Janus type architectures

It is noteworthy that polymers of practical interest that exhibit a globular shape and unsymmetrical faces of the Janus-type architecture, not easy to make by conventional methods [89, 90], can be prepared by sequential ring-opening metathesis copolymerization of two different norbomenyl macromonomers. To this end, sequential polymerization of co-norbomyl polystyrene and a-norbornyl-poly(ethylene oxide) macromonomers in the presence of the Schrock initiator Mo(NAr)(ChrBu)(OC(CH3)(CF3)2)2 produced poly[polystyrene xycarbonyl-norbornene)-b-poly(ethylene oxide) xymethylene-norbomene)] block copolymer (122) in high yield [88] [Eq. (54)]. 

The synthesis of polyelectrolytes with well-defined architectures, however, has imposed many challenges to the polymer chemists. Many polymerization techniques are not tolerable to the ionic functional groups. In most cases, preparation of polyelectrolytes involves the protection and deprotection of the ionic groups in the monomer. For polyelectrolytes with different architectures, various synthetic strategies are required. Recently, we have synthesized various complex architectures containing polyelectrolytes with different nonlinear topologies, such as combshaped [22], hyperbranched [23-25], Janus-type [26], stars [27, 28] and brushes [29-31],... 

Percec et al. [41,42] studied and reviewed various complex self-assembled structures in detail that can be obtained from dendritic molecules. Especially multicompartment capsules obtained by the self-assembly of a library of amphiphilic Janus-type dendrimers are impressive. The chemical linkage of two dissimilar dendritic building blocks results in Janus dendrimers and produces a break in the spherical symmetry characteristic to dendrimers. Consequently, these stmctures spontaneously promote the self-assembly upon injection of its ethanol solution to form stable unilamellar vesicular nanostructures and other complex architectures (Eig. 6.17). Dendriniersom.es... 

Several prominent examples of polynuclear poly-NHC metal complexes with original architectures were produced by the group of Hahn. To name but a few, in 2011, the group reported on the preparation of highly unusual di-NHC-based molecular squares (structure 58, Fig. 12) tetra-nuclear Ir(III) complexes with bridging Janus-type dicarbene Hgands were obtained from a tetranuclear complex precursor upon cycHzation of coordinated diisocyanides. More recently, the same group presented... 

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