Star-shaped structures

relatively low power conversion efficiencies (5.16, 0.32 % 5.17, 0.14 %) were reported, whereas a fairly high hole mobility (1.1 x 10 cm V s ) was observed in OFET measurements. 

Miller el al. prepared tris[4-(2-thienyl)phenyl] amine 5.18a by Pd°-catalyzed coupling of 2-thienylmagnesium bromide with tris(4-bromophenyl)amine in 79% yield (Chart 1.65) [467]. Yamamoto et al. [468] synthesized an analogous bithiophene derivative 5.18b by bromination of 

Electropolymerization of star-shaped oligomers 5.18a-c resulted in the formation of highly redox active, cross-linked hyperbranched polymers which led to systems with good conductivities, indicating the presence of multiple pathways for charge carriers provided by the branching units [472], 

Reagent and condition (i) Thiophene-2-boronic acid, Pd(PPh3)4, THF, NaHC03/H20. (ii) NBS, CHCI3. 

Oxidative polymerization of 5.25 (n = 1) by FeCls in chloroform afforded hyperbranched polymer 5.26 (Chart 1.67), which is highly soluble in organic solvents. The polymer absorption (352 nm) and emission (491 nm) are bathochromically shifted with respect to monomer 5.25 due to further extension of conjugation in the polymer. 

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The assumption of the association of Hb in the pores of carboxylic cation exchangers has been advanced in Ref. [47] on the basis of electron microscopy at the maximum filling, almost all the pore surface is filled with Hb associates which are ordered star-shaped structures. Interprotein interaction in the adsorption immobilization of enzymes have been reported in Refs. [74, 75]. 

This technique is based on the use of well-defined soluble multifunctional initiators, which, in contrast to anionic multifunctional initiators, are readily available. From these multiple initiating sites a predetermined number of arms can grow simultaneously when the initiating functions are highly efficient independently of whether the other functions have reacted or not. Under these conditions the number of arms equals the number of initiating functions and living polymerization leads to well defined star polymers with controlled MW and narrow MWD. Subsequent end-functionalization and/or sequential monomer addition can also be performed leading to a variety of end-functionalized An or (AB)n star-shaped structures. 

Cyclic derivatives of type III include cyclic Mannich bases, such as dihydroben-zoxazines 497, employed as detergents for lubricating oils, - and cyclic urcides 498, precursors of crosslinking agents for fabrics, as well as other cyclic derivatives prepared by conversion of Mannich bases. Macromolecular derivatives of type IV are relatively small in size and have branched (star-shaped) structures they are of considerable importance as, for example, corrosion inhibitors 499, plastics stabilizers 500, - pre-polymers for epoxy-based electrophoretic paints, and polyols in polyurethane synthesis. ... 

Star-shaped structures may also be obtained using hydroxylated fuUerenes, the so-caUed fuUerenoles, and, for example, isocyanate-terminated polymers. These are Unked by a condensation that yields urethane units (Figure 2.68b). The resulting material is highly viscous and soluble in common organic solvents. 

In the first case, the arms are grown from a single core with a given number of potentially active sites or a well-defined multifunctional initiator. In contrast to anionic multifunctional initiators, weU-defined soluble multifunctional cationic initiators are readily available. These multifunctional initiators with 3-8 initiating sites have been successfully applied for the synthesis of 3-8 arm star homo- and block copolymers of vinyl ethers, styrene and styrene derivatives, and IB. For example, six-arm star polystyrenes were prepared using initiator with six phenylethylchloride-type functions emanating from a central hexa-substituted benzene ring [250]. By subsequent end functionalization, a variety of end-functionaUzed A or (AB) (see above) star-shaped structures can also be obtained. 

Into a special category should be placed starburst dendrimer polymers. These molecules are formed by growing them in three dimensions. These materials often possess radially symmetrical star-shaped structures with successive cascades of branched polymer structures. For additional discussions see Chap. 6. 

Starblock Polymers, While many star-shaped structures can be formed, the usual structure referred to may be designated... 

If, on the other hand, we start with a circular puddle and pull on four equidistant points, the outcome is a star-shaped structure (see Figure 3.10b) with four circular arcs, the curvature of which is inverted. In this case, the internal pressure p2 is negative. 

In this paper the synthesis and characterization of a number of novel low molecular weight oxadiazole derivatives and polymers is described. The compounds show different molecular shapes, e.g. rod-like and star-shaped structures have been realized. 

The discovery of the living character of the anionic polymerization by M. Szwarc [93] has contributed tremendously to the domain of macromolecular engineering and especially to the synthesis of star-shaped polymers. Not only can the molar mass and the molar mass distribution of the branches be controlled in advance, but anionic polymerization has also demonstrated its efficiency in controlling the functionality of the star-shaped polymers. Earlier attempts to apply anionic polymerization to build star-shaped structures were focused essentially on arm-first methods. Well-defined star-shaped polymers exhibiting homopolymeric branches could thus be obtained. These samples have been studied to confirm expected structures or have served as models. Two decisive improvements have been made in the domain of application of anionic polymerization to the synthesis of well-defined star-shaped polymers ... 

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