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submitted on 08.02.2020 and posted on 10.02.2020by Shigeru Yamago, Yangtian Lu
The controlled synthesis of highly branched (HB) poly(methyl methacrylate) (PMMA) with a molecular weight of up to 88 × 103 gmol and low dispersity (Ð < 2.0) was achieved by the radical copolymerization of vinyltelluride, H2C=CHTePh (4cD), and MMA in the presence of the organotellurium chain transfer agent 6cI 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 4cD for the structural control of HB-PMMA synthesis comes from the hierarchical reactivity of the C-Te bond of 4cD, which serves as the branching point only after 4cD reacts and is incorporated into the polymer chain. In contrast, copolymerization using previously reported vinyltellurides 4aA (H2C=C(Me)TeMe) and 4aB (H2C=C(Me)-CH=CHTeMe) could not control the branching structure due to the b-carbon fragmentation reaction from the intermediate radicals generated from 4aA and 4bB. The theoretical calculations suggest that the suppression of the undesired fragmentation reaction when using 4cD 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 t-butyl methacrylate, and polar functional groups, such as N,N-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.