A novel and useful linear triene compound represented by the following formula (1) is co-polymerized with an α -olefin to obtain an ethylenically unsaturated copolymer which is superior in weatherability, heat resitance and fastness to ozone, together with superior scorch stability and vulcanizability at high velocity.
in which R 1 , R 2 , R 3 , R 4 , R 5 and R 6 stand each, independently of each other, for hydrogen atom or an alkyl having 1 - 3 carbon atoms, R 7 represents an alkyl having 1 - 3 carbon atoms and n is an integer of 0 - 5, with the proviso that each of R 4 s or of R 5 s may be identical with or different from each other, respectively, when n is 2 or greater.