Nickel-mediated Polymerization of Methyl Methacrylate

Nickel-mediated Polymerization of Methyl Methacrylate Abstract: The Ni(II) complexes [Ni(5-C5H3 R2)(X)(NHC)] 1a–f combined with MAO was tested in methylmethacrylate (MMA) polymerization. The complex 1f, bearing the bulky 2,6-diisopropenylphenyl substituents in the NHC ligand was found to be the most effective in the polymerization of MMA with TOF up to 200 h-1 resulting in a syndiotactic, high molecular weight PMMAs which can be explained by anionic, MAO-centered polymerization mechanism. Introduction: A great deal of attention is currently being paid to polymers containing polar monomers,  which may give rise to new high-performance materials with high adhesion and toughness and good dyeing and moisture adsorption properties.1 Metal-based catalysts tolerant of polar functionalities, which perform homopolymerization, and if possible copolymerization with nonpolar olefins, are being sought. Late transition metal complexes look promising because of their lower oxophilicity,2 and probable tolerance against polar monomers, and against impurities in polar olefins polymerization. Acrylates are polymerized and copolymerized for many different uses including coatings,  textiles, adhesives, and paper.3 Commercial poly(methyl methacrylate) has been produced since 1927.4 Like many other polar monomers, acrylates are commonly polymerized by 18radical5 or anionic mechanisms. In addition, polymerization of acrylates with late transition metal complexes has been studied.6 Metallocene  group IV complexes are known to be excellent for this type of polymerization. Half-sandwich nickel(II) complexes with N heterocyclic carbenes (NHC) of the general formula [Ni(5-C5H4R)(X)(NHC)] (R = H or alkyl, X= Cl, Br, I) was synthesized by reacting nickelocene or its derivatives and suitable imidazolium salts . The diamagnetic property of these compounds helps in showing some C-C bond forming reactions. But, complexes 1 are very active in aryl dehalogenation and aryl amination, hydrothiolation of alkynes and oxidation of secondary alcohols as a precatalyst. Experimental: Materials and synthesis: Methyl methacrylate (MMA) Methyl acrylate (MA), [Ni(acac)2], Toluene, Purified THF, and hexane 1,3-bis(1,1-dimethylbut-3- enyl)cyclopentadiene complexes 1a–d and 1f [Ni(5-C5H5)(CH3CN)(IMes)]+(PF6)− [5] [Ni(5-C5H5)(Cl) (PPh3)] MAO (10% wt. solution in toluene) Synthesis of 1e: A hexane solution of n-BuLi (2.5 mL, 5.1 mmol) and a THF (5 mL) solution of  1,3-bis(1,1-dimethylbut-3-enyl) cyclopentadiene (4.83 mmol) was added and the mixture was stirred for 2 h at ambient temperature. This solution was added to the solution of [Ni(acac)2] (1.199 g, 4.67 mmol) in THF (10 mL) at −78 oC. A color change immediately from green to red is observed and a suspension of 1,3-dimesitylimidazolinium chloride  [12] (1.693 g, 4.96 mmol) in THF (10 mL) was quickly added at this temperature. The reaction mixture was allowed to warm up to ambient temperature and stirred for a further 2 h. The volatiles were removed under reduced pressure. The solid residue was extracted with hexane (20 mL) and filtered through Celite. Complex 1e was isolated by crystallization as a red, microcrystalline solid. Polymerization: 14mg of Complex 1f(0.0255 mmol) dissolved in 15ml of toluene in a schlenk tube with a magnetic stirrer in it. To this solution, MAO ((5.10 mL, 10% wt. in toluene, 7.65 mmol) which is red in color was added by a gas tight pipette which results in a brown solution. The obtained brown solution was stirred at ambient temperature for half an hour. Now MMA(2.72 mL, 0.0255 mol) was added and the apparatus is placed in a oil bath maintaining 50oC with vigorous stirring. The reaction mixture was now quenched with excess of CH3OH (200 mL) and then filtered. PMMA was collected by filteration and washed with CH3OH and kept for over night drying. The obtained polymer is purified with small volume of CHCl3 and stirred overnight with 10% aq. HCl. The organic and the aqueous phases are separated and the organic phase is poured into excess of CH3OH. A white solid PMMA was isolated by filteration. 