undergo reversible reduction at -40 °C. The materials are photo-... 

Hb polyethers that have been widely applied for the preparation of star polymers are mainly hbPG and hb polyoxetanes. Frey and co-workers presented the synthesis of poly (propylene oxide) (PPO) multiarm star polymers via... 

Hb polyethers based on 3-alkyl-3-(hydroxymethyl)oxetane have also been widely applied as core molecules for the preparation of multiarm star polymers. Carlmark et al. synthesized PMA star polymers with a similar route as mentioned above by ATRP after modification of hb poly[3-ethyl-3-(hydroxymethyl) oxetane] (hbPEHO) with 2-bromoisobutyryl bromide. The star polymers were prepared with CuBr/Mce-TREN as the catalyst in ethyl acetate at room temjjerature. In order to prevent gelation, the polymerization was conducted at low concentra tions and stopped after low conversion or by deaeasing o t e amoimt of catalyst used. The authors reported that e ratio initiating sites/catalyst could not exceed 1 0.1, otherwise, ge a tion occurred or no control over polymerization was possi... 

Materials studied include polyesters and polyethers [73], PMMA [74], star-shaped styrene block copolymers [75, 76], PC [77], isoprene-styrene graft copolymers [76], polyethylene oxide-maleic anhydride-vinyl methyl ether copolymers [78], polybutylene terephthalate [79], PE [80], (phenoxymethyl)thizrane [81], polytrimethylene carbonate [82], polybutylene succinate [83], polymethyldiundecenylsilane [84], poly(N-vinyl carbazole) [85], titanium-containing copolymers [86], styrene-macro zwitterion polymers [87], and poly(octadecene-alt-maleic anhydride) [88]. 

Thus, the rearrangement of cyclic vinyl acetals of type 1 yields tetrahydrofuran-3-carbaldehydes 2, 3), which are useful precursors in the synthesis of polyether antibiotics. The rearrangement of acyclic vinyl acetals (4) produces the aldol ethers Sand 6 stereoselectively. E. g., star-tingwiththe 1,3-dioxolanyl vinyl acetal7or the 1,3-dioxanyl vinyl acetalft the aldehydes 12are obtained, which contain the 1,2- and the 1,3-diol structural subunit... 

Karger-Kocsis J, FrOhlich J, Gryshchuk 0, Kautz H, Frey H and Mulhaupt R (2004) Synthesis of reactive hyperbranched and star-like polyethers and their use for toughening of viiiylester-urethane hybrid resins. Polymer 45 1185-1195. 

Scheme 20 Preparation of star-shaped polymer conjugates with cholic acid (CA) core and polyether arms functionalized with pendant COOH or NH2 groups [150] (reprinted with permission from American Chemical Society)...

Well-established materials, such as hyperbranched polyether polyols, have been used to develop exciting hybrid stmctures, from multiarm star polymers to LHBCs. Chemical modification of the core as well as the multiple terminal and interior groups leads to multifunctional materials for... 

Furthermore, (AB)3-type star block copolymer was also prepared using ATRP, CGCP, and a click reaction (Scheme 33) [74]. ATRP of styrene was carried out in the presence of 2,4,6-tris(bromomethyl)mesitylene as a trifunctional initiator, and then the terminal bromines of the polymer were transformed to azide groups with NaNs. The azide-terminated polystyrene was then used for click reaction with alkyne-terminated aromatic polyether, obtained by CGCP with an initiator bearing an acetylene unit. Excess alkyne-terminated aromatic polyether was removed from the crude product by means of preparative high-performance liquid chromatography (HPLC) to yield the (AB)3-type star block copolymer. 

The morphologies of star copolymers AB2, A2B, and (AB)3 and linear block copolymer AB, which were annealed under vacuum at 150°C for 2 days, were observed by means of transmission electron microscopy (TEM) (Fig. 4). In the case of a sample of AB-type diblock copolymer, lamellar morphology consisting of alternating dark polystyrene and bright aromatic polyether regions was observed (Fig. 4a). On the other hand, samples of AB2, A2B, and (AB)3 star copolymers showed spherical or plate-like morphology (Fig. 4b-d). Such unexpected and novel... 

Scheme 33 Synthesis of (AB)3-type star block copolymer of polystyrene and polyether...

An effective way to obtain amorphous polyethers is by grafting low molecular weight PEO to the polymer skeleton and form comb- or star-like structures. Since ionic conduction is closely related to the movement of chain segments, it can be expected that a polymer with an amorphous structure together with low Tg will meet the need for fast ionic conduction at room temperature. There are two common ways to synthesize comb polyethers [1] ... 

It was,and still is, a purpose of our work to illustrate the synthetic potential of "a-b monomers" in the field of aromatic polyethers, polyesters and polyamides (concentrating on polyesters in the present contribution). The preparation of star-shaped and hyperbranched polycondensates is plagued by side-reactions resulting in crosslinks, and thus, clean step-growth processes are a basic requirement for a successfid synthesis. In this connection the potential of silicon mediated polycondensations should be explored, because polycondensations of silylated monomers may be a cleaner process than that of the corresponding nonsilylated (protonated) monomers, for instance, because proton catalyzed side reactions, such as the Fries-rear-rangement, are avoided. 

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