Dendritic architectural copolymers

Percec and coworkers [184] utilized a similar strategy for the conversion of perfluorinated alkylene functionalized 3,4,5-trihydroxy benzoic acid-type dendrons into methyl methacrylate functionalized dendritic macromonomers. Characterization of the resulting linear-dendritic architectural copolymers involved DSC, x-ray diffraction, and thermal optical polarized microscopy. It was concluded that the self-assembly of the pendant dendritic mesogens forced the linear backbone into a tilted, helical ribbon-type structure. The self-assembly behavior was largely controlled by the multiplicity, composition, and molecular weights of the pendant dendritic mesogens. 

Hybridization of Architectural States Dendritic-linear Copolymer Hybrids... 

In order to explore the properties that may be obtained by hybridizing the linear and dendritic architectural states, both diblock and triblock copolymer... 

Controlling the size, shape and ordering of synthetic organic materials at the macromolecular and supramolecular levels is an important objective in chemistry. Such control may be used to improve specific advanced material properties. Initial efforts to control dendrimer shapes involved the use of appropriately shaped core templates upon which to amplify dendritic shells to produce either dendrimer spheroids or cylinders (rods). The first examples of covalent dendrimer rods were reported by Tomalia et al. [43] and Schluter et al. [44], These examples involved the reiterative growth of dendritic shells around a preformed linear polymeric backbone or the polymerization of a dendronized monomer to produce cylinders possessing substantial aspect ratios (i.e. 15-100) as observed by TEM and AFM. These architectural copolymers consisting of linear random... 

For polymer chemists it is interesting to know how well-known linear polymers can be linked with dendritic architectures and what the supramolecular consequences of this approach might be. Combination of dendrimers with linear polymers in hybrid linear-dendritic block copolymers has been employed to achieve particular self-assembly effects. Block copolymers with a linear polyethylene oxide block and dendritic polybenzylether block form large micellar structures in solution that depend on the size (i.e., the generation) of the dendritic block [10]. Amphiphilic block copolymers have been prepared by the combination of a linear, apolar polystyrene chain with a polar, hydrophilic poly(propylene imine) dendrimer [11] as well as PEO with Boc-substituted poly-a, -L-lysine dendrimers, respectively [12]. Such block copolymers form large spherical and cylindrical micelles in solution and have been described as superamphi-philes and hydra-amphiphiles , respectively. 

Anionic polymerization of functionalized cyclotrisiloxanes is a good method for the synthesis of well-defined functionalized polysiloxane with control of molecular mass, polydispersion, and density and arrangement of functional groups. These polymers may serve as reactive blocks for the building of macromolecular architectures, such as all-siloxane and organic-siloxane block and graft copolymers, star-, comb- and dendritic-branched copolymers and various polysiloxane-inorganic solid hybrids. 

Dendritic layer copolymers have also been prepared via the hypercore approach,87 and by divergent growth from the periphery of convergently prepared dendrimers,446 or dendronized polymers.398 This layered dendritic architecture has been used by a number of groups to probe the nature of chirality. 

Figure 6. Schematic representation of three different architectures that can be considered dendritic block copolymers.

Gitsov. L Lambrych. K.R. Remnant. V.A. Pracitto. R. Micelles with highly branched nanoporous interior Solution properties and binding capabilities of amphiphilic copolymers with linear dendritic architecture. J. Polym. Sci., A, Polym. Chem. 2000. 38, 2711-2727. 

In the example above, the key role of the dendritic architecture is to act as a multivalent crossUnking imit in the formation of the gel-phase materials. Gitsov and Zhu have also utiUsed a similar approach to the appHcation of dendritic architectures. They reacted Fr chet-type dendritic benzyl bromides and polyethylene glycol to generate hybrid covdently crosshnked dendritic-linear copolymers, which acted as hydrogels [49]. 

Figure 20 A rotaxane with dendritic stoppers. An example of a dendritic-linear-cyclic architectural copolymer. (Courtesy Chem. Rev. 97 1701, 1997. Copyright 1997 American Chemical Society.)...

Cylindrical, rod-shaped dendrimer assemblies were first synthesized by TomaUa et al. as early as 1987 [35,37,177]. These structures represent some of the first examples of hybridized dendritic architecture. Since they possess a linear polymeric core and dendritic arms, they are called architectural copolymers or dendronized, linear polymers. This work was recently reported in detail [160]. The method involved the divergent dendronization of //near poly(ethyleneimine) (PEI) cores... 

Gitsov, I. (2000) Hybrid dendritic capsules properties and binding capabilities of amphiphilic copolymers with dendritic architecture. In J.E. Glass (ed.), Associative Polymers in Aqueous Media, ACS Symposium Series 765. American Chemical Society, Washington, DC, pp. 72-92. Kurjata, J., Chojnowski, J., Yeoh, C.T., Rossi, N.A.A. and Holder, S.J. (2004) Synthesis of poly[dimethylsiloxane-block-oligo(ethylene glycol) methyl ether methacrylate] an amphiphilic copolymer with comb-like block. Polymer, 45,6111-6121. 

Polyphosphazenes form amphiphilic block copolymers with organic polymers, such as poly (ethylene oxide), polystyrene, or poly(dimethylsiloxane). Comb, star, and dendritic architectures were also obtained. There are also... 

Motivated by the preparation of wdl-defined hyperbranched polyglyddols, a variety of polyglyddol-based complex polymer architectures were synthesized. These include linear-dendritic block copolymers,random copolymers, and multiarm star copolymers. ... 

Later on, such ambient temperature synthesis approach was extended to a variety of organo-substituted phosphoranimines, to directly synthesize polyphosphazenes with controlled molecular weight and low polydispersities, so that PDCP preparation and following chlorine substitution steps were eliminated [26]. Such living cationic condensation polymerization method also allows the preparation of polyphosphazenes with complex structures such as comb, star, and dendritic architectures, as well as block and graft copolymers with organic macromolecules [18]. 

Among the many unusual properties that the arborescent architecture leads to, most notable is the discovery that block copolymers with a high MW dendritic (arborescent) polyisobutylene core and poly(para-methylstyrene) end blocks can manifest themselves either as a rubber, or as a plastic, depending on their environment (Figures 7.16 and 7.17). The behavior is thermally irreversible. 

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