Macromonomers dendritic

The supramolecular transformation from sphere to cylinder is supported by X-ray data indicating that the spherical polymers adopt a cubic phase, whereas the cylindrical polymers adopt a hexagonal phase [23b]. Further studies involving a library of dendritic macromonomers led to the conclusion that the effect of DP on polymer shape is a general phenomenon [24], More recently, scanning... 

It is also possible to introduce polymerizable groups at the focal point of dendritic macromolecules and a number of authors have demonstrated the synthesis of novel hybrid dendritic-linear block copolymers by this methodology [69-73]. Initial experiments in the use of the dendritic macromonomers involved the preparation of a series of polyether dendrimers, such as the third generation derivative, 37, which contains a single styrene at its focal point [74]. Copolymerization of 37 with styrene then affords a hybrid block copolymer, 38, in which... 

In conclusion it has turned out to be difficult to polymerize all but the first generation dendritic macromonomer. Higher generation dendrimers need to be attached through a long series of bonds to the polymer backbone. This in turn prevents any strong conformational influence on the backbone and no interesting new properties have been detected so far. 

The second approach involved the covalent attachment of Fr6chet-type monodendrons (i.e., G = 1-3) to appropriate polymerizable reagents such as styrenes [178,181] or methacrylates [ 179] (Figure 27). Suitable radical catalysts were used to polymerize these dendritic macromonomers into structures that were observed to be cylindrical, rod-like architectures [179,181,182]. The area of dendronized, linear polymers has been extensively reviewed by Schluter et al. [183]. 

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. 

Using a variation of this dendritic macromonomer method, Percec et al. [185,186] synthesized a variety of dendritic 7-oxanorbornene macromonomers and polymerized them with ROMP catalysts [186] as shown in Figure 28, as well as with free radical or anionic catalysts. 

Figure 31 Scheme describing conversion of dendritic macromonomers to either spheroidal or cylindrical architectures depending on the degree of polymerization (DP). (Courtesy of J. Am. Chem. Soc. 1997, 199, 12978. Copyright 1997 American Chemical Society.)... 

Hawker and Frechet [50] prepared a dendritic macromonomer using the convergent-growth route to prepare a polyether dendron. The dendron core functional group (R in Scheme 9) was a hydroxymethyl group that was reacted with chloromethylstyrene to form the styrene-functionalized dendritic macromonomer. This macromonomer was copolymerized with slyrene monomer using standard free-radical polymerization conditions. 

Xi and co-workers [52] prepared methacrylate-functionalized dendritic macromonomers by conversion of the hydroxymethyl group of the polyether dendron to the corresponding bromide and then functionalization with methacrylic acid. Free-radical polymerization of the macromonomer corresponding to a second-generation dendron resulted in formation of a relatively low molecular weight product (X = 6-7). 

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