Preparation of butyl rubber based graft co-polymers from halobutyl elastomers using phase transfer catalysts in the presence of a solution of an alkali metal salt of an oxygen or sulfur nucleophile that is bound to a polymeric substrate. Graft co-polymers can be produced of a butyl polymer (isobutene-coisoprene) and polymeric substrates such as polyethylene, polypropylene, polystyrene, polybutadiene, polysilanes, polysiloxanes, polyethylene glycol, polyethylene oxide, polyphosphazenes, polyferrocenes or their hybrids.