The anionic polymerization of isoprene with monolithium initiators and functionalized initiators having the structure R.sup.1 R.sup.2 R.sup.3 Si--O--A'--Li wherein R.sup.1, R.sup.2, and R.sup.3 are preferably alkyl, alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A' is preferably a branched or straight chain bridging group having at least 2 carbon atoms produces unsaturated and hydrogenated isoprene polymers having high 1,4-addition of the isoprene, from about one to two terminal functional groups per molecule, and low viscosity.