The present invention is directed to a method of making a functionalized elastomer, comprising the step of polymerizing monomers comprising a conjugated diene monomer in the presence of a lathanide-based coordination polymerization catalyst activated with a magnesium compound of formula 1 ##STR00001## where R.sup.1 is phenylene, or a linear or branched alkane diyl group containing 2 to 10 carbon atoms, or a combination of one or more phenylene groups and one or more linear or branched alkane diyl groups containing 1 to 10 carbon atoms; Q is of formula 2 or 3 ##STR00002## where R.sup.2 is phenyl, or a linear or branched alkyl group containing 2 to 10 carbon atoms; ##STR00003## where R.sup.3 and R.sup.4 are independently phenyl or a linear or branched alkyl group containing 1 to 10 carbon atoms, or R.sup.2 and R.sup.3 taken together with the nitrogen atom represent a nitrogen containing heterocyclic group containing from 4 to 12 carbon atoms.

The present invention is directed to a method of making a functionalized elastomer, comprising the step of polymerizing monomers comprising a conjugated diene monomer in the presence of a lanthanide-based coordination polymerization catalyst activated with a magnesium compound of formula 1

Q-R.sup.1MgR.sup.1-Q1

where R.sup.1 is phenylene, or a linear or branched alkane diyl group containing 2 to 10 carbon atoms, or a combination of one or more phenylene groups and one or more linear or branched alkane diyl groups containing 1 to 10 carbon atoms; Q is of formula 2 or 3

SR.sup.22

where R.sup.2 is phenyl, or a linear or branched alkyl group containing 2 to 10 carbon atoms;

##STR00001##

where R.sup.3 and R.sup.4 are independently phenyl or a linear or branched alkyl group containing 1 to 10 carbon atoms, or R.sup.2 and R.sup.3 taken together with the nitrogen atom represent a nitrogen containing heterocyclic group containing from 4 to 12 carbon atoms.