Application of novel ionic liquids for reverse atom transfer radical polymerization of methacrylonitrile without any add
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Reverse atom transfer radical polymerization of methacrylonitrile (MAN) initiated by azobisisobutyronitrile (AIBN) was approached for the first time in the absence of any ligand in four novel ionic liquids, 1-methylimidazolium acetate ([mim][AT]), 1-methylimidazolium butyrate ([mim][BT]), 1-methylimidazolium caproate ([mim] [CT]), and 1-methylimidazolium heptylate ([mim][HT]). The polymerization in [mim] [AT] not only showed the best control of molecular weight and its distribution but also provided a more rapid reaction rate with the ratio of [MAN]:[FeCl3]:[AIBN] at 300:2:1. The block copolymer PMAN-b-PSt was obtained via a conventional ATRP process in [mim][AT] by using the resulting PMAN as a macroinitiator. After simple purification, [mim][AT] and FeCl3 could be easily recycled and reused and had no effect on the living nature of reverse atom transfer radical polymerization of MAN.
I. INTRODUCTION
Atom transfer radical polymerization (ATRP) has become a powerful tool for synthesis of polymer materials with predictable molecular weight, narrow polydispersity, and well-defined architecture.1,2 ATRP involves an equilibrium reversible redox reaction between a transition metal complex, and the halogen containing initiator, or dormant species forming a radical and the metal halide in a higher oxidation state.3–10 To overcome the oxidation of the catalyst Mnt/LX in ATRP, the use of conventional radical initiators in the presence of complexes of transition metals in their higher oxidation state has been reported and referred to as reverse ATRP by Matyjaszewski11–13 and other researchers.14 Reverse ATRP has become an extensively studied system and has received increasing attention.15,16 To achieve a higher polymerization rate in ATRP and reverse ATRP processes, a large amount of catalyst and higher solubility of catalyst in reaction media are ordinarily needed. Removal of catalyst and ligand from the resultant polymer to avoid contamination becomes very necessary and important. Novel reaction media are being developed. Using ionic liquids as reaction media would make this easy to realize. Ionic liquids are organic salts that are liquid at ambient temperatures. They have been considered and used as a new generation of green solvents for a number of polymerizations as they are nonvolatile, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0199
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 5, May 2009 Downloaded: 18 Mar 2015
nonflammable, recyclable, and have good solubility to many organic and inorganic compounds.17–24 Carmichael et al.25 first reported the successful use of 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), a frequently used room temperature ionic liquid, as a solvent for ATRP of methyl methacrylate (MMA). Matyjaszewski26 discussed the ATRP of MMA in ionic liquids containing different counterions, and Kubisa27 studied the effects of different substituents on ATRP of acrylates in [C4mim][PF6]. The other studies in this fie
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