Synthesis of structurally controlled hyperbranched polymers using a monomer having hierarchical reactivity

Hyperbranched polymers (HBPs) have attracted significant attention because of their characteristic topological structure associated with their unique physical properties compared with those of the corresponding linear polymers. Dendrimers are the most structurally controlled HBPs, but the necessity of a stepwise synthesis significantly limits their applications in materials science. Several methods have been developed to synthesize HBPs by a one-step procedure, as exemplified by the use of AB2 monomers and AB′ inimers under condensation and self-condensing vinyl polymerization conditions. However, none of these methods provides structurally controlled HBPs over the three-dimensional (3D) structure, i.e., molecular weight, dispersity, number of branching points, branching density, and chain-end functionalities, except under special conditions. Here, we introduce a monomer design concept involving two functional groups with hierarchical reactivity and demonstrate the controlled synthesis of dendritic HBPs over the 3D structure by the copolymerization of the designed monomer and acrylates under living radical polymerization conditions.

Magnesium (0.27 g, 11 mmol), an aliquot of I2, and anhydrous THF (5 ml) were charged into a threeneck-flask equipped with a dripping funnel. 2-Bromo-propane (0.9 ml, 10 mmol) and anhydrous THF (20 ml) was charged to the funnel and were added dropwisely into the flask after color of I2 was faded. The mixture was stirred at room temperature for 2 hours and the resulting Grignard reagent solution was cooled to -78 °C. To a separated two-neck flask containing dimethyl ditelluride (1.43 g, 5.0 mmol) and anhydrous THF (20 ml), bromine (0.26 ml, 5.0 mmol) was added at 0 °C. After 30 mins of stirring at 0 °C, the dark red liquid formed was added dropwisely into the Grignard reagent solution by a cannula at -78 °C. After stirring at this temperature for 30 mins, the mixture was pour into ice water (300 ml) with vigorous stirring. The aqueous phase was extracted with pentane (30 ml) for 5 times. The combined organic phase was washed with water (20 ml) for 10 times to remove THF. The organic residue was dried over MgSO4 and filtered through a short plug of silica gel, and the solvent was removed by distillation at To a suspension of Te powder (6.37 g, 50 mmol) in anhydrous THF (20 ml) was added MeLi (1.19 mol L -1 in diethyl ether, 43.0 ml, 51 mmol) dropwisely through a dripping funnel at 0 °C. After string at room temperature for 30 mins, the solvent was partially removed in vacuum to leave ca. 7.5 ml of solution.
Me3SiCl (7.6 ml, 60 mmol) was added, and the reaction mixture was string at room temperature for 1 hour. The product and THF were collected in a liquid N2 trap by vacuum transfer (6.5 mmHg) at room temperature to obtain a THF solution of Me3SiTeMe (9.0 ml, 1.18 mol L -1 , Yield 21%). The solution was used directly for the reduction without further purification.  Conversion of 6a (95%) and MA (74%) was determined from 1 H NMR spectroscopy of crude mixture.
The crude mixture was dissolved in anhydrous THF (5 ml), and CH3OH (0.8 ml, 20 mmol) and Me3-SiTeMe from 1 H NMR spectroscopy. Mn(SEC) (1.89 × 10 4 g/mol) and PDI (1.73) were determined by SEC using NMR sample. The crude mixture was dissolved with anhydrous THF (5 ml) and separated into two fractions. One of the fraction was added CH3OD (100 µl, 2.5 mmol) and Me3SiTeMe (1.18 mol L -1 in THF, 100 µl, 0.12 mmol), and the resulting solution was stirred for 1 hour at room temperature. The polymer solution was precipitated in 100 ml hexane for twice. The resulting milky solution was centrifuged to obtain 0.23 g of colorless polymer. This sample was subjected to 2 H and 13 C NMR analyses.
The other fraction was added CH3OH (100 µl, 2.5 mmol) and Me3SiTeMe (1.18 mol L -1 in THF, 100 µl, 0.12 mmol), and the resulting solution was stirred for 1 hour at room temperature. The polymer solution was precipitated in 100 ml hexane for twice. The resulting milky solution was centrifuged to obtain 0.21 g of colorless polymer. This sample was subjected to 13 C NMR analysis.

Results of SEC and NMR analyses
Supplementary Figure 15. Correlation between elution time and weight average molecular weight of 10a (Table 1,