Synthesis of Well-Defined Poly(acrylates) in Ionic Liquids via Copper(II)-Mediated Photoinduced Living Radical Polymerization

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• 作者：Athina Anastasaki ; Vasiliki Nikolaou ; Gabit Nurumbetov ; Nghia P. Truong ; George S. Pappas ; Nikolaos G. Engelis ; John F. Quinn ; Michael R. Whittaker ; Thomas P. Davis ; David M. Haddleton
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：August 11, 2015
• 年：2015
• 卷：48
• 期：15
• 页码：5140-5147
• 全文大小：387K
• ISSN：1520-5835

文摘

Herein we report the photoinduced living radical polymerization of acrylates in a variety of ionic liquids (ILs). 1-Ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO₄], 1-heptyl-3-methylimidazolium bromide [C₇mim][Br], 1-hexyl-3-methylimidazolium tetrafluoroborate [C₆mim][BF₄], 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆mim][PF₆], and 1-octyl-3-methylimidazolium hexafluorophosphate [C₈mim][PF₆] were employed as solvents for the homopolymerization of a variety of acrylates including methyl acrylate (MA), n-butyl acrylate (n-BA), ethylene glycol methyl ether acrylate (EGA), and poly(ethylene glycol) methyl ether acrylate (PEGA, M_n 鈮?480). Polymerization of MA, EGA, and PEGA in [C₆mim][BF₄], [C₆mim][PF₆], and [C₈mim][PF₆] proceeded in a controlled manner, as evidenced by kinetic studies, narrow molecular weight distributions (膼 鈮?1.1), and quantitative conversions (>99%) within 30 min. MALDI-ToF-MS and ¹H NMR confirmed very high end-group fidelity, which was further exemplified by in situ chain extensions and block copolymerizations, yielding well-defined block copolymers in a quantitative manner. While polymerization of n-BA in [C₆mim][BF₄] and [C₆mim][PF₆] yielded polymers with bimodal molecular weight distribution (potentially due to poor solubility), polymerization of the same monomer in [C₈mim][PF₆] was well-controlled yielding materials with a monomodal polymer peak distribution and low dispersity. Interestingly, all polymerizations in ILs experienced a significant acceleration on the rate of polymerization without compromising the end-group fidelity, as opposed to the slower rates observed when DMSO was used as the solvent. The versatility of the approach was also demonstrated by polymerization of MA to a number of chain lengths (M_n 鈮?4500鈥?0鈥?00 g mol^鈥?) furnishing poly(acrylates) with low dispersities in all cases (膼 鈮?1.1). Importantly, extraction of the obtained polymer with toluene allowed the IL/catalyst solution to be reused as the solvent for further polymerizations without affecting the living nature of the polymerization. Moreover, the polymer extracted into the toluene (copper-free) can be used directly for post-polymerization modifications (e.g., click reactions).