A terpolymer containing: a) from 90% to 50% by weight; preferably from 90% to 70% by weight of ethylene derived units; b) from 5% to 40% by weight; preferably from 5% to 20% by weight of derived units of alpha olefin of formula CH2═CHA wherein A is a C1-C20 alkyl radical; c) from 2% to 30% by weight, preferably from 5% to 20% by weight of cycloolefins derived units. Said terpolymer being characterized by the following features i) distribution of molecular weight Mw/Mn lower than 3.5; preferably lower than 3; more preferably lower than 2.7 ii) solubility in xylene at 25° C. higher than 99%.