Crosslinkable or crosslinked polymer compositions are provided, the compositions including a copolymer of ethylene and C.sub.3 to C.sub.12 alpha-olefin comonomer, the copolymer having a CDBI of at least 70%, a melt index I.sub.2.16 of from 0.1 to 15 g/10 min, a density of from 0.910 to 0.940 g/cm.sup.3, a melt index ratio I.sub.21.6/I.sub.2.16 of from 30 to 80, and an Mw/Mn ratio of from 2.5 to 5.5; and a silane grafting composition including a silane compound and a free radical initiator; or reaction products thereof. The crosslinkable or crosslinked compositions are particularly suitable for electrical applications, such as in insulating, semiconducting or jacketing layers of power cables, telecommunications cables, and combined power/telecommunications cables.