Modified methylaluminoxanes

Styrene monomer was purified by vacuum distillation over CaHi. Inhibitor in styrene was removed using activated alumina. N-heptane was purified by distillation over sodium to remove tire trace of residual moisture. The purified slyreaie and n-heptane were stored over activated alumina under nitrogen blanket. Et[Ind]2ZrCl2 Strem Chem.), MAO (modified methylaluminoxane, type 3A, Akzo Novel) wee used without fiirtha" purification. 

Modified methylaluminoxanes (MMAO) have also been offered commercially since the early 1990s. MMAO (32) is a generic term encompassing all products wherein some of the methyl groups are replaced by other alkyl groups. The most commonly used modifiers are isobutyl and n-octyl groups. 

Most modified methylaluminoxanes are prepared by reaction with water (eq 6.3). There are several formulations of MMAO (differentiated by a suffix, e.g., "MMAO-3A"), each with different composition and properties. One commercially available MMAO is produced by the nonhydrolytic... 

Modified methylaluminoxanes exhibit much improved storage stability and several are highly soluble in aliphatic hydrocarbons. (Manufacturers of polyethylene prefer to avoid toluene because of toxicity concerns, especially if resins are destined for food contact.) Most importantly, because yields are higher, modified methylaluminoxane formulations are less costly than MAO. However, since modified methylaluminoxanes contain other types of alkylaluminoxanes, they do not match the performance of conventional methylaluminoxane in some single site catalyst systems. Consequently, modified methylaluminoxanes should be considered niche cocatalysts for single site catalysts. 

Though methylaluminoxane, modified methylaluminoxanes and arylboranes/ borates are the cocatalysts most often used with single site catalysts, there are other compounds that function as cocatalysts. These include compositions such as PhjC ", AKOCjF.)". To date, however, these have not achieved significant usage in industry. Caution Aluminum compounds containing fluoroalkyl and fluoroaryl groups have been known to decompose violently when heated (20,36). 

MeOsalen = N,N/-ethylenebis(5-methoxysalicylideneiminate) Me3tacn = /V,/V/,/V//-trimethyl-1,4,7-triazacyclononane MMAO = modified methylaluminoxane MMTP = l-methoxy-2-methyl-l-trimethylsiloxypropene MOCVD = metal organic chemical vapor deposition Ms = mesityl = 2,4,6-trimethylphenyl NBD = norbornadiene NBS = iV-bromosuccinimide NitOH = p-nitrophenol Np = 3-neopentyl OAc = acetate OBz = benzoate... 

The same complex anchored now onto MWCNTs functionalized with modified methylaluminoxane (MMAO MAO where about 3 methyl units per 100 were substituted by longer alkyl chains such as isobutyl for better solubilization)... 

Conventional MAO has very low solubility in aliphatic solvents as well as poor storage stability in solution, which considerably limits its utility. Other more soluble and commonly used aluminoxanes are ethylaluminoxane and isobutylaluminoxane, which are synthesized by the partial hydrolysis of triethyl-aluminum (TEA) and triisobutylaluminum (TIBA), respectively. However, these alkylaluminoxanes do not perform as well as MAO in metallocene-mediated olefin polymerization. " It was reported, however, that tetrakis(isooctyl) alumoxane [(i-octyl)2—O—Al-(i-octyl)2], prepared by reaction of Al(i-octyl)3 with 0.5 equiv of water, exhibits remarkable cocatalytic activity, comparable to or even greater than that obtained with MAO, for ethylene polymerization catalyzed by racemic an5a-bis(indenyl)-type zir-conocene dichlorides. Furthermore, commercial modified methylaluminoxanes (MMAO) available from... 

Several catalysts have been found to produce iPP through the chain-end control mechanism. These include the Cp2TiR2/MAO systems (Cp = C5H5 or substituted Cp R = Ph or Cl) " and (pyridyldiimine)FeCl2/modified methylaluminoxane catalysts. Low polymerization temperatures are required to achieve moderate isotacticity with both classes of catalysts. The frequency of misinsertions produces an average stereoblock length of less than 16 units, the minimum required for... 

Ban, H. T. Tsunogae, Y. Shiono, T. Synthesis and characterization of cw-polybutadiene-Wuck-syn-polystyrene copolymers with a cyclopentadienyl titanium trichloride/modified methylaluminoxane catalyst. J. Polym. Sci., Part A Polym. Chem. 2004, 42, 2698-2704. 

Shiono T (2013) Trialkylaluminum-free modified methylaluminoxane as a cocatalyst for living polymerization of olefins. Adv Polym Sci. doi 10.1007/12 2013 211... 

Trialkylaluminum-Free Modified Methylaluminoxane as a Cocatalyst for Living Polymerization of Olefins... 

Living polymerization Modified methylaluminoxane Single-site catalyst Supported catalyst... 

MAO methylaluminoxane, MMAO modified methylaluminoxane See Scheme 4 lO gmor (Fe) h ... 

Table 6.2 Complexes for the polymerization of ethene (modified methylaluminoxane = MMAO, dry methyl-aluminox-ane = DMAO, co-polymeric isobutyl methylaluminoxane = coMAO, triisobutylaluminium = TIBAL). 

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