Substantially random ethylene and/or -olefin copolymers containing units derived from vicinally disubstituted olefin monomers are described. The vicinally disubstituted olefin monomers may be represented by the generic formula (R¹)CHCH(R²), where R¹ and R² independently comprise hydrocarbyl or silyl-hydrocarbyl groups containing 1 or more carbon atoms, or may be linear, branched or cyclic substituted or unsubstituted hydrocarbyl groups having from 1-100 carbon atoms, or they may contain 30 or less carbon atoms. The copolymers may be prepared by coordination polymerization by means of contacting at least one vicinally disubstituted olefin monomer and ethylene and/or -olefin, optionally with one or more other coordination polymerizable monomers, with a catalyst system comprising a monocyclopentadienyl heteroatom-containing Group 4 transition metal catalyst component.