Single-Electron Transfer Living Radical Polymerization (SET−LRP) of Methyl Methacrylate (MMA) with a Typical RAFT Agent as an Initiator

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• 作者：Zhengbiao Zhang ; Wenxiang Wang ; Hongda Xia ; Jian Zhu ; Wei Zhang ; Xiulin Zhu
• 刊名：Macromolecules
• 出版年：2009
• 出版时间：October 13, 2009
• 年：2009
• 卷：42
• 期：19
• 页码：7360-7366
• 全文大小：879K
• 年卷期：v.42,no.19(October 13, 2009)
• ISSN：1520-5835

文摘

A typical reversible addition−fragmentation chain transfer (RAFT) agent, 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN), was used as a single electron transfer-living radical polymerization (SET−LRP) initiator for methyl methacrylate (MMA) polymerization at 25 °C. At 1:1 molar ratio of [CPDN]₀/[Cu(0)]₀, the apparent rate constants of propagation (k_p^app) were 0.037, 0.049, and 0.072 h⁻¹ for [MMA]₀/[CPDN]₀ of 225/0.2, 225/0.5, and 225/1, respectively. The number-average molecular weight of poly(methyl methacrylate) (PMMA) increased linearly with monomer conversion, and narrow molecular weight distributions (M_w/M_n < 1.50) were found at most cases. At high molar ratio of [CPDN]₀ to [Cu(0)]₀, such as 1:0.1 in this work, the polymerization was also controllable, whereas it a presented markedly depressed polymerization rate and an obvious induction period. ¹H NMR spectroscope and matrix assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that PMMA chain was end-capped by CPDN species with high fidelity. The tacticity of PMMA from ¹H NMR calculation was about 3.15% isotactic (mm), 29.65% atactic (mr) and 67.20% syndiotactic (rr) triads, consistent with the tacticity distribution for traditional radical polymerizations. Chain extension reactions substantiated further that the obtained PMMA from CPDN mediated SET−LRP was living, and can be reactivated for chain extension reaction. This work demonstrates that a typical RAFT agent can act as a SET−LRP initiator as well as an atom transfer radical polymerization initiator. Furthermore, these results also suggested that the single electron transfer initiation-reversible addition−fragmentation chain transfer control (SET−RAFT) invented by Dhamodharan may not be RAFT at all, but rather SET−LRP initiated by a RAFT reagent, or a combination of SET−LRP and RAFT. Analogously, the exact polymerization process in this work may also proceed in two manners, a fully SET−LRP process and a combination of SET−LRP/RAFT process, which is needed to clarify in the future.