Alfin catalyst system

From the results of Tables II and III, the polybutadiene samples identified by different catalyst systems can be arranged in order of increasing polydispersity butyllithium, nickel based, titanium based, cobalt based, alfin, emulsion. Considering variations in polydispersity from sample to sample, the agreement of this order with the published results of Alliger, Johnson, and Foreman (21) and Hulme and McLeod (22) is excellent. 

Likewise, the samples can be arranged in the order of decreasing coil size and increasing branching, as determined by g COrr and g", again using the catalyst systems to identify the samples. The most linear polymers are the reference butyllithium samples followed by the nickel-based polymer, butyllithium, alfin, cobalt based, titanium based, and emulsion. The correction to the branching factor for polydispersity makes the nickel-based and alfin polybutadienes less branched with respect to the other polymers examined. 

Using Alfin catalysts, butadiene polymers were already obtained in the 1940s. The Alfin catalytic system consists of three components (formed in statu nascendi from alkyl chloride, metallic sodium, alcohol and olefin) sodium salt of secondary alcohol (e.g. sodium isopropoxide), alkenylsodium (e.g. allyl-sodium) and finely dispersed sodium chloride (the name Alfin originates from a/cohol + olefin) [2,3], Since the molecular weight of polybutadiene obtained with Alfin catalysts is very high (it can reach a value of a few millions), 1,4-dihydronaphthalene is often added to the polymerisation system for the regulation of molecular weight [1],... 

On the other hand, changes in the recipes of alkali metal polymerizations frequently make appreciable changes in the microstructures of the resultant polymers (2, 10, 12). Thus, sodium polybutadiene, or sodium polyisoprene, has a microstructure different from that of the corresponding potassium-catalyzed polymer. It also has been established that promoters or modifiers like dioxane or dimethoxytetraglycol affect the microstructure in these alkali metal catalyzed systems. One further example is afforded by the Alfin catalyst, which is apparently related to alkali metal catalysts but which gives a polybutadiene or polyisoprene with a microstructure very different from that of the corresponding alkali metal polymers. 

Acrylonit e is one of the most reactive monomers toward anionic catalysts. A wide range of initiators of this type has been used and include the alfin catalysts, alkoxides, butyUithium, metal ketyls, and solutions of alkali metals in ethers. In a number of anionic polymerizations, there is no termination reaction if pure reagents are used, and so-called living polymers are formed. Sudi living" systems are more difficult to observe in the case of acrylonitrile owing to the insolubility of the polymer in most of the usual solvents. It is possible to produce block co-polymers with acrylonitrile from other living" polymeric anions. 

Another better studied system is the Alfin (alkoxide—olefin) catalyst, which is composed of a sodium salt, sodium alkoxide, and aHylsodium (222). Similarly, there are many different modifications of the system to produce polymers with different 1,2- to 1,4-addition ratios as well as other properties (223). 

Thus the isotactic control of polystyrene requires a significantly anionic initiator system such as alfin, alkyl sodium and sodium ketyl catalysts. Ethyllithium is at the border line in ionicity to produce isotactic polystyrene. Only when a somewhat more basic component such as lithium hydroxide is present, can steric control be realized. Even in these cases the amount of steric control is not large. The less anionic... 

Alkyllithium-transition metal halide catalysis is completely different from the sodium ketyl and alfin catalysis. Natta, Danusso, Scanesi and Macchi (36) have found that the polymerization of styrene and substituted styrenes by titanium tetrachloride-triethyl aluminum catalysts was different from the above anionic systems. A plot of the log of the rate of the polymerization against Hammett s sigma constant produced a straight line with a rho value of —1.0. Electron releasing groups facilitated this polymerization. 

The catalysts can either be free-radical (usually allowed to react under emulsion conditions), anionic, e.g. Na (not used now, but originally used to give Buna rubber), alkyl lithium, Alfin (which is an insoluble mixture of Na, isopropanol and n-butyl chloride—the active species is probably a solvated alkyl sodium), or a Ziegler coordination system, such as Til4/A1R3, CoX2/AlEt2Cl/H20. 

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