Synthesis of Structurally Controlled, Highly Branched Polymethacrylates) by Radical Polymerization Through the Design of a Monomer Having Hierarchical Reactivity
The controlled synthesis of highly branched (HB) poly(methyl methacrylate) (PMMA) with a molecular weight of up to 88 × 10<sup>3 </sup>gmol and low dispersity (<i>Ð</i> < 2.0) was achieved by the radical copolymerization of vinyltelluride, H<sub>2</sub>C=CHTePh (<b>4cD</b>), and MMA in the presence of the organotellurium chain transfer agent <b>6cI</b> at 30 °C. Control of the branching structure was suggested by the Mark-Hauwink-Khun-Sakurada plots corresponding to samples in solution and trapped ion mobility spectroscopy-time of flight mass spectrometry in the gas phase. The mechanism of <b>4cD</b> for the structural control of HB-PMMA synthesis comes from the hierarchical reactivity of the C-Te bond of <b>4cD</b>, which serves as the branching point only after <b>4cD</b> reacts and is incorporated into the polymer chain. In contrast, copolymerization using previously reported vinyltellurides <b>4aA</b> (H<sub>2</sub>C=C(Me)TeMe) and <b>4aB</b> (H<sub>2</sub>C=C(Me)-CH=CHTeMe) could not control the branching structure due to the <i>b</i>-carbon fragmentation reaction from the intermediate radicals generated from <b>4aA</b> and <b>4bB</b>. The theoretical calculations suggest that the suppression of the undesired fragmentation reaction when using <b>4cD</b> is due to the acceleration of the desired propagation reaction forming a branched structure instead of decelerating the fragmentation reaction. Due to the versatility of radical polymerization, methacrylates with bulky substituents, such as <i>t</i>-butyl methacrylate, and polar functional groups, such as <i>N,N</i>-dimethylethyl methacrylate (DMAEM), were also used as monomers to afford structurally controlled corresponding HB polymers. These studies clearly open a new possibility for the use of HB polymers in macromolecular engineering.