Polymers with controlled molecular architecture: Control of surface functionality in the synthesis of dendritic hyperbranched macromolecules using the convergent approach

The synthesis of unsymmetrically or non-uniformly surface-functionalized dendritic macromolecules using a stepwise convergent-growth approach is described. By stepwise alkylation of the monomer unit, 3,5-dihydroxybenzyl alcohol, with unsubstituted and substituted benzylic bromides, followed by activation of the group located at the focal point, dendritic 'wedges' can be obtained in which there is only a single substituent such as a cyano group at the periphery. Use of only substituted benzylic bromides in the first step of growth allows fully functionalized dendritic wedges to be obtained. Coupling to a polyfunctional core such as 1,1,1-tris-(4'-hydroxyphenyl)ethane can also be done in a stepwise manner with both mono or fully substituted and unsubstituted 'wedges' to give dendritic macromolecules containing one, two, or three cyano groups or sixteen or thirty-two bromine atoms at the periphery of the macromolecule. These hyperbranched dendritic polymers were purified by normal flash chromatography and fully characterized by a combination of spectroscopic and chromatographic techniques. By using variations of this general scheme both the number and placement of the functional groups at the periphery of the dendritic macromolecule can be accurately controlled to afford a large variety of functionalized hyperbranched moieties.