Macromonomers with hyperbranched structure

The self-condensing copper-catalyzed polymerization of macromonomer of poly(tBA) with a reactive C—Br bond (H-6) affords hyperbranched or highly branched poly(tBA).447 Copolymerization of H-1 and TV-cyclohexylmaleimide induced alternating and self-condensing vinyl polymerization.448 The residual C—Cl bond was further employed for the copper-catalyzed radical homopolymerization of styrene to give star polymers with hyperbranched structures. Hyperbranched polymers of H-1 further serve as a complex multifunctionalized macroinitiator for the copper-catalyzed polymerization of a functional monomer with polar chromophores to yield possible second-order nonlinear optical materials.325... 

Dendritic macromolecules are hyperbranched fractal-like structures that emanate from a central core and contain a large number of terminal groups. Two synthetic approaches have been reported for the preparation of these macromolecules the divergent [76-78] and convergent growth approaches [79-82]. In both methods many synthetic steps are necessary to produce high molecular weight materials. To avoid synthetic problems, the macromonomer with hyperbranched dendritic moiety may be one of the most useftil materials for the dendritic macromolecules. 

In a previous work, Cheng et al. [322] performed the same synthesis but without any ligand excess. The resulting macromonomer was similar to that described in Scheme 69 but with a chain-end bromine atom. This macromonomer was polymerized by the ATRP process, leading to a hyper-grafted polymer. The Mark-Houwink coefficient was 0.47, which characterized the hyperbranched structure. Hydrolysis of such a polymer led to the corresponding poly(acrylic acid). Similarly, Hua et al. [323] performed the synthesis of brushlike poly(acrylic acid). 

Another kind of hyperbranched macromonomer containing an oligomeric segment in the monomer unit has been reported. Thus, 3,5-dihydroxy-(oligo)ethyleneoxy ethyl benzoate was condensed in the molten state to give a hyperbranched structures with varying lengths of functional spacer. The polymer complexed with alkali metals picrate [43]. 

Successfully prepared Seesaw-type diblock macromonomer (Na-PS- -PCL-N3) and model hyperbranched hetero-subchain copolymer [HB-(PS-f>-PCL)n] with controllable and uniform PS and PCL subchains, and found that such prepared hyperbranched copolymer chains still have a fractal-like structure, and the PCL subchains inside HB-(PS-f>-PCL)n crystallize less as the branching degree increases and the PS subchain becomes longer. This work demonstrates that we can use the chain topology to control the crystallization of PCL subchains inside hyperbranched copolymers to regulate their biodegradation for biomedical applications. 

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