Arming core assembly

In the arm-first approach the arms are prepared and then self-assembled to form the core. There are two main variants that will be considered. 

Fig. 12 Neat melamine Hekates 40, their 1 1 host-guest complexes 41,42 and the 1 3 aggregates of a melamine core with three arms 43 and 44. The disk-shaped aggregates 41 stack in a Colrd phase [99]. The Janus-type Hekate 42 arrange in a Colh phase with hexagonal superstructure of the nanosegregated semi-perfluorinated chains [105]. The supramolecular Hekate discs 43-45 self-assemble by hydrogen bonding of the three arms around a melamine core...

Less usual carbosilane dendrimers were synthesised by reaction of acetyl-protected hydroxyethyl glycosides with chlorosilanes. Introduction of the carbohydrate component proceeds via alcoholysis of the chlorosilane with formation of silicon-oxygen bonds a carbosilane core unit is formed with carbosiloxane side arms [82]. Reverse assembly of carbosilanes with a carbohydrate core is also feasible [54]. 

The word dendrimer is derived from the Greek words for tree- or branchlike (dendron) and part (meros). The strictly controlled structure of ideal dendrimers results from the layered assembly of BC surrounding the core, which is attained through sequential reaction cycles. This can be achieved in two different ways, namely, by divergent (core-first) or convergent (arm-first/core-last) methods. 

Yi and coworkers have also studied a similar hydrogen bonded complex 52, formed by V-shaped acid containing nitril azobenzene groups in each of the arms around l,3,5-triazine-2,4-diamine core [71]. Such complex forms a hquid crystalline phase and reveals response to both stimuli of hght irradiation and electric field. The induced molecular orientation can be held after the removal of the stimuli. This kind of self-assembled complex may have potential applications in imaging and data storage. 

Fig. 4 Proposed inhomogeneous core-corona structure of the macromolecular co-assemblies formed in aqueous mixtures of (PAA)2i stars (in the form of sodium salt) and P2VPQ. In structure /, some of the arms of the star-shaped HPE are embedded in the core and others are extended. In structure II, all of the arms contribute segments of equal length to the core. Reprinted from [80] with permission from Springer...

An interesting example of macromolecular co-assemblies derived from starshaped polyionic species was reported by Ge et al. [81]. The authors found that a star-shaped double hydrophilic poly(methacrylic acid)-poly(ethylene oxide) heteroarm copolymer [(PMAA)x-PDVB-(PEO)x, with PDVB being poly(divinylbenzene) and X denoting the number of PMAA and PEG arms] can interact in alkaline media with a double hydrophilic poly(ethylene oxide)-block-quaternized poly[2-(dimethylamino)ethyl methacrylate] (PEO- -PDMAEMAQ) diblock copolymer. At Z = [PDMAEMAQ]/[PMAA] = 1, well-defined water-soluble onion-like (core-shell-corona) macromolecular co-assemblies are formed, with a hydrophobic core consisting of a PDVB microgel. The interaction of the PMA arms of the hybrid coronas of such copolymer stars with the PDMAEMAQ+ blocks of the diblock copolymer generates an insoluble inner layer (shell) around a PDVB core. Meanwhile, PEG blocks from both PEG- -PDMAEMAQ and (PMAA)x-PDVB-(PEG)x build up a hydrophilic nonionic corona that stabilizes the whole complex in aqueous media. 

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