This invention relates to methods for producing an alkene terminated polystyrene, including: contacting a styrenic block copolymer and an alkene in the presence of a metathesis catalyst under conditions sufficient to produce an alkene terminated polystyrene having an unsaturation functionality of at least 0.7 and a MWD of about 1.5 or less. Methods for producing functionalized polymers and polyethylene blend composition comprising these functionalized polymers are also disclosed.