The invention provides a resin composition comprising a crosslinking silyl-terminated stellar-structure vinyl polymer or a stellar-structure vinyl block copolymer or chain-extended vinyl block copolymer. The invention provides a method of producing a stellar-structure vinyl block copolymer or chain-extended vinyl block copolymer which comprises forming a block copolymer using living radical polymerization and adding a compound having two or more polymerizable carbon-carbon double bonds at the end point of polymerization of the block copolymer.