selected from the group of carbonates thiocarbonates and sulfites of the general formula str6 r 1 and r 2 may be the same or different and are selected from a hydrocarbyl group containing from 1 to 20 carbon atoms and a b and y are oxygen or sulfur x is carbon or sulfur with the stipulation that when x is sulfur y must be oxygen examples of the coupling agents are dimethyl carbonate diethyl carbonate di n propyl carbonate diisopropyl carbonate di n butyl carbonate diisobutyl carbonate di n octyl carbonate dicyclohexyl carbonate diphenyl carbonate ethyl phenyl carbonate di p tolyl carbonate cyclohexyl phenyl carbonate cyclopentyl butyl carbonate o o diethyl thiocarbonate o s diethyl thiocarbonate s s diethyl dithiocarbonate o s diethyl dithiocarbonate diethyl trithiocarbonate diphenyl trithiocarbonate dimethyl sulfite diphenyl sulfite ethyl phenyl sulfite and mixtures thereof the amount of a coupling agent used may be expressed in relation to the amount of polymerization initiator used above the scavenger level which theoretically corresponds to the number of live polymer ends present in the solution generally the molar ratios of a coupling agent to carbon metal bond for example carbon lithium bond useful in this invention are from 0 05 1 to 5 1 preferably 0 2 1 to 3 1 the coupling agent may be used neat or dissolved in an inert solvent the reaction with a coupling agent is normally carried out with the solution containing non terminated polymer however for convenience and other considerations the solution may be further diluted.