Butadiene polymerization, sodium catalyzed

Next in importance is the polymerization of butadiene, if the use of sodium is ignored in the production of such inorganic compound as sodium cyanide, sodium peroxide, and titanium. Buna rubber, prepared by the sodium-catalyzed copolymerization of butadiene and styrene, was of considerable importance during World War II, especially in Germany. More recently, Morton s alfin catalyst has caught the attention of the rubber industry because of the exceptional quality of polybutadiene prepared by his techniques. 

The teiminal groups in Equations 7.64a and 7.64b cannot propagate and, consequently, effectively terminate polymer growth. Equations 7.64c-7.64e involve proton transfer from the solvent to the growing chain resulting in a dead polymer. This is exemplified by the sodium-catalyzed polymerization of butadiene in toluene ... 

Polybutadiene-type resins n. Unsaturated, thermosetting hydrocarbons cured by a peroxide-catalyzed, vinyl-type polymerization reaction, or by sodium-catalyzed polymerization of butadiene or blends of butadiene and styrene. Liquid systems, curable in the presence of monomers, are used for casting, encapsulation, and potting of electrical components, and in making laminates. Molding compounds, often containing fillers and modified with other resins or rubbers, may be compression or transfer molded. Syndiotactic 1,2-butadiene, introduced in 1974 in Japan, is thermoplastic, with semicrystalline nature, with good transparency and flexibility without plasticization. In the presence of a photosensitizer such as p,p -tetramethyl... 

With the advent of World War I the situation in Germany, as far as the supply of natural rubber was concerned, became acute and renewed research efforts were made. Isoprene was expensive and, although quite a good rubber could be made from it by heat polymerization, yields were poor. Sodium-catalyzed polymerizations gave higher yields but inferior products. Since at that time butadiene was both very difiicult and expensive to prepare, dimethyl butadiene became the preferred monomer. In 1917 the Germans commenced the first substantial commercial production of a man-made rubber, from dimethyl butadiene. Two versions were made. Methyl Rubber W, by heat polymerization at about 70 C over a period of five months and... 

For the next few years synthetic rubber research was minimal but two stimuli occurred about 1926. First, Staudinger was establishing the long chain nature of the rubber molecule and secondly the price of rubber was rising once again. The IG Farben Company of which the old Bayer Company had become a part, instituted research which showed the beneficial effects of polymerizing the monomers in aqueous emulsion, particularly in the presence of about 1% benzoyl peroxide. At the same time improvements were made in the sodium-catalyzed polymerization of butadiene and this led to the advent of the Buna rubbers (the name derived from butadiene and natrium, the New Latin term for sodium) production of which went on to the end of World War II. 

Many solvents form dangerous levels of peroxides during storage e.g., dipropyl ether, divinylacetylene, vinylidene chloride, potassium amide, sodium amide. Other compounds form peroxides in storage but concentration is required to reach dangerous levels e.g., diethyl ether, ethyl vinyl ether, tetrahydrofuran, p-dioxane, l,l-diethox) eth-ane, ethylene glycol dimethyl ether, propyne, butadiene, dicyclopentadiene, cyclohexene, tetrahydronaphthalenes, deca-hydrona-phthalenes. Some monomeric materials can form peroxides that catalyze hazardous polymerization reactions e.g., acr) lic acid, acr)Ionitrile, butadiene, 2-chlorobutadiene, chlorotrifluoroethylene, methyl methacrylate, styrene, tetrafluoroethylene,... 

The reactive intermediates used in chain-growth polymerizations include radicals, carbanions, carbocations, and organometallic complexes. Of the three common metal catalyzed polymerizations - coordination-insertion, ring-opening metathesis and diene polymerization - the last appears to possess the greatest tolerance toward protic solvents. The polymerization of butadiene in polar solvents was first reported in 1961 using Rh salts [18]. It was discovered that these polymerizations could be performed in aqueous solution with an added emulsifier (sodium dodecyl sulfate, for example). 

Lithium differs from the other alkali metals in that it directs the polymerization of butadiene or isoprene predominantly to 1,4 addition structures. In the case of lithium-catalyzed polyiso-prene, the 1,4 addition structures are all cis. The other alkali metals direct the polymerization of butadiene largely to the 1,2 addition structure and isoprene largely to the 3,4 addition structure. The differences in physical properties, accompanying the structural variations mentioned above, are illustrated by the example of lithium-catalyzed polybutadiene. Lithium, sodium, and potassium are used most conveniently as polymerization catalysts by converting them to metal dispersions in petroleum jelly or other inert hydrocarbons. Special care must be used in handling rubidium or cesium metal. 

The microstructures of the polybutadienes, butadiene-styrene copolymers, and polyisoprenes were determined by infrared spectroscopic methods (1,3). The spectra of alkali metal-catalyzed polybutadienes and polyisoprenes show that other reactions occur during polymerization in addition to those involving cis- and trans 1,4, 1,2, and 3,4 additions. For sodium and potassium polybutadienes and polyisoprenes, the absorbances of the bands arising from these additional structures could be taken into account satisfactorily by the methods described. No foreign structures are found in lithium-catalyzed polyisoprenes and the additional band foimd near 14.2 microns in polybutadiene spectra does not appear to affect the cis-1,4 band at 14.7 microns. (Cesium and rubidium, as well as additives such as dimethoxy-tetraglycol, affect the polymerization of butadiene so markedly that it was not possible to obtain satisfactory analyses of such polymers. The effect of these catalysts in isoprene polymerizations does not appear to be so marked and satisfactory analyses were obtained by the method described. 

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