2.4. Characterization NMR spectr at ambient temperature on a Mercury-400BB spectrometer operating at 400 MHz for 1H NMR was recorded and at 101 MHz for 13C NMR was recorded. EI (70 eV) mass spectra on an AMD-604 spectrometer was recorded. MALDI-TOF mass spectra w with a Bruker Daltonics ultrafleXtremeTM mass spectrometer using HABA matrix was recorded. The average molecular weights were measured on a LabAlliance liquid chromatograph equipped with a Jordi Gel DVB Mixed Bed column (250 mm Ãâ€" 10 m) using CH2Cl2 as the mobile phase at 30 à ¢- ¦C and calibrated with standard PMMAs. 2.5. Crystal structure determination The selected single crystals mounted in inert oil were transferred to the cold gas stream of the diffractometer. Diffraction data was collected at 100(2) K on the Oxford Diffraction Gemini A Ultra diffractometer with graphite-monochromated Mo-K radiation. Cell refinement, data collection, data reduction and analysis were performed with the CrysAlisPRO [13]. Empirical absorption correction using spherical harmonics was applied. The structure was solved in monoclinic space group P21/c by direct methods using the SHELXS program . It is worth noting here that the skew angle ÃŽ ² is very close to 90à ¢- ¦. Full-matrix least-squares refinement against F2 values was carried (SHELXL-97 and OLEX2. Table 1 Crystal data, data collection and refinement parameters for complex 1e. Complex 1e Empirical formula C38H51ClN2Ni Crystal size (mm) 0.07 Ãâ€" 0.07 Ãâ€" 0.40 M ·(g mol−1) 629.96 Crystal system Monoclinic Space group P21/c (no. 14) Z 4 F(0 0 0) 1352 Temperature (K) 100(2) Dcalc. (g cm−3) 1.251 Absorption coefficient (mm−1) 0.688 Radiation Mo-K ( = 0.71073A)ËÅ ¡ range (à ¢- ¦) 3.3–30.0 Index range −20 ≠¤ h ≠¤ 20; −13 ≠¤ k ≠¤ 13; −13 ≠¤ l ≠¤ 13 Reflections collected 37,962 Unique data 9684, Rint = 0.0355 Observed refl. [I > 2ÏÆ'(I)] 8195 Data/restraints/parameters 9684/17/415 Goodness-of-fit on F2 a 1.043 Results and discussion: Synthesis: The series of Ni(II) complexes 1a–d and 1f (Scheme 1) was prepared from nickelocene or 1,1’ bis(allyl)nickelocene and the suitable imidazolium salt. Complex 1e bearing the 1,3-disubstituted cyclopentadienyl ligand could not be obtained by this route. Therefore, it was synthesized form the pentamethylcyclopentadienyl congener [4e] from [Ni(acac)2] by the one-pot two-step procedure intermediate {(5-1,3- R2C5H3)Ni(acac)} (Scheme 2). Scheme 1. Ni(II) complexes used in this study, where R = allyl (1d) or 1,1-dimethyl-but-3-en-1-yl (1e); Mes = 2,4,6-trimethylphenyl, Dipp = 2,6-diisopropylphenyl. Scheme 2. The synthesis of complex 1e, where R = 1,1-dimethyl-but-3-en-1-yl, Mes = 2,4,6-trimethylphenyl. From the symmetry of the molecule, it is found that the geometry of the molecule was trigonal planar. The bond angles and the lengths between nickel and its substituents are approximately same compared to the related compounds. Due to week contact between H(29A) hydrogen of mesityl methyl group C(29) and the chlorine ion [H(29A) ·Cl(1) 2.57 and C(29A) ·Cl(1) 3.5346(15)A] it resulted in the formation of a week intra molecular C H ·Cl hydrogen bond. 3.2. Polymerization: Polymerization