A thermoplastic elastomer produced without a hydrogenation step is functionalized utilizing a free radical initiator and a functionalizing monomer having at least one point of unsaturation. The base polymers can be produced by copolymerizing an .alpha.-olefin capable of producing an amorphous backbone with a comonomer which provides a "hook" for grafting to with a living polystyrene chain. Another method is to copolymerize an .alpha.-olefin monomer system capable of producing an amorphous backbone with a comonomer containing a functional group from which an anionically polymerizable monomer is grown from the backbone. A third method involves copolymerizing an .alpha.-olefin monomer system capable of giving an amorphous backbone with an olefin-terminated polystyrene comonomer. In a less preferred embodiment, a conventional EPDM polymer can be metallated and a monoalkenyl aromatic compound anionically polymerizable monomer grown from the backbone.