Polydiene rubbers are commonly compounded with carbon black in making a wide variety of rubber articles including tires, hoses and belts. It is generally desirable for the carbon black to be well dispersed throughout the polydiene in order to attain optimal physical properties. For instance, the traction and rolling resistance of tires which are made utilizing such rubbers can be improved by better dispersing the carbon black throughout the polydiene. The subject invention discloses a technique for capping polydienes in order to improve their affinity for carbon black. The present invention more specifially reveals a process for preparing a polydiene having a high level of affinity for carbon black which comprises reacting a metal terminated polydiene with a capping agent selected from the group consisting of (a) halogenated nitriles having the structural formula X--A--C.tbd.N where X represents a halogen atom and wherein A represents an alkylene group containing from 1 to 20 carbon atoms, (b) heterocyclic aromatic nitrogen containing compounds, and (c) alkyl benzoates. Both ends of polydiene chains can be capped with polar groups by utilizing functionalized initiators, such as lithium amides.