was performed under the similar environment of the styrene polymerization with an excess of commercial MAO. A toluene solution of complex 1 was treated with an excess of MAO (Al:Ni = 100:1) for 30 min at ambient temperature. Then MMA (MMA:Ni = 1000:1) was added and the polymerization was run in a sealed Schlenk tube for 3 h at 50 à ¢- ¦C. The reaction mixture was separated as a homogenous mixture. Molecular structure of complex 1e. Polymerization of methyl methacrylate with complexes 1–3 and MAOa. The bromide analog 1b displayed slightly higher activity compared to 1a, while complex 1c bearing the alkyl-aryl NHC ligand was somewhat more productive than 1b in the productivity of the [Ni(Cp)(X)(NHC))]/MAO catalytic system. Substiuted cyclopentadienyl ligands was examined and complex 1d with allylcyclopentadienyl ligand gave the same result as 1a. It was reasoned that the allyl group might be too small to induce any effect. Therefore complex 1e with two bulky substituents was synthesized and tested to give the same conversion as 1d. By introducing the more bulky 2,6-diisopropylphenyl substituents in the NHC ligand (complex 1f) the yield of PMMA was 34% and when the excess of MAO was increased (Al:Ni = 300:1), the isolated yield of PMMA was increased to 60%. Changing the solvent resulted in a disappointing yield which was predicted to be due to the solubility problem. 1H and 13C NMR spectroscopy were used to determine the microstructure of PMMA. Syndiotactic-rich polymers were resulted toluene where atactic PMMA was obtained with hexane and this was because of the formation of MMA polymers via different mechanism in hexane and toluene. Isolated Methanol soluble oligomeric MMA were studied by MALDI-TOF MS which suggests more than one mechanism was operating the reaction. Scheme 3. Rationale for the formation of poly(methyl methacrylate) with [Ni(Cp)(X)(NHC)]/MAO. The structure of Ni complex had considerable effect on the overall yield of MMA with no influence on the molecular weight distribution or tacticity of the resulting polymer and the Al : Ni ratio do not effect the tacticity of the polymer. It was supposed that MMA polymerized by co ordinative anionic mechanism described in scheme 3. Conclusion: It can summarized that the complexes 1a-f and 2 can initiate polymerization of MMA in the presence of MAO with TOF up to 200h-1. The results of PMMA with GPC, NMR and MS imply a anionic, MAO-centered mechanism of polymerization catalyzed by Ni(II) species. References: 1. H. Martin in Ziegler Catalysis (Eds. G. Fink, R. Mà ¼lhaupt, H. H. Brintzinger), Springer  Verlag, Berlin, 1995, p 15. 2. G. Natta, P. Pino, G. Mazzanti, U. Giannini J. Am. Chem. Soc. 79 (1957) 2975. 3. A. Andresen, H.-G. Cordes, J. Herwig, W. Kaminsky, A. Merck, R. Mottweiler, J. Pein, H.  Sinn, H.-J. Vollmer Angew. Chem. 88 (1976) 689. 4. H. Sinn, W. Kaminsky, H.-J. Vollmer, R. Woldt Angew. Chem. 92 (1980) 396. 5. (a) H. Sinn, W. Kaminsky Adv. Organomet. Chem. 18 (1980) 99. (b) H. H. Brintzinger, D.  Fischer, R. Mà ¼lhaupt, B. Rieger, R. M. Waymouth Angew. Chem. Int. Ed. Engl. 34  (1995) 1143 and references therein. (c) W. Kaminsky, Makromol. Chem. Phys. 197  (1996) 3907. (d) M. Bochmann, J. Chem. Soc. Dalton Trans. 3 (1996) 255. (e) L.  Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 100 (2000) 1253. 6. (a) M. R. Kesti, G.W. Coates, R.M. Waymouth, J. Am. Chem. Soc. 114 (1992) 9679. (b) X.  Yang, C.L. Stern, T.J. Marks J. Am. Chem. Soc. 116 (1994) 10015. (c) D.J. Crowther,  N.C. Baenziger, R.F. Jordan, J. Am. Chem. Soc. 113 (1991) 1455. (d) P. Aaltonen, G.  Fink, B. Là ¶fgren, J. Seppà ¤là ¤, Macromolecules 29 (1996) 5255.

