Abstract
The polymerization of methacrylates with lithium N-benzyltrimethylsilylamide (BnTMSNLi) in the presence of aluminum compounds afforded syndiotactic or heterotactic polymethacrylates with narrow MWD quantitatively. The end-group analysis of these polymers revealed that benzylamino end-group was quantitatively introduced at the initiating chain-ends of the polymers. The initiator efficiency of the polymerization was slightly lower than unity (0.8–0.9), suggesting possible side reactions in the initiation process. The crude reaction mixture from methyl methacrylate (MMA) polymerization with BnTMSNLi was found to contain a small amount of N-benzylmethacrylamide, which should be formed through the 1,2-addition (carbonyl addition) of BnTMSNLi to MMA in the initiation step of the polymerization. The in situ formed silyl-substituted methacrylamide was not involved in the further polymerization process, as MALDI-TOF mass analysis of the formed polymer indicated the absence of the respective unit in the polymer chain. The methacrylamide remained intact was transformed to N-benzylmethacrylamide when the polymerization was terminated with acidified methanol. Therefore, 1,4-/1,2-addition selectivity in the initiation step could be estimated by NMR spectroscopic quantification of the benzylamino end-group in the polymer and N-benzylmethacrylamide in the polymerization mixture. A lithium amide with bulky triisopropylsilyl substituent, BnTIPSNLi, completely suppressed the 1,2-addition and thus the methacrylamide formation, while 15% of BnTMSNLi and 2% of BnTBSNLi, tert-butyldimethylsilyl derivative, underwent the 1,2-addition.
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Kitaura, T., Kitayama, T. Anionic Polymerization of (Meth)acrylates with Trialkylsilyl-protected Lithium N-Benzylamide. Polym J 40, 37–45 (2008). https://doi.org/10.1295/polymj.PJ2007029
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DOI: https://doi.org/10.1295/polymj.PJ2007029