of the trans 1 4 polybutadiene does not change as a function of polymerization temperature the pressure used will normally be sufficient to maintain a substantially liquid phase under the conditions of the polymerization reaction the polymerization is conducted for a length of time sufficient to permit substantially complete polymerization of monomers in other words the polymerization is normally carried out until high conversions are attained the polymerization can then be terminated using a standard technique the polymerization can be terminated with a conventional noncoupling type of terminator such as water an acid a lower alcohol and the like or with a coupling agent for instance coupling agents can be used in order to improve the cold flow characteristics of the trans 1 4 polybutadiene rubber and rolling resistance of tires made therefrom it also leads to better processability and other beneficial properties a wide variety of compounds suitable for such purposes can be employed some representative examples of suitable coupling agents include multivinylaromatic compounds multiepoxides multiisocyanates multiimines multialdehydes multiketones multihalides such as tin tetrachloride and silicon tetrachloride multianhydrides multiesters which are the esters of polyalcohols with monocarboxylic acids and the diesters which are esters of monohydric alcohols with dicarboxylic acids and the like after the copolymerization has been completed the trans 1 4 polybutadiene can be recovered from the organic solvent the trans 1 4 polybutadiene can be recovered from the organic solvent and residue by means such as decantation filtration centrification and the like it is often desirable to precipitate the trans 1 4 polybutadiene from the organic solvent by the addition of lower alcohols containing from about 1 to about 4 carbon atoms to the polymer solution.