Butadiene complexes polymerization

Table 1. Solution polymerization results for butadiene usir cobalt(II) pyridyl bis(imine) complexes. Polymerization conditions [l,3-butadiaie]= 1 mol/L [Cal.] = 2.00 x 10" mol/L ...

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

Some [MX]+ ions enter into reactions in which the ligand X and the reacting molecule become chemically bonded. Polymerization processes have been observed involving the [MC4H4]+ ions (147). The butadiene complex ions [MC4H4]+ of Co and Ni are unreactive to ethyne but the Fe, Ru, and Rh ions react to yield benzene and the bare metal ion. The [MC4H4]+ complex ions of Os+, Ir+, and Pt+ react with ethyne to form the MC4I I4 + ions that probably correspond to the benzyne complexes previously observed for platinum (126). 

The copolymerization with alkyllithium to produce uniformly random copolymers is more complex for the solution process than for emulsion because of the tendency for the styrene to form blocks. Because of the extremely high rate of reaction of the styryl-lithium anion with butadiene, the polymerization very heavily favors the incorporation of butadiene units as long as reasonable concentrations of butadiene are present. This observation initially was somewhat confusing because the homopolymerization rate of styrene is seven times that for butadiene. However, the cross-propagation rate is orders of magnitude faster than either, and it therefore dominates the system. For a 30 mole percent styrene charge the initial polymer will be almost pure butadiene until most of the butadiene is polymerized. Typically two-thirds of the styrene charged will be found as a block of polystyrene at the tail end of the polymer chain ... 

Independently of the interest of the CG complexes in polymerization catalysis, similar reactivity to that of metallocenes can be observed. For instance, the metathetical reaction of [(C5H4)SiMe2(Nt-Bu)]ZrCl2 with [Mg(C4H6)(thf)2] affords the Zr-butadiene complex (39)." ... 

Butadiene is polymerized by rhodium compounds in aqueous or alcoholic solution [178]. It is generally accepted that the active species is a TT-allyl rhodium complex of low valency [28, 179] which is not rapidly terminated by reaction with water or alcohol. No clear kinetic pattern was observed in the earlier papers but a recent investigation [180] has shown the rate and molecular weight data to be accommodated by a scheme involving monomer transfer and physical immobilization of the active centres in precipitated polymer. In the initial stages the polymerization is first order in rhodium and, at constant monomer concentration, is (pseudo) zero order E = 14.8 kcal mole" ). This is followed by a declining rate which is almost independent of temperature. Molecular weights rise slowly to a maximum value with time (ca. 4000 after 22 h at 70°C). 

The general reaction model for the allylnickel complex-catalyzed 1,4-polymerization of butadiene is outlined in [26]. From the starting / -allylnickel(II) complex, which has a quasi-planar structure, two structurally different butadiene complexes are formed as the actual catalysts by successive ligand or anion substitution a monoligand allylnickel(II) complex, which may also contain the anion X instead of the neutral ligand L, with an coordinated butadiene, and a ligand-free complex with an t/ -cis coordinated butadiene. The concentration of these complexes, which is also limited by the double- bond coordination from the growing chain, and their reactivity determine the catalytic activity. 

During a very short initiation period the cation [Ni(Ci2H 9)] , which is present mainly in the thermodynamically more stable syn form b, reacts via the less stable but more reactive anti form a with insertion of butadiene into the anti--polybutadienyl complex c. As a result of the very rapid anti-syn isomerization this complex also exists in equilibrium (cf. Kf) with the more stable syn complex d, which must be regarded as the stable storage complex under the conditions of polymerization. With butadiene the polybutadienyl-butadiene complexes e and f are formed as the actual catalysts. By the much higher reactivity of the less stable anti complex e, the formation of cis units is catalyzed. Since all the equilibria can be assumed to be rapid, the insertion reaction of butadiene (/ 2c) has to be taken as the rate-determining step in the catalytic cycle. Thus, the catalytic activity is dertermined thermodynamically by the concentration of the -c/5-butadiene complex in the anti form e and kinetically by its reactivity k2c-... 

Cationic -allylnickel complexes polymerize 1,3-butadiene to produce the cis- 1,4-polymer. Taube investigated the polymer growth via smooth and selective insertion of the diene into the -allyl-Ni bond of the growing polymer, both from experimental and theoretical aspects. The reaction catalyzed by the cationic Ci2-allylnickel(II) complex shows kinetics that agree with a chain propagation transfer model [67]. The reaction mechanism of the cis-1,4-polymerization using technical Ni catalysts is also discussed [68]. He compared the mechanism of the reaction catalyzed by allylnickel complexes [69]. 

Ti-lnteractions between phenyl rings and alkali metals can even occur in some more exotic molecular structures as exemplified by the unusual heterobimetallic lutetium butadiene complex [K(THF)2(/r-Ph2C4H4)2Lu(thf) ] , 73 [73]. In 73 the central Lu atom is coordinated by two 4-diphenyl-1,3-butadiene ligands and two THF molecules. Self-assembly with the formation of one-dimensional polymeric chains occurs because potassium forms / -interactions with the -systems of two phenyl substituents from neighboring molecules. 

