. . . . "The poylether which is reacted with the silane compound (a) contains a group having ethylenic double bond represented by formula (b): wherein R13 is preferably hydrogen atom or a hydrocarbon group, and most preferably hydrogen atom; and Z is a divalent group containing a divalent hydrocarbon group, ether bond, ester bond, urethane bond, carbonate bond, or carbonyl bond, which is typically selected" .