Ionic liquids, in polymerization

Room temperature ionic liquids arc currently receiving considerable attention as environmentally friendly alternatives to conventional organic solvents in a variety of contexts.144 The ionic liquids have this reputation because of their high stability, inertness and, most importantly, extremely low vapor pressures. Because they are ionic and non-conducting they also possess other unique properties that can influence the yield and outcome of organic transformations. Polymerization in ionic liquids has been reviewed by Kubisa.145 Commonly used ionic liquids are tetra-alkylammonium, tetra-alkylphosphonium, 3-alkyl-l-methylimidazolium (16) or alkyl pyridinium salts (17). Counter-ions are typically PF6 and BF4 though many others are known. 

A similar principle is applied in dispersion polymerization in ionic liquids produced particles are in sub-micron range (41,42). The monomer, initiator and colloidal stabilizer are soluble in the liquid medium, but the obtained polymer is not. Different kinds of ionic liquids may be used, such as for styrene l-butyl-3-methylimidazolium tetrafluoroborate or N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide. In general, radical polymerization in ionic liquids provides higher polymerization rate and higher molecular weights than the process in bulk or organic solvents (homogenous system). 

Woecht I, Schmidt-Naake G, Beuermann S, et al. Propagation kinetics of free-radical polymerizations in ionic liquids. J. Polym. ScL, Part A Polym. Chem. 2008. 46, 1460-1469. 

Xie M, Han H, Ding L et al (2009) Promotion of atom transfer radical polymerization and ring-opening metathesis polymerization in ionic liquids. J Macromol Sci R, Part C Polym... 

Schmidt-Naake G, Woecht I, SchmalfuB A et al (2009) Free adical polymerization in ionic liquids-solvent influence of new dimension. Macromol Symp 275-276 204-218... 

Lipase-catalyzed Polymerization in Ionic Liquids 337 13.3 Enzymatic Polymerization under Biphasic Conditions 339... 

An ionic liquid also has vast possibilities because the hquid properties as a solvent can be altered by designing the molecular structure. There are a few reports of enzymatic ring-opening polymerization in ionic liquids. The hpase-catalyzed polymerization of e-CL was carried out in ionic solvents, such as the l-butyl-3-methyl-imidazolium salts [169]. In order to establish the compatibihty of enzymes with ionic liquids, the hpase-catalyzed transesterification of 2-hydroxymethyl-1,4-benzodioxane was studied [170]. 

In addition, Cui-N-propyl-2-pyridylmethanimine mediated "living" radical polymerization of vinyl monomers by use of l-butyl-3-methylimidazolium hexafluorophosphate as solvent has been reported (Carmichael et al., 2000). It has been pointed out that the rate of polymerization was enhanced in comparison to other polar/coordinating solvents. Moreover, the polymerization product was made copper free by a simple solvent wash, which avoids the contamination of the polymer product by the catalyst. Other atom transfer radical polymerizations in ionic liquids have recently been reported (Sarbu Matyjaszewski, 2001 Biendron Kubisa, 2001). 

Figures 2 and 3 show the effect of ionic liquid on the radical polymerization of styrene (St) and methyl methacrylate (MMA), respectively, initiated by BPO in the presence of carbon black. As shown in Figures 2 and 3, in toluene as solvent, the polymerization was remarkably retarded. On the contrary, the retardation of polymerization observed in the presence of carbon black was almost eliminated in the initi stage of the polymerization in ionic liquid.

The effect of ionic liquid as solvent on the radical graft polymerization of MMA initiated by CB-Azo was investigated. Figure 9 shows the relationship between reaction time and conversion in ionic liquid and 1,4-dioxane. It was found that the rate of the polymerization in ionic liquid was considerably larger than that in 1,4-dioxane. 

Based on the above result, the number of the grafted polymers on the silica surface was calculated. The results are shown in Table 3. The number of grafted polySt on silica obtained from the polymerization in ionic liquid was about 5-times larger than that in 1,4- dioxane as schematically shown in Figure 15. The proportion used for the grafting site to azo group on the surface (R) was about 5 % in 1,4-dioxane, but about 25 % in ionic liquid. 

Andrzejewska, E. Podgorska-Golubskaa, M. Stepmiaka, L Andrzejewski, M. Photoinitiated polymerization in ionic liquids Kinetics and viscosity effects. Polymer 2009, 50, 2040-2047. 

Ho and cowvorkers also demonstrated that trigonal [(IPr)NiH][OTf] species can be used for hydroalkenylation (see also Section 10.11) or polymerization in ionic liquids. Later, the same group proposed the first tail-to-tail vinyl ether dimerization favored by a synergistic effect between [(IPr)NiH][OTf] catalyst and PhN02 or t-BuN02 [eqn (10.41)]. ... 

Table 1.9 Chain-length averaged termination rate coefficients for MMA polymerization in ionic liquids at 10 °C referring to the regime of short chains (i< 100) and (kt) of MMA in bulk for i< 1000.

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