Diazo-Initiated Polymers. Preparation, Properties, and Evaluation

Throughout the great majority of the many investigations on rubberlike synthetic polymers, the initiators employed have been peroxides, either water-soluble (potassium persulfate being the chief example) or oil-soluble, such as benzoyl peroxide or diisopropylbenzene monohydroperoxide. The most notable departure from these initiators has been the use of the diazothio ethers, 4-methoxybenzenediazomercapto-2-naphthalene (MDN) and 4-methylbenzenediazomercapto-2-naphthalene (TDN). These materials have proved to be suitable initiators and also to have some activity as modifiers. However, their possibilities have been explored principally at a polymerization temperature of 41° F. Thus, the field of initiators has been subject to less widespread investigation than most of the other variables in a typical synthetic rubber recipe. The purpose of the present investigation was to develop different initiators, if possible, of a type which would lead to improvement of polymer structure at 122° F. It was felt from the outset that diazo-type compounds offered the best possibilities for development along these lines. During a preliminary survey of these materials, the object was to find examples which did not have the two disadvantages of the diazothio ethers—high cost and low stability. The use of diazo-type compounds as polymerization initiators has been known for many years. The work of Buizov on the polymerization of butadiene with diazoaminobenzene is an example of this. A number of patents have been issued relating to the use of diazo compounds in general as polymerization initiators or activators. These patents, however, were directed toward improving the rate of polymerization, and did not indicate any outstanding improvement in polymer properties. After detailed study of the properties and reactions of diazo materials in general, stabilized salts of diazotized aromatic amines were selected as the specific type of compound with the greatest chance of success. The program was begun with the laboratory preparation and evaluation of diazo salts.