The mono-Cp butadiene complexes 35 and 36 have been found to polymerize ethylene at moderate rates as well (35.23 and 5.69 g/mmol(M)/h/atm, respectively, at 20°C, with 500 eq. MAO) (107). At low temperatures, the polymerizations appear to be living in nature (see imder Living Polymerization). 

Other Mo complexes have shown a similar behavior. Half-sandwich complexes with a-diimine ligands (type XLI, Figure 31) behave similarly to the related phosphine and butadiene complexes of Figure 18, with good control for styrene polymerization by ATRP (initiation by 1-bromoethytlbenzene) by XLIa-d and reasonable control by OMRP-RT for XLc (initiation by AIBN at 100 °C, with linearly growing up to 30% conversion and 1.6). In combination with the A1... 

Economic considerations in the 1990s favor recovering butadiene from by-products in the manufacture of ethylene. Butadiene is a by-product in the C4 streams from the cracking process. Depending on the feedstocks used in the production of ethylene, the yield of butadiene varies. Eor use in polymerization, the butadiene must be purified to 994-%. Cmde butadiene is separated from C and C components by distillation. Separation of butadiene from other C constituents is accomplished by salt complexing/solvent extraction. Among the solvents used commercially are acetonitrile, dimethyl acetamide, dimethylform amide, and /V-methylpyrrolidinone (13). Based on the available cmde C streams, the worldwide forecasted production is as follows 1995, 6,712,000 1996, 6,939,000 1997, 7,166,000 and 1998, 7,483,000 metric tons (14). As of January 1996, the 1995 actual total was 6,637,000 t. 

Reaction between oxygen and butadiene in the Hquid phase produces polymeric peroxides that can be explosive and shock-sensitive when concentrated. Ir(I) and Rh(I) complexes have been shown to cataly2e this polymerisation at 55°C (92). These peroxides, which are formed via 1,2- and 1,4-addition, can be hydrogenated to produce the corresponding 1,2- or 1,4-butanediol [110-63-4] (93). Butadiene can also react with singlet oxygen in a Diels-Alder type reaction to produce a cycHc peroxide that can be hydrogenated to 1,4-butanediol. 

The conjugated stmcture of 1,3-butadiene gives it the abiUty to accept nucleophiles at both ends and distribute charge at both carbon 2 and 4. The initial addition of nucleophiles leads to transition states of TT-ahyl complexes in both anionic and transition-metal polymerizations. 

The mid-block monomers are primarily isoprene and butadiene. These diolefins can polymerize in several ways. The isomeric structure of the final polymer has a strong impact on its properties and thermal stability. Isomeric composition is easily varied by changing the polymerization solvent or adding complexing agents. The typical isomeric structures for isoprene and butadiene mid-blocks are shown in Fig. 2. 

The polymerization filling was effected by the ion-coordination mechanism [17-19]. The monomers were ethylene, propylene, allene, os-butylene, butadiene. The fillers were mineral materials such as ash, graphite, silica gel, glass fibers. The ultimate aim of filler conditioning prior to polymerization is to secure, on its surface, metal complex or organometallic catalysts by either physical or chemical methods [17-19],... 

The application of these catalysts in the initial state (without any special treatment of the surface organometallic complexes of such cata-lysts) for ethylene polymerization has been described above. The catalysts formed by the reaction of 7r-allyl compounds with Si02 and AUOj were found to be active in the polymerization of butadiene as well (8, 142). The stereospecificity of the supported catalyst differed from that of the initial ir-allyl compounds. n-Allyl complexes of Mo and W supported on silica were found to be active in olefin disproportionation (142a). 

Finally it should be stressed that the complexation affects the microstructure of poly dienes. As was shown by Langer I56) small amounts of diamines added to hydrocarbon solutions of polymerizing lithium polydienes modify their structure from mainly 1,4 to a high percentage of vinyl unsaturation, e.g., for an equivalent amount of TMEDA at 0 °C 157) the fraction of the vinyl amounts to about 80%. Even more effective is 1,2-dipiperidinoethane, DIPIP. It produces close to 100% of vinyl units when added in equimolar amount to lithium in a polymerization of butadiene carried out at 5 °C 158 159), but it is slightly less effective in the polymerization of isoprene 160>. 

Measurements of polymerization rate and parallel measurements on the resultant polymer microstructure in the butadiene/DIPIP system cannot be reconciled with the supposition that only one of the above diamine solvated complexes (eg. Pi S) is active in polymerization 162). This is probably true of other diene polymerizations and other diamines. The observations suggest a more complex system than described above for styrene polymerization in presence of TMEDA, This result is clearly connected with the increased association number of uncomplexed diene living ends which permits a greater variety of complexes to be formed. 

Highly c/s-selectivity and low molecular weight distribution polymerization of l -butadiene with cobalt(II) pyridyl bis(imine) complexes in the presence of ethylaluminum sesquischloride effect of methyl position in the ligand... 

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