Composition tempo

Living free-radical polymerization has recently attracted considerable attention since it enables the preparation of polymers with well-controlled composition and molecular architecture previously the exclusive domain of ionic polymerizations, using very robust conditions akin to those of a simple radical polymerization [77 - 86]. In one of the implementations, the grafting is achieved by employing the terminal nitroxide moieties of a monolith prepared in the presence of a stable free radical such as 2,2,5,5-tetramethyl-l-pyperidinyloxy (TEMPO). In this way, the monolith is prepared first and its dormant free-... 

We wish to report here on a new and highly efficient catalyst composition for the aerobic oxidation of alcohols to carbonyl derivatives (Scheme 1). The catalyst system is based on 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), Mg(N03)2 (MNT) and N-Bromosuccinimide (NBS), utilizes ecologically friendly solvents and does not require any transition metal co-catalyst. It has been shown, that the described process represents a highly effective catalytic oxidation protocol that can easily and safely be scaled up and transferred to technical scale. 

Our initial work on the TEMPO / Mg(N03)2 / NBS system was inspired by the work reported by Yamaguchi and Mizuno (20) on the aerobic oxidation of the alcohols over aluminum supported ruthenium catalyst and by our own work on a highly efficient TEMP0-[Fe(N03)2/ bipyridine] / KBr system, reported earlier (22). On the basis of these two systems, we reasoned that a supported ruthenium catalyst combined with either TEMPO alone or promoted by some less elaborate nitrate and bromide source would produce a more powerful and partially recyclable catalyst composition. The initial screening was done using hexan-l-ol as a model substrate with MeO-TEMPO as a catalyst (T.lmol %) and 5%Ru/C as a co-catalyst (0.3 mol% Ru) in acetic acid solvent. As shown in Table 1, the binary composition under the standard test conditions did not show any activity (entry 1). When either N-bromosuccinimide (NBS) or Mg(N03)2 (MNT) was added, a moderate increase in the rate of oxidation was seen especially with the addition of MNT (entries 2 and 3). 

The starting point here was the 16 mmol scale oxidation reaction using the standard conditions shown in Figure 4a (curve 1). Full conversion was achieved over 22 min at a TOF of 68h. In the next experiment (curve 2), the hexan-l-ol concentration was doubled (32mmol scale, 2.7M, 33.3% v/v) while the concentration of the AA-TEMPO-MNT-NBS composition was kept at the same level. Again,... 

B. Oxidation procedure for the small-scale experiments. The required amounts of hexan-l-ol, AA-TEMPO, Mg(N03)2, NBS and HOAc were loaded in the reactor and the flask was connected to the volumetric manifold. The flask was flushed three times with oxygen and immersed in the thermostated water bath held at the reaction temperature for two minutes to equilibrate the system. The oxygen was admitted to the reaction pressure and the continuous monitoring of the oxygen uptake initiated and recorded against the time. After the reaction was completed the product composition was analyzed by GC using dioxane as an internal standard. 

When the optimized reference oxidation was run without solvent, using MeO-TEMPO, KBr and NaHCOs buffer a 91% aldehyde yield was obtained over a 90 min reaction time (Table 1). In the second run, the NaHCOs buffer was replaced with Na2B40r, at ten times lower concentration, using the catalyst composition of MeO-TEMPO/KBr. The aldehyde yield was 95% over the same reaction time. This favorable result was achieved mostly through gains in the product selectivity. 

Narrow distribution in the backbone length as well as in the chemical composition or the branch frequency may be expected from a living-type copolymerization between a macromonomer and a comonomer provided the reactivity ratios are close to unity. This appears to have been accomplished to some extent with anionic copolymerizations with MMA of methacrylate-ended PMMA, 29, and poly(dimethylsiloxane) macromonomers, 30, which were prepared by living GTP and anionic polymerization, respectively [50,51]. Recent application [8] of nitroxide (TEMPO)-mediated living free radical process to copolymerizations of styrene with some macromonomers such as PE-acrylate, la, PEO-methacr-ylate, 27b, polylactide-methacrylate, 28, and poly(e-caprolactone)-methacrylate, 31, may be a promising approach to this end. 