Suicide :: essays research papers

Suicide As I researched suicide I found that the numbers are staggering. Suicide is the ninth leading cause of death in the US, with 31,204 deaths recorded in 1995. It was at number eight on the list in 1998, and as the numbers are steadily increasing it threatens to move up the list. This approximates to around one death every seventeen minutes. There are more suicides than homicides each year in the United States. In 1993, the suicide rate was 11.3/100,000. Two-thirds of all suicides under the age of 25 were committed with firearms (accounting for most of the increase in suicides from 1980 to 1992). The second most common method was hanging, third was poisoning. 61% of all suicides involve firearms. From 1952 to 1992 suicides among teens nearly tripled. Today, it is the third leading cause of death for teenagers aged 15-19 (after motor vehicle accidents and unintentional injury). Suicide is increasing, particularly for teens and for those over 65. In young people, the suicide rate is relatively low (13.5/100,000 in 1993), but it is still a leading cause of death. In older people, the suicide rate is very high, but it is not a leading cause of death (in white males over 85, the suicide rate in 1993 was 73.6/100,000). In all age groups, men commit suicide successfully more than women (around four times as much). However, females are more likely to attempt suicide than males do. In 1998, white males accounted for 73% of all suicides. Together, white males and white females accounted for over 90% of all suicides. In teenagers, the average ratio is 5.5:1. The ratio increases with age within this group. (http://www.cdc.gov/ncipc/pub-res/10lc92c.htm / http://www.befrienders.org/info/statistics.htm) The previously listed facts are staggering and a surprise to most. Another surprising or should I say confusing area is depression and its relation to suicide. Most suicides occur by people who are suffering from depression. Certain life difficulties such as the loss of a loved one, divorce, stress at work, or a series of disappointments can contribute to depression. And sometimes, depression may just run in the family. More than 19 million Americans, approximately one in 10 adults, suffer from depression each year. Everyone feels sad at some point, but what doctors call clinical depression is very different from just being "down in the dumps." The main difference is that the sad or empty mood doesn't go away after a couple of weeks, and everyday activities like sleeping, socializing or working can be affected.

How to Make Rotel Dip

How to Make Rotel Dip Rotel dip is my favorite dip to make for the football games on Saturday! It’s something easy and delicious that everyone likes. When I was younger I used to make my mom make if just because. So finally one day she made me learn how to make it so I could make it myself. Rotel dip is a fun food that you can serve as an appetizer or entree. With less than 30 minutes of preparation time, Rotel dip is easy to make, and it's ideal for parties, a child's sleep over or for a movie-night snack. You can learn how to make Rotel dip in just a few steps.First you have to gather your ingredients, make sure you have all the utensils you will need, then prepare your food. I. Gathering your ingredients. A. 1 can of Rotel dip. 1. you can choose different flavors of rotel as in mild or hot B. 8 ounces of velveeta cheese C. some kind of meat. 1. it could be deer meat or hamburger meet, whichever you prefer. D. 1 bag of tortilla chips II. Make sure you have all the untensil y ou will need A. first you will need a large skillet 1. this is to cook your meat in. B. you will need a spatula to flip your meat to get it to cook. C.You will then need a drainer to drain all the grease from your meat. D. Next you will need a knife to cut your cheese into small squares. E. Most important thing you will need is a crockpot where you will cook all the ingredients together and you will use a large spoon to stir it periodically. III. Finally you will get to prepare your food A. Turn the crockpot on medium heat. 1. Slice the Velveeta cheese into cubes and add them to the heated crockpot. B. Turn the stove on medium-heat 1. add the ground beef to the skillet and us the spatula to flip and stir the ground beef. 2.Cook the meat until brown and drain the grease. C. Add the can of Rotel sauce and the meat to the crockpot and stir. 1. cover the crockpot for about 3 mins. D. Check to see if the cheese is melted and stir again. E. Place the tortilla chips on a plate and pour the rotel dip over the chips and serve. Now you have a great way of making an easy chip dip for any occasion. I would suggest cooking it about 2 hours before time to serve it for best results on making sure the cheese is nice and melted and everything is combined evenly. I hope you enjoy what I consider the best rotel dip around.

What Are Your Recommendations For Using Fossil Fuels And...

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