Monocationic initiator

Schematic of the synthesis of monocationic initiator. (Reproduced from Mittal, V., Philosophical Magazine, 90,2489-506,2010. With permission from Taylor and Francis.)...

X-ray diffractograms of clay (I) modified using asymmetrical monocationic initiator in an amount corresponding to 30% of CEC and dimethyldidodecylammonium in an amount corresponding to 70% of CEC, (11) the clay of I when reacted with lauryl methacrylate in nonliving conditions, and (III) the clay of I when reacted with lauryl methacrylate in living conditions. The peak at 8.84° 26 corresponds to mica platelets used as internal standard. (Reproduced from Mittal, V., Philosophical Magazine, 90, 2489-506,2010. With permission from Taylor and Francis.)... 

The combination of these two possibiUties makes the intercalated structure less spatially ordered which accounts for the broadened reflection for this sample as compared with the peak of the clay intercalated by the monocationic initiator. Furthermore, since XRD collects the average information from a large area of a powder sample, a synergic effect of these two possibilities accounts for an intermediate d spacing value. This interpretation is schematically shown in Fig. 

By comparison, an intercalated monocationic initiator is more easily delaminated than a bicationic initiator. The monocationic initiator molecule is also more organophilic. The weaker van der Waals interaction between the alkyl headgroups of the monocationic initiator and clay surfaces makes the intercalated clay more easily swelled by the solvent and monomer. Once the clay intercalated with monocationic initiator is exfoliated by sonicating and stirring, the attached initiators have more accessibility to monomer and thus results in better monomer intercalative diffusion. 

Subsequent NMR experiments indicate that the monocationic species (24) is formed initially as a donor-acceptor complex and then a second chloride abstraction could provide the dication (25). At temperatures above — 60° C... 

Although we initially proposed that the water was inhibiting the phosphine ligand dissociation and bimetallic fragmentatiOTi from generating inactive 12r and 13rr [44], the actual situation is quite different. The dicationic dihydride catalyst llr/llr can easily deprotonate to form a new monocationic monohydride dirhodium catalyst. This is supported by in situ FT-IR, NMR, the acidity of the catalyst solution, and DPT computational studies. A 1 mM catalyst solution in 30% water/acetone after exposure to H2/CO has a pH of 3.1, while a 10 mM solution has a pH of 2.2 - consistent with a strong monoprotic acidic species. 

The DFT calculated energetics for the main hydroformylation reaction steps based on 15r starting with the 15r-alkene complex are shown in Fig. 14. The two largest activation barriers are for the initial alkene-hydride migratory insertion step (16.8 kcal/mol) and for the final reductive elimination of the acyl and hydride (21.6 kcal/mol). The computational prediction, therefore, is that the final aldehyde reductive elimination is the rate determining step for the monocationic catalyst 15r. The largest activation barrier for the dicationic dirhodium catalyst (Fig. 8) is only 13 kcal/mol, indicating that the monocationic dirhodium catalyst should be less active on a per molecule basis, which is completely consistent with the impact of... 

Addition of 2 equivalents of NEts to either the dicationic catalyst in acetone or the monocationic catalyst in water/acetone dramatically slows the hydroformylation. In acetone the initial TOF is reduced by 34%, while in water/acetone... 

X. Fan, C. Xia, and R. C. Advincula, Grafting of polymers from clay nanoparticles via in situ free radical surface-initiated polymerization Monocationic versus bicationic mitiators. Langmuir, 19 (2003), 4381-9. 

Similarly, trials of polymerization of lauryl methacrylate from the surface were also reported [7,8]. For this purpose, two initiators were synthesized, one being monocationic and the other being dicationic. Figures 2.9 and 2.10... 

The synthetic schemes and structures of these initiators are shown in Figs 5.7(a) and 5.7(b). They are both AIBN-analogue initiators for free radieal polymerization. The use of another symmetric bicationic azo compound, 2,2 -azobis(isobutyramidine hydrochloride) (AIBN), has also been proven to be feasible for styrene SIP on high surface area mica powder. " However, no structural information for these SIP products has been reported. Asymmetric azo initiators in the form of silanes have also been successfully employed to free radically polymerize styrene from spherical silica gel surfaces. To the best of our knowledge, there have been no reports on a direct free radical SIP approach from surface-bound monocationic azo initiators on individual clay nanoparticles. 

On further analysis, the d spacing values seemed to be inconsistent with the steric sizes of the two initiators. The d spacing of bicationic intercalated clay (1.52 nm) is substantially smaller flian diat of the monocationic intercalated clay although their molecular dimensions are comparable (both chain length values are 2.20 nm, as estimated by Chem 3D software). The bicationic initiator molecule possesses charged groups on bofti ends that can have two intercalation possibilities ... 

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