The Preparation, Modification and Applications of Nonfunctional Liquid Polybutadienes

This review will be restricted to the applications of liquid polybutadienes (BR) which, as prepared, are devoid of functional groups other than the unsaturation left after polymerization. These products should not be confused with the so called telechelic BRs in which terminal functional groups are deliberately introduced during preparation. The preparative techniques and applications relating to the latter polymers have been described both by French and more recently by Athey. For many applications, it is necessary to introduce functional groups into the “nonfunctional” liquid BRs as a subsequent stage to polymerization. However, such chemical modification is often carried out to yield a relatively high level of functionality and, more significantly, the functional groups are randomly distributed along the polymer backbone. Therefore, there is still a clear distinction between chemically modified, nonfunctional BRs and the telechelic polymers. Whereas the latter have often been included under the “liquid rubber” classification, this term would be incorrect for the nonfunctional BRs with respect to the majority of their applications. Liquid BRs are not a new range of materials. To the writer's knowledge the first commercial liquid BR to be produced by a polymerization process was Plastikator 32. This polymer was produced in Germany, apparently from about 1925. Between about 1950 and the mid-1960s many of the major polymer producing companies developed production techniques and investigated the applications of liquid BRs. However, with the notable exceptions of Du pont's “Budium” and the Richardson Co.'s “Ricon” range (formerly known as Enjay Buton and now manufactured by Colorado Chemicals Specialities Inc.), they did not become fully commercial. It was not until the late 1960s and early 1970s that liquid BRs achieved significant commercial tonnages. This was largely associated with the advent, in Western Europe and Japan, of the use of liquid BRs as the feedstock for electrodeposition primers for car bodies and for chlorinated rubber paints and inks. A reasonable estimate for annual production of liquid BRs in the mid-1970s would be between 8000 and 15 000 (tons.) This ready commercial availability of liquid BRs, encompassing a wide range of microstructure and molecular weight (M.W.) has prompted an equally wide ranging evaluation of their potential applications. It is impossible to define a M.W. above which a BR is no longer construed as being a liquid. BRs up to a M.W. around 50×103 have been included in this loose definition, but the most common range is 1×103−10×103. Apart from M.W. and molecular weight distribution, M.W.D., the viscosity of a BR is very dependent upon the polymer structure. The same parameters which affect viscosity also have a strong influence on the chemical modification and application properties of liquid BRs. Previous articles describing applications of liquid BRs have tended to concentrate on products having a particular type of microstructure. Since the technique of preparation often controls the microstructure and M.W.D., it is relevant to describe aspects of the preparation and chemical modification as a prelude to discussing the applications of liquid BRs.