Calixarene derivative initiator

Recently, Kennedy and co-workers [37] have reported the synthesis of well-defined star polymers having well-defined arms of PIB emanating fi-om a calix-arene derivative initiator. Calixarene derivative initiators in conjunction with... 

He also prepared a poly(styrene-g-styrene) polymer by this technique [114], The lack of crosslinking in these systems is indeed proof of the control achieved with this technique. An eight-arm star polystyrene has also been prepared starting from a calixarene derivative under ATRP conditions [115]. On the other hand, Sawamoto and his coworkers used multifunctional chloroacetate initiator sites and mediation with Ru2+ complexes for the living free-radical polymerization of star poly(methylmethacrylate) [116,117]. More recent work by Hedrick et al. [84] has demonstrated major progress in the use of dendritic initiators [98] in combination with ATRP and other methodologies to produce a variety of structure controlled, starlike poly(methylmethacrylate). 

Initially it was believed that this anomalous behaviour was linked to the rotation of a tetraethylammonium guest within the capsule which has been observed. This proved not to be the case, as was confirmed by the use of lower symmetry calixarene derivatives to reduce the ambiguity of the NMR spectra. Molecular dynamics calculations were employed to show that the size of the tetraethylammonium guest means that the capsule has to be significantly expanded in order for it to fit within the cavity. The result of this expansion is that the ureas are only... 

Our first simulations involving interfaces concerned ionophores L, free or complexed by cations As these molecules are not soluble in water, but are soluble in organic liquids or membranes, it was anticipated that, when placed initially on the border between the two liquids, they would diffuse to chloroform. This turned out not to be the case. Whatever the nature or conformation of L, it adsorbed on the chloroform side of the interface, anchored via the polar moities solvated by a few water molecules ("water fingers" ). Some of the ligands studied (calixarene derivatives podants CMPO s alkyl phosphates. .) are... 

The synthesis of eight arm star PIB was recently described by Jacob et al. [37], where eight PIB arms emanate from a calixarene core (multifunctional initiators 20 (tert-hydroxy derivative) and 21 (terf-methoxy derivative)). The synthetic strategy is shown in Scheme 3. 

Around the same time as this, Reinhoudt developed a calix[4]arene system with only two urea or thiourea functionalities attached on opposite faces 70-72 [167]. These less substituted systems display both inter- and intramolecular hydrogen bonding as a result of the calixarene adopting a pinched cone conformation (demonstrated by the use of NOESY NMR). In some spectra it is impossible for the connectivities to be made within a single molecule, so the only possibility left is that dimerisation occurs. As with the initial experiments of Rebek and Bohmer, the extent of hydrogen bonding was observed to be solvent dependent. Concentration dependant FTIR was also used, to observe the effects on the NH stretching vibrations, but no concentration dependence was observed. Of the three urea derivatives used, only 72 showed no evidence of dimerisation... 

Calixarenes are [1 Jmetacyclophanes (1) that acquired their name because of the resemblance of the shape of one of the conformers of the smallest member of their family to a type of Greek vase called a calix crater (Figure 1.1). The name was initially chosen to apply specifically to the phenol-derived cyclic oligomers, but it has subsequently taken on a more generic aspect and is now applied to a wide variety of structurally related types of compounds. The calixarenes were first discussed in comprehensive fashion in 1989 in the first volume of Monographs in Supramolecular Chemistry, where the literature on the subject that had been published up to that time was covered in reasonably complete detail in 222 pages. Since 1989, however, there has been such a rapid expansion of the field that a somewhat less comprehensive coverage of topics is now necessary if this... 

Even if the parent p-fert-butyl derivatives of calixarenes and their de-alkylated analogues can be considered as amphiphiles, chemical modifications of the macrocycle allows enhancing the amphiphilic properties of the resulting derivatives. The synthetic routes to amphiphilic calixarenes are often initiated by the introduction of the UpophiUc moieties of the molecule that are typically saturated hydrocarbon chains (Fig. 37.2). This is explained by the low chemical reactivity of these lipophilic moieties, which do not hinder the further chemical modification of the macrocycle to introduce the polar functions. 

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