Other LC-based copolymers incorporating styrene-based monomers were prepared by Ober et al. [149] who chain extended pAcOSt-TEMPO (Mn=7000, Mw/Mn=1.18) with [(4 -methoxyphenyl)4-oxybenzoate]-6-hexyl (4-vinylbenzoate) (MPVB, Fig. 10). The reactions were controlled, with molecular weights ranging from Mn=12,600-23,000 and Mw/Mn=1.19-1.44. The content of pMPVB in the copolymer determined by XH NMR increased as the molar ratio of the MPVB to pAcOSt-TEMPO increased [149]. For two out of the three copolymers prepared a smectic-isotropic transition was observed however, it was at a value lower than expected based on the composition of the copolymer, even after annealing. X-Ray diffraction patterning indicated that the copolymer was oriented in a lamellar morphology and that the smectic layers were perpendicular to the block copolymer lamellae [149]. 

The study of the structure and chemical composition of the universe proceeds today at an increasing tempo. There is more work to be done than our telescopes can handle. Research projects, for example, are programmed on a tight schedule for in advance for Mt. Palomar s great telescope with its 200-inch reflecting mirror. 

To determine the composition of the copolymers a series of polymerizations taken to low conversion (<10%) were performed. The polymerizations were done in a Parr pressure reactor with a total monomer volume of 70 mL. The relative amounts of the two monomers were varied to give mole fractions of isoprene from 0.1-0.9. The reactions were conducted at 125 C under an atmosphere of argon using 0.2 g of BPO and 0.17 g of TEMPO. After a period of 5-30 min (see Table II), the reaction mixture was cooled to room temperature and a sample taken for GPC, TGA and GC measurements the remainder of the mixture was precipitated into methanol to isolate the polymer for NMR analysis. 

To demonstrate the livingness of styrene-acrylonitrile random copolymerizations, TEMPO (0.084 g) and BPO (0.101 g) were dissolved in 30 mL of styrene and 10 mL of acrylonitrile. The reaction mixture was stirred and purged with argon. The flask was sealed, lowered into a oil bath at 125 C and the mixture allowed to reflux. Periodically the flask was removed from the bath, cooled and a sample withdrawn for GPC analysis. To measure the composition of the copolymers, a series of polymerizations taken to low conversion were done in a Parr pressure reactor. The total moles of monomer were kept constant at 0.55, and the relative amounts of the two monomers were adjusted to vary the mole fraction of acrylonitrile from 0.1-0.9. 

Using the difiinctional monomer methodology, star-block copolymers were afforded with a great variety of chemically different chains in terms of molecular weight and composition. The synthetic strategy involved the preparation of TEMPO-terminated linear chains and subsequent coupling with the difiinctional monomer DVB and a bis(maleimide) derivative. 

A variation in controlled/ living polymerization of vinyl acetate by the use of a bidentate ligand, 2,2 -bipyridyl and TEMPO composition in 2 1.2 ratio that was reported by Mardare and Matyjaszewski [267]. The following mechanism was proposed. 

Figure 25.6 displays the ESR spectra of four different types of nitroxide spin probes (TEMPO (I), TEMPOL (II), EGONO (4-ethylene glycoloxy-TEMPO) (III) and BZONO (4-benzyloxy-TEMPO) (IV)) dispersed in NR matrix. The molecular weights and molecular volume are different for different types of spin probes. The spin probes (I, II and III) in the NR matrix show composite spectrum but the only difference between them is the intensity of the broad component, which increases with increasing molecular volume of the probes. Alternatively, the largest spin probe (IV) exhibits only one component in... 

Schoutens JE, Tempo K, Introduction to Metal Matrix Composites, MMCCIAC Tutorial Series, MMC No. 272. 

Figure 2.9 The fraction of anisotropic j ase as a function of reaction time at different reaction tempo atures. Monomer composition is 73G7 ABA/ANA.

Where the sub-index 0 indicates initial conditions and T is the induction period. kdim in equation 1 has been measured with precision by Kothe and Fischer as fcdim = 2.51x10 exp (-93,500/(/f2)) L moP -s with R in J moP °K and T, the temperature, in °K. In order to obtain initial estimates of the value of fedsma we performed reactions for the system S-MA in presence of OH-TEMPO [N]) in a capillary dilatometer in order to measure the induction period and the conversion - time curve after induction. Different compositions of the pair S-MA and of the nitroxide mixture increased its volume by thermal expansion until thermal equilibrium was established. At that point zero time was marked and the volume contraction of the reaction mixture with time was correlated with conversion via standard calculations that use the density of the monomer mixture and the polymer. ° Table 1 contains a summary of the results and Figure 3... 

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