I. INTRODUCTION

The development of synthetic rubber played a special role in the history of polymerization chemistry. This was due primarily to the fact that attempts to synthesize rubber were made long before there was even the faintest idea of the nature of polymerization reactions. Such attempts began very soon after the elegant analytical work of Williams [1] in 1860, which clearly demonstrated that Hevea rubber was composed of isoprene. Thus, Bouchardat [2] in 1879 was actually able to prepare a rubberlike substance from isoprene (which he obtained from rubber pyrolysis), using heat and hydrogen chloride. Tilden [3] repeated this process in 1884 but used isoprene obtained from pyrolysis of turpentine to demonstrate that it was not necessary to use the mother substance of rubber itself. These explorations were soon followed by the work of Kondakow (1900) [4] with 2,3-dimethylbutadiene, that of Thiele (1901) [5] with piperylene, and finally that of Lebedev (1910) [6] on butadiene itself. Mention should also be made of the almost simultaneous, and apparently independent, discoveries in 1910 by Harries [7] in Germany and Matthews and Strange [8] in England of the efficient polymerization in isoprene by sodium.

Although all of these attempts had a noble purpose indeed, the means used could hardly be considered a contribution to science, as the transformation of the simple